Abstract The Lantian-Xiaoqinling region, located at the southern margin of the North China Craton (S-NCC), exposes large-scale Late Mesozoic granitoids associated with molybdenum and hydrothermal gold deposits. This study presents zircon U-Pb-Hf isotope, whole-rock element and Sr-Nd-Pb isotope data of granitoids from two representative plutons (Laoniushan and Huashan) of the Lantian-Xiaoqinling region including previous data from the Lantian pluton. Zircon U Pb dating supports a prolonged magmatic history from c. 150 to 130 Ma. Different to the thick continental crust-derived high Sr/Y granitoids from the Dabie Mts., the granitoids of the Lantian-Xiaoqinling region are ordinary calc-alkaline granitoids which show evidence for fractional crystallization, implying no need for the existence of a thick continental crust during magmatism. The plutons share similar high whole-rock initial 87Sr/86Sr values ranging from 0.7070 to 0.7109, but variable eNd(t) (−23.4 to −9.0) and zircon eHf(t) values (−46.9 to −2.7) as well as continental crust-like initial Pb isotopes with 206Pb/204Pb(t) ratios of 17.1 to 17.9; 207Pb/204Pb(t) of 15.40 to 15.57 and 208Pb/204Pb(t) of 37.6 to 38.35. Nd-Hf-Pb isotopic compositions are more depleted compared to ancient lower NCC crust as represented by the Taihua and Xiong'er Groups and suggest involvement of some juvenile materials into the magma source. Positive correlation between SiO2 and eNd(t) values suggests that the juvenile material was silica-rich with slightly negative eNd(t) values. Such material cannot be produced from a mantle source as previously stated. These compositional features make Neoproterozoic continental crust of Yangtze Block a likely source for the juvenile material. It is argued that the juvenile material originated from partial melting of subducted Neoproterozoic continental crust with abundant black shale. We propose that the Late Mesozoic granitoid plutons in the Lantian-Xiaoqinling region stem from a composite source, including rocks similar to the ancient lower NCC crust and a juvenile felsic melt derived from the subducted Yangtze plate. Heat input and melting was triggered by asthenosphere upwelling caused by subduction of the Paleo-Pacific oceanic plate.

中文翻译：

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蓝田-小秦岭地区晚中生代花岗岩的锆石U-Pb-Hf、地球化学和Sr-Nd-Pb同位素系统学：对构造背景和成岩作用的意义

摘要 蓝田-小秦岭地区位于华北克拉通南缘，出露大型晚中生代花岗岩，伴生钼和热液金矿床。本研究提供了蓝田-小秦岭地区两个具有代表性的岩体（老牛山和华山）花岗岩的锆石 U-Pb-Hf 同位素、全岩元素和 Sr-Nd-Pb 同位素数据，包括来自蓝田岩体的先前数据。锆石 U Pb 定年支持从 c. 开始的长期岩浆历史。150 到 130 毫安。与大别山厚陆壳衍生的高Sr/Y花岗岩不同，蓝田-小秦岭地区的花岗岩为普通钙碱性花岗岩，有分异结晶的证据，表明不需要厚陆壳存在。岩浆活动期间的地壳。岩体具有相似的高全岩初始 87Sr/86Sr 值，范围从 0.7070 到 0.7109，但可变 eNd(t)（-23.4 到 -9.0）和锆石 eHf(t) 值（-46.9 到 -2.7）以及大陆206Pb/204Pb(t) 比率为 17.1 至 17.9 的地壳状初始铅同位素；207Pb/204Pb(t) 为 15.40 至 15.57 和 208Pb/204Pb(t) 为 37.6 至 38.35。Nd-Hf-Pb 同位素组成比以太华和熊耳群为代表的古代华北克拉通下地壳更为贫乏，表明一些年轻物质参与了岩浆源。SiO2 和 eNd(t) 值之间的正相关表明幼年材料富含二氧化硅，eNd(t) 值略为负。如前所述，这种材料不能从地幔来源产生。这些成分特征使扬子地块新元古代大陆地壳成为可能的新生物质来源。认为幼年物质起源于俯冲的新元古代大陆地壳的部分熔融，其中含有丰富的黑色页岩。我们提出蓝田-小秦岭地区晚中生代花岗岩类岩体来源于一个复合源，包括类似于古代华北克拉通下地壳的岩石和来自俯冲扬子板块的新生长英质熔体。热量输入和融化是由古太平洋大洋板块俯冲引起的软流圈上升引发的。我们提出蓝田-小秦岭地区晚中生代花岗岩类岩体来源于一个复合源，包括类似于古代华北克拉通下地壳的岩石和来自俯冲扬子板块的新生长英质熔体。热量输入和融化是由古太平洋大洋板块俯冲引起的软流圈上升引发的。我们提出蓝田-小秦岭地区晚中生代花岗岩类岩体来源于一个复合源，包括类似于古代华北克拉通下地壳的岩石和来自俯冲扬子板块的新生长英质熔体。热量输入和融化是由古太平洋大洋板块俯冲引起的软流圈上升引发的。