| Indosinian Tectonic Setting of the Southern Yidun Arc： Constraints from SHRIMP Zircon Chronology and Geochemistry of Dioritic Porphyries and Granites |
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| 作者姓名： | LIU Shuwen WANG Zongqi YAN Quanren LI Qiugen ZHANG Dehui WANG Jianguo YANG Bin GU Libing and ZHAO Fengshan The Key Laboratory of Orogenic Belts and Crustal Evolution Ministry of Education School of Earth and Space Sciences Peking University Beijing |
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| 作者单位： | LIU Shuwen，WANG Zongqi，YAN Quanren，LI Qiugen，ZHANG Dehui，WANG Jianguo，YANG Bin，GU Libing and ZHAO Fengshan The Key Laboratory of Orogenic Belts and Crustal Evolution，Ministry of Education，School of Earth and Space Sciences，Peking University，Beijing 100871 |
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| 摘 要： | A mass of granitoid and dioritic intrusions are distributed in the southern Yidun Arc, among which the representative Indosinian intrusions include the Dongco and Maxionggou granitoid intrusions in Daocheng County and hypabyssal intrusions intruding into arc volcanic rocks near the Xiangcheng town. The Dongco and Maxionggou granitoid intrusions consist mainly of porphyraceous monzogranites, megacryst monzogranites and aplite granites. The Xiangcheng hypabyssal intrusions are composed dominantly of dioritic porphyries. SHRIMP zircon ages of 224±3 Ma and 222±3 Ma have been obtained for the Dongco granitoid intrusion and the Xiangcheng dioritic porphyries, respectively. The Xiongcheng dioritic porphyries show a cak-alkaline geochemical feature, and are characterized by higher Sr/Y ratios, depletive Nb, Ta, P and Ti, enriched LILEs, and lower εNd (t) (= -3.27), suggesting that they might be derived from mantle source magmas that were obviously contaminated by continent crustal materials. However, the Dongco and Maxionggou granitoids belong to high-potassium calc alkaline series with a per-metaluminous feature, and are characterized by higher CaO/(∑FeO+MgO) and Al2O3/(∑FeO+ MgO) ratios, lower (La/Yb)n and Sr/Y ratios, depletive Nb, Ta, Sr, P and Ti, enriched LILEs, and very low εNd (t) (= -8.10), indicating that the granitoids might be derived from partial melting of continental crust materials mainly of graywacke. Petrogenesis of Dongco and Maxionggou granitoids implies that there was an oceanic crust between the Zongza continental block (ZCB) and western margin of the Yangtze Craton (WMYZC). And the oceanic crust slab subducted westward during the Indosinian Epoch, producing an Andes-type continent marginal arc and a back arc basin at the WMSCC. Then the oceanic basin closed and a sinistrally lateral collision occurred at ca. 224 Ma-222 Ma between the ZCB and the WMYZC, causing partial melting of sediments in the back-arc basin to generate granitoid magmas of the Dongco and Maxionggou intrusions.
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| 关 键 词： | 地质年代学 锆石 地球化学 同位素 |
| 收稿时间： | 2005-01-10 |
| 修稿时间： | 2005-12-13 |
Indosinian Tectonic Setting of the Southern Yidun Arc: Constraints from SHRIMP Zircon Chronology and Geochemistry of Dioritic Porphyries and Granites |
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| Authors: | LIU Shuwen WANG Zongqi YAN Quanren LI Qiugen ZHANG Dehui WANG Jianguo YANG Bin GU Libing and ZHAO Fengshan The Key Laboratory of Orogenic Belts and Crustal Evolution Ministry of Education School of Earth and Space Sciences Peking University Beijing |
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| Abstract: | Abstract A mass of granitoid and dioritic intrusions are distributed in the southern Yidun Arc, among which the representative Indosinian intrusions include the Dongco and Maxionggou granitoid intrusions in Daocheng County and hypabyssal intrusions intruding into arc volcanic rocks near the Xiangcheng town. The Dongco and Maxionggou granitoid intrusions consist mainly of porphyraceous monzogranites, megacryst monzogranites and aplite granites. The Xiangcheng hypabyssal intrusions are composed dominantly of dioritic porphyries. SHRIMP zircon ages of 224±3 Ma and 222±3 Ma have been obtained for the Dongco granitoid intrusion and the Xiangcheng dioritic porphyries, respectively. The Xiongcheng dioritic porphyries show a calc‐alkaline geochemical feature, and are characterized by higher Sr/Y ratios, depletive Nb, Ta, P and Ti, enriched LILEs, and lower ?Nd (t) (= ?3.27), suggesting that they might be derived from mantle source magmas that were obviously contaminated by continent crustal materials. However, the Dongco and Maxionggou granitoids belong to high‐potassium calcalkaline series with a per‐metaluminous feature, and are characterized by higher CaO/(σFeO+MgO) and Al2O3/(σFeO+ MgO) ratios, lower (La/Yb)n and Sr/Y ratios, depletive Nb, Ta, Sr, P and Ti, enriched LILEs, and very low ?Nd (t) (= ?8.10), indicating that the granitoids might be derived from partial melting of continental crust materials mainly of graywacke. Petrogenesis of Dongco and Maxionggou granitoids implies that there was an oceanic crust between the Zongza continental block (ZCB) and western margin of the Yangtze Craton (WMYZC). And the oceanic crust slab subducted westward during the Indosinian Epoch, producing an Andes‐type continent marginal arc and a back‐arc basin at the WMSCC. Then the oceanic basin closed and a sinistrally lateral collision occurred at ca. 224 Ma‐222 Ma between the ZCB and the WMYZC, causing partial melting of sediments in the back‐arc basin to generate granitoid magmas of the Dongco and Maxionggou intrusions |
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| Keywords: | southern Yidun Arc dioritic porphyries and monzogranites SHRIMP zircon age geochemistry and Nd isotope petrogenesis and geodynamics |
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