For permission to copy, contact editing@geosociety.org © 2022 Geological Society of America GSA Bulletin; Month/Month 2022; 0; p. 1–20; https://doi.org/10.1130/B36452.1; 16 figures; 2 tables; 1 supplemental file. published online 7 July 2022 1 Albian–Cenomanian granitoid magmatism in Eastern and Central Tibet as a result of diachronous, continental collision induced slab tear propagation Xue Gao 1 and Yildirim Dilek 1,2,† 1 State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China 2 Department of Geology and Environmental Earth Science, Miami University, Oxford, Ohio 45056, USA ABSTRACT A discrete belt of Albian–Cenomanian granitoid plutons occurs in the Lhasa and Qiangtang terranes in the Central (CTP) and Eastern Tibetan Plateau (ETP) and repre- sents a major magmatic pulse in the plateau’s crustal evolution during the Cretaceous. The geochemistry, petrogenesis, and magmatic development of these granitoids are different from those of magmatic arc granitoids along the southern edges of the Lhasa and Qiang- tang terranes, indicating different heat and melt sources and tectonic setting of their for- mation. We present here new mineral, whole- rock and isotope geochemistry, and zircon U-Pb age data from the Xiasai pluton in the ETP and discuss its geochemical-petrological characteristics and magmatic development in comparison to the other Cretaceous plutons in the ETP and CTP, and within the tectonic framework of the Mesotethyan geology of Tibet. Zircons from the Xiasai and other plu- tons in the ETP have yielded U-Pb ages rang- ing from 106 Ma to 93 Ma in comparison to 115 Ma and 100.3 Ma zircons from the South- ern Qiangtang Terrane (SQT) and 113.4 Ma and 109 Ma zircons from the Northern Lhasa Terrane (NLT) farther west. The Cretaceous granitoids in the ETP and CTP range in com- position from granite, K-feldspar granite to monzogranite and biotite monzogranite, rep- resenting highly fractionated I-type granites with relatively high SiO 2 and K 2 O contents, variable (Na 2 O + K 2 O)/CaO and FeO T /MgO ratios, and (Zr + Nb + Ce + Y) abundances. They display signifcant negative Eu anoma- lies (Eu/*Eu) = 0.04–0.12) and strong deple- tions in Sr and Ba, and are strongly enriched in large ion lithophile elements but depleted in high feld strength elements. Their εHf (t) values correspond to wide ranging Hf iso- tope crustal model ages (T DM C ) of 0.3–1.9 Ga, and their Sr-Nd isotopic signatures show el- evated ( 87 Sr/ 86 Sr) i ratios (0.7034–0.7105) and negative εNd (t) values of –8.8 to –4.9. These high whole-rock ( 87 Sr/ 86 Sr) i ratios and rela- tively high Th/Nb and Th/Yb ratios indicate incorporation of melts derived from partial melting of subducted sediments into the melt evolution of these granitoids that involved partial melting of the subduction-metasoma- tized lithospheric mantle and the mafc- to intermediate-composition continental crust. The extant zircon crystallization ages of the granitoid intrusions in the CTP and ETP show eastward younging of their emplace- ment from 115 Ma to 93 Ma, suggesting an apparent eastward migration of the heat source through time. A diachronous collision of the NLT with the SQT during 145–120 Ma and the subsequent slab breakoff induced, eastward propagated slab tear and asthe- nospheric upwelling produced the hybrid melts of the Albian–Cenomanian granitoids and their emplacement in a discrete, narrow magmatic belt in the CTP and ETP. INTRODUCTION The Tibetan Plateau is a tectonic mosaic of lithospheric-scale terranes and crustal blocks, derived from East Gondwana that were accreted progressively to the southern margin of Eurasia as the Paleotethyan, Mesotethyan, and Neotethyan ocean basins closed progres- sively through time between the late Paleozoic and late Cenozoic (Yin and Harrison, 2000; Ding et al., 2003; Pan et al., 2012). The most salient terranes include, from the north to the south, the Kunlun, Songpan-Garze, Qiang- tang, Lhasa, and Himalaya terranes (Fig. 1) that are bounded by the A’nyemaqen, Jin- shajiang (JSJS), Baongong-Nujiang (BNSZ), and Indus-Yarlung suture zones, respectively. The main mechanism of crustal growth of the Tibetan Plateau throughout the Mesozoic and Cenozoic was, therefore, the development of subduction-accretion complexes at conver- gent margins of different continental terranes, the collisions and accretions of these terranes, and the emplacement of ophiolites and ensi- matic arc complexes onto their passive mar- gins (Aitchison et al., 2003; Guilmette et al., 2009; Hébert et al., 2012; Dilek and Furnes, 2014; Dong et al., 2016; Li et al., 2019b; Qian et al., 2020). Another important mechanism that contributed both to the lateral and vertical growth of the Tibetan crustal growth was large- scale magmatism, which produced regional magmatic arc systems, such as the Mesozoic Gangdese arc (Zhang et al., 2021, and refer- ences therein) in the Southern Lhasa Terrane and the Jurassic–Early Cretaceous magmatic arc along the southern edge of the Qiangtang Terrane (Li et al., 2014a; Zhang et al., 2017; Liu et al., 2019). These two magmatic arc complexes developed above the Neotethyan and Mesotethyan (also known as the Bangong- Nujiang oceanic lithosphere) subducting slabs, respectively, and hence their volcanic and plu- tonic rock assemblages refect the dynamics of complex geochemical and isotopic recycling systems and exchanges between the subducting oceanic plates and the continental upper plates. Another important mechanism that contrib- utes to crustal growth via magmatism in the absence of active subduction is slab breakoff- induced magmatism in collision zones (Dilek and Sandvol, 2009; Dilek et al., 2010; Jamali et al., 2010; Altunkaynak and Dilek, 2013, and references therein; Holm et al., 2015; Chazot et al., 2017). This magmatic construction is facilitated by asthenospheric upwelling, which develops when a subducting oceanic lithosphere breaks off and starts sinking into the mantle as continental crust in its trailing end enters and chokes the subduction zone due to its positive buoyancy (Davies and von Blanckenburg, 1995). Slab breakoff and associated magmatism com- monly occurs in collision zones (arc-continent and continent-continent collisions) and are spa- tially and temporally associated with extensional tectonics and sedimentary basin development in Yildirim Dilek https://orcid.org/0000-0003- 2387-9575 † Corresponding author: dileky@miamioh.edu. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/doi/10.1130/B36452.1/5646925/b36452.pdf by Miami University user on 07 July 2022