Isotopic study of the Manaslu granite (Himalaya, Nepal): inferences on the age and source of Himalayan leucogranites
Isotopic study of the Manaslu granite (Himalaya, Nepal): inferences on the age and source of Himalayan leucogranites
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DOI：
10.1007/bf00375529
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发表时间：
1987-05
影响因子：
3.5
通讯作者：
C. Deniel;P. Vidal;Á. Fernández;P. Fort;J. Peucat
中科院分区：
文献类型：
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作者：
C. Deniel;P. Vidal;Á. Fernández;P. Fort;J. Peucat
对玛纳斯鲁浅色花岗岩进行了详细的同位素研究。获得了25 Ma的U-Pb年龄和18 Ma的全岩Rb-Sr等时线，表明岩浆活动至少持续了7 Ma。初始Sr同位素比值很高（0.740 ~ 0.760），而初始Nd同位素比值很低（Nd：Ndin：−13 ~ −16），即使在米尺度上也显示出很大的同位素变化。这些不是流体扰动的结果，而是它们反映了源物质的初始同位素不均匀性，这些不均匀性没有被岩浆过程（例如，熔融，对流混合）所消除。这些结果也支持了该浅色花岗岩的地壳成因。西藏板状副片麻岩的Sr、Nd同位素比值与花岗岩的相似，其年龄为20 Ma，是最可能的母岩。浅色花岗岩和片麻岩的Nd模式年龄均在1.5- 2Ga之间。马纳斯卢花岗岩的形成模式是由不同批次的岩浆聚结与目前的数据是一致的。
A detailed isotopic study of the Manaslu leucogranite was carried out. A U-Pb age of 25 Ma and a whole rock Rb-Sr age isochron of 18 Ma were obtained, suggesting that the magmatic activity lasted at least 7 Ma. Initial Sr isotopic ratios are very high (0.740 to 0.760) and initial Nd isotopic ratios are low (ɛNdin: −13 to −16), and they show the existence of large isotopic variations even at the metre scale. These are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes (e.g. fusion, mixing by convection). These results also support the crustal origin of this leucogranite. The Tibetan slab paragneisses, whose Sr and Nd isotopic ratios are very similar to those of the granite at an age of 20 Ma, are the most probable parental material. Nd model ages for both the leucogranite and the gneisses are in the range 1.5–2 Ga. A model of formation of the Manaslu granite by coalescence of different batches of magma is in agreement with the present data.