Obduction-type granites within the NE Jiangxi Ophiolite: Implications for the final amalgamation between the Yangtze and Cathaysia Blocks
Obduction-type granites within the NE Jiangxi Ophiolite: Implications for the final amalgamation between the Yangtze and Cathaysia Blocks
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DOI：
10.1016/j.gr.2007.12.010
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发表时间：
2008-04
影响因子：
6.1
通讯作者：
Wu-Xian Li;Xian‐Hua Li;Zheng‐Xiang Li;F. Lou
中科院分区：
文献类型：
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作者：
Wu-Xian Li;Xian‐Hua Li;Zheng‐Xiang Li;F. Lou
江西西湾蛇绿混杂岩中发现了浅色花岗质透镜体。浅色花岗岩只产于蛇绿岩套的蛇纹化橄榄岩单元内。SHRIMP锆石U-Pb定年结果表明，这些花岗岩形成于880±19 Ma，并在230 Ma左右受到印支期构造热事件的叠加。浅色花岗岩是过铝质的（A/CNK=1.0-1.24），其特征是高Al 2 O3（14-18.33%）和Na 2 O（6.5-10%），与蛇绿岩套的其他岩石单元相比，εNd（T）值明显较低，为0.8至−3.9。根据淡色花岗岩的稀土元素特征，可将其分为三组。第I组浅色花岗岩表现出最明显的LREE富集模式（LaN/YbN和LaN/SmN比值分别为30.1-75.0和2.3-3.9）。第II组浅色花岗岩具有中等分馏的LREE富集模式（LaN/YbN和LaN/SmN比值分别为13.1-26.5和0.8-1.9）。第Ⅲ组浅色花岗岩的稀土元素总量明显偏低，稀土元素配分模式平坦，Eu正异常明显，可能是部分熔融程度较低的结果。所有这些浅色花岗岩可能形成的部分熔融的沉积岩从一个边缘盆地在造山带的扬子一侧，在一个主要的逆冲断层的蛇绿岩仰冲到大陆地壳。它们与世界上许多地方发现的蛇绿岩中与仰冲有关的花岗岩大致相似。CA的识别。赣东北蛇绿岩中880 Ma逆冲型花岗岩的发现，为蛇绿岩逆冲到陆壳上的时间提供了岩石学上的制约。结合双溪坞弧岩浆活动的终止时间。890 Ma，新元古代弧后盆地的闭合和扬子陆块与华夏陆块拼合作用的结束发生在约890 Ma。880 Ma.
Leucogranitic lenses are found within the Xiwan ophiolitic mélange in northeastern Jiangxi Province, South China. The leucogranites occur exclusively within the serpentinized peridotite unit of the ophiolite suite. SHRIMP U–Pb zircon dating results indicate that these granites were formed at 880±19 Ma, and were overprinted by an Indosinian tectono-thermal event at ~ 230 Ma. The leucogranites are peraluminous (A/CNK=1.0–1.24), characterized by high Al2O3(14–18.33%) and Na2O (6.5–10%) and clearly low εNd(T) values of 0.8 to −3.9 compared with the other rock units of the ophiolite suite. On the basis of their REE characters, the leucogranites can be divided into three groups. Group I leucogranites show the most fractionated LREE-enrichment patterns (with LaN/YbNand LaN/SmNratios of 30.1–75.0 and 2.3–3.9, respectively). Group II leucogranites have moderately fractionated LREE-enrichment patterns (with LaN/YbNand LaN/SmNratios of 13.1–26.5 and 0.8–1.9, respectively). Group III leucogranites are characterized by obviously low total REE contents and flat REE patterns with significant positive Eu anomalies, probably due to small degrees of partial melting. All these leucogranites were likely formed by partial melting of sedimentary rocks from a marginal basin at the Yangtze side of the orogen, beneath a major thrust fault during the obduction of the ophiolite onto the continental crust. They are broadly similar to obduction-related granites within ophiolites identified in many places worldwide. Identification of the ca. 880 Ma obduction-type granites in the NE Jiangxi ophiolite provides a petrological constraint on the timing of the ophiolite obduction onto the continental crust. In combination with the termination of the Shuangxiwu arc magmatism at ca. 890 Ma, we interpret that the close of the Neoproterozoic back-arc basin and the termination of the continental amalgamation between the Yangtze and Cathaysia Blocks occurred at ca. 880 Ma.