Early Permian mafic dikes in the Nagqu area, central Tibet, China, associated with embryonic oceanic crust of the Meso‐Tethys Ocean

Abstract

During the latest Carboniferous to Early Permian, a possible mantle plume initiated continental rifting along the northern Gondwana margin, which subsequently developed into the Meso‐Tethys Ocean. However, the nature and timing of the embryonic oceanic crust of the Meso‐Tethys Ocean remain poorly understood. Here we present for the first time a combined analysis of petrological, geochronological, geochemical, and Sr‐Nd isotopic data for mafic rocks from the Nagqu area, central Tibet. Zircons from the mafic rocks yield a concordant age of ~277.8 ± 1.8 Ma, which is slightly younger than the age of mantle plume activity (~300–279 Ma), as represented by the large igneous province (LIP) on the northern Gondwana margin. Geochemical features suggest that the Nagqu mafic rocks, which display normal mid‐ocean ridge basalt affinities, are different from those of the LIP, which display oceanic island basalt‐type affinities. The Nagqu mafic rocks result from a relatively high degree of melting of depleted asthenospheric mantle. Combined with observations from previous studies, we suggest that the late Early Permian Nagqu magmatism fully records processes of early stage rifting and incipient formation of oceanic crust. Moreover, the patterns of magmatism are consistent with patterns of rift‐related sedimentation that records the transition from predominantly continental to marine deposition in the region during the Carboniferous‐Permian. We therefore suggest that rifting of the eastern Cimmerian and northern Gondwana continents started at ~277.8 Ma, and the rifting culminated in the opening of the Meso‐Tethys Ocean.

Middle Permian fusulines from the Thitsipin Formation of Shan State, Myanmar and their palaeobiogeographical and palaeogeographical implications

“…In addition, the early Permian (278 Ma) mafic dyke in the Nagqu area has been considered to mark the initial opening of the Bangong–Nujiang Ocean (Chen et al . ). These lines of evidence strongly suggest that the Bangong‐Nujian Ocean had opened before the Midian (Fig.…”

Geochronology, geochemistry, origin, and tectonic implications of high‐pressure mafic granulites of the Amdo region, Central Tibet

“…The BNO initially opened in the Late Cisuralian based on the presence of ophiolites (Chen, Shi, Fan, Gong, & Wu, 2017;Zhang et al, 2016Zhang et al, , 2017 and the different sedimentary facies found in the SQB and Lhasa terranes (Zhang, Zhang, Yuan, Xu, & Qiao, 2019). The northward subduction of the BNO began during the Mesozoic (Huang et al, 2017;Kapp, DeCelles, Gehrels, Heizler, & Ding, 2007).…”

Initial Rifting of the Lhasa Terrane from Gondwana: Insights From the Permian (~262 Ma) Amphibole‐Rich Lithospheric Mantle‐Derived Yawa Basanitic Intrusions in Southern Tibet

“…(a) Whole‐rock 87 Sr/ 86 Sr i versus ε Nd (t) and (b) ε Nd (t) versus ε Hf (t) diagrams for the Yawa intrusions. Data sources are as follows: Pikang granite from Zhu et al (), Lhasa middle‐upper continental crust is the Ningzhong strongly peraluminous granites and Amdo orthogneiss (Liu et al, ; Xu et al, ), ~273‐Ma Naqu mafic rocks are from Chen et al (), Qiangtang mafic rocks from Zhang and Zhang (), ~260 Ma Selong Traps from Zhu et al (), Panjal traps from Shellnutt, ), and mantle array from Chauvel and Blichert‐Toft ().…”

“…However, the paleogeographic history of the Lhasa Terrane remains a key unknown in late Paleozoic paleogeographic reconstructions of eastern Asia during the breakup of the Gondwana supercontinent. Given that the Lhasa, Qiangtang, and Himalayan terranes were covered by similar Paleozoic shelf strata containing glacial diamictites and cold-to cool-water faunas, they are considered to have been connected N-S-trending segments situated on the northern passive continental margin of the Indian Plate in Gondwana, which drifted northward during the Permian-Early Triassic as the Meso-and Neo-Tethys oceans opened (e.g., Ali et al, 2013;Chen et al, 2017;Gehrels et al, 2011;Metcalfe, 2002Metcalfe, , 2011Yin & Harrison, 2000). However, the geochemistry of Permian igneous rocks and the detrital zircon provenance of late Paleozoic strata in the Lhasa Terrane are somewhat different to those in the Himalayan and Qiangtang terranes (arc-type vs. rift-type and detrital zircon age populations of~1,170 vs. 950 Ma, respectively; e.g., Ferrari et al, 2008;Metcalfe, 2013;Stampfli & Borel, 2002;Zhang et al, 2013;Zhu et al, 2009Zhu et al, , 2010Zhu, Zhao, Niu, Dilek, et al, 2011).…”

“…In addition, paleomagnetism can only constrain the paleolatitude of a kinematically independent plate, not its paleolongitude, and the Permian paleolatitudes of the Indian and Australian parts of Gondwana were probably similar (Li et al, 2016). Therefore, the key to resolving this issue is to identify the tectonic setting of the Lhasa Terrane (i.e., continental rift vs. subduction-collision) in the Permian (e.g., Chen et al, 2017;Metcalfe, 2002Metcalfe, , 2009Metcalfe, , 2011Metcalfe, , 2013Yin & Harrison, 2000;Zhu et al, 2010Zhu et al, , 2013. Although studies favoring the first model argue that the diversity of Paleozoic strata in the Lhasa Terrane does not represent robust evidence against off the northern Indian Plate (e.g., Chen et al, 2017;Gehrels et al, 2011;Jin et al, 2015), the range of igneous rocks in these terranes must be explained.…”