| 安徽铜陵铜官山矿区中生代侵入岩的形成过程——岩浆底侵、同化混染和分离结晶 |
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| 引用本文： | 杜杨松,李顺庭,曹毅,秦新龙,楼亚儿.安徽铜陵铜官山矿区中生代侵入岩的形成过程——岩浆底侵、同化混染和分离结晶[J].现代地质,2007,21(1):71-77. |
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| 作者姓名： | 杜杨松 李顺庭 曹毅 秦新龙 楼亚儿 |
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| 作者单位： | 中国地质大学,地质过程与矿产资源国家重点实验室,北京,100083 |
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| 基金项目： | 国家自然科学基金;教育部科学技术研究重点项目 |
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| 摘 要： | 对安徽铜陵铜官山矿区的小铜官山岩体进行了SHRIMP锆石U-Pb定年,并对天鹅抱蛋山岩体及其辉长岩和闪长岩包体进行了全岩主量元素和稀土元素以及锶-钕同位素分析,结合对区内老庙基山和小铜官山岩体及其辉长岩和闪长岩包体的岩石学和地球化学资料的综合整理,讨论了这些岩体及其包体的成因。小铜官山岩体的SHRIMP锆石U-Pb年龄为(139.5±2.9)Ma,表明它属于长江中下游晚侏罗世—早白垩世岩浆作用的产物。辉长岩和闪长岩包体具有低w(SiO2)(52.03%-54.61%)、w(Al2O3)(12.87%-14.43%)和全碱含量w(Na2O+K2O)(5.26%-6.30%),但高w(MgO)(5.41%-11.66%)的特征;寄主岩与此相反,具有高w(SiO2)(59.97%-64.44%)、w(Al2O3)(16.43%-17.59%)和全碱含量(6.67%-8.25%),但低w(MgO)(1.52%-2.50%)的特征。辉长岩和闪长岩包体的稀土元素总量为165.70×10-6-190.40×10-6,寄主岩的稀土元素总量为166.12×10-6-185.95×10-6,二者十分相近,它们的稀土元素球粒陨石标准化配分模式也十分相似。但辉长岩和闪长岩包体的轻、重稀土比值为3.39-4.27,明显小于寄主岩的轻、重稀土比值(4.86-5.94)。辉长岩和闪长岩包体具明显的正铕异常,而寄主岩具有弱负铕异常。从辉长岩到寄主岩,εNd(t)从-4.9--9.9减小到-11.4--11.9,(87Sr/86Sr)o从0.7064-0.7073增加到0.7072-0.7084。上述资料表明,铜陵铜官山矿区晚侏罗世—早白垩世侵入岩及其辉长岩和闪长岩包体可能是由基性到中酸性岩浆通过幔源岩浆底侵、同化混染和分离结晶过程形成的,而基性到中酸性岩浆则是由底侵的玄武岩浆与不同量的中下地壳物质发生一系列复杂的相互作用形成的。
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| 关 键 词： | 晚侏罗世—早白垩世 玄武岩浆底侵 同化混染和分离结晶 中酸性火成岩 岩石包体 长江中下游 |
| 文章编号： | 1000-8527(2007)01-0071-07 |
| 收稿时间： | 11 8 2006 12:00AM |
| 修稿时间： | 12 28 2006 12:00AM |
UAFC-Related Origin of the Late Jurassic to Early Cretaceous Intrusions in the Tongguanshan Ore Field, Tongling, Anhui Province, East China |
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| DU Yang-song,LI Shun-ting,CAO Yi,QIN Xin-long,LOU Ya-er.UAFC-Related Origin of the Late Jurassic to Early Cretaceous Intrusions in the Tongguanshan Ore Field, Tongling, Anhui Province, East China[J].Geoscience——Journal of Graduate School,China University of Geosciences,2007,21(1):71-77. |
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| Authors: | DU Yang-song LI Shun-ting CAO Yi QIN Xin-long LOU Ya-er |
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| Abstract: | This paper presents petrographic observations and geochemical analyses on the Laomiaojishan,Xiaotongguanshan and Tianebaodanshan intrusions with quartz monzonitic dioritic composition and xenoliths with gabbroic to dioritic compositions exposed in the Tongguanshan ore field,Tongling,Anhui Province,East China,and provides some evidence for the origin of the intrusions and xenoliths.The Xiaotongguanshan intrusion is dated at(139.5±2.9) Ma using the SHRIMP zircon U-Pb method and represents product of the Late Jurassic to Early Cretaceous magmatism in the lower valley of Yangtze River.The gabbro and diorite autoliths are low in SiO2(52.03 %-54.61 %),Al2O3(12.87 %-14.43 %) and total alkalis (Na2O+K2O)(5.26 %-6.30 %),but high in MgO(5.41 %-11.66 %),relative to the hosts which have high SiO2 (59.97 %-64.44 %),Al2O3(16.43 %-17.59 %) and total alkalis(6.67 %-8.25 %),but low in MgO (1.52 %-2.50 %).The gabbro and diorite autoliths have similar total REE content ranging from 165.70×10-6 to 190.40×10-6 to that of the hosts from 166.12×10-6 to 185.95×10-6,but have smaller ratios of LREE to HREE ranging from 3.39 to 4.27 than those of the hosts from 4.86 to 5.94.All of the rocks show very similar REE patterns,but the gabbro and diorite autoliths display evident positive Eu anomalies,and the hosts indicate slightly negative Eu anomalies.The values of epsilon Nd(t) vary from-4.9——9.9 in the gabbro autoliths to-11.4——11.9 in the hosts.Initial 87Sr/86Sr ratios define ranges of 0.706,4-0.707,3 in the gabbro and diorite autoliths and 0.707,2-0.708,4 in the quartz monzonitic diorite hosts,respectively.The petrological and geochemical features of the Late Jurassic to Early Cretaceous intrusions with gabbroic to dioritic autoliths in the Tongguanshan ore field are consistent with an origin from basic to intermediate-acidic magmas that were possibly formed by a series of complex interactions of the underplated basaltic magma with different amount of middle to lower crustal materials through a process of mantle-derived magma underplating followed by assimilation-fractionation crystallization. |
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| Keywords: | Late Jurassic to Early Cretaceous basaltic magma underplating assimilation and fractionation crystallization intermediate-acidic igneous rock xenolith lower valley of Yangtze River |
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