Pre-cenozoic evolution of the northern Qilian Orogen from zircon geochronology: Framework for early growth of the northern Tibetan Plateau
Li, B., Zuza, A. V., Chen, X., Wang, Z., Shao, Z., Levy, D. A., Wu, C., Xu, S., and Sun, Y. -- 2020 The northern Qilian Shan, located along the northeastern margin of the Tibetan Plateau, experienced multiple phases of orogeny throughout the Phanerozoic, culminating in fold-thrust and strike-slip deformation associated with the Cenozoic India-Asia collision. Earlier phases of deformation in the Qilian Shan have been severely reactivated or transformed by the most recent Cenozoic strain. To better understand the tectonic evolution of this complex region, we conducted an integrated investigation of field observations, U–Pb dating of igneous and detrital zircons, and a synthesis of previously published data to constrain and reconstruct the pre-Cenozoic history of the northern Qilian Shan. This effort reveals five major age populations important to the history of this region: 2550–2350, 1850–1750, 1050–950, 500–435, and 320–240 Ma. Using this dataset, we identified three major depositional shifts and/or variations in drainage patterns that affected sediment provenance of the northern Qilian Orogen. Observed regional geologic constraints, the magmatic history, and new geophysical observations of the deep structure allow us to propose a coherent tectonic model for the pre-Cenozoic evolution of the northeastern margin of the Tibetan Plateau. (1) Late Neoproterozoic to Cambrian rifting opened the Qilian Ocean. (2) Early Cambrian subduction initiation along the margins of Qaidam and North China–Tarim continents resulted in Cambrian-Ordovician bivergent subduction, arc magmatism within these two continents, and consumption of the Qilian Ocean. (3) Final ocean closure and continental collision occurred at ca. 440 Ma and was associated with syn- and post-orogenic magmatism. (4) Collisional orogeny variably eroded the basement rocks, reorganized drainage networks, and altered sedimentary provenance for the lower Paleozoic to upper Paleozoic deposits. (5) Mesozoic extension led to the development of thick Jurassic–Cretaceous terrestrial basins. This pre-Cenozoic history resulted in preexisting weaknesses and/or low-friction detachment horizons that played a decisive role in controlling the pattern, distribution, and timing of Cenozoic deformation across the northern Tibetan Plateau. |
Palaeogeography, Palaeoclimatology, Palaeoecology
In press https://doi.org/10.1016/j.palaeo.2020.110091 |
Geologic field evidence for non-lithostatic overpressure recorded in the North American Cordillera hinterland, northeast Nevada
Zuza, A. V., Levy, D. A., Mulligan, S. R. -- 2020 There is a long-standing discrepancy for numerous Cordilleran metamorphic core complexes, USA, between geobarometric pressures recorded in the exhumed rocks and their apparent burial depths based on palinspastic reconstructions from geologic field data. In particular, metamorphic core complexes in eastern Nevada are comprised of well-documented ~12–15 km thick Neoproterozoic–Paleozoic stratigraphy of Laurentia's western passive margin, which allows for critical characterization of field relationships. In this contribution we focus on the Ruby Mountain–East Humboldt Range–Wood Hills–Pequop Mountains (REWP) metamorphic core complex of northeast Nevada to explore reported peak pressure estimates versus geologic field relationships that appear to prohibit deep burial. Relatively high pressure estimates of 6–8 kbar (23–30 km depth, if lithostatic) from the lower section of the Neoproterozoic–Paleozoic passive margin sequence require burial and or repetition of the passive margin sequence by (2–3) × stratigraphic depths. Our observations from the least migmatized and/or mylonitized parts of this complex, including field observations, a transect of peak-temperature (Tp) estimates, and critical evaluation of proposed thickening/burial mechanisms cannot account for such deep burial. From Neoproterozoic–Cambrian (Z_) rocks part of a continuous stratigraphic section that transitions ~8 km upsection to unmetamorphosed Permian strata that were not buried, we obtained new quartz-in-garnet barometry via Raman analysis that suggest pressures of ~7 kbar (~26 km). A Tp traverse starting at the same basal Z_ rocks reveals a smooth but hot geothermal gradient of ≥40 °C/km that is inconsistent with deep burial. This observation is clearly at odds with thermal gradients implied by high P-T estimates that are all ≤25 °C/km. Remarkably similar discrepancies between pressure estimates and field observations have been discussed for the northern Snake Range metamorphic core complex, ~200 km to the southeast. We argue that a possible reconciliation of long-established field observations versus pressures estimated from a variety of barometry techniques is that the rocks experienced non-lithostatic tectonic overpressure. We illustrate how proposed mechanisms to structurally bury the rocks, as have been invoked to justify published high pressure estimates, are entirely atypical of the Cordillera hinterland and unlike structures interpreted from other analogous orogenic plateau hinterlands. Proposed overpressure mechanisms are relevant in the REWP, including impacts from deviatoric/differential stress considerations, tectonic mode switching, and the autoclave effect driven by dehydration melting. Simple mechanical arguments demonstrate how this overpressure could have been achieved. This study highlights that detailed field and structural restorations of the least strained rocks in an orogen are critical to evaluate the tectonic history of more deformed rocks. |
Kinematic evolution of a continental collision: Constraining the Himalayan-Tibetan orogen via bulk strain rates
Zuza, A. V., Yann, G., Haproff, P. J., Wu, C. -- 2020 We investigated temporal variations of the bulk strain rate across the Himalayan-Tibetan orogen, which impact the magnitudes, rates, and distribution of deformation across the orogen. The present-day strain rate estimated from geodesy is ~5-6×10-16 s-1 and estimation of past rates depends on the orogenic shortening rate and effective orogen width. Plate-circuit reconstructions provide constraints on time-varying India-Asia convergence rates, showing a marked deceleration since initial collision at ca. 58 Ma. Geologic evidence suggests that most of the Tibetan crust started deforming shortly after initial collision, which simplifies estimation of the initial orogen width. We examined several kinematic models: (1) Greater Indian and Tibetan crust started deforming immediately after collision, (2) only Tibetan crust deformed initially, (3) plate convergence was decoupled from crustal shortening, with Tibetan crust deforming slower than plate rates, or (4) a hard India-Asia collision at ca. 45 Ma following closure of the Xigaze backarc. Models 1, 3, and 4 yield early Cenozoic bulk strain rates that match present-day rates (5-6×10-16 s-1), whereas Model 2 yields faster rates (1.2×10-15 s-1) that must have decreased through time to avoid shortening exceeding total plate convergence. Using these bounds, we constrain crustal shortening across the entire orogen and along its southern and northern margins, defined by the Himalaya and Qilian Shan, respectively. Application of these models to Tibetan crustal thickening suggests that the plateau reached its present-day value (~70 km) by ca. 15 Ma, which corresponds to the onset of lateral deformation (e.g., strike-slip and normal faulting). Lateral deformation in the Himalayan-Tibetan orogen may have resulted from progressive crustal thickening and reorientation of the intermediate principal stress axis. At the thrust-belt scale, our modeling yields shortening rates and magnitudes that match geologic observations. This approach provides testable external kinematic constraints to guide future geological and geophysical investigations. |
Cenozoic cooling history and fluvial terrace development of the western domain of the Eastern Kunlun Range, northern Tibet
Wu, C., Li, J., Zuza, A. V., Liu, C., Liu, W., Chen, X., Jiang, T., and Li, B. -- 2020 The growth of the Tibetan Plateau resulted primarily from Cenozoic India-Asia collision and continued convergence, and thus the deformation timing and geomorphic evolution of northern Tibet are critical to understanding the dynamics of orogenic plateau growth. Although previous studies have suggested that the Altyn Tagh Shan and the Eastern Kunlun Range of northern Tibet have experienced differential faulting and exhumation history, our knowledge of the temporal and spatial distribution of the growth of the northwestern Tibetan Plateau is still lacking. In this study, we integrate new geologic mapping, low-temperature themochronometry (18 apatite-fission track ages), and Optically Stimulated Luminescence (OSL) dating to provide constraints on the Cenozoic cooling history of northwestern Tibet and late Quaternary fluvial terrace development. We focus on where Altyn Tagh Shan structures are juxtaposed against Eastern Kunlun Range structures. New fission-track cooling ages from one traverse along the Aksu River yielded three cooling age domains: Paleocene, Miocene, and early Pliocene. With this new knowledge of ~12–10 Ma initiation of Jianxiashan thrusting and exhumation, we suggest a refined N-S shortening rate of this thrust system of 2.0–2.4 mm/yr and strain rates of 8–9 × 10−16 s−1. Thermal history modeling suggests that the study area experienced two broad events, including slow cooling through the AFT PAZ since the early Eocene and rapid cooling during the late Miocene. Our OSL dating results from the Aksu drainage reflect two separate processes of aggradation and incision that occurred during the late Pleistocene and Holocene, respectively, which are interpreted to result from long-term forcing of incision by a constant rate of tectonic uplift modulated by late Quaternary climatic variations. We interpret that this incision occurred at a rate of ~1 mm/yr, which is faster than exhumation rates inferred from the AFT data (0.3–0.5 mm/yr). These Quaternary exhumation rates may reflect faster recent exhumation or uplift associated with the proximal Altyn Tagh fault. In accordance with previous studies, we present a refined Cenozoic tectonic model for the evolution history of northern Tibet. The deformation pattern of northern Tibet results from clockwise rotation of preexisting weaknesses and transpressional deformation along the Kunlun fault and the Haiyuan fault. |
Palaeogeography, Palaeoclimatology, Palaeoecology
v. 560 https://doi.org/10.1016/j.palaeo.2020.109971 |
Permian plume-strengthened Tarim lithosphere controls the Cenozoic deformation pattern of the Himalayan-Tibetan orogen
Xu, X., Zuza, A. V., Yin, A., Lin, X., Chen, H., Yang, S. -- 2020 The high strength of the Tarim Basin lithosphere, widely regarded as a Precambrian craton, is evidenced by its resistance to Cenozoic deformation in the Himalayan-Tibetan orogen. However, Neoproterozoic suturing and early Paleozoic shortening within the Tarim Basin suggest that its rigidity is a relatively recent phenomena with unknown cause. We reprocessed high-resolution magnetic data that show a 300-400 km dimeter radial pattern of linear anomalies emanating from a central region characterized by mixed positive-negative anomalies. We suggest that this pattern was generated by the previously hypothesized Permian (ca. 300-270 Ma) plume beneath the Tarim Basin. Constrained by published geochemical and geochronological data of plume-related igneous rocks, we propose that the ~30-Myr Permian plume activity resulted in a more viscous, depleted, thicker, dehydrated, and low-density mantle lithosphere. The resulting stronger lithosphere deflected strain from the Cenozoic India-Asia convergence around Tarim Basin, including Pamir overthrusting to the northwest and Altyn Tagh left-slip displacement to the northeast, thus shaping the geometry of the Himalayan-Tibetan orogen. |
Early Permian tectonic evolution of the Last Chance thrust system: An example of induced subduction initiation along a plate boundary transform
Levy, D. A., Zuza, A. V., Haproff, P. J., Odlum, M. L. -- 2020 The late Paleozoic is an important precursor stage in the development of the Mesozoic Cordilleran subduction system along the western margin of North America, but the tectonic history remains ambiguous due to complex overprinting deformation and magmatism. Determining the driving mechanism of large magnitude Permian shortening in southwest Laurentia is critical to understanding the late Paleozoic transition from transform margin to subduction zone. We investigated the driving mechanism of the Permian Last Chance thrust system in east-central California to understand this transition prior to the development of the Mesozoic Cordilleran arc. Here, we present the results of new geological mapping, detrital zircon U-Pb geochronology, and a synthesis of regional tectonics to inform a kinematic model of the Last Chance thrust system and outline the Permian−Triassic tectonic evolution of the plate boundary during induced subduction initiation. The record of subduction initiation along an inferred late Paleozoic transform fault (the California-Coahuila transform) is preserved by (1) Permian arc magmatism, (2) the onset of volcaniclastic sedimentation, and (3) the development of a regional transpressional system in present-day east-central California. The evolution of this transpressional system and subduction zone is recorded by development of the Last Chance thrust system of the Death Valley region. Geological mapping in the Last Chance Range, northern Death Valley National Park, and the Inyo Mountains reveals the east-directed Last Chance thrust system was constructed by repetitive out-of-sequence deformation consistent with transpressional strain. The Last Chance thrust system accommodated a minimum of >75 km (60%) shortening, based on cross-section restorations guided by regional stratigraphic relationships and restoration of subsequent Mesozoic deformation. Our revised model of Jurassic extensional exhumation of the Snow Lake terrane argues the Last chance thrust was not reactivated during the Mesozoic. Large-magnitude shortening along the California-Coahuila transform accommodated a significant component of the convergent plate motion as the Panthalassan crust was thrust below the continental margin before initial slab sinking. Numerical models show the forces resisting subduction are greatest before initial slab sinking takes place, and compression is transmitted in board from the plate boundary. We argue the Last Chance thrust system developed in response to this compression. Early-middle Permian plutons and late Permian detrital zircons in coeval basins suggest subduction was well established by the early Permian. Collectively, the preservation of a thrust system, early arc magmatism, and syntectonic sedimentary basins, which are features typically destroyed by subduction magmatism and deformation, allow for the evaluation of subduction initiation mechanisms based on field observations. |
Structural and Thermochronologic Constraints on the Cenozoic Tectonic Development of the Northern Indo-Burma Ranges
Haproff, P. J., Odlum, M. L., Zuza, A. V., Yin, A., Stockli, D. F. -- 2020. The ~1500-km-long, north-trending Eastern Flanking Belt of the Himalayan-Tibetan orogenic system is located along the eastern margin of the Indian subcontinent. Although the belt is a key element of the Cenozoic India-Asia collisional zone, its tectonic evolution remains poorly understood. This lack of knowledge has impacted our ability to differentiate between competing hypotheses for the evolution of the India-Asia collision. To address this problem, we integrate constraints on the structural framework and magnitude of Cenozoic shortening strain with thermochronology of the northernmost segment of the belt located directly southeast of the eastern Himalayan syntaxis (i.e., the northern Indo-Burma Ranges). The study area exposes a southwest-directed thrust belt that is bounded by the Indian craton in the west and the right-slip Jiali fault zone in the east. New and existing (U-Th)/He and 40Ar/39Ar thermochronologic data indicate that thrust-related cooling occurred from ~36 Ma in the northeast to ~5.6 Ma in the southwest. Out-of-sequence thrusting occurred at ~30-20 Ma, ~14-12 Ma, and ~11-6 Ma within the thrust belt. Restoration of the thrust belt yields a minimum horizontal shortening of ~280 km (~86%). This work combined with (1) the recorded local absence of several major Himalayan Tibetan lithologic units (i.e., Tethyan Himalayan Sequence, Greater Himalayan Crystalline Complex, and southern Gangdese batholith) and (2) the southward decrease in the thrust-belt width (33-5 km) suggests a complex history of thrusting in the northern Indo-Burma Ranges and an increase in Cenozoic crustal shortening and/or continental underthrusting from west to east across the eastern Himalayan syntaxis. |
Sedimentary Paleaoenvironment of the eastern Hexi Corridor, NW China: Constraints from the chert geochemistry and sedimentary analysis of early Paleozoic strata
Zhang, Y., Zhang, J., Chen, X., Zuza, A. V., Zhang, B., Zhao, H. -- 2020 The eastern Hexi Corridor, northwest China, is located at the tectonic junction of the Alxa Block, North China craton, and Qinling‐Qilian orogen. The early Paleozoic Xiangshan Group strata record critical information regarding paleaoenvironment, paleoclimate, and paleotectonic setting, and here we present a focused study on chert beds within the Xiangshan Group. Through field mapping, microstructural observation, whole‐rock geochemistry, detrital zircon dating of the chert, we suggest that the Xiangshan Group chert deposited along a passive continental margin, formed primarily via biological activities with minor hydrothermal contamination and terrestrial input. The characteristics of chert support a low latitude sedimentary paleaoenvironment, and reveal a fact that the Alxa Block was separated from the North China Block while emerged some paleogeographic affinity with Qilian region in the Middle‐Late Cambrian. |
Acta Geologica Sinica
(English Edition) v. 94, no. 4, p. 1223-1237 https://doi.org/10.1111/1755-6724.14569 |
Late Pliocene onset of the Cona rift, eastern Himalaya, confirms eastward propagation of extension in Himalayan-Tibetan orogen
Bian, S., Gong, J., Zuza, A. V., Yang, R., Tian, Y., Ji, J., Chen, H., Xu, Q., Chen, L., Cheng, X., Tu, J., Yu, X. -- 2020 Several competing hypotheses have been proposed to explain east-west extension observed across the Himalayan orogen, based primarily on observations from the western and central Himalaya. They make predictions for the temporal and spatial patterns of deformation in the eastern Himalaya. These tectonic models include radial spreading or oroclinal bending of the Himalayan arc, oblique convergence of the Indian continent, tearing or lateral detachment of the Indian slab and eastward flow of lithosphere. Here, for the first time we constrain the activity history of the Cona rift, the only north-trending rift in the eastern Himalaya, based on biotite and K-feldspar 40Ar/39Ar and zircon and apatite (U-Th)/He thermochronology, to test these proposed rifting mechanisms. Low-temperature thermochronological results suggest that the Cona rift is the youngest rift system in the Himalayas: after a slow phase of exhumation since ~14 Ma (~0.2–0.13 mm/yr), normal faulting initiated here at ~3.0–2.3 Ma with a fault slip rate of ~1.6–3.8 mm/yr and a horizontal extension magnitude of ~2–5 km. Analysis of rifting across the Himalayas shows that rift initiation ages young eastward, which is matched by eastward decreasing rift-extension magnitudes. Monotonically eastward younging rift development is consistent with the tectonic model involving eastward lithospheric flow driven by Indian slab dynamics and coupled gravitational collapse. |
Crustal tilting and differential exhumation of Gangdese Batholith in southern Tibet revealed by bedrock pressure
Cao, W., Yang, J., Zuza, A. V., Ji, W., Ma, X., Chu, X., Burgess, Q. P. -- 2020 The exhumation history of the Gangdese Batholith, southern Tibet, bears on how magmatism and tectonism interact with surface processes in a long-lived magmatic orogen. In this study, we applied Al-in-hornblende barometry across the central-western Gangdese Batholith to obtain pluton emplacement pressures. Our results, together with existing bedrock pressure data, reveal the regional paleo-depth pattern across the Gangdese Batholith. The western part of the batholith near Lhasa exposes plutons emplaced at 1-2 kbar whereas the eastern part, near Nyingchi, exposes crust recording pressures typically of 6-12 kbar. We coupled pressure data with new and published U-Pb zircon ages to constrain the exhumation history of the Gangdese Batholith. The results show that since 100 Ma, the upper crust experienced limited exhumation except a pronounced Oligocene-Miocene pulse. In contrast, the middle-lower crust experienced a complex exhumation and burial history, reflecting major tectonic events including the development of continental arc and continent-continent collision. Since ca. 10 Ma, the eastern Nyingchi domain experienced fast exhumation (total exhumation > 40 km), which was related to the exhumation of the Eastern Himalayan Syntaxis. The Lhasa domain experienced comparatively limited exhumation (total exhumation <10 km). Such dramatic differential exhumation along the E-W direction requires that the Gangdese Batholith was tilted to present-day exposure levels. Our study shows that during the evolution of a magmatic orogen, the upper and middle-lower crust can behave differently, and the exhumation history reflects integrated tectonic, magmatic, and surface processes. The surface erosion rate estimates can be used to calculate CO2 consumption and evaluate the roles of magmatic orogens in the long-term carbon cycle. Given its great exposures of plutonic and metamorphic rocks across a relatively continuous crustal section, the Gangdese Batholith has great potential to serve as a natural laboratory to understand the structures and evolution of the continental crust. |
Late Miocene Transition between Basin and Range Extension and Walker Lane Tectonics, Northern Pine Nut Mountains, Nevada: New Insights from Geologic Mapping and 40Ar/39Ar Geochronology
Say, M., and Zuza, A. V. -- 2020 The westward encroachment of Basin and Range extension on the relatively stable Sierra Nevada block occurred during the Miocene. To better bracket the timing, magnitude, and kinematics of this transition, we conducted new geologic mapping, 40 Ar/ 39 Ar geochronology, and geochemical analyses in the northern Pine Nut Mountains , NV, which are the westernmost structural and topographic expression of the Basin and Range extensional province. Structural mapping suggests that north-striking normal faults developed during the initiation of Basin and Range extension and were later reactivated as northeast-striking oblique-slip faults following the onset of Walker Lane transtensional deformation in the Carson Domain. Newly obtained 40 Ar/ 39 Ar radiometric dates collected from 30-36° NW-dipping intermediate to felsic (~55-65% SiO 2) volcanic and sedimentary rocks in the northern Pine Nut Mountains show that deformation initiated after 7.15 ± 0.10 Ma. Tilting of the range was accommodated by a major east-dipping normal fault that defines the eastern flank of the range. Extension magnitude recorded in the northern Pine Nut Mountains (14% extension) and westward towards the rigid Sierra Nevada is significantly less than the highly extended Singatse and Wassuk Ranges (~150-180% extension) to the east. Subsequently, Walker Lane transtension initiated and dextral shear in the Carson Domain induced clockwise rotation of structural blocks bounded by northeast-striking left-slip faults orthogonal to the dextral shear zone. This resulted in a northeast-striking oblique-slip and transtensional structure in the northern Pine Nut Mountains. Although this oblique left-slip normal fault system is covered by young alluvium and inactive today, we infer this structure may have served as a major kinematic component of left-lateral shear similar to other left-slip faults identified in the Carson Domain to the north and south. It may have become inactive because it became mechanically unfavorable as the Carson Doman rotated and slip was accommodated on the other parallel left-slip faults. Recently active, north-striking east-dipping curvilinear faults on the western flank of the range show dip-slip to oblique right-slip normal kinematics that may have accommodated some dextral shear as conjugate Riedel shears of the Carson Domain. |
Seismogenic thickness of California: implications for thermal structure and seismic hazard
Zuza, A. V., and Cao, W. -- 2020 The seismogenic thickness of the crust, a proxy for brittle-crust thickness, is a geometric parameter related to crustal strength, seismic hazard, and the crust's thermo-mechanical nature. We use highresolution earthquake-location data from California to construct a topographic map of the base of the seismogenic crust by calculating the depth above which 95% of seismicity (D95) is located for fixed width bins. Seismogenic thickness is highly variable, ranging from ~5 km to >30 km, with thicker D95 values in the Great Valley-Sierra Nevada and thinner values in the Walker Lane and northern coastal California. Seismogenic thickness is inversely correlated with surface heat flow in most locations, consistent with a steady-state conductive crust, and local deviations probably reflect non-steady-state conditions related to magmatism and/or hydrothermal circulation. Such correlation suggests that, at regional scale, brittle-ductile transition (BDT) depth is mostly controlled by geothermal gradients, and the base of the seismogenic crust essentially represents a BDT isotherm (~300-350°C for quartz-dominated lithologies). Spatial variations of D95 depths across California can be used to evaluate or constrain the locations of future seismicity, propagation direction of earthquake ruptures, and maximum depth, rupture area, and magnitude of future strike-slip earthquake events. Thicker seismogenic crust has a greater integrated strength. Seismogenic depth asperities, which represent mechanically stronger crustal patches, may focus and nucleate future earthquake events and/or impede rupture propagation. |
Cenozoic multi-phase deformation in the Qilian Shan and out-of-sequence development of the northern Tibetan Plateau
Li, B., Zuza, A. V., Chen, X., Hu, D., Shao, Z., Qi, B., Wang, Z., Levy, D. A., and Xiong, X. -- 2020 Uplift of the Tibetan Plateau and the distribution of deformation across it are the result of India-Asia collision, which bring an opportunity of understanding intracontinental tectonics in the context of continent-continent collision. The Tibetan Plateau is bound on the northern margin by the Qilian Shan thrust belt and the strike-slip Haiyuan fault. These Cenozoic fault systems play a critical role in accommodating continental convergence, yet the initiation age, deformation sequence and mechanisms of deformation are debated. In this study, integrated geologic mapping, field observations, and apatite fission track thermochronology were conducted to constrain the initiation ages of the localized thrust faults and the exhumation history of the central and northern Qilian Shan, northern Tibet. Our analyses reveal the central and northern Qilian Shan underwent rapid cooling during the Cretaceous as a result of a far-field tectonic event. In the Eocene-Oligocene, a period of thrust-related cooling occurred along the Shule Nan Shan, Tuolai Nan Shan and Tuolai Shan faults. Reactivation of the proximal thrust faults and initiation of the western segment of the Haiyuan fault occurred at ca. 16 Ma and drove final accelerated Miocene cooling and denudation to the surface. We argue that the Qilian Shan thrust belt has persisted as the stationary and internally deformed northern boundary of the Himalayan-Tibetan orogen since the early Cenozoic, involved overprinting out-of-sequence development starting by Eocene related to initiation of India-Asia collision, and the basins and ranges across the northern Tibetan Plateau have since experienced multi-phase of growth. |
Pulsed Mesozoic deformation in the Cordilleran hinterland and evolution of the Nevadaplano: Insights from the Pequop Mountains, NE Nevada
Zuza, A. V., Thorman, C. H., Henry, C. D., Levy, D. A., Dee, S., Long, S. P., Sandberg, C. A., and Soignard, E. -- 2020 Mesozoic crustal shortening in the North American Cordillera's hinterland was related to the construction of the Nevadaplano orogenic plateau. Petrologic and geochemical proxies in Cordilleran core complexes suggest substantial Late Cretaceous crustal thickening during plateau construction. In eastern Nevada, geobarometry from the Snake Range and Ruby Mountains-East Humboldt Range-Wood Hills-Pequop Mountains (REWP) core complexes suggests that the ~10-12-km-thick Neoproterozoic-Triassic passive-margin sequence was buried to great depths (>30 km) during Mesozoic shortening and was later exhumed to the surface via high-magnitude Cenozoic extension. Deep regional burial is commonly reconciled with structural models involving cryptic thrust sheets, such as the hypothesized Windermere thrust in the REWP. We test the viability of deep thrust burial by examining the least-deformed part of the REWP in the Pequop Mountains. Observations include a compilation of new and published peak temperature estimates (n=60) spanning the Neoproterozoic-Triassic strata, documentation of critical field relationships that constrain deformation style and timing, and new 40Ar/39Ar ages. This evidence refutes models of deep regional thrust burial, including (1) recognition that most contractional structures in the Pequop Mountains formed in the Jurassic, not Cretaceous, and (2) peak temperature constraints and field relationships are inconsistent with deep burial. Jurassic deformation recorded here correlates with coeval structures spanning western Nevada to central Utah, which highlights that Middle-Late Jurassic shortening was significant in the Cordilleran hinterland. These observations challenge commonly held views for the Mesozoic-early Cenozoic evolution of the REWP and Cordilleran hinterland, including the timing of contractional strain, temporal evolution of plateau growth, and initial conditions for high-magnitude Cenozoic extension. The long-standing differences between peak-pressure estimates and field relationships in Nevadan core complexes may reflect tectonic overpressure. |
Diachronous uplift in intra-continental orogeny: 2D thermo-mechanical modeling of the India-Asia collision
Bian, S., Gong, J., Chen, L., Zuza, A. V., Chen, H., Lin, X., Cheng, X., and Yang, R. -- 2020 The Cenozoic India-Asia collision reactivated several ancient thrust belts in the interior of the Asian continent, including the West and East Kunlun ranges in central Tibet, and the Tian Shan and Qilian Shan further north. Both basin sedimentary records and thermochronological data show that the uplift of the South Tian Shan and Qilian Shan at the north occurred earlier than that of the West and East Kunlun ranges at the south. Diachronous continental deformation and initiation of uplift during orogeny is contrary to the general notion that the stress transfer in response to the India-Asia collision should propagate sequentially from south to north. Here we systematically conducted 2D thermo-mechanical simulations to investigate possible factors for this diachronous deformation pattern. The results show that a hotter Tian Shan lithosphere, with Moho temperatures >100 °C hotter than that of the proto-southern Asia, leads to an earlier and higher uplift of the Tian Shan. Additionally, a faster convergence rate of the India-Asia collision results in a more efficient transfer of boundary force into the upper plate's interior, giving rise to a larger amount of uplift in the Tian Shan. We conclude that intra-continental ranges with weaker lithosphere, such as the Tian Shan or Qilian Shan, uplift earlier than stronger regions, such as the West and East Kunlun ranges. Faster convergence rates amplify this situation. Our results imply that the unique diachronous growth of the Tibetan plateau arises from its complex pre-collisional history, which includes collided arc-continent terranes with hotter and weaker lithosphere that respond to the effects of far-field stress transfer. |
Structural analysis and tectonic evolution of the western domain of the Eastern Kunlun Range, northwest Tibet
Wu, C., Liu, C., Fan, S., Zuza, A. V., Ding, L., Liu, W., Ye, B., Yang, S., and Zhou, Z. -- 2019 The Tibetan Plateau, the largest highland on Earth, formed due to the collision of India-Asia over the past 50–60 m.y., and the evolution of the Tibetan Plateau impacts our knowledge of continental tectonics. Examination of the northernmost margin of the Tibetan Plateau is key to unravelling the deformation mechanisms acting in northern Tibet. The left-slip Altyn Tagh fault system defines the northwest margin of the Tibetan Plateau, separating the Western and Eastern Kunlun Ranges in the southwest. Both Cenozoic and pre-Cenozoic crustal deformation events at this junction between the Altyn Tagh and Kunlun Ranges were responsible for the construction of northwestern Tibet, yet the relative contribution of each phase remains unconstrained. The western domain of the Eastern Kunlun Range is marked by active NE-trending, left-slip deformation of the Altyn Tagh fault and an E-striking Cenozoic thrust system developed in response India-Asia collision. To better constrain the Paleozoic Altyn Tagh and Kunlun orogens and establish the Cenozoic structural framework, we conducted an integrated investigation involving detailed geologic mapping (~1:50,000 scale), U-Pb zircon geochronology, and synthesis of existing data sets across northwestern Tibet. Our new zircon analyses from Paleoproterozoic–Cretaceous strata constrain stratigraphic age and sediment provenance and highlight Proterozoic–Paleozoic arc activity. We propose a tectonic model for the Neoproterozoic–Mesozoic evolution of northwestern Tibet wherein restoration of an ~56-km-long balanced cross section across the western domain of the Eastern Kunlun suggests that Cenozoic minimum shortening strain was ~30% (~24 km shortening). Field evidence suggests this shortening commenced after ca. 25–20 Ma, which yields an average long-term shortening rate of 1.2–0.9 mm/yr and strain rates of 4.7 × 10-16 s–1 to 2.3 × 10-16 s–1. Geometric considerations demonstrate that this contractional deformation did not significantly contribute to left-slip offset on the Altyn Tagh fault, which has ~10 mm/yr slip rates. |
GSA Bulletin
v. 132, no. 5-6, p. 1291–1315. https://doi.org/10.1130/B35388.1 Supporting Information Supplemental Tables |
Footwall rotation in a regional detachment fault system: Evidence for horizontal-axis rotational flow in the Miocene Searchlight pluton, NV
Zuza, A. V., Cao, W., Hinz, N. H., DesOrmeau, J. W., Odlum, M., and Stockli, D. F. -- 2019 The Miocene Searchlight pluton, exposed in the Colorado River extensional corridor of southern Nevada, tilted up to 90° on its side in the footwall of the east-directed Dupont Mountain detachment fault system. Rapid extension and rotation occurred immediately after the ca. 17-16 Ma emplacement of this 10×10 km granite-monzogranite body. To constrain the mechanism and timing of rapid footwall exhumation, we conducted detailed field, microstructural, electron backscatter diffraction (EBSD), and zircon (U-Th)/He (ZHe) and 40Ar/39Ar hornblende thermochronological analyses. Steeply dipping fabrics across this pluton formed over a range of temperature conditions, from magmatic to high- to low-temperature sub-solidus strain, and display distributed eastside-up shear. ZHe cooling ages are consistent with constraints from tilted volcanic strata and cross-cutting dikes that suggest initial rapid rotation (~75°/Myr) at 16.2-15.7 Ma followed by more modest exhumation rates until ca. 13 Ma. Our observations are used to test tilting models for the Searchlight pluton, including rigid-body rotation, antithetic imbrication, or flow-like rotation. Available observations are most consistent with a flow-like tilting mechanism. We present scaling analyses that highlight how footwall tilting-dominated extension more effectively cools the upper crust than pure-shear extension because the hottest deep materials exhumed rapidly toward the cooler surface. This extensional mechanism efficiently cools the upper crust, causing a negative feedback whereby the rapidly cooled crust becomes strong enough to halt further fast simple-shear extension. This may explain why rapid extension was transient and further extension is mostly accommodated by high-angle low-offset magnitude normal faults that developed in a colder stronger crust. |
Mesozoic-Cenozoic evolution of the Eastern Kunlun Range, central Tibet, and implications for basin evolution during the Indo-Asian collision
Wu, C., Zuza, A. V., Zhou, Z., Yin, A., McRivette, M. W., Chen, X., Ding, L., and Geng, K. -- 2019 The present-day Tibetan plateau, which is the largest highland on Earth, formed primarily due to the India-Asia collision since 50–60 Ma. The development of the plateau has been associated with the Cenozoic development of two large intra-plateau sedimentary basins in north-central Tibet: the Qaidam and Hoh Xil basins to the north and south of the Eastern Kunlun Range, respectively. We conducted an integrated study of these two basins and the Eastern Kunlun Range that separates them to understand the timing and mechanisms of their development in order to decipher the growth and uplift history of the plateau. Crustal shortening in the Fenghuoshan-Nangqian and Qilian Shan-Nan Shan thrust belts initiated no later than the early Eocene, which formed the northern and southern boundaries of the combined Hoh Xil and Qaidam basins in central Tibet. The distinct two-stage development of the Hoh Xil basin suggests emergence of a topographic barrier between the Hoh Xil basin in the south and Qaidam basin in the north in the early Neogene, which is supported by the existing and new apatite fission-track data from the Eastern Kunlun Range that suggest rapid cooling after ca. 20 Ma. Previous and newly collected geochronological, petrological, and thermochronological data are best interpreted in the context of the Paleogene Paleo-Qaidam hypothesis, which requires Hoh Xil and Qaidam basins to have been parts of a single integrated basin during the early stage of the Cenozoic Tibetan plateau development. |
Lithosphere
v. 11, no. 4, p. 524-550. https://doi.org/10.1130/L1065.1 Data Repository File Supplemental Tables |
Hydrothermal circulation cools continental crust under exhumation
Cao, W., Lee, C-T. A., Yang, J., and Zuza, A. V. -- 2019 The formation of continental crust in magmatic arcs involves cooling of hot magmas to a relatively colder crust enhanced by exhumation and hydrothermal circulation in the upper crust. To quantify the influence of these processes on the thermal and rheological states of the crust, we developed a one-dimensional thermal evolution model, which invokes conductive cooling, advection of crust by erosion-driven exhumation, and cooling by hydrothermal circulation. We parameterized hydrothermal cooling by adopting depth-dependent effective thermal conductivity, which is determined by the crustal permeability structure and the prescribed Nusselt number at the surface. Different combinations of erosion rate and Nusselt number were tested to study the evolution of crustal geotherms, surface heat flux, and cooling rate. Simulations and scaling analyses quantify how erosion and hydrothermal circulation promote cooling via increasing total surface heat flux compared to pure conductive cooling. Hydrothermal circulation imposes intense short-term and persistent long-term cooling effects. Thinner, warmer, fast exhuming crust, with higher permeability and more vigorous hydrothermal circulation, leads to higher steady-state total surface heat flux. Hydrothermal cooling at steady state is more effective when the Péclet number is small. Hydrothermal cooling also changes crustal rheological state and thickens the brittle crust. This in turn promotes the initiation of brittle deformation in the upper crust in magmatic arcs or in regions undergoing exhumation. Interpretation of low-temperature thermochronological data could overestimate average cooling rates if hydrothermal cooling is not considered. |
Tectonics of the Eastern Kunlun Range: Cenozoic reactivation of a Paleozoic-early Mesozoic orogen
Wu, C., Zuza, A. V., Chen, X., Ding, L., Levy, D. A., Liu, C., Liu, W., Jiang, T., and Stockli, D. F. -- 2019 The Eastern Kunlun Range in north Tibet, located along the northern margin of the eastern Tethyan orogenic system, records evidence for continental break-up and ocean development in the Neoproterozoic, Paleozoic-early Mesozoic subduction and continental collision, Mesozoic intracontinental extension, and Cenozoic contractional deformation. The Kunlun region is marked by active left-lateral strike-slip deformation of Kunlun fault system, one of the major intracontinental strike-slip faults in Tibet, that developed in response India-Asia. To better constrain the tectonic evolution of the Eastern Kunlun Range and the closure of the various Kunlun oceans, we conducted detailed investigation integrating new geologic mapping, geochronology, and whole-rock geochemistry with a synthesis of existing datasets across north Tibet. The Eastern Kunlun Range experienced three major deformation events in the Neoproterozoic, early Paleozoic, and Late Paleozoic-early Mesozoic, which were associated with collision of the Proto-, Paleo-, and Neo-Kunlun arcs, respectively. Our new detrital zircon analyses from Mesoproterozoic-Cenozoic strata constrain stratigraphic age and sediment provenance and highlight the importance of three periods of arc activity. Our stratigraphic synthesis, including new field observations, provides new insights into connections between sediment dispersal and changes in tectonism and paleogeography. Miocene-to-present strike-slip activity on the Kunlun fault and the associated strain pattern can be explained by clockwise rotation of the Kunlun fault and its wallrock as a bookshelf-fault system, which has been proposed for northern Tibet as a result of distributed north-south right-lateral shear. The development of this fault system was facilitated by the presence of a Triassic suture that provided a pre-existing weakness. |
Geologic framework of the northern Indo-Burma Ranges and lateral correlation of Himalayan-Tibet lithologic units across the eastern Himalayan syntaxis
Haproff, P J., Zuza, A. V., Yin, A., Harrison, T. M., Manning, C. E., Dubey, C., S., Ding, L., Wu, C., and Chen, J. -- 2019 The Cenozoic India-Asia collision generated both the east-trending Himalayan orogen and the north-trending Eastern and Western Flanking Belts located along the margins of the Indian subcontinent. Although the tectonic development of both flanking belts is key to understanding mechanisms of continental deformation during indenter-induced collision, few field-based studies coupled with geochronological and geochemical methods have been applied to these tectonic domains. In this study, we investigate the lateral correlation of lithologic units between the northern Indo-Burma Ranges, the northernmost segment of the Eastern Flanking Belt, and the eastern Himalayan-Tibetan orogen by integrating field observations, U-Pb zircon geochronology, and whole-rock geochemistry. Our findings provide new quantitative constraints to interpretations that the northern Indo-Burma Ranges expose the eastward continuation of several lithologic units of the Himalayan orogen and Lhasa terrane. Our field work indicates that a stack of thrust-bounded lithologic units is present in the study area. The northernmost and structurally highest Lohit Plutonic Complex consists of Mesoproterozoic basement rocks (~1286 Ma) and late Jurassic-Cretaceous granitoids (~156-69 Ma) with positive ƐNd values and initial 87Sr/86Sr ratios of ~0.705, which are correlative to the Bomi-Chayu complex and the northern Gangdese batholith, respectively. The structurally lower Tidding-Mayodia mélange complex, composed of basalt, gabbro, ultramafic rocks, and mafic schist of a dismembered ophiolite sequence, is interpreted in this study as the eastward extension of the Indus-Yarlung suture zone. Structurally below the suture zone are the Mayodia gneiss and Lalpani schist, which are interpreted to correlate with the Lesser Himalayan Sequence based on comparable metamorphic lithologies, negative ƐNd values, and similar Mesoproterozoic-Cambrian detrital zircon age spectra. In contrast to the above metamorphic units, the structurally lowest Tezu unit consists of siliciclastic strata that may be correlated with the Miocene-Pliocene Siwalik Group of the Himalayan orogen. Despite the above correlations, notable Himalayan-Tibetan lithologic units are absent in the northern Indo-Burma Ranges, including the Mesozoic-Cenozoic southern Gangdese batholith belt and its cover sequence of the Linzizong volcanic rocks, Xigaze forearc basin, Tethyan Himalayan Sequence, and Greater Himalayan Crystalline Complex of south-central Tibet and the central Himalaya. We interpret the absence of these lithologic units to be a result of a greater magnitude of crustal shortening and/or underthrusting of the Indian cratonal rocks than that across the Himalayan orogen to the west. This interpretation is supported by a southward decrease in the map-view distance between the active range-bounding thrust and the Indus-Yarlung suture zone in the northern Indo-Burma Ranges, from ~200 km in the north near the eastern Himalayan syntaxis to ~5 km in the south across a distance of ~200-300 km. |
Cenozoic cooling history of the North Qilian Shan, northern Tibetan Plateau, and the initiation of the Haiyuan fault: Constraints from apatite- and zircon-fission track thermochronology
Li, B., Chen, X., Zuza, A. V., Hu, D., Ding, W., Huang, P., and Xu, S. -- 2019 The growth of the Tibetan Plateau resulted primarily from India-Asia convergence since initial collision at 65–55 Ma. The Cenozoic Qilian Shan thrust belt and the left-slip strike Haiyuan fault system together define the northeastern margin of the plateau. Although these thrust and strike-slip fault systems play an important role in accommodating continental convergence, our knowledge of the temporal and spatial distribution of upward and outward growth of the northeastern Tibetan Plateau is still lacking. In this study, we integrate new geologic mapping and low-temperature themochronometry (apatite- and zircon-fission-track ages) to provide constraints on the uplift and cooling history of the North Qilian Shan and the initiation of the Haiyuan fault. Cooling ages and thermal history modeling from a traverse across a prominent restraining bend on the Haiyuan fault suggest the North Qilian Shan experienced a three-phase cooling history, including: (1) broad cooling during the Late Triassic to early Cenozoic, (2) long-term tectonic quiescence from late Cretaceous to middle Miocene, and (3) rapid cooling and exhumation from ~15–10 Ma to present. We relate this most recent local cooling (~15–10 Ma) to the initiation of strike-slip faulting along the central Haiyuan fault, which corroborates other recent studies, suggesting a middle Miocene activation of strike-slip deformation along the Haiyuan fault in northern Tibet. |
Tectonophysics
v. 751, p. 109-124 https://doi.org/10.1016/j.tecto.2018.12.005 AFT age table AFT length table |
Underthrusting and duplexing beneath the northern Tibetan Plateau and the evolution of the Himalayan-Tibetan orogen
Zuza, A. V., Wu, C., Wang, Z., Levy, D. A., Li, B., Xiong, X., and Chen, X. -- 2019 The Cenozoic Qilian Shan thrust belt is the northern margin of the Tibetan Plateau, which developed in part due to progressive India-Asia convergence during Himalayan-Tibetan orogeny. Available geologic observations suggest that this thrust belt started deforming shortly after initial India-Asia collision at 60–55 Ma, and thus its kinematic development is intrinsically related to the construction and evolution of the Tibetan Plateau. Here, we present new field observations from a geologic traverse across the Qilian Shan to elucidate the style of deformation across the active thrust belt. In particular, we infer protracted out-of-sequence deformation here that is consistent with this thrust system remaining a stationary northern boundary to the Tibetan Plateau since the early Cenozoic. We present a lithosphere-scale model for this region that highlights the following: (1) coupled distributed crustal shortening and underthrusting of the North China craton beneath Tibet, which explains the spatial and temporal distribution of observed crustal shortening and thickness, (2) this underthrusting exploited the south-dipping early Paleozoic Qilian suture paleo–subduction mélange channel, and (3) development of a lower-crustal duplex at the lithospheric underthrusting ramp. This last inference can explain the relatively high elevation, low relief, and thickened crust of the central Qilian Shan, as well as the comparative aseismicity of the region, which experiences fewer earthquakes due to less upper-crustal faulting. Both the northern and southern margins of the Himalayan-Tibetan orogen appear to have developed similarly, with continental underthrusting and crustal-scale imbrication and duplexing, despite vastly different climatic and plate-velocity boundary conditions, which suggests that the orogen-scale architecture of the thrust belt is controlled by neither of these forcing mechanisms. Instead, strength anisotropies of the crust probably control the kinematics and style of deformation, including the development of northern Tibet, where thrust systems are concentrated along pre-Cenozoic suture zones. |
A 1.9-Ga mélange along the northern margin of the North China craton: Implications for the assembly of Columbia supercontinent
Wu, C., Zhou, Z., Zuza, A. V., Wang, G., Liu, C., and Jiang, T -- 2018 The involvement and location of the Neoarchean-Paleoproterozoic North China craton in the supercontinent Columbia remains enigmatic, and the tectonic history along its margins impacts our understanding of connections between North China and other continents. Here we present structural observations from a Paleoproterozoic mélange that is located along its northern margin and which we refer to as the Bayan Obo mélange. It is composed of a structurally complex tectonic mixture of metapelites and metasedimentary rocks mixed with exotic blocks of ultramafic-mafic rocks, meta-basalts, metacarbonate and alkaline rocks, and tonalite-trondhjemite gneisses (TTG). New zircon geochronology of the various constituent blocks suggest that it formed, and was subsequently deformed, at ca. 1.9 Ga. The oldest intra-mélange blocks are 2.45-2.54 Ga TTG rocks and granitoids that signify the stabilization of the northern North China in the Neoarchean-Paleoproterozoic. A ca. 2.45 Ga plagiogranite block probably originated by partial melting of the older TTG rocks. We suggest this mélange formed in a sedimentary setting near the subduction trench, on the basis of mixing of upper and lower plate volcanic rocks and textural relationships. The Bayan Obo mélange thus represents one of the oldest documented sedimentary mélanges on Earth, yet its fundamental characteristics strongly resemble Phanerozoic subduction complexes. Based on similar ages and styles of deformation, this zone may represent the ca. 1.9 Ga collisional zone between North China and the southwestern margin of the Siberia craton. In this context, the North China craton became an integral component of the supercontinent Columbia starting at ca. 1.9 Ga. |
Tectonic evolution of the Qilian Shan: An early Paleozoic orogen reactivated in the Cenozoic
Zuza, A. V., Wu, C., Reith, R.C., Yin, A., Zhang, Y., Zhang, J., Li, J., Wu, L., and Liu, W. -- 2018 The Qilian Shan, located along the northeastern margin of the Tibetan Plateau, experienced multiple episodes of tectonic deformation, including Neoproterozoic continental break up, early Paleozoic subduction and continental collision, Mesozoic extension, and Cenozoic intracontinental orogenesis resulting from the India-Asia collision. In the central Qilian Shan, pre-Mesozoic ophiolite complexes, passive-continental margin sequences, and strongly deformed forearc strata were juxtaposed against arc plutonic/volcanic rocks and ductilely deformed crystalline rocks during the early Paleozoic Qilian orogen. To better constrain this orogen and the resulting closure of the Neoproterozoic-Ordovician Qilian Ocean, we have conducted an integrated investigation involving geologic mapping, U-Th-Pb zircon and monazite geochronology, whole-rock geochemistry, thermobarometry, and synthesis of existing data sets across northern Tibet. The central Qilian Shan experienced two phases of arc magmatism at 960–870 Ma and 475–445 Ma that were each followed by periods of protracted continental collision. Integrating our new data with previously published results, we propose the following tectonic model for the Proterozoic-Paleozoic history of northern Tibet. (1) Early Neoproterozoic subduction accommodated the convergence and collision between the South Tarim-Qaidam and North Tarim-North China continents. (2) Late Neoproterozoic rifting partially separated a peninsular Kunlun-Qaidam continent from the southern margin of the linked Tarim-North China craton and opened the Qilian Ocean as an embayed marginal sea; this separation broadly followed the trace of the earlier Neoproterozoic suture zone. (3) South-dipping subduction along the northern margin of the Kunlun-Qaidam continent initiated in the Cambrian, first developing as the Yushigou supra-subduction zone (SSZ) ophiolite and then transitioning into the continental Qilian arc. (4) South-dipping subduction, arc magmatism, and the convergence between Kunlun-Qaidam and North China continued throughout the Ordovician, with a trench-parallel intra-arc strike-slip fault system that is presently represented by high-grade metamorphic rocks that display a pervasive right-lateral shear sense. (5) Counter-clockwise rotation of the peninsular Kunlun-Qaidam continent toward North China led to the closure of the Qilian Ocean, which is consistent with the right-lateral kinematics of intra-arc strike-slip faulting observed in Qilian Shan and the westward tapering map-view geometry of Silurian flysch-basin strata. Continental collision at ~445–440 Ma led to widespread plutonism across the Qilian Shan and is recorded by recrystallized monazite (~450–420 Ma) observed in this study. Our tectonic model implies the parallel closure of two oceans of different ages along the trace of Qilian suture zone since ~1.0 Ga. In addition, the Qilian Ocean was neither the Proto- nor Paleo-Tethys (i.e., the earliest ocean separating Gondwana from Laurasia) as previously suggested, but was rather a relatively small embayed sea along the southern margin of the Laurasian continent. We also document >200 km of Cenozoic north-south shortening across the study area. The observed shortening distribution supports models of Tibetan Plateau development that involve distributed crustal shortening and southward underthrusting of Eurasia beneath the plateau. This India-Asia convergence-related deformation is focused along the sites of repeated ocean closure. Major Cenozoic left-slip faults parallel these sutures, and preexisting subduction-mélange channels may have facilitated Cenozoic shortening and continental underthrusting. |
What can strike-slip fault spacing tell us about the plate boundary of western North America?
Zuza, A. V., and Carlson, C. W. -- 2018 The spacing of parallel continental strike-slip faults can constrain the mechanical properties of the faults and fault-bounded crust. In the western US, evenly spaced strike-slip fault domains are observed in the San Andreas (SA) and Walker Lane (WL) fault systems. Comparison of fault spacing (S) versus seismogenic zone thickness (L) relationships of the SA and WL systems indicates that the SA has a steeper S/L slope (~8 vs 1, respectively). If a stress-shadow mechanism guides parallel fault formation, the S/L slope should be controlled by fault strength, crustal strength and/or regional stress. This suggests that the SA-related strike-slip faults are relatively weaker, with lower fault friction: 0.13–0.19 for the SA versus 0.20 for WL. The observed mechanical differences between the SA and WL systems may be attributed to variations in the local geology of the fault-hosting crust and/or the regional boundary conditions (e.g., geothermal gradient or strain rate). |
West-directed thrusting south of the eastern Himalayan syntaxis indicates clockwise crustal flow at the indenter corner during the India-Asia collision
Haproff, P. J., Zuza, A. V., and Yin, A. -- 2018 Whether continental deformation is accommodated by microplate motion or continuum flow is a central issue regarding the nature of Cenozoic deformation surrounding the eastern Himalayan syntaxis. The microplate model predicts southeastward extrusion of rigid blocks along widely-spaced strike-slip faults, whereas the crustal-flow model requires clockwise crustal rotation along closely-spaced, semi-circular right-slip faults around the eastern Himalayan syntaxis. Although global positioning system (GPS) data support the crustal-flow model, the surface velocity field provides no information on the evolution of the India-Asia orogenic system at million-year scales. In this work, we present the results of systematic geologic mapping across the northernmost segment of the Indo-Burma Ranges, located directly southeast of the eastern Himalayan syntaxis. Early research inferred the area to have experienced either right-slip faulting accommodating northward indentation of India or thrusting due to the eastward continuation of the Himalayan orogen in the Cenozoic. Our mapping supports the presence of dip-slip thrust faults, rather than strike-slip faults. Specifically, the northern Indo-Burma Ranges exposes south- to west-directed ductile thrust shear zones in the hinterland and brittle fault zones in the foreland. The trends of ductile stretching lineations within thrust shear zones and thrust sheets rotate clockwise from the northeast direction in the northern part of the study area to the east direction in the southern part of the study area. This clockwise deflection pattern of lineations around the eastern Himalayan syntaxis mirrors the clockwise crustal-rotation pattern as suggested by the crustal-flow model and contemporary GPS velocity field. However, our finding is inconsistent with discrete strike-slip deformation in the area and the microplate model. |
The Trace Element Distribution Patterns of Ediacaran-Early Cambrian Black Shales and the Origin of Selenium in the Guangning Area, Western Guangdong Province, South China
Tian, X., Luo, K., and Zuza, A. V. -- 2017 The Ediacaran and early Cambrian black shales are widespread across the South China Craton (Yangtze and Cathaysia blocks). However, the trace element distribution patterns of the Ediacaran and early Cambrian black shales in the Cathaysia Block are still unclear. In this study, thirtyfour black shale samples in the Lechangxia Group (Ediacaran) and thirteen black shale samples in the lower Bacun Group (early Cambrian) from Guangning area, western Guangdong Province, South China, were analyzed for major and trace elements concentrations. Compared to the upper continental crust, the Ediacaran black shales exhibit strongly enriched Se, Ga, and As with enrichment factor values (EF) higher than 10, significantly enriched Bi and Rb (10>EF>5), weakly enriched Mo, Ba, Cs, V, In, Be, Tl, and Th (5>EF>2), normal U, Cr, Cd, Sc, Pb, Cu, and Li (2>EF>0.5), and depleted Ni, Zn, Sr, and Co. Early Cambrian black shales display strongly enriched Se, Ga, and As, significantly enriched Ba, Bi, and Rb, weakly enriched Mo, Cs, Cd, V, U, Be, In, and Tl, normal Sc, Th, Cr, Li, Cu, Ni, and Pb and depleted Co, Zn, and Sr. Moreover, Se is the most enriched trace element in the Ediacaran and early Cambrian black shales: concentrations vary from 0.25 to 30.09 ppm and 0.54 to 5.01 ppm, and averaging 4.84 and 1.72 ppm, with average EF values of 96.87 and 34.32, for the Ediacaran and early Cambrian shales respectively. The average concentration of Se in the Ediacaran black shales is 2.8 times higher than that of early Cambrian black shales. Se contents in the Ediacaran and early Cambrian black shales exhibit significant variation (P = 0.03). Provenance analysis showed that Se contents of both the Ediacaran and early Cambrian black shales were without detrital provenance and volcanoclastic sources, but of hydrothermal origin. The deep sources of Se and the presence of pyrite may explain the higher Se contents in the Ediacaran black shales. Similar with the Se-rich characteristics of the contemporaneous black shales in the south Qingling Mountain and Yangtze block, the Ediacaran and early Cambrian black shales in Guangning area, Cathaysia, are also enriched in Se, which may provide a clue for looking for the selenium-rich resources in western Guangdong Province. |
Acta Geologica Sinica
(English Edition) v. 91, no. 6, p. 1978-1991 https://doi.org/10.1111/1755-6724.13445 |
Balkatach hypothesis: A new model for the evolution of the Pacific, Tethyan, and Paleo-Asian oceanic domains
Zuza, A. V., and Yin, A. -- 2017 The Phanerozoic history of the Paleo-Asian, Tethyan, and Pacific oceanic domains is important for unraveling the tectonic evolution of the Eurasian and Laurentian continents. The validity of existing models that account for the development and closure of the Paleo-Asian and Tethyan Oceans critically depends on the assumed initial configuration and relative positions of the Precambrian cratons that separate the two oceanic domains, including the North China, Tarim, Karakum, Turan, and southern Baltica cratons. Existing studies largely neglect the Phanerozoic tectonic modification of these Precambrian cratons (e.g., the effects of India-Arabia-Eurasia convergence and post-Rodinia rifting). In this work we systematically restore these effects and evaluate the tectonic relationships among these cratons to test the hypothesis that the Baltica, Turan, Karakum, Tarim, and North China cratons were linked in the Neoproterozoic as a single continental strip, with variable along-strike widths. Because most of the tectonic boundaries currently separating these cratons postdate the closure of the Paleo-Asian and Tethyan Oceans, we are able to establish a >6000-km-long Neoproterozoic contiguous continent referred to here as Balkatach (named from the Baltica–Karakum–Tarim–North China connection). By focusing on the regional geologic history of Balkatach’s continental margins, we propose the following tectonic model for the initiation and evolution of the Paleo-Asian, Tethyan, and Pacific oceanic domains and the protracted amalgamation and growth history of the Eurasian continent. (1) The early Neoproterozoic collision of the combined Baltica–Turan–Karakum–South Tarim continents with the linked North Tarim–North China cratons led to the formation of a coherent Balkatach continent. (2) Rifting along Balkatach’s margins in the late Neoproterozoic resulted in the opening of the Tethyan Ocean to the south and unified Paleo-Asian and Pacific Oceans to the north (present-day coordinates). This process led to the detachment of Balkatach-derived microcontinents that drifted into the newly formed Paleo-Asian Ocean. (3) The rifted microcontinents acted as nuclei for subduction systems whose development led to the eventual demise of the Paleo-Asian Ocean during the formation of the Central Asian Orogenic System (CAOS). Closure of this ocean within an archipelago-arc subduction system was accommodated by counterclockwise rotation of the Balkatach continental strip around the CAOS. (4) Initial collision of central Balkatach and the amalgamated arcs and microcontinents of the CAOS in the mid-Carboniferous was followed by a bidirectional propagation of westward and eastward suturing. (5) The closure of the Paleo-Asian Ocean in the early Permian was accompanied by a widespread magmatic flare up, which may have been related to the avalanche of the subducted oceanic slabs of the Paleo-Asian Ocean across the 660 km phase boundary in the mantle. (6) The closure of the Paleo-Tethys against the southern margin of Balkatach proceeded diachronously, from west to east, in the Triassic–Jurassic. |
Geochronology and geochemistry of Neoproterozoic granitoids in the central Qilian Shan of northern Tibet: Reconstructing the amalgamation processes and tectonic history of Asia
Wu, C., Zuza, A. V., Yin, A., Liu, C., Reith, R. C., Zhang, J., Liu, W., and Zhou, Z. -- 2017 Our understanding of the assembly history of Asia depends critically on the tectonic relationships between its major cratons, including Siberia, North China, South China, and Tarim. The intervening microcontinents between these cratons can provide insight into the paleogeographic and paleotectonic relationships of the cratons, but there is currently a general lack of knowledge regarding the basement geology of these microcontinents. Here we present results from systematic geologic mapping, U-Pb zircon dating, whole-rock geochemical analysis, and synthesis of existing data to establish the Proterozoic to early Paleozoic evolution of the central Qilian basement to the south of the North China craton in northwest China. Our results indicate that the region underwent three major periods of magmatic activity at 960–880, 877–710, and 550–375 Ma. Our geochemical analysis suggests that the ca. 900 Ma plutons were generated during arc magmatism and/or syncollisional crustal melting, whereas the ca. 820 Ma plutons are A-type granitoids, which are typically associated with extensional tectonism. Igneous zircons from a high- and ultrahigh-pressure eclogite in the north-central Qilian Shan have a U-Pb age of ca. 916 Ma, whereas dating of the recrystallized rims suggests that eclogite facies metamorphism occurred at ca. 485 Ma. Our detrital zircon geochronology also indicates that a widespread metasedimentary unit in the region was deposited between ca. 1200 and ca. 960 Ma, prior to the onset of a rift-drift event at ca. 750 Ma. Based on regional geologic constraints and the magmatic history, we propose the following tectonic history: (1) the paleo–Qilian Ocean bound the combined North Tarim–North China craton to the south (present-day coordinates) in the Mesoproterozoic; (2) the paleo–Qilian Ocean closed between 900 and 820 Ma following the collision of North Tarim–North China craton and the South Tarim–Qaidam–Kunlun continent; (3) the younger Qilian Ocean opened at ca. 775 Ma along the previous suture trace of the paleo–Qilian Ocean as a marginal sea within southern Laurasia; and (4) this ocean closed by ca. 445–440 Ma as a result of collision between the Tarim–North China cratons and the Qaidam-Kunlun continent along a south-dipping subduction system. |
Lithosphere
v. 9, no. 4, p. 609-636 https://doi.org/10.1130/L640.1 Supplementary U-Pb zircon and geochemistry data |
The relationship between magma and mineralization in Chaobuleng iron polymetallic deposit, Inner Mongolia
Wu, C., Wang, B., Zhou, Z., Wang, G., Zuza, A.V., Liu, C., Jiang, T., Liu, W., and Ma, S. -- 2017 The Chaobuleng iron polymetallic deposit, an important ore system in China that is genetically related to the early Cretaceous Chaobuleng pluton, is located in the eastern part of Lizi Shan-Dong Ujimqin Banner metallogenic belt of Inner Mongolia. To understand the relationship of magmatism and mineralization in this iron polymetallic deposit, we have conducted a detailed geologic field study in conjunction with systematic investigation of U-Pb zircon and Re-Os isochron geochronology, mineralogy, petrology, major-and trace-element geochemistry, and synthesis of existing datasets across the Chaobuleng region. We use these observations to identify the origins and petrogenesis of mafic enclaves and the host granitoid, and to place new constraints on the tectonic setting at the time of magmatism. New U-Pb geochronology of magmatic zircons and Re–Os isochron ages of hydrothermal molybdenite from the iron polymetallic deposit allow us to constrain the sources of the hydrothermal components and the relationship between iron polymetallic mineralization and regional geodynamic evolution. The geology, paragenesis, and estimated P-T conditions suggest that the Chaobuleng iron polymetallic deposit was formed as a shallow, proximal skarn deposit. The ore-forming early Cretaceous Chaobuleng pluton can be divided into three distinct units based on crystallization age, texture, and composition: (1) a 138.1–140.6 Ma syenogranite porphyry, (2) a 137.4–138.6 Ma enclave bearing porphyritic syenogranite, and (3) a 133.9–135.98 Ma coarse-grained porphyritic syenogranite. We suggest that the A-type Chaobuleng pluton was formed in a post-orogenic extensional setting with significant magma mixing from high-temperature melts (i.e., a Zr saturation temperature of 800–900°C). During the magmatic process, the Chaobuleng pluton crystallized under temperatures as low as 720–770°C and pressures of 0.5–1.0 kbar. The chemical composition of biotite shows that the Chaobuleng magma was enriched in F (1.5–3.5%). We attribute the observed embayed texture of quartz to a three coexisting-phase equilibrium model that operated during the magmatic-hydrothermal transition and can be used to constrain the mineralization process and physico-chemical conditions. Due to a loss of volatiles, the residual melt was quickly quenched and crystallized into a fine-grained groundmass. The Re–Os model ages of samples from the inner pluton-mineralization contact belt are 135.0 ± 2.1 Ma and 131.2 ± 4.1 Ma, and a sample from the outer-contact belt yields an isochron age of 140.7 ± 1.8 Ma. The Chaobuleng deposit formed during protracted activity of the magmatic-hydrothermal system, which is similar to many mineralization systems around the world. However, the major mineralization stage (iron oxide stage) of the Chaobuleng deposit occurred during the early stage of magmatism, consistent with the emplacement time of syenogranite porphyry at ~139 Ma. |
Gondwana Research
v. 45, p. 228-253 http://dx.doi.org/10.1016/j.gr.2017.02.006 Supplementary U-Pb zircon dating table Supplementary geochemistry data |
Spacing and strength of active continental strike-slip faults
Zuza, A.V., Yin, A., Lin, J., and Ming, S. -- 2017 Parallel and evenly-spaced active strike-slip faults occur widely in nature across diverse tectonic settings. Despite their common existence, the fundamental question of what controls fault spacing remains unanswered. Here we present a mechanical model for the generation of parallel strike-slip faults that relates fault spacing to the following parameters: (1) brittle-crust thickness, (2) fault strength, (3) crustal strength, and (4) crustal stress state. Scaled analogue experiments using dry sand, dry crushed walnut shells, and viscous putty were employed to test the key assumptions of our quantitative model. The physical models demonstrate that fault spacing (S) is linearly proportional to brittle-layer thickness (h), both in experiments with only brittle materials and two-layer trials involving dry sand overlying viscous putty. The S/h slope in the two-layer sand-putty experiments may be controlled by the (1) rheological/geometric properties of the viscous layer, (2) effects of distributed basal loading caused by the viscous shear of the putty layer, and/or (3) frictional interaction at the sand-putty interface (i.e., coupling between the viscous and brittle layers). We tentatively suggest that this third effect exerts the strongest control on fault spacing in the analogue experiments. By applying our quantitative model to crustal-scale strike-slip faults using fault spacing and the seismogenic-zone thickness obtained from high-resolution earthquake-location data, we estimate absolute fault friction of active strike-slip faults in Asia and along the San Andreas fault system in California. We show that the average friction coefficient of strike-slip faults in the India-Asia collisional orogen is lower than that of faults in the San Andreas fault system. Weaker faults explain why deformation penetrates >3500 km into Asia from the Himalaya and why the interior of Asia is prone to large (M > 7.0) devastating earthquakes along major intra-continental strike-slip faults. Our new approach of estimating absolute fault strength may be useful in future studies of continental deformation and earthquake mechanics. |
Continental deformation accommodated by non-rigid passive bookshelf faulting: An example from the Cenozoic tectonic development of northern Tibet
Zuza, A.V., and Yin, A. -- 2016 Collision-induced continental deformation commonly involves complex interactions between strike-slip faulting and off-fault deformation, yet this relationship has rarely been quantified. In northern Tibet, Cenozoic deformation is expressed by the development of the > 1000-km-long east-striking left-slip Kunlun, Qinling, and Haiyuan faults. Each have a maximum slip in the central fault segment exceeding 10s to ~ 100 km but a much smaller slip magnitude (~< 10% of the maximum slip) at their terminations. The along-strike variation of fault offsets and pervasive off-fault deformation create a strain pattern that departs from the expectations of the classic plate-like rigid-body motion and flow-like distributed deformation end-member models for continental tectonics. Here we propose a non-rigid bookshelf-fault model for the Cenozoic tectonic development of northern Tibet. Our model, quantitatively relating discrete left-slip faulting to distributed off-fault deformation during regional clockwise rotation, explains several puzzling features, including the: (1) clockwise rotation of east-striking left-slip faults against the northeast-striking left-slip Altyn Tagh fault along the northwestern margin of the Tibetan Plateau, (2) alternating fault-parallel extension and shortening in the off-fault regions, and (3) eastward-tapering map-view geometries of the Qimen Tagh, Qaidam, and Qilian Shan thrust belts that link with the three major left-slip faults in northern Tibet. We refer to this specific non-rigid bookshelf-fault system as a passive bookshelf-fault system because the rotating bookshelf panels are detached from the rigid bounding domains. As a consequence, the wallrock of the strike-slip faults deforms to accommodate both the clockwise rotation of the left-slip faults and off-fault strain that arises at the fault ends. An important implication of our model is that the style and magnitude of Cenozoic deformation in northern Tibet vary considerably in the east–west direction. Thus, any single north–south cross section and its kinematic reconstruction through the region do not properly quantify the complex deformational processes of plateau formation. |
Testing models of Tibetan Plateau formation with Cenozoic shortening estimates across the Qilian Shan-Nan Shan thrust belt
Zuza, A.V., Cheng, X., and Yin, A. -- 2016 Competing models that account for the construction of the Tibetan Plateau include continental subduction, underthrusting, distributed shortening, channel flow, and older crustal-structure inheritance. Well-constrained estimates of crustal shortening strain serve as a diagnostic test of these plateau formation models and are critical to elucidate the dominant mechanism of plateau development. In this work we estimate the magnitude of Cenozoic shortening across the northern Qilian Shan–Nan Shan thrust belt, along the northeastern plateau margin, based on detailed analysis and reconstruction of three high-resolution seismic reflection profiles. By integrating surface geology, seismic data, and the regional tectonic history, we demonstrate that this thrust system has accumulated >53% Cenozoic strain (∼50 km shortening), accommodated by several south-dipping thrust faults. Based on the observed strain distribution across northern Tibet, including lower strain (30%–45%) within the interior of the Qilian Shan–Nan Shan thrust belt, we suggest that a combination of distributed crustal shortening and minor (<250 km) southward underthrusting of the Asian lithosphere is responsible the development of the northern Tibetan Plateau. Focused shortening along the Qilian Shan frontal thrust system accommodates much of the present-day convergence between Tibet and North China, which implies that the northern plateau margin may have developed in a similar manner to that of southern Tibet through Himalayan-style continental underthrusting. We also argue that the Qilian Shan–Nan Shan, North Qaidam, and Qaidam Basin thrust systems have absorbed a minimum of 250–350 km north-south Cenozoic shortening, which is double the commonly cited value of ∼150 km. |
Geosphere
v. 12, no. 2, p. 501-532 doi:10.1130/GES01254.1 Supplementary Information Hi-res Geologic Map |
Pre-Cenozoic Geologic History of the Central and Northern Tibetan Plateau and the Role of Wilson Cycles in Constructing the Tethyan Orogenic System
Wu, C., Yin, A., Zuza, A.V., Zhang, J., Liu, W., and Ding, L. -- 2016 In order to better constrain the evolution of the Tethyan orogenic system, we conducted an integrated investigation involving U-Pb dating of igneous and detrital zircon, geochemical analysis of igneous rocks, compositional analysis of sedimentary strata, and a synthesis of existing work across the Qilian Shan, Qaidam Basin, and the Eastern Kunlun Range of central and northern Tibet. This effort reveals five stages of arc magmatism at 1005–910 Ma, 790–720 Ma, 580–500 Ma, 490–375 Ma, and 290–195 Ma, respectively. Arc activities were interrupted by repeated continent-continent collision followed by ocean opening along the older suture zones first created in the Neoproterozoic. This suggests that Wilson cycles have played a controlling role in constructing the southern Asian continent. The magmatic history and regional geologic constraints allow us to construct a coherent tectonic model that has the following key features. (1) The linked South Qilian suture in the west and North Qinling suture in the east formed the northern boundary of the coherent Kunlun–Qaidam–North Qinling Terrane in the early Paleozoic. (2) The Songpan-Ganzi Terrane has been the western part of the Yangtze craton since the Neoproterozoic. (3) Development of the wide (>700 km) Permian–Triassic arc across the Kunlun-Qaidam Terrane was induced by flat subduction and rapid slab rollback, which also caused extreme extension of the Songpan-Ganzi Terrane. (4) The formation of the Anymaqen-Kunlun-Muztagh Ocean (= the Neo–Kunlun Ocean in this study) was created within Laurasia rather than being a preexisting ocean between Gondwana and Laurasia as postulated by most early studies. |
Mechanics of evenly spaced strike-slip faults and its implications for the formation of tiger-stripe fractures on Saturn's moon Enceladus
Yin, A., Zuza, A.V., and Pappalardo, R.T. -- 2016 We present the first mechanical analysis based on realistic rheology and boundary conditions on the formation of evenly spaced strike-slip faults. Two quantitative models employing the stress-shadow concept, widely used for explaining extensional-joint spacing, are proposed in this study: (1) an empirically based stress-rise-function model that simulates the brittle-deformation process during the formation of evenly spaced parallel strike-slip faults, and (2) an elastic plate model that relates fault spacing to the thickness of the fault-hosting elastic medium. When applying the models for the initiation and development of the tiger-stripe fractures (TSF) in the South Polar Terrain (SPT) of Enceladus, the mutually consistent solutions of the two models, as constrained by the mean spacing of the TSF at ∼35 km, requires that the brittle ice-shell thickness be ∼30 km, the elastic thickness be ∼0.7 km, and the cohesive strength of the SPT ice shell be ∼30 kPa. However, if the brittle and elastic models are decoupled and if the ice-shell cohesive strength is on the order of ∼1 MPa, the brittle ice shell would be on the order of ∼10 km. |
Tectonic Development of the northeastern Tibetan Plateau as constrained by high-resolution deep seismic-reflection data
Gao, R., Wang, H., Yin, A., Kang, Z., Zuza, A.V., Li, W., and Xiong, X. -- 2013 A 180-km-long, high-resolution seismic-reflection survey that imaged the entire crust and the uppermost mantle lithosphere was conducted across the northeastern Tibetan Plateau. This work had three aims: (1) to examine whether the left-slip Haiyuan and Tianjing faults defining the margin of NE Tibet are crustal- or lithospheric-scale structures, (2) to determine whether seismic fabrics are consistent with middle- and/or lower-crustal channel flow, and (3) to establish the minimum amount of Cenozoic shortening strain in the region. Analysis of our newly obtained seismic-reflection data suggests that the left-slip Haiyuan and Tianjing faults have multiple strands and cut through the upper and middle crust. The faults likely terminate at a low-angle detachment shear zone in the lower crust, because the flat Moho directly below the projected traces of the faults is continuous. The seismic image displays subvertical zones of highly reflective sequences containing parallel and subhorizontal reflectors that are truncated by seismically transparent regions with irregular shape. The transparent regions in the middle crust are traceable to the seismically transparent lower crust and are interpreted as early Paleozoic plutons emplaced during the construction of the Qilian arc in the region. The presence of the undisturbed subvertical contacts between zones of highly reflective and seismically transparent regions rules out the occurrence of channel flow in the middle crust, as this process would require through-going subhorizontal reflectors bounding the channel above and below. The lack of continuous reflectors longer than a few kilometers in the lower crust makes a laminar mode of channel flow unfavorable, but lateral lower-crustal flow could have occurred via small-scale ductile deformation involving folding (less than a few kilometers in wavelength and amplitude). Integrating surface geology and the seismic data, we find that the upper crust along a segment of the seismic surveying line experienced up to 46% crustal shortening postdating the Cretaceous and is thus interpreted as entirely accumulated in the Cenozoic. If the estimated shortening strain is representative across northeastern Tibet, its magnitude is sufficient to explain the current elevation of the region without an appeal for additional contributing factors such as channel flow and/or a thermal event in the upper mantle. |
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