Geochemistry, zircon U–Pb geochronology and Hf isotopes of Jurassic-Cretaceous granites in the Tengchong terrane, SW China: implications for the Mesozoic tectono-magmatic evolution of the Eastern Tethyan Tectonic Domain

Recently identified Early Jurassic, Early Cretaceous, and Late Cretaceous granites of the Tengchong terrane, SW China, help to refine our understanding of the Mesozoic tectonic-magmatic evolutionary history of the region. We present new zircon U–Pb geochronological, Lu–Hf isotopic and geochemical data on these rocks. The zircon LA-ICP-MS U–Pb ages of the Mangzhangxiang, Laochangpo, and Guyong granites, and Guyong granodioritic microgranular enclaves are 185.6, 120.7, 72.9, and 72.7 Ma, respectively. Geochemical and Hf isotopic characteristics suggest the Mangzhangxiang and Laochangpo S-type granites were derived from partial melting of felsic crust and that the Guyong I-type granite and associated MMEs were generated through magma mixing/mingling. Mesozoic magmatism in the Tengchong terrane can be divided into three episodes: (1) the Triassic syn- and post-collisional magmatic event was related to the closure of the Palaeo-Tethyan Ocean, as represented by the Changning-Menglian suture zone; (2) the Jurassic to Early Cretaceous magmatism was related to the subduction of the Meso-Tethyan oceanic crust, as represented by the Myitkyina ophiolite belt; and (3) the Late Cretaceous magmatism was related to the subduction of the Neo-Tethyan oceanic crust, as represented by the Kalaymyo ophiolite belt.

中国西南腾冲地体新近识别出的早侏罗世、早白垩世及晚白垩世花岗岩，有助于厘清该区域中生代构造-岩浆演化历史。本文报道了这些岩体的全新锆石U-Pb年代学、Lu-Hf同位素及地球化学数据。芒掌乡、老厂坡、古永花岗岩以及古永花岗闪长质微粒包体的锆石LA-ICP-MS U-Pb年龄分别为185.6 Ma、120.7 Ma、72.9 Ma和72.7 Ma。地球化学与Hf同位素特征表明，芒掌乡、老厂坡S型花岗岩（S-type granite）起源于长英质地壳的部分熔融；古永I型花岗岩（I-type granite）及其伴生的MME（微粒包体，microgranular enclave）则通过岩浆混合/混杂作用形成。腾冲地体的中生代岩浆作用可划分为三期：（1）三叠纪同碰撞-后碰撞岩浆事件，以昌宁-孟连缝合带为代表，与古特提斯洋（Palaeo-Tethyan Ocean）的闭合相关；（2）侏罗纪至早白垩世岩浆作用，以密支那蛇绿岩带（Myitkyina ophiolite belt）为代表，与中特提斯洋（Meso-Tethyan Ocean）洋壳的俯冲作用相关；（3）晚白垩世岩浆作用，以卡拉谬蛇绿岩带（Kalaymyo ophiolite belt）为代表，与新特提斯洋（Neo-Tethyan Ocean）洋壳的俯冲作用相关。