Re-Os dating of the Raoba- zhai ultramafic massif in North Dabie
Re-Os dating of the Raoba- zhai ultramafic massif in North Dabie
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DOI：
10.1360/03wd0225
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发表时间：
2004-03
影响因子：
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通讯作者：
Jin Yongbin;Zhi Xiachen;Meng Qing;Gao Tianshan;Peng Zicheng
中科院分区：
文献类型：
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作者：
Jin Yongbin;Zhi Xiachen;Meng Qing;Gao Tianshan;Peng Zicheng
北大别老坝寨超镁铁质地块位于扬子克拉通与华北克拉通的缝合带上。利用该块体的Re-Os同位素组成分析了参与大陆俯冲和掘出的超镁铁质岩石的成因和构造。沿老坝寨地块主SE-NW轴方向的5个钻孔采集了15个样品。样品中MgO、Yb和al2o3的主微量元素组成呈线性相关。这表明该地块经历了不同程度的部分熔融，玄武岩成分由富到贫。对选定的9个样品进行了Re-Os同位素组成分析。Re含量为0.004 ~ 0.376 ng/g， Os含量为0.695 ~ 3.761 ng/g， 187 Re/ 188 Os比值为0.022 ~ 2.564,187 Os/ 188 Os比值为0.1165 ~ 0.1306。这表明该地块是一块变化衰竭的大陆岩石圈地幔。利用187os / 188os与Yb和al2o3的正相关关系，得到了老坝寨超镁铁地块的代用等时线年龄（1.8±0.1 Ga），解释为古次大陆岩石圈地幔的一个片段。扬子克拉通在华北克拉通下的三叠纪俯冲过程中，部分次大陆岩石圈地幔楔体侵入俯冲带，并在地幔深处经过超高压变质作用，与俯冲的地壳板块一起被挖出至地壳水平。这个古老的岩石圈地幔现在以造山橄榄岩块的形式暴露出来。
The ultramafic massif at Raobazhai in North Dabie is located in the suture zone between the Yangtze craton and North China craton. The Re-Os isotope compositions of the massif are used to decipher the origin and tectonics of the ultramafic rocks involved in continental subduction and exhumation. Fifteen samples were collected from five drill holes along the main SE-NW axis of the Raobazhai massif. Major and trace element compositions of the samples show linear correlations between MgO, Yb and Al 2 O 3 . This suggests that the massif experienced partial melting with variable degrees and is from fertile to deplete in basaltic compositions. Nine selected samples were analyzed for Re-Os isotope compositions. Re contents range from 0.004 to 0.376 ng/g, Os contents from 0.695 to 3.761 ng/g, 187 Re/ 188 Os ratios from 0.022 to 2.564 and 187 Os/ 188 Os ratios from 0.1165 to 0.1306. These indicate that the massif is a piece of continental lithospheric mantle with variable depletion. Using the positive correlations between 187 Os/ 188 Os and Yb and Al 2 O 3 respectively, a proxy isochron age of 1.8±0.1 Ga is obtained for the Raobazhai ultramafic massif, which is interpreted to represent a fragment of the ancient subcontinental lithospheric mantle. During Triassic subduction of the Yangtze craton beneath the North China craton, part of the wedge of subcontinental lithospheric mantle was intruded into the subduction belt, and then exhumed to crustal level together with the subducted crustal plate after ultrahigh pressure metamorphism at mantle depths. This ancient lithospheric mantle is now exposed as an orogenic peridotite massif.