Metamorphic records for subduction erosion and subsequent underplating processes revealed by garnet‐staurolite‐muscovite schists in central Qiangtang, Tibet

Abstract

Subduction erosion is confirmed as a crucial geodynamic process of crustal recycling based on geological, geochemical, and geophysical observations at modern convergent plate margins. So far, not a single metamorphic record has been used for constraining a general tectonic evolution for subduction erosion. Here we first revealed metamorphic records for a subduction erosion process based on our study of the Late Paleozoic garnet-staurolite-muscovite schists in the central Qiangtang block, Tibet. Provenance analyses suggest that the protoliths of garnet-staurolite-muscovite schists have the Northern Qiangtangaffinity and were deposited in an active continental margin setting. Mineral inclusion data show that the early metamorphic stage (M 1 ) recorded blueschist facies pressure-temperature (P-T) conditions of 0.8-1.1 GPa and 402-4418C, indicating that a part of the material from the overriding plate had been abraded into the subduction channel and undergone high-pressure/low-temperature metamorphism. The peak metamorphic stage (M 2 ) recorded amphibolite facies P-T conditions of 0.3-0.5 GPa and 470-5208C. The 40 Ar/ 39 Ar cooling ages (263-259 Ma) yielded from muscovite suggest the amphibolite facies metamorphism (>263 Ma) occurred at oceanic subduction stage. The distinctly staged metamorphism defines a clockwise and warming decompression P-T-t path which reveals an underplating process following the early subduction erosion. During the tectonic process, the eroded low-density material escaped from the cold subduction channel and rise upward into the warm middle-lower crust of the upper plate, undergoing amphibolite facies metamorphism. Our new results revealed a complete evolutional process from the early subduction erosion to the subsequent underplating during the northward subduction of the Paleo-Tethys Ocean.

Sedimentary Evolution and Provenance of the late Permian‐middle Triassic Raggyorcaka Deposits in North Qiangtang (Tibet, Western China): Evidence for a Forearc Basin of the Longmu Co‐Shuanghu Tethys Ocean

“…On the other hand, the in situ suture model with northward oceanic subduction under the NQB (Li et al, , Li, Chen, et al, , Li, Huang, et al, , ; Zhai, Zhang, et al, , Zhai, Jahn, et al, ; Liang et al, , ; Li et al, ; Wang et al, ) could potentially better explain the late Devonian‐middle Triassic geological evolution in the southern NQB (Figure ), primarily based on the following evidence. First, the Longmu Co‐Shuanghu Tethys Ocean, which once separated the NQB and SQB (Li, ; Li et al, ), was demonstrated to be a diachronous ocean as supported by the continuous Cambrian‐early Triassic (501–242 Ma) ophiolite suites (Fan et al, ; Hu et al, ; Li et al, , Li, Chen, et al, , Li, Huang, et al, , ; Wang, Pan, et al, ; Wu et al, ; Zhai, Jahn, Wang, et al, , ; Zhang et al, ; Zhu et al, ). Second, obvious biota and paleogeography differences have been recently verified across the NQB and the CQMB/SQB.…”

“…Tectonics 2018). Polyphase foliated clastic rocks mainly consisting of late Carboniferous-Permian submarine siliciclastic flysch Li et al, 1995; surround many other blocks, including Permian-Triassic HP-LT metamorphic rocks (Deng et al, 2000;Kapp et al, 2000Kapp et al, , 2003Li et al, 1995;Li, Zhai, Dong, et al, 2006;Liang et al, 2012Liang et al, , 2017Pullen et al, 2008;Zhao et al, 2014Zhao et al, , 2015Zhang et al, 2017), a late Carboniferous-early Permian gabbro dyke swarm Zhai, Jahn, Su, Ernst, et al, 2013), Paleozoic ophiolite relics Wang, Pan, et al, 2008;Wu et al, 2010;Zhang et al, 2017;Zhu et al, 2006), Permian-early Triassic oceanic island/seamount slices Y. C. Zhang, Shen, et al, 2012), middle-late Triassic abyssal sedimentary rocks (Deng et al, 1996;Li et al, 1997), and Ordovician quartzite and limestone slices (Dong et al, 2011;.…”

“…In the in situ suture model, a long‐lived early Paleozoic‐Triassic ocean or the main branch of the Paleo‐Tethys Ocean separated the NQB, which showed a Cathaysian affinity from the SQB, which showed a Gondwana affinity (Li, ; Li et al, ; Li, Zhai, Dong, et al, ; Li, Zhai, Chen, et al, ; Li, Chen, et al, ; Li, Huang, et al, ; Li, Zhai, Chen, et al, , ; Liu et al, ). This inference is based on the Paleozoic‐early Triassic ophiolite suites discovered within the hanging wall of the detachment fault (Li et al, ; Li, Chen, et al, ; Li, Huang, et al, , ; Zhu et al, ; Wang, Pan, et al, ; Wu et al, ; Zhai, Jahn, Wang, et al, , ; Zhang et al, ; Fan et al, ) and the distinct stratigraphy and biota in the two blocks (Li, ; Li et al, ;Li, Chen, et al, ; Li, Huang, et al, , ; Liu et al, ; Metcalfe, ). The in situ suture model is also supported by the observation that the CQMB features multistage penetrative deformations associated with oceanic subduction and the ensuing late Triassic‐early Jurassic continental collision between the NQB and SQB (Liang et al, , ; Li et al, ; Wang et al, ; Zhao et al, ).…”

“…Numerous studies have investigated the CQMB, especially the Permian (283–259 Ma) and Triassic (244–211 Ma) HP‐LT metamorphic rocks (Figure ; Deng et al, ; Kapp et al, ; Li et al, ; Li, Zhai, Dong, et al, ; Li, Zhai, Chen, et al, ; Liang et al, , ; Yin & Harrison, ; Zhao et al, , ; Zhang et al, ) and Paleozoic‐early Triassic ophiolites (Li et al, ; Li, Chen, et al, ; Li, Huang, et al, , ; Zhu et al, ; Wang, Pan, et al, ; Wu et al, ; Zhai, Jahn, Wang, et al, , ; Zhang et al, ). In contrast, the southern margin of the NQB, especially the late Paleozoic‐Triassic sedimentary evolution and its tectonic relationship with the CQMB, remains poorly studied.…”

“…However, this concept has been largely refuted based on careful interpretation of paleontological data Song et al, 2017) and detrital zircon provenance data Kapp et al, 2003;Pullen et al, 2008). Numerous studies have investigated the CQMB, especially the Permian (283-259 Ma) and Triassic (244-211 Ma) HP-LT metamorphic rocks ( Figure 1; Deng et al, 2000;Kapp et al, 2003;Li et al, 1995;Li, Zhai, Dong, et al, 2006;Liang et al, 2012Liang et al, , 2017Zhao et al, 2014Zhao et al, , 2015Zhang et al, 2017) and Paleozoic-early Triassic ophiolites Zhu et al, 2006;Wang, Pan, et al, 2008;Wu et al, 2010;Zhang et al, 2017). In contrast, the southern margin of the NQB, especially the late Paleozoic-Triassic sedimentary evolution and its tectonic relationship with the CQMB, remains poorly studied.…”