Detrital zircon geochronology of pre-Tertiary strata in the Tibetan-Himalayan orogen (original) (raw)
Related papers
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.
Basin Research, 2007
Sedimentary strata in the Lhasa terrane of southern Tibet record a long but poorly constrained history of basin formation and inversion.To investigate these events, we sampled Palaeozoic and Mesozoic sedimentary rocks in the Lhasa terrane for detrital zircon uranium^lead (U^Pb) analysis. The 4700 detrital zircon U^Pb ages reported in this paper provide the ¢rst signi¢cant detrital zircon data set from the Lhasa terrane and shed new light on the tectonic and depositional history of the region. Collectively, the dominant detrital zircon age populations within these rocks are 100^150, 500^600 and 1000^1400 Ma. Sedimentary strata near Nam Co in central Lhasa are mapped as Lower Cretaceous but detrital zircons with ages younger than 400 Ma are conspicuously absent.The detrital zircon age distribution and other sedimentological evidence suggest that these strata are likely Carboniferous in age, which requires the existence of a previously unrecognized fault or unconformity. Lower Jurassic strata exposed within the Bangong suture between the Lhasa and Qiangtang terranes contain populations of detrital zircons with ages between 200 and 500 Ma and 1700 and 2000 Ma.These populations di¡er from the detrital zircon ages of samples collected in the Lhasa terrane and suggest a unique source area.The Upper CretaceousTakena Formation contains zircon populations with ages between100 and160 Ma, 500 and 600 Ma and1000 and1400 Ma. Detrital zircon ages from these strata suggest that several distinct £uvial systems occupied the southern portion of the Lhasa terrane during the Late Cretaceous and that deposition in the basin ceased before 70 Ma. Carboniferous strata exposed within the Lhasa terrane likely served as source rocks for sediments deposited during Cretaceous time. Similarities between the lithologies and detrital zircon age-probability plots of Carboniferous rocks in the Lhasa and Qiangtang terranes and Tethyan strata in the Himalaya suggest that these areas were located proximal to one another within Gondwanaland. U^Pb ages of detrital zircons from our samples and di¡erences between the geographic distribution of igneous rocks within theTibetan plateau suggest that it is possible to discriminate a southern vs. northern provenance signature using detrital zircon age populations.
U–Pb geochronology of basement rocks in central Tibet and paleogeographic implications
Journal of Asian Earth Sciences, 2012
The ages and paleogeographic affinities of basement rocks of Tibetan terranes are poorly known. New U-Pb zircon geochronologic data from orthogneisses of the Amdo basement better resolve Neoproterozoic and Cambro-Ordovician magmatism in central Tibet. The Amdo basement is exposed within the Bangong suture zone between the Lhasa and Qiangtang terranes and is composed of granitic orthogneisses with subordinate paragneisses and metasedimentary rocks. The intermediate-felsic orthogneisses show a bimodal distribution of Neoproterozoic (920-820 Ma) and Cambro-Ordovician (540-460 Ma) crystallization ages. These and other sparse basement ages from Tibetan terranes suggest the plateau is underlain by juvenile crust that is Neoproterozoic or younger; its young age and weaker rheology relative to cratonic blocks bounding the plateau margins likely facilitated the propagation of Indo-Asian deformation far into Asia. The Neoproterozoic ages post-date Rodinia assembly and magmatism of similar ages is documented in the Qaidaim-Kunlun terrane, South China block, the Aravalli-Delhi craton in NW India, the Eastern Ghats of India, and the Prince Charles mountains in Antarctica. The Amdo Neoproterozoic plutons cannot be unambiguously related to one of these regions, but we propose that the Yangtze block of the South China block is the most likely association, with the Amdo basement representing a terrane that possibly rifted from the active Yangtze margin in the middle Neoproterozoic. Cambro-Ordovician granitoids are ubiquitous throughout Gondwana as a product of active margin tectonics following Gondwana assembly and indicate that the Lhasa-Qiangtang terranes were involved in these tectono-magmatic events. U-Pb detrital zircon analysis of two quartzites from the Amdo basement suggest that the protoliths were Carboniferous-Permian continental margin strata widely deposited across the Lhasa and Qiangtang terranes. The detrital zircon age spectra of the upper Paleozoic Tibetan sandstones and other rocks deposited in East Gondwana during the late Neoproterozoic and Paleozoic are all quite similar, making it difficult to use the age spectra for paleogeographic determinations. There is a suggestion in the data that the Qiangtang terrane may have been located further west along Gondwana's northern boundary than the Lhasa terrane, but more refined spatial and temporal data are needed to verify this configuration.
Chemical Geology, 2008
The Trans-Himalayan magmatism, which occurred extensively in the Lhasa terrane of southern Tibet, has long been related to the Neotethyan subduction before the India-Asia collision. To better delineate the magmatic duration, we report a geochronological study with 25 SHRIMP zircon U-Pb ages from the Gangdese Batholith that represents the largest Trans-Himalayan plutonic complex. The results suggest two distinct stages of plutonism in the Late Cretaceous (ca. 103-80 Ma) and early Paleogene (ca. 65-46 Ma), respectively. Our new data confirm if not refine the notion that a Gangdese magmatic gap or quiescent period existed between ca. 80 and 70 Ma. It is furthermore identified that the early stage ended with adakitic intrusion and the latter stage is marked by a peak activity at ca. 50 Ma. We attribute the cessation of the early stage, and following magmatic gap, to a flattening of the northward Neotethyan subduction, and the initiation of the latter stage to rollback of the subducted slab. The proposed scenarios can also account for the southward migration and intensification of Cretaceous to Paleogene volcanism in the Lhasa terrane that demonstrates a coeval, eruptive "flare-up" event around 50 Ma, interpreted as the result of detaching the Neotethyan oceanic slab from the adherent, more buoyant Indian continental lithosphere owing to the India-Asia collision. Our model is, moreover, in general accord with sedimentary and structural geologic records from southern Tibet where subduction-related orogenesis appears to have evolved through time before India started colliding Asia.
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.
The Journal of Geology
This article presents zircon U-Pb and Hf isotope data, together with the whole-rock major-and trace-element composition, of Early Carboniferous granitoids newly identified from the Jiacha and Langxian areas in the southern Lhasa terrane, southern Tibet. The Jiacha rocks are monzogranites that yield zircon U-Pb ages of 347-345 Ma and Hf (t) values from Ϫ5.4 to Ϫ4.9. The Langxian rocks are granodiorites with slightly older zircon U-Pb ages of 355-352 Ma and lower Hf (t) values from Ϫ6.8 to Ϫ6.5. Our data suggest that these granitoids were generated largely by reworking of Paleoproterozoic ( Ga) basement materials. In conjunction with literature data, it is further argued C T p 1.78-1.67 DM that the southern and central parts of the Lhasa terrane, separated by the Sumdo eclogite belt, should have been an integrated block before the late Paleozoic. Our study supports the notion that the Lhasa terrane was derived from the northern margin of Gondwanaland, in association with formation of at least two stages of Tethyan Ocean basins, now exposed as the Sumdo belt and the Indus-Tsangpo suture.
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.
Cenozoic anatexis and exhumation of Tethyan Sequence rocks in the Xiao Gurla Range, Southwest Tibet
2011
In order to advance our understanding of the suturing process between continental landmasses, a geologic and geochronologic investigation was undertaken just south of the India-Asia suture in southwestern Tibet. The focus of this study, the Xiao Gurla Range, is located near the southeastern terminus of the active, rightlateral strike-slip Karakoram fault in southwestern Tibet. The range exposes metasandstone, phyllite, schist (locally of sillimanite facies), calc-gneiss and marble, paragneiss (± pyroxene), quartzite, metagranite, and variably deformed leucogranite. These metamorphic rocks are exposed in the footwall of a domal, top-to-thewest low-angle normal (detachment) fault, structurally beneath Neogene-Quaternary basin fill and serpentinized ultramafic rocks of the Kiogar-Jungbwa ophiolite. The detachment is interpreted to be the northeastern continuation of the Gurla Mandhata detachment fault system that bounds metamorphic rocks of the Gurla Mandhata Range~60 km to the southwest. U-Pb geochronology on five detrital zircon samples of schist, phyllite, and quartzite yielded maximum depositional ages that range from 644-363 Ma and age probability distributions that are more similar to Tethyan sequence rocks than Lesser Himalayan sequence rocks. A felsic gneiss yielded a metamorphic zircon age of 35.3 ± 0.8 Ma with a significant population of early Paleozoic xenocrystic core ages. The gneiss is interpreted to be the metamorphosed equivalent of the Cambro-Ordovician gneiss that is exposed near the top of the Greater Himalayan sequence. Leucogranitic bodies intruding metasedimentary footwall rocks yielded two distinct U-Pb zircon ages of~23 Ma and~15 Ma. Locally, rocks exposed in the hanging wall of this fault and of the southward-dipping, northward-verging Great Counter thrust to the north consist of serpentinite-bearing mélange and conglomerate of inferred Paleogene age dominated by carbonate clasts. The mélange is intruded by a 44 Ma granite and the stratigraphically highest conglomerate unit yielded detrital zircon U-Pb ages similar to Tethyan sequence rocks. We attribute the middle Eocene magmatism south of the suture to break-off of the Neo-Tethyan oceanic slab. In addition, our observations are consistent with the late Eocene shortening and crustal thickening within the Tethyan Himalayan sequence, early-middle Miocene leucogranite emplacement being related to underthrusting and melting of the Greater and possibly Lesser Himalayan sequences, and late Miocene arcparallel extension in the hinterland of the southward propagating Himalayan thrust belt. Tectonophysics j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t e c to and detrital zircon samples. The results provide a better understanding of the history of crustal deformation, metamorphism, and anatexis within the hinterland of the Himalayan fold-thrust belt during middle Eocene-late Miocene time.
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 Metamorphic Geology, 2000
The eastern Himalayan syntaxis in southeastern Tibet consists of the Lhasa terrane, High Himalayan rocks and Indus-Tsangpo suture zone. The Lhasa terrane constitutes the hangingwall of a subduction zone, whereas the High Himalayan rocks represent the subducted Indian continent. Our petrological and geochronological data reveal that the Lhasa terrane has undergone two stages of medium-P metamorphism: an early granulite facies event at c. 90 Ma and a late amphibolite facies event at 36-33 Ma. However, the High Himalayan rocks experienced only a single high-P granulite facies metamorphic event at 37-32 Ma. It is inferred that the Late Cretaceous (c. 90 Ma) medium-P metamorphism of the southern Lhasa terrane resulted from a northward subduction of the Neo-Tethyan ocean, and that the Oligocene (37-32 Ma) high-P (1.8-1.4 GPa) rocks of the High Himalayan and coeval medium-P (0.8-1.1 GPa) rocks of the Lhasa terrane represent paired metamorphic belts that resulted from the northward subduction of the Indian continent beneath Asia. Our results provide robust constraints on the Mesozoic and Cenozoic tectonic evolution of south Tibet.