Geochemical and Sr–Nd–Hf isotopic constraints on the origin of Late Triassic granitoids from the Qinling orogen, central China: Implications for a continental arc to continent–continent collision
Geochemical and Sr–Nd–Hf isotopic constraints on the origin of Late Triassic granitoids from the Qinling orogen, central China: Implications for a continental arc to continent–continent collision
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DOI：
10.1016/j.lithos.2010.02.014
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发表时间：
2010-06
期刊：
影响因子：
3.5
通讯作者：
Yao-Hui Jiang;Guodong Jin;S. Liao;Qing Zhou;Peng Zhao
中科院分区：
文献类型：
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作者：
Yao-Hui Jiang;Guodong Jin;S. Liao;Qing Zhou;Peng Zhao
秦岭-大别-苏鲁造山带是华北陆块和华南陆块的交接带。然而，在秦岭造山带的华北和华南块体的最终合并的确切时间是缺乏约束。本文报道了秦岭造山带5个早中生代花岗质岩体的SHRIMP锆石U-Pb年代学、主量元素、微量元素和Sr-Nd-Hf同位素数据。SHRIMP锆石U-Pb定年结果表明，4个岩体侵位于晚三叠世卡尼期（227- 218 Ma），呈向南侵位趋势，1个岩体侵位于晚三叠世诺利期（211 Ma）。卡尼期岩体由高钾钙碱性花岗岩类（石英二长闪长岩、石英二长岩、花岗闪长岩和二长花岗岩）和钙碱性闪长岩组成。这些岩石主要是偏铝质的，具有高Sr、低Y和Yb含量，高Sr/Y和La/Yb比值，高Mg#，高于纯地壳熔体。诺里安岩体由高钾钙碱性二云母花岗岩组成，呈过铝质。这些花岗岩具有低Sr和高Y和Yb含量，并显示出类似于纯地壳熔体的Mg#。详细的元素和同位素数据表明，卡尼岩体侵位在大陆弧设置耦合向北俯冲的古特提斯洋壳。俯冲沉积物的部分熔融引发的下伏火成岩洋壳的脱水，与随后的熔体与上覆地幔楔相互作用，形成了高钾钙碱性花岗岩岩浆。板片熔融导致混杂橄榄岩地幔楔部分熔融，形成钙碱性闪长质岩浆。诺利安岩体是在南秦岭陆块与华南陆块碰撞过程中侵位的，标志着南北陆块的最终整合。碰撞（逆冲）带浅部（<30 km）俯冲沉积物的部分熔融可以解释诺利安过铝花岗岩的成因。新资料表明，华北陆块和华南陆块在秦岭造山带的最终拼合与大别-苏鲁造山带的拼合并不同步，因此，华北陆块和华南陆块之间的古特提斯洋盆很可能呈“剪刀状”，东部（大别-苏鲁）中三叠世安尼期（约240 Ma）和西部（秦岭）晚三叠世诺利期（约211 Ma）封闭。
The Qinling–Dabie–Sulu orogen marks the junction between the North and South China Blocks. However, the exact timing of the final coalescence of the North and South China Blocks in the Qinling orogen is poorly constrained. This paper presents new SHRIMP zircon U–Pb chronology, major and trace elements, and Sr–Nd–Hf isotope data for five early Mesozoic granitic plutons across the Qinling orogen. SHRIMP zircon U–Pb dating shows that four plutons were emplaced in the Carnian (227–218Ma) of Late Triassic with a southward-younging trend and one pluton was emplaced in the Norian (∼211Ma) of Late Triassic. The Carnian plutons consist of high-K calc-alkaline granitoids (quartz monzodiorite, quartz monzonite, granodiorite and monzogranite) and calc-alkaline diorite. These rocks are mainly metaluminous and are characterized by high Sr and low Y and Yb contents, with high Sr/Y and La/Yb ratios, and by high Mg#, higher than pure crustal melts. The Norian pluton is composed of high-K calc-alkaline two-mica granites, which are peraluminous. These granites have low Sr and high Y and Yb contents and show similar Mg# to pure crustal melts. Detailed elemental and isotopic data suggest that the Carnian plutons were emplaced in a continental arc setting coupled with the northward subduction of the Paleo-Tethyan oceanic crust. Partial melting of subducted sediments triggered by dehydration of the underlying igneous oceanic crust, with subsequent melts interacting with the overlying mantle wedge, formed the high-K calc-alkaline granitic magmas. Partial melting of the hybridized peridotitic mantle wedge induced by slab melts generated the calc-alkaline dioritic magma. The Norian pluton was emplaced during continental collision between the South Qinling terrane and South China Block, which marks the final integration of the North and South China Blocks. Partial melting of subducted sediments at a shallow depth (<30km) in the collision (overthrust) zone could account for the origin of the Norian peraluminous granites. Our new data suggest that the final coalescence of the North and South China Blocks in the Qinling orogen is not synchronous with that in the Dabie–Sulu orogen, and thus, the Paleo-Tethyan oceanic basin between the North and South China Blocks most likely occurred as a ‘scissors-like’ shape, with closure in the Anisian (∼240Ma) of Middle Triassic in the eastern part (Dabie–Sulu) and in the Norian (∼211Ma) of Late Triassic in the western part (Qinling).