Early Paleozoic collision-related magmatism in the eastern North Qilian orogen, northern Tibet: A linkage between accretionary and collisional orogenesis

Research Article| November 29, 2018 Early Paleozoic collision-related magmatism in the eastern North Qilian orogen, northern Tibet: A linkage between accretionary and collisional orogenesis Dong Fu; Dong Fu 1Center for Global Tectonics, School of Earth Sciences, State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Timothy Kusky; Timothy Kusky † 1Center for Global Tectonics, School of Earth Sciences, State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China †Corresponding author: tkusky@gmail.com. Search for other works by this author on: GSW Google Scholar Simon A. Wilde; Simon A. Wilde 2Department of Applied Geology, Curtin University, Perth, Western Australia, Australia Search for other works by this author on: GSW Google Scholar Ali Polat; Ali Polat 1Center for Global Tectonics, School of Earth Sciences, State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China3Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada Search for other works by this author on: GSW Google Scholar Bo Huang; Bo Huang 1Center for Global Tectonics, School of Earth Sciences, State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Zhipeng Zhou Zhipeng Zhou 1Center for Global Tectonics, School of Earth Sciences, State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar GSA Bulletin (2019) 131 (5-6): 1031–1056. https://doi.org/10.1130/B35009.1 Article history received: 14 Apr 2018 rev-recd: 27 Aug 2018 accepted: 05 Oct 2018 first online: 30 Nov 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Dong Fu, Timothy Kusky, Simon A. Wilde, Ali Polat, Bo Huang, Zhipeng Zhou; Early Paleozoic collision-related magmatism in the eastern North Qilian orogen, northern Tibet: A linkage between accretionary and collisional orogenesis. GSA Bulletin 2018;; 131 (5-6): 1031–1056. doi: https://doi.org/10.1130/B35009.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Collision-related magmatism in accretionary-to-collisional orogens records a tectonic transition from early subduction-accretionary processes to collisional orogenesis, and also plays a significant role in continental growth. Here, we present an integrated study of field observations, geochemistry, whole-rock Rb-Sr and Sm-Nd isotopes, and zircon U-Pb ages and Lu-Hf isotopes for the Laohushan mafic to felsic magmatic rocks related to initial collision between the Alxa terrane and the Central Qilian block along the North Qilian orogenic belt, northeastern Tibet. The Laohushan magmatic rocks are dominated by quartz diorites (ca. 426 Ma), with minor tonalites enclosing dioritic enclaves (ca. 430 Ma) and hornblendite xenoliths (ca. 448 Ma), and some coeval dolerite dikes (ca. 427 Ma) intruded into the accretionary complex. The quartz diorites are characterized by light rare earth element (LREE)- and large ion lithophile element (LILE)-enrichment but have high field strength element (HFSE)-depleted trace element patterns and negative initial εNd (–1.6 to –2.9) and positive zircon initial εHf (+3.0 to +6.2) values. The dioritic enclaves are also characterized by LREE-enriched and HFSE-depleted patterns and have mostly negative initial εNd (–9.2 to +0.03) but positive zircon initial εHf (+3.0 to +5.9) values. These geochemical and isotopic features, together with isotopic mixing calculations, suggest that the quartz diorites were likely derived from partial melting of the lower crust dominated by accreted mafic oceanic rocks with minor sediments, whereas the dioritic enclaves originated from underplated mantle-derived magmas mixed with crust-derived melts. The hornblendite xenoliths have high MgO, Cr, and Ni contents, positive Th, U, and Pb anomalies, and negative Nb, Ta, and Ti anomalies. They have negative initial εNd (–2.8), near chondritic zircon initial εHf (–0.4 to +1.4) values and an Archean Nd model age (TDM = 2.74 Ga), suggesting that the hornblendites were likely produced by partial melting of subcontinental lithospheric mantle peridotite that was metasomatized by subduction-related melts beneath the Archean–Proterozoic Alxa terrane. We propose that partial melting of the lower crust of the early Paleozoic North Qilian orogenic belt was in response to slab breakoff and asthenospheric upwelling during the initial stage of collisional orogenesis. This study demonstrates that heterogeneous magma sources, involving accretionary materials (i.e., accreted oceanic crust and sediments) and various mantle-derived components, were mixed to form the collision-related magmatic rocks. It also highlights the significance of collision-related magmatism in continental growth and stabilization of newly-assembled crust in accretionary-to-collisional orogens. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.