An early Paleozoic monzonorite-granite suite in the South China block: implications for the intracontinental felsic magmatism
An early Paleozoic monzonorite-granite suite in the South China block: implications for the intracontinental felsic magmatism
复制标题
华南地块早古生代二长岩-花岗岩套：对陆内长英质岩浆作用的启示
DOI：
10.1007/s00710-016-0488-5
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发表时间：
2017
影响因子：
1.8
通讯作者：
Xu Xisheng
中科院分区：
文献类型：
--
作者：
Xu Wenjing;Xu Xisheng
根据野外观察和同位素研究，大陆地壳内的大型花岗岩类杂岩被认为与幔源岩浆有密切联系。然而，有关幔源岩浆在中下地壳深部长英质岩浆生成中的作用，特别是幔源镁铁质岩浆与生成的长英质熔体之间的相互作用的细节，并没有很好地受到岩石学和矿物学研究的约束。本文通过对华南陆块早古生代二长花岗岩-花岗岩套的详细研究，并与该地区约22，000 km ~ 2的同时代岩浆岩进行对比，进一步揭示了陆内环境下幔源岩浆的底侵/内侵作用和长英质岩浆的生成过程。结果表明，二长岩既有幔源岩浆（MgO，Cr和Ni的大量含量;橄榄石和斜方辉石的存在）和壳源岩浆（SiO2，K2 O，Rb，Ba和轻稀土元素的大量含量;钾长石，石英和低钙斜长石的存在）的签名。有趣的是，二长岩、花岗岩和镁铁质微粒包体（MME）的Sr-Nd-Hf同位素组成非常均匀，具有高的初始87 Sr/86 Sr比值（0.7081-0.7098）、低的εNd（t）值（−6.8-−6.3）和低的锆石εHf（t）值（−8.0-−7.4）。对同一地区二长花岗岩-花岗岩套和同时代岩浆岩的岩石学、矿物学和地球化学数据的综合研究表明，地壳成分的输入对于解释二长花岗岩的异常特征至关重要。岩石成因模拟和同位素组成表明，在壳源长英质岩浆的生成中，幔源镁铁质岩浆的贡献是由热量输入和少量质量输入表示的，同时，我们更愿意解释不寻常的地球化学特征的二长岩壳源长英质熔体的选择性污染。
Large granitoid complexes within the continental crust are believed to be closely linked to mantle-derived magmas based on field observations and isotopic studies. However, details on the contribution of mantle-derived magmas in the generation of felsic magmas deep in the lower to middle crust, especially the interaction between the mantle-derived mafic magmas and the generated felsic melts, are not well constrained by petrological and mineralogical studies. Here we present a detailed study of an early Paleozoic monzonorite–granite suite from the South China Block and comparison with the other coeval magmatic rocks (~22,000km2) in the region, to provide more details on the underplating/intraplating of mantle-derived magmas and the generation of felsic magmas in intracontinental settings. It is shown that the monzonorite has signatures of both mantle-derived magmas (substantial contents of MgO, Cr, and Ni; presence of olivine and orthopyroxene) and crust-derived magmas (substantial contents of SiO2, K2O, Rb, Ba, and light rare-earth elements; presence of K-feldspar, quartz and low-calcium plagioclase). Interestingly, the monzonorite, granite and the mafic microgranular enclaves (MME) are remarkably uniform in Sr–Nd–Hf isotopic compositions, with high initial87Sr/86Sr ratios (0.7081–0.7098), low εNd(t) values (−6.8 to −6.3) and low zircon εHf(t) values (−8.0 to −7.4). An integrated study of petrological, mineralogical, and geochemical data of the monzonorite–granite suite and coeval magmatic rocks from the same region makes it clear that the input of crustal components is essential to explain the unusual signatures of the monzonorite. Petrogenetic modelling and isotopic compositions suggest that the contribution of mantle-derived mafic magmas in the generation of crust-derived felsic magmas is represented by heat input and minor mass input, and in the meantime, we prefer to explain the unusual geochemical signatures of the monzonorite by selective contamination of crust-derived felsic melts.