| Xiba Granitic Pluton in the Qinling Orogenic Belt, Central China: Its Petrogenesis and Tectonic Implications |
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| 作者姓名： | ZHANG Fan LIU Shuwen CHEN Xu LI Qiugen DAI Junzhi YANG Kai WU Fenghui and CHEN Youzhang |
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| 作者单位： | 1 The Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, Peking University, Beijing 100871
2 Northwest Bureau of Geological Exploration of China National Nonferrous Metals Industry Corporation, Xi’an, Shaanxi 710054 |
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| 基金项目： | This study is financially supported by the National projects of Scientific and Technological Support (Grant Nos.2011BAB04B05 and 2006BAB01A11) and National Natural Science Foundation of China (Grant Nos. 41072143 and 41072169). |
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| 摘 要： | Xiba granitic pluton is located in South Qinling tectonic domain of the Qinling orogenic belt and consists mainly of granodiorite and monzogranite with significant number of microgranular quartz dioritic enclaves. SHRIMP zircon U–Pb isotopic dating reveals that the quartz dioritic enclaves formed at 214±3 Ma, which is similar to the age of their host monzogranite (218±1 Ma). The granitoids belong to high-K calc-alkaline series, and are characterized by enriched LILEs relative to HFSEs with negative Nb, Ta and Ti anomalies, and right-declined REE patterns with (La/Yb)N ratios ranging from 15.83 to 26.47 and δEu values from 0.78 to 1.22 (mean= 0.97). Most of these samples from Xiba granitic pluton exhibit εNd(t) values of ?8.79 to ?5.38, depleted mantle Nd model ages (TDM) between 1.1 Ga and 1.7 Ga, and initial Sr isotopic ratios (87Sr/86Sr)i from 0.7061 to 0.7082, indicating a possible Meso- to Paleoproterozoic lower crust source region, with exception of samples XB01-2-1 and XB10-1 displaying higher (87Sr/86Sr)i values of 0.779 and 0.735, respectively, which suggests a contamination of the upper crustal materials. Quartz dioritic enclaves are interpreted as the result of rapid crystallization fractionation during the parent magmatic emplacement, as evidenced by similar age, texture, geochemical, and Sr-Nd isotopic features with their host rocks. Characteristics of the petrological and geochemical data reveal that the parent magma of Xiba granitoids was produced by a magma mingling process. The upwelling asthenosphere caused a high heat flow and the mafic magma was underplated into the bottom of the lower continent crust, which caused the partial melting of the lower continent crustal materials. This geodynamic process generated the mixing parent magma between mafic magma from depleted mantle and felsic magma derived from the lower continent crust. Integrated petrogenesis and tectonic discrimination with regional tectonic evolution of the Qinling orogen, it is suggested that the granitoids are most likely products in a post-collision tectonic setting.
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| 关 键 词： | Xiba granitoids SHRIMP U-Pb ages geochemistry and Sr-Nd isotopic systematics petrogenesis and tectonic implication Qinling orogenic belt |
| 收稿时间： | 2011/3/11 0:00:00 |
| 修稿时间： | 5/5/2012 12:00:00 AM |
Xiba Granitic Pluton in the Qinling Orogenic Belt,Central China: Its Petrogenesis and Tectonic Implications |
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| Authors: | ZHANG Fan LIU Shuwen CHEN Xu LI Qiugen DAI Junzhi YANG Kai WU Fenghui CHEN Youzhang |
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| Institution: | 1. The Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, Peking University, Beijing 100871;2. Northwest Bureau of Geological Exploration of China National Nonferrous Metals Industry Corporation, Xi'an, Shaanxi 710054 |
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| Abstract: | Xiba granitic pluton is located in South Qinling tectonic domain of the Qinling orogenic belt and consists mainly of granodiorite and monzogranite with significant number of microgranular quartz dioritic enclaves. SHRIMP zircon U–Pb isotopic dating reveals that the quartz dioritic enclaves formed at 214±3 Ma, which is similar to the age of their host monzogranite (218±1 Ma). The granitoids belong to high‐K calc‐alkaline series, and are characterized by enriched LILEs relative to HFSEs with negative Nb, Ta and Ti anomalies, and right‐declined REE patterns with (La/Yb)N ratios ranging from 15.83 to 26.47 and δEu values from 0.78 to 1.22 (mean= 0.97). Most of these samples from Xiba granitic pluton exhibit εNd(t) values of –8.79 to –5.38, depleted mantle Nd model ages (TDM) between 1.1 Ga and 1.7 Ga, and initial Sr isotopic ratios (87Sr/86Sr)i from 0.7061 to 0.7082, indicating a possible Meso‐ to Paleoproterozoic lower crust source region, with exception of samples XB01‐2‐1 and XB10‐1 displaying higher (87Sr/86Sr)i values of 0.779 and 0.735, respectively, which suggests a contamination of the upper crustal materials. Quartz dioritic enclaves are interpreted as the result of rapid crystallization fractionation during the parent magmatic emplacement, as evidenced by similar age, texture, geochemical, and Sr‐Nd isotopic features with their host rocks. Characteristics of the petrological and geochemical data reveal that the parent magma of Xiba granitoids was produced by a magma mingling process. The upwelling asthenosphere caused a high heat flow and the mafic magma was underplated into the bottom of the lower continent crust, which caused the partial melting of the lower continent crustal materials. This geodynamic process generated the mixing parent magma between mafic magma from depleted mantle and felsic magma derived from the lower continent crust. Integrated petrogenesis and tectonic discrimination with regional tectonic evolution of the Qinling orogen, it is suggested that the granitoids are most likely products in a post‐collision tectonic setting. |
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| Keywords: | Xiba granitoids SHRIMP U‐Pb ages geochemistry and Sr‐Nd isotopic systematics petrogenesis and tectonic implication Qinling orogenic belt |
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