Browsing by Author "Cai, Fulong"

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The Ancestral Lhasa River: A Late Cretaceous trans-arc river that drained the proto-Tibetan Plateau
(2019-09-19) Laskowski, Andrew K.; Orme, Devon A.; Cai, Fulong; Ding, Lin
Late Cretaceous trench basin strata were deposited in the subduction zone that consumed Neo-Tethyan oceanic lithosphere along the southern margin of the proto–Tibetan Plateau. We conducted detrital zircon (DZ) U-Pb geochronology on six trench basin samples (n = 1716) collected near Dênggar, Tibet (∼500 km west of Lhasa), to assess the provenance of these rocks and reconstruct Late Cretaceous sediment transport pathways. They contained DZ ages that point to a unique source around Lhasa city, north of the Late Cretaceous Gangdese magmatic arc. The modern Lhasa River catchment contains the requisite sources, and its main trunk transects the Gangdese magmatic arc, joining with the Yarlung River at a barbed junction at the India-Asia suture. We infer that the Lhasa River is an ancient feature that transported sediment to the subduction zone in Late Cretaceous time and persisted during India-Asia collision.
Configuration and Timing of Collision Between Arabia and Eurasia in the Zagros Collision zone, Fars, Southern Iran
(American Geophysical Union, 2021-08) Cai, Fulong; Ding, Lin; Wang, Houqi; Laskowski, Andrew K.; Zhang, Liyun; Zhang, Bo; Mohammadi, Ali; Li, Jinxiang; Song, Peiping; Li, Zhenyu; Zhang, Qinghai
The configuration and timing of the Arabia-Eurasia continental collision, part of the broader Alpine-Himalayan collisional system, remains controversial. We conducted sandstone petrology, detrital zircon U-Pb-Hf isotopic and trace element analysis, and Cr spinel electron microprobe geochemical analysis of samples from Paleocene to Miocene peripheral foreland strata in interior Fars, southern Iran. These data were used to test competing models for ophiolite obduction and Arabia-Eurasia collision. In addition, we applied these data to compare the history of outward and upward growth of the Zagros and Himalayan-Tibetan segments of the Alpine-Himalayan collisional orogenic belt. The first appearance of radiolarian-rich chert conglomerate, 100–90 Ma detrital zircons with positive ɛHf(t) values from +1 to +20 and midocean ridge geochemical affinity, and suprasubduction zone (SSZ) affinity Cr-spinel is in the lower and middle Sachun Formation. These data indicate that obduction occurred before deposition of the upper Maastrichtian-lower Paleocene Sachun Formation and developed in an intra-oceanic setting rather than an Arabia-Eurasia collision setting. Abundant continental-arc affinity detrital zircon with 180–160 Ma and 50–27 Ma age-probability peaks and varied ɛHf(t) values are present in the upper Oligocene-lower Miocene Razak and Agha Jari formations, indicating sedimentary overlap with Eurasia. SSZ-affinity Cr-spinel in all samples indicates that ophiolitic rocks were a continual source of detritus in the foreland basin since Paleocene. The depositional age of the basal Razak Formation is between 25.7 and 21.5 Ma. Therefore, we interpret that collision between Arabia and Eurasia must have been initiated before deposition of the Razak Formation.
Field Report: Research along the Yarlung Suture Zone in Southern Tibet, a persistent geological frontier
(2018-03) Laskowski, Andrew K.; Ding, Lin; Cai, Fulong; Chen, Yaofei; He, Songlin
The Yarlung Suture Zone in Southern Tibet marks the boundary between India and Asia–formerly separated by an ocean basin–and is a critical record of the tectonic processes that created the Tibetan Plateau. The Yarlung Suture Zone is also a frontier research area, as difficulty of access has limited research activity, providing ample opportunities for new discoveries. This paper documents field research conducted by the authors along the Yarlung suture zone in eastern Xigaze (Shigatse, Rikaze) County, ∼250 km west of the city of Lhasa, in July 2017. The goal of this research was to map the Suture Zone structure in detail, and more specifically to understand the branching relationships between two major fault systems—the Great Counter Thrust and Gangdese Thrust. A summary of early geological exploration is included to provide context for this research.
Gangdese Culmination Model: Oligocene—Miocene Duplexing along the India-Asia Suture Zone, Lazi Region, Southern Tibet
(2018-02) Laskowski, Andrew K.; Kapp, Paul; Cai, Fulong
The mechanisms for crustal thickening and exhumation along the Yarlung (India-Asia) suture in southern Tibet are under debate, because the magnitudes, relative timing, and interaction between the two dominant structures—the Great Counter thrust and Gangdese thrust—are largely unconstrained. In this study, we present new geologic mapping results from the Yarlung suture zone in the Lazi region, located ∼350 km west of the city of Lhasa, along with new igneous (5 samples) and detrital (5 samples, 474 ages) U-Pb geochronology data to constrain the crystallization ages of Jurassic–Paleocene Gangdese arc rocks, the provenance of Tethyan Himalayan and Oligocene–Miocene Kailas Formation strata, and the minimum age (ca. 10 Ma) of the Great Counter thrust system. We supplement these data with a compilation of 124 previously published thermochronologic ages from Gangdese batholith, Kailas Formation, and Liuqu Formation rocks, revealing a dominance of 23–15 Ma cooling contemporaneous with slip across the Great Counter thrust system and other potentially linked structures. These data are systematically younger than 98 additional compiled thermochronologic ages from the northern Lhasa terrane, recording mainly Eocene cooling. Structural and thermochronologic data were combined with regional geological constraints, including International Deep Profiling of Tibet and the Himalaya (INDEPTH) seismic reflection data, to develop a new structural model for the Oligocene–Miocene evolution of the Tethyan Himalaya, Yarlung suture zone, and southern Lhasa terrane. We propose that a hinterland-dipping duplex beneath the Gangdese mountains, of which the Gangdese thrust is a component, is kinematically linked with a foreland-dipping passive roof duplex along the Yarlung suture zone, the Great Counter thrust system. The spatial and temporal convergence between the proposed duplex structures along the Yarlung suture zone and the South Tibetan detachment system indicate that they may be kinematically linked, though this relationship is not directly addressed in this study. Our interpretation, referred to as the Gangdese culmination model, explains why the Gangdese thrust system is only locally exposed (at relatively deeper structural levels) and provides a structural explanation for early Miocene crustal thickening along the Yarlung suture zone, relief generation along the modern Gangdese Mountains, early Miocene Yarlung River establishment, and creation of the modern internal drainage boundary along the southern Tibetan Plateau. The progression of deformation along the suture zone is consistent with tectonic models that implicate subduction dynamics as the dominant control on crustal deformation.
Sedimentology and provenance of newly identified Upper Cretaceous trench basin strata, Dênggar, southern Tibet: Implications for development of the Eurasian margin prior to India–Asia collision
(Wiley, 2021-04) Orme, Devon A.; Laskowski, Andrew K.; Zilinsky, Misia F.; Chao, Wang; Guo, Xudong; Cai, Fulong; Lin, Ding
Trench basins preserved along the southern margin of the Lhasa Terrane, Tibet, are sedimentologic records of convergent margin processes preceding Cenozoic India–Asia collision. We present new sedimentologic, petrographic and geochronologic data from the Rongmawa Formation and surrounding strata near Dênggar, Tibet, to determine depositional environment, provenance and age. Depositional ages range from ca. 92 to 87 Ma and lithofacies are consistent with deposition by low- and high-density turbidity currents and suspension settling of pelagic detritus in a deep-marine, trench basin setting. Sandstone modal analyses and U–Pb geochronology indicate that trench basin detritus in this region was derived from the Lhasa Terrane. We interpret that the Cretaceous subduction trench received detritus from an axial sediment dispersal system that transported sediment from headwaters in the central-southern Lhasa terrane near Lhasa City directly to the trench and then flowed westwards parallel to the trench. The preservation of trench basin strata deposited during Late Cretaceous time compared with the lack of trench deposits prior to ca. 92 Ma and after ca. 80 Ma suggests the margin experienced a period of significant accretion during this interval. In addition, deposition of trench basin strata occurred during Late Cretaceous adakitic magmatism and high-temperature metamorphism, which are hypothesized to be explained by subduction of an oceanic ridge or subduction zone retreat and related upper plate extension along the southern margin of the Lhasa terrane. Subduction of an oceanic ridge may provide a mechanism to potentially erode forearc basin strata and promote increased sediment delivery directly to the trench.