- 责任者：Liu Chunhua (State Key Laboratory of Continental Tectonics and Dynamics ; Institute of Geology ; Chinese Academy of Geological Sciences ; Beijing 100037 ; China) ; Wu Cailai
- 刊名：Earth Science Frontiers
- 出版年：2013
- 卷期：20(5
- 关键词：铀—铅计时 ; U-Pb dating ; 花岗岩类 ; granitoid ; 秦岭 ; Qinling Mountains
- 页码：p.36-56
- 图表：11 illus., 4 tables, 62 refs.
- 分类号：0801
- issnNo：ISSN1005-2321
- isbnNo：CN11-3370/P
Machihe country and Shahewan granitoid rock masses are located in the south of Shang Dan fault. Zircon laser ablation inductively coupled plasma mass spectrometry （LA-ICPMS） was used for U Pb chronologic analysis to determine crystallization ages for Machihe country granite and Shahewan quartz monzonite magma of 490. 8 ± 2. 9 Ma （Early Ordovician）, and （240. 6 ±1.5）-（228. 2±1.5） Ma （Middle Triassic）, respectively. The results of zircon in-situ Lu Hf isotopic analysis indicate that the two stage Hf model ages （t_DM2） of zircon are 759 - 1096 Ma and 891 - 1516 Ma, respectively. The source-rock material of Machihe country granite is Neoproterozoic and Mesoproterozoic depleted mantle material. Shahewan quartz monzonite is the mixing product of crustal with mantle materials at different levels in the Mesoproterozoic and Neoproterozoic time. In the northward subduction of the QinLing oceanic crust beneath North Qinling, the oceanic crust and the upper mantle interacted to produce the hybridized liquid and formed Machihe country granite by crystallization differentiation in the Irate Cambrian to the Early Ordovician. Shahewan rock mass was formed during at least two geological events with large time spans between （240. 6± 1.5）-（228.2 ± 1.5） Ma and 214 - 197 Ma, respectively. After the closure of the Mian-LiAe oceanic basin at about 250 Ma, a collision event occurred between the Yangtze and the North China plates in the Qinling orogenic belt. This collision resulted in the subduction of the continental Yangtze plate beneath South Qinling, in which a small part of the crust melted to form the Early-Middle Triassic granitoids at （ 240. 6 ± 1. 5）- （228. 2±1. 5） Ma. After this collision, approximately at 220 Ma, the detachment of the slab induced the upwelling of the asthenosphere material. The subducted continental crust began to uplift, and under the conditions of mantle heat and tectonic stress, widespread partial melting of the subducted continental crust and the upper lithosphere mantle occurred to form granitoids with various degrees of adakite characteristics in the Late Triassic （214- 197 Ma） and associated with mafic inclusions.