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We present a detailed study of geochronology, mineral chemistries, bulk-rock major and trace element abundances, and Sr–Nd–Hf isotope compositions of the granodiorite and associated dioritic dikes in the Hongqilafu pluton at the northwestern margin of the Tibetan Plateau. The granodiorite and dioritic dikes yielded zircon U–Pb ages of ~ 104 Ma and ~ 100 Ma, respectively. The dioritic dikes comprise varying lithologies of gabbroic diorite, diorite porphyry and granodiorite porphyry, exhibiting a compositional spectrum from intermediate to felsic rocks. Their mineral compositions display disequilibrium features such as large major element compositional variations of plagioclase, clinopyroxene and amphibole crystals. These dioritic dikes are enriched in incompatible elements (Ba, Rb, Th, U, K) and Sr–Nd–Hf isotopes ( 87 Sr/ 86 Sr i : 0.7066 to 0.7071, ε Nd (t): − 5.3 to − 7.4, ε Hf (t): − 3.6 to − 6.2). We suggest that the dioritic dikes were most likely derived from partial melting of mantle wedge metasomatized by the subducted/subducting seafloor with a sediment component, followed by AFC processes with fractional crystallization of clinopyroxene, amphibole and plagioclase and assimilation of lower continental crust. The mantle-wedge derived magma parental to the dioritic dikes underplated and induced the lower continental crust to melt, forming the felsic crustal magma parental to the granodiorite with mantle melt signatures and having more enriched isotope compositions ( 87 Sr/ 86 Sr i : 0.7087 to 0.7125, ε Nd (t): − 9.5 to − 11.6, ε Hf (t): − 10.3 to − 14.1) than those of the dioritic dikes. The Hongqilafu pluton is thus the product of mantle–crust interaction at an active continental margin subduction setting over the period of several million years. This understanding further indicates that the closure timing of the Shyok back-arc basin and the collision between the Kohistan–Ladakh Arc and the Karakoram Terrane may have taken place later than ~ 100 Ma. [ABSTRACT FROM AUTHOR]

The West Kunlun orogenic belt (WKOB) at the northwest margin of the Greater Tibetan Plateau records seafloor subduction, ocean basin closing and continental collision with abundant syncollisional granitoids in response to the evolution of the Proto- and Paleo-Tethys Oceans from the early-Paleozoic to the Triassic. Here we present a combined study of detailed zircon U-Pb geochronology, whole-rock major and trace elements and Sr-Nd-Hf isotopic geochemistry on the syncollisional Arkarz (AKAZ) pluton with mafic magmatic enclaves (MMEs) exposed north of the Mazha-Kangxiwa suture (MKS) zone. The granitoid host rocks and MMEs of the AKAZ pluton give the same late Triassic age of ~ 225 Ma. The granitoid host rocks are metaluminous granodiorite and monzogranite. They have initial 87 Sr/ 86 Sr of 0.70818 to 0.70930, ε Nd (225 Ma) = − 4.61 to − 3.91 and ε Hf (225 Ma) = − 3.01 to 0.74. The MMEs are more mafic than the host with varying SiO 2 (51.00–63.24 wt.%) and relatively low K 2 O (1.24–3.02 wt.%), but have similar Sr-Nd-Hf isotope compositions to the host (( 87 Sr/ 86 Sr) i = 0.70830–0.70955, ε Nd (225 Ma) = − 4.88 to − 4.29, ε Hf (225 Ma) = − 2.57 to 0.25). Both the host and MMEs have rare earth element (REE) and trace element patterns resembling those of bulk continental crust (BCC). The MMEs most likely represent cumulate formed from common magmas parental to the granitoid host. The granitoid magmatism is best explained as resulting from melting of amphibolite of MORB protolith during continental collision, which produces andesitic melts with a remarkable compositional similarity to the BCC and the inherited mantle-like isotopic compositions. Simple isotopic mixing calculations suggest that ~ 80% ocean crust and ~ 20% continental materials contribute to the source of the AKAZ pluton. Thus, the hypothesis “continental collision zones as primary sites for net continental crust growth” is applicable in the WKOB as shown by studies in southern Tibet, East Kunlun and Qilian orogens. In addition, we also propose a new view for the tectonic evolution of the Paleo-Tethys Ocean in geological regions recorded and represented by the MKS. [ABSTRACT FROM AUTHOR]