Kunlun Orogen Research Articles

Magmatic response to the closure of the Proto-Tethys Ocean: A case study from the middle Paleozoic granitoids in the Kunlun Orogen, western China

Magmatic response to the closure of the Proto-Tethys Ocean: A case study from the middle Paleozoic granitoids in the Kunlun Orogen, western China

Geochemistry and tectonic setting of Middle Ordovician MORB-like basalts in the Kunlun Orogen: implications for a back-arc environment

The Central Kunlun ophiolitic melange zone, northern Tibetan Plateau, represents a remnant of the Early Paleozoic oceanic lithosphere. The Middle Ordovician Longshigeng basalts (LBs) are located in south of this melange zone and have important significance for reconstructing the opening and subduction processes of the Proto-Tethys Ocean. This study presents petrological, whole-rock geochemical, and zircon U-Pb data for these basalts. LA-ICP-MS U-Pb zircon data indicate that these basalts formed ca. 463 Ma. Geochemically, the basalts are characterized by low SiO2 (47.00–50.63 wt%) and K2O (0.22–1.05 wt%), intermediate Mg# (47–57) and high TiO2 (1.51–2.72 wt%), and are identified as tholeiitic basalts. Their chondrite-normalized REE patterns feature slight enrichments in LREEs (LREE/HREE = 2.11–3.08) with mild Eu anomalies (δEu = 0.89–1.06), and their patterns are similar to the reference line of enriched mid-ocean ridge basalt (EMORB). The primitive mantle-normalized trace element diagrams also show similarities with EMORB and are characterized by overall enrichments in large ion lithophile and high field strength elements, without notable Nb, Ta, and Ti depletions. Combining these data with the tectonic discrimination diagrams, we infer that these rocks formed in a back-arc environment in response to the northward subduction of the Proto-Tethys Ocean (South Kunlun Ocean) in the East Kunlun region, northern Tibetan Plateau.

Triassic turbidites in the West Qinling Mountains, NW China: Part of the collisional Songpan-Ganzi Basin or an active forearc basin?

Lower to Middle Triassic clastic rocks in the West Qinling Mountains along NE margin of the Qinghai-Tibet Plateau are generally regarded as part of the Songpan-Ganzi flysch Basin. However relatively little attention has been paid to the age and provenance of these units. New petrological and geochemical results demonstrate that these sediments accumulated along an active continental margin and are dominated by feldspathic litharenite and lithic arkose with low mineral and compositional maturity. They were derived primarily from a continental arc source dominated by intermediate to felsic igneous rocks, with a minor contribution from older metamorphosed and sedimentary sources. Turbidite samples yielded two primary detrital zircon U-Pb age populations of ca. 273 Ma and ca. 435 Ma, which is different from the Early Triassic (ca. 252 Ma) and Middle Silurian (ca. 427 Ma) age populations that dominate the Songpan-Ganzi Basin. These data together with paleocurrent results indicate that the South Qilian Belt was the primary source origin because this belt contains both early Paleozoic Andean-type igneous and magmatic rocks and has a basement of Precambrian metamorphosed rocks. Regionally, an Andean-type arc traverses the South Qilian belts and extends into the West Qinling Mountains and Kunlun Orogen, which formed by north-directed subduction of the Paleo-Tethyan Ocean during the Early to Middle Triassic. Voluminous detritus that originated from the Qilian and Kunlun orogens as they were uplifted and eroded was transported to the south and deposited in the forearc area in front of the A’nimaqen-Mianlue suture.

Structural analysis and tectonic evolution of the western domain of the Eastern Kunlun Range, northwest Tibet

AbstractThe 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–1 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.

WITHDRAWN: Triassic turbidites in the West Qinling Mountains, NW China: Part of the collisional Songpan-Ganzi Basin or an active forearc basin?

Abstract Lower to Middle Triassic clastic rocks in the West Qinling Mountains along NE margin of the Qinghai-Tibet Plateau are generally regarded as part of the Songpan-Ganzi flysch Basin. However relatively little attention has been paid to the age and provenance of these units. New petrological and geochemical results demonstrate that these sediments accumulated along an active continental margin and are dominated by feldspathic litharenite and lithic arkose with low mineral and compositional maturity. They were derived primarily from a continental arc source dominated by intermediate to felsic igneous rocks, with a minor contribution from older metamorphosed and sedimentary sources. Turbidite samples yielded two primary detrital zircon U-Pb age populations of ca. 273 Ma and ca. 435 Ma, which is different from the Early Triassic (ca. 252 Ma) and Middle Silurian (ca. 427 Ma) age populations that dominate the Songpan-Ganzi Basin. These data together with paleocurrent results indicate that the South Qilian Belt was the primary source origin because this belt contains both early Paleozoic Andean-type igneous and magmatic rocks and has a basement of Precambrian metamorphosed rocks. Regionally, an Andean-type arc traverses the South Qilian belts and extends into the West Qinling Mountains and Kunlun Orogen, which formed by north-directed subduction of the Paleo-Tethyan Ocean during the Early to Middle Triassic. Voluminous detritus that originated from the Qilian and Kunlun orogens as they were uplifted and eroded was transported to the south and deposited in the forearc area in front of the A’nimaqen-Mianlue suture.

Late Permian–Triassic siliciclastic provenance, palaeogeography, and crustal growth of the Songpan terrane, eastern Tibetan Plateau: evidence from U–Pb ages, trace elements, and Hf isotopes of detrital zircons

In order to constrain the detrital provenance of the siliciclastic rocks, palaeogeographic variations, and crustal growth history of central China, we carried out simultaneously in situ U–Pb dating and trace element and Hf isotope analyses on 368 detrital zircons obtained from upper Permian–Triassic sandstones of the Songpan terrane, eastern Tibetan Plateau. Two groups of detrital zircons, i.e. magmatic and metamorphic in origin, have been identified based on cathodoluminescence images, zircon Ti-temperatures, and Th/U ratios. Our data suggest that the derivation of siliciclastic rocks in the Songpan terrane was mainly from the Qinling, Qilian, and Kunlun orogens, whereas the Yangtze and North China Cratons served as minor source areas during late Permian–Triassic times. The detrital zircons from Middle–Late Triassic siliciclastic rocks exhibit wide age spectra with two dominant populations of 230–600 Ma and >1600 Ma, peaking at ~1.8–1.9 Ga and ~2.4–2.5 Ga, suggestive of a derivation from the Qinling, Qilian, and Kunlun orogens and the Yangtze Craton being the minor source area. The proportions of detrital zircon populations from the northern Qinling, Qilian, and Kunlun orogens distinctly decreased during Middle–Late Triassic time, demonstrating that the initial uplift of the western Qinling occurred then and it could have blocked most of the detritus from the Qilian–northern Qinling orogens and North China Cratons into the main Songpan–Ganzi depositional basin. The relatively detrital zircon proportions of the Yangtze Craton source decreased during Early-Middle Late Triassic time, indicating that the Longmenshan orogen was probably being elevated, since the early Late Triassic and gradually formed a barrier between the Yangtze Craton and the Songpan terrane. In addition, our Lu–Hf isotopic results also reveal that the Phanerozoic magmatic rocks in central China had been the primary products of crustal reworking with insignificant formation of a juvenile crust.

Crustal Structures beneath West Qinling‐East Kunlun Orogen and its Adjacent Area ‐Result of Wide‐Angle Seismic Reflection and Refraction Experiment

AbstractA 637km long wide‐angle seismic reflection and refraction profile was carried out in the northeast margin of Tibet plateau, which crosses A'nyemaqen suture belt in the north‐south direction. The crust section obtained from the seismic data shows that the depth of the Moho is about 48‐51 km. The crust is slightly thicker in the south than in the north and it varies smoothly toward the north along the profile with different structures in the various tectonic blocks. The clearly identified overcritical reflections P3, P4 on the seismic record sections indicate that the lower crust features multi‐layer structure and strong reflectivity in this area. There are severe deformations on the interfaces of the crust, and low velocity distributions on the south of Aba arcuate fault and near A'nyemaqen suture belt. The low velocity zone in the mid and lower crust beneath A'nyemaqen suture belt may be explained as the extension of the suture belt into the crust. The crust structure from the West Qinling fold zone to Songpan‐Garze block is characterized by strong reflections from the mid and lower crust, and relatively weak Moho reflections on the seismic record sections.