Detrital zircon geochronology of Carboniferous?Cretaceous strata in the Lhasa terrane, Southern Tibet (original) (raw)
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Detrital zircon geochronology of pre-Tertiary strata in the Tibetan-Himalayan orogen
Tectonics, 2011
1] Detrital zircon data have recently become available from many different portions of the Tibetan-Himalayan orogen. This study uses 13,441 new or existing U-Pb ages of zircon crystals from strata in the Lesser Himalayan, Greater Himalayan, and Tethyan sequences in the Himalaya, the Lhasa, Qiangtang, and Nan Shan-Qilian Shan-Altun Shan terranes in Tibet, and platformal strata of the Tarim craton to constrain changes in provenance through time. These constraints provide information about the paleogeographic and tectonic evolution of the Tibet-Himalaya region during Neoproterozoic to Mesozoic time. First-order conclusions are as follows: (1) Most ages from these crustal fragments are <1.4 Ga, which suggests formation in accretionary orogens involving little pre-mid-Proterozoic cratonal material; (2) all fragments south of the Jinsa suture evolved along the northern margin of India as part of a circum-Gondwana convergent margin system; (3) these Gondwana-margin assemblages were blanketed by glaciogenic sediment during Carboniferous-Permian time; (4) terranes north of the Jinsa suture formed along the southern margin of the Tarim-North China craton; (5) the northern (Tarim-North China) terranes and Gondwana-margin assemblages may have been juxtaposed during mid-Paleozoic time, followed by rifting that formed the Paleo-Tethys and Meso-Tethys ocean basins; (6) the abundance of Permian-Triassic arc-derived detritus in the Lhasa and Qiangtang terranes is interpreted to record their northward migration across the Paleo-and Meso-Tethys ocean basins; and (7) the arrival of India juxtaposed the Tethyan assemblage on its northern margin against the Lhasa terrane, and is the latest in a long history of collisional tectonism.
Journal of Earth Science, 2016
This paper reports geochronological data of detrital zircons from the country rock and sedimentary xenoliths of the Cilincuo pluton (79±0.7 Ma) in the southern Yidun arc belt and the inherited zircons from the Late Triassic granites in the eastern Yidun arc belt, eastern Tibet Plateau. Detrital zircons ages from the sedimentary xenoliths have four prominent peaks at 2.5-2.4 Ga, 1.9-1.8 Ga, 480-400 Ma, and 350-300 Ma, whereas those from the country rock exhibit another four prominent peaks at 1.9-1.8 Ga, 850-700 Ma, 480-400 Ma, and 300-250 Ma. Based on comparison with age data from previous studies, we suggest that the sedimentary xenoliths are from the Lanashan Formation and the major provenance of them is Qiangtang Block, Zhongza massif and South China Block, whereas the country rock belongs to the Lamaya Formation and the major provenance of them is similar to those of the neighbouring Songpan-Garzê terrane. In addition, the inherited zircons from the Late Triassic granites in the eastern Yidun arc belts have a prominent Neoproterozoic age population (900-700 Ma), which suggests that there is an old basement with west Yangtze Craton affinity beneath the Triassic sediments. Combining with previous studies, we propose that the provenances of the formations vary from the Lanashan Formation to the Lamaya Formation which may indicate a record of the final closure of the Garzê-Litang Ocean.
Journal of Sedimentary Research, 2007
Sedimentary strata in southern Tibet indicate that upper crustal deformation occurred throughout the region during Early Cretaceous time, suggesting that construction of the Tibetan plateau commenced tens of millions of years before the Late Cretaceous-early Tertiary Indo-Asian collision. Lower Cretaceous strata in the northern portion of the Lhasa terrane are characterized by lithic-rich conglomerate beds deposited in shallow marine and meandering-river fluvial environments. Sediments in these units were derived from two primary sources: volcanic rocks associated with Early Cretaceous intrusions, and sedimentary strata eroded from the northern Lhasa and southern Qiangtang terranes. The majority of detrital zircons from Lower Cretaceous fluvial conglomerate beds in northern Lhasa have U-Pb ages between 125 and 140 Ma and provide a maximum depositional age for these units of 125 6 2 Ma. Lower Cretaceous strata in the southern portion of the Lhasa terrane consist of mudstone, quartzose sandstone, and subordinate quartzite-pebble conglomerate beds that were deposited in shallow marine and fluvial environments. Populations of detrital zircons in Lower Cretaceous conglomerate beds in southern Lhasa have U-Pb ages between 140 and 150 Ma, 500 and 600 Ma, and 850 and 950 Ma, and provide a maximum depositional age for these units of 143 6 2 Ma. Both the modal composition and detrital-zircon U-Pb ages of the Lower Cretaceous conglomerate exposed in northern and southern Lhasa suggest different source areas, diachronous deposition, and possibly distinct genetic histories. Throughout most of the Lhasa terrane, the Lower Cretaceous clastic strata are overlain by a widespread limestone of Aptian-Albian age that was deposited in a shallow carbonate sea containing rudist patch reefs and muddy inter-reef zones. With respect to the tectono-sedimentary setting of the Lhasa terrane during Early Cretaceous time, the sedimentological and stratigraphic data are most consistent with a peripheral foreland basin model, which is interpreted to have resulted from the collision between the northern margin of the Lhasa terrane and the southern margin of Asia (the Qiangtang terrane). Several characteristics of the Aptian-Albian succession can be attributed to a peripheral foreland basin setting, although deposition within the region may have been influenced by a combination of mechanisms. Sedimentary characteristics of Lower Cretaceous rocks in the Lhasa terrane are consistent with recent ideas suggesting that portions of southern and central Tibet were deformed and above sea level before the Indo-Asian collision.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2019
Determining the provenance of Cenozoic strata in the Qaidam Basin is key to understanding the basin-mountain coupling history in the northern Tibetan Plateau (TP). However, the specific source areas of Cenozoic strata in the northern Qaidam Basin remain highly debated. Here, we combine analyses of detrital zircons U-Pb geochronology for recent and ancient fluvial sediments from the northern Qaidam Basin to trace source areas of Cenozoic strata and reconstruct related mountain-building processes. The results indicate that the diagnostic 270-240 Ma zircon U-Pb peak, which was previously recognized as the unique input of a southern source area, is widespread in the recent fluvial sediments of the northern Qaidam Basin. Given our new zircon U-Pb data, the source-to-sink transport processes of Cenozoic sediments in the northern Qaidam Basin can be summarized as follows. (1) The northern Qaidam Basin has received the eroded detrital material from a dominantly northern source throughout the Cenozoic. (2) The Qaidam BeiShan was uplifted already at least by the early Eocene and served as the single contributor of detritus to the Dahonggou (DHG) region, suggesting that far-field stress due to the India-Asia collision had been propagated to this region as early as the early Eocene. (3) An abrupt change in provenance is observed in the DHG region during 46.5-43.7 Ma. We interpret this middle Eocene source change as reflecting the onset of growth of the North Altyn Tagh Range, implying that the North Altyn Tagh Range was already serving as an important source area for the DHG region by the middle Eocene. (4) The South Qilian Range served again as the dominant source area for the DHG region after 24.6 Ma. The shift in provenance from the North Altyn Tagh Range to the South Qilian Range can be attributed to the uplift of the Saishiteng Shan.
Gondwana Research, 2011
Age-dating of detrital zircons from 22 samples collected along, and adjacent to, the Yarlung-Tsangpo suture zone, southern Tibet provides distinctive age-spectra that characterize important tectonostratigraphic units. Comparisons with data from Nepal, northern India and the Lhasa and Qiangtang terranes of central Tibet constrain possible sources of sediment, and the history of tectonic interactions. Sedimentary rocks in the Cretaceous-Paleogene Xigaze terrane exhibit strong Mesozoic detrital zircon peaks (120 and 170 Ma) together with considerable older inheritance in conglomeratic units. This forearc basin succession developed in association with a continental volcanic arc hinterland in response to Neotethyan subduction under the southern edge of the Eurasia. Conspicuous sediment/source hinterland mismatches suggest that plate convergence along this continental margin was oblique during the Late Cretaceous. The forearc region may have been translated N 500 km dextrally from an original location nearer to Myanmar. Tethyan Himalayan sediments on the other side of the Yarlung-Tsangpo suture zone reveal similar older inheritance and although Cretaceous sediments formed 1000s of km and across at least one plate boundary from those in the Xigaze terrane they too contain an appreciable mid-Early Cretaceous (123 Ma) component. In this case it is attributed to volcanism associated with Gondwana breakup. Sedimentary overlap assemblages reveal interactions between colliding terranes. Paleocene Liuqu conglomerates contain a cryptic record of Late Jurassic and Cretaceous rock units that appear to have foundered during a Paleocene collision event prior the main India-Asia collision. Detrital zircons as young as 37 Ma from the upper Oligocene post-collisional Gangrinboche conglomerates indicate that subductionrelated convergent margin magmatism continued through until at least Middle and probably Late Eocene along the southern margin of Eurasia (Lhasa terrane). Although the ages of detrital zircons in some units appear compatible with more than one potential source with care other geological relationships can be used to further constrain some linkages and eliminate others. The results document various ocean closure and collision events and when combined with other geological information this new dataset permits a more refined understanding of the time-space evolution of the Cenozoic India-Asia collision system.
Geological Society of America Bulletin, 2015
The tectonic evolution of the Lhasa terrane (southern Tibetan Plateau) played a fundamental role in the formation of the Tibetan Plateau. However, many uncertainties remain with regard to the tectonic and paleogeographic evolution of the Lhasa terrane prior to the India-Asia collision. To determine the early tectonic processes that controlled the topographic evolution of the Lhasa terrane, we analyze the Cretaceous strata exposed in the Coqen Basin (northern Lhasa subterrane), which comprises the Langshan and Daxiong Formations. The Langshan Formation unconformably overlies the volcanic rocks of the Lower Cretaceous Zelong Group and consists of ~80 m of Orbitolina-bearing limestones, which were deposited in a low-energy, shallow marine environment. Micropaleontological analysis indicates that the Langshan Formation in the Coqen Basin was deposited from late Aptian to early Cenomanian times (ca. 113-96 Ma). The overlying Daxiong Formation (~1700 m thick) consists of conglomerate, coarse sandstone, and siltstone with interbedded mudstone, and represents deposits of alluvial fans and braided rivers. The Daxiong Formation was deposited after the early Cenomanian (ca. 96 Ma) and accumulated until at least ca. 91 Ma, indicating accumulation rates of greater than 0.3 km m.y. -1 . By combining paleo current data, sandstone petrology, detrital zircon U-Pb ages, and Hf isotope analysis, we demonstrate that the Daxiong Formation was derived from Lower Cretaceous volcanic rocks and pre-Cretaceous strata in the northern Lhasa subterrane. During Late Cretaceous time, two thrust systems with opposite vergence were responsible for transforming the northern Lhasa subterrane into an elevated mountain range. This process resulted in the evolution from a shallow marine environment (Langshan Formation) into a terrestrial depositional environment (Daxiong Formation) on the southern margin of the northern Lhasa subterrane. Given the regional paleogeographic context, we conclude that the Daxiong Formation in the Coqen Basin records local crustal shortening and fl exure resulting in foreland basin development on the southern margin of the northern Lhasa subterrane, which implies early topographic growth of the northern Lhasa subterrane in southern Tibet prior to the India-Asia collision.
Geosystems and Geoenvironment, 2023
We present new U-Pb detrital zircon ages, depositional history and tectonic model for the Liuqu Conglomerate (LQC) in southern Tibet that represents a critical geochronometer for the collision history of the Tibetan-Himalayan Orogenic Belt. LQC is a ∼5 km–thick, late Mesozoic–Cenozoic molasse deposit occurring strictly within the Yarlung Zangbo Suture Zone (YZSZ) and is tectonically overlain to the north by the Cretaceous Xigaze ophiolite and to the south by the Mesozoic Tethyan Himalaya sequence. It con- sists of matrix- and clast-supported conglomerates with sandstone intercalations, and its matrix includes poorly to moderately sorted sandstone and mudstone. New U–Pb detrital zircon dating of LQC sandstones has revealed a youngest zircon age of 307 ± 13 Ma and an oldest zircon age of 3362 ± 51 Ma. The age spectrum of zircons displays a prominent peak of ∼935 Ma, two large peaks at ∼516 Ma and 1474 Ma, and two small clusters of ∼2429 Ma and ∼2772 Ma that point to East Gondwana as the likely provenance for the LQC depocenter. The LQC represents fluvial deposits of an axial river system, which developed in an orogen-parallel, transtensional accommodation space within the YZSZ, after the collision of the Late Jurassic-Early Cretaceous Trans–Tethyan arc–trench system with the northern edge of India in the latest Cretaceous. The Indian subcontinent with the accreted Tethyan ophiolites and the intra–suture LQC de- pocenter arrived at and collided with the active margin of Eurasia during the latest Oligocene ( ∼23 Ma). The LQC depocenter started receiving clastic material and zircons for the first time from the Gangdese Magmatic Belt and the Xigaze forearc basin to the north by ∼20 Ma. The ensuing continent–continent collision resulted in significant crustal uplift across the collision zone, and in the inversion and rapid exhumation of the LQC strata by the early–Middle Miocene. The depositional and exhumation history of the fluvial LQC formation within the YZSZ involved two discrete collision events during the evolution of the Tibetan-Himalayan Orogenic system.
2018
Foreland basin deposits of the Tansen Group of Lesser Himalayan association in central Nepal record passive margin sedimentation of the Indian continent with direct deposition onto eroded Precambrian rocks, succeeded by detritus from orogenesis as the Indian continent collided with Asia on a north-dipping subduction zone. Samples collected from Tansen Basin (Amile, Bhainskati, and Dumri formations), Higher and Tethys Himalaya were examined detrital zircon U-Pb dating and through petrographically. The Cretaceous-Paleocene Amile Formation is dominated by a broad detrital zircon U-Pb~1830Ma age peak with hosts a significant proportion (23%) of syndepositional Cretaceous zircons (121 to 105Ma) would be contributions from the Lower Lesser Himalayan volcanosedimentary arc, Gangdese batholith (including Xigazeforearc). The Bhainskati and Dumri Formation of the Tansen Group are more similar to Tethyan units than to Higher Himalaya Crystalline (HHC). The presence of ~23+/-1Ma zircons from th...