Petrogenesis and tectonic setting of Triassic granitoids in the Qiangtang terrane, central Tibet: Evidence from U–Pb ages, petrochemistry and Sr–Nd–Hf isotopes

• The Shuanghu and Rongma granitoids are distributed in the Qiangtang terrane, central Tibet.
• Zircon U–Pb dating shows that the intrusions formed at ∼220 Ma and ∼210 Ma.
• Sr–Nd and zircon Hf isotopic compositions possibly suggest they were derived from melting of southern Qiangtang crust.
• These intrusions likely formed in a collisional setting between southern and northern Qiangtang terrane.

Triassic granitoids, including the ∼220 Ma Shuanghu and ∼210 Ma Rongma granitoids studied here, are widely distributed around the Longmu–Shuanghu suture and in the Qiangtang terrane, central Tibet. The majority of these granitoids can be classified as high-K calc-alkaline in nature and yield negative Ba and Sr anomalies on primitive mantle-normalized diagrams. In addition, they are: enriched in light rare earth elements (LREE) ((La/Yb)N = 1.61–21.79); strongly enriched in large ion lithophile elements (LILE: e.g., Cs, Rb, and K), and depleted in high field strength elements (HFSE: e.g., Nb and Ti). Magma mixing played a role in the genesis of the Shuanghu granodiorites, as indicated by the occurrence of dioritic enclaves and the wide range in zircon Hf compositions (εHf(t) = −15.0 to −2.5). The I-type Shuanghu granodiorites and S-type Shuanghu and Rongma granites might have been derived from melting of southern Qiangtang crust given the high initial Sr (0.7131–0.7272), low εNd(t) (−8.9 to −11.1) and zircon εHf(t) values (−15 to −7.2). The granitoids may have formed during melting of southern Qiangtang crust, heated by upwelling asthenosphere mantle, a result of break-off and delamination of the Paleo-Tethys slab in a collisional setting.