Dual mixing for the formation of Neoproterozoic granitic intrusions within the composite Jiuling batholith, South China
Dual mixing for the formation of Neoproterozoic granitic intrusions within the composite Jiuling batholith, South China
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DOI：
10.1007/s00410-020-01757-2
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发表时间：
2021-01
影响因子：
3.5
通讯作者：
Di Wang;Xiaolei Wang
中科院分区：
文献类型：
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作者：
Di Wang;Xiaolei Wang
花岗岩基岩记录了大陆地壳形成和分异过程。 ~ 4000km2复式新元古代九岭岩基是中国南部最大的基岩之一，由4个侵位在828~810km2的过铝质花岗岩类侵入体组成。这些花岗岩类定义了从陆地向海水NdHf同位素阵列移动的趋势，表明这些岩浆的来源随着时间的推移包含了越来越多的海洋沉积物质。新的地质年代学和地球化学资料表明，新元古代九岭复式岩基是通过多批次壳源熔体侵入而逐渐形成的。岩基内侵入岩的特征是Rb/Sr比值降低，Na/K比值和εHf(T)值升高，表明源岩成分随时间的变化。这些侵入体间的变化可以很好地解释为部分熔融前岩浆源(成熟、未成熟的沉积物和长英质弧型花岗岩类)中的三组分混合，个别侵入体内的样品间变化是不同熔体批次随后混合的结果。这些岩浆源区内混合的第一阶段涉及源区成分的显著变化，不能反映不均匀的变质沉积源区的简单熔融。第二阶段混合发生在岩浆上升和储存期间，并通过矿物成分(如锆石)的变化来记录。这些侵入体间和样品间的地球化学变化提供了过铝九岭岩基是岩浆源区内混合和多批次花岗岩熔体混合两种混合作用的证据。这种双重混合可以解释世界各地过铝花岗岩类岩石中存在的显著的地球化学多样性。
Granite batholiths record the processes that occur during the formation and differentiation of the continental crust. The ~ 4000 km2composite Neoproterozoic Jiuling batholith is one of the largest batholiths in southern China and consists of four peraluminous granitoid intrusions that were emplaced atca.828–810 Ma. These granitoids define a trend that moves from the terrestrial towards the seawater Nd–Hf isotope array, indicating the source of these magmas incorporated increasing amounts of marine sedimentary material over time. Our new geochronological and geochemical data suggest that the composite Neoproterozoic Jiuling batholith formed incrementally via the intrusion of multiple batches of crustally derived melts. The intrusions within the batholith are characterized by decreasing Rb/Sr ratios and increasing Na/K ratios and εHf(t) values, suggesting variations in source composition over time. These inter-intrusion variations can be well explained by three-component mixing in magma sources (mature, immature sediments and felsic arc-related granitoids) prior to partial melting, with inter-sample variations within individual intrusions occurring as a result of the subsequent mixing of different melt batches. The first stage of mixing within the source of these magmas involves a significant variation in source compositions and cannot reflect the simple melting of a heterogeneous metasedimentary source region. The second stage of mixing occurred during magma ascent and storage, and is recorded by variations in mineral compositions (e.g., zircon). These inter-intrusion and inter-sample geochemical variations provide evidence that the peraluminous Jiuling batholith formed as a result of two mixing processes, namely mixing within the magma source region and mixing of multiple batches of granitic melts. This dual mixing could explain the significant geochemical diversity present within peraluminous granitoid rocks worldwide.