Early Paleozoic intracontinental felsic magmatism in the South China Block: petrogenesis and geodynamics
Early Paleozoic intracontinental felsic magmatism in the South China Block: petrogenesis and geodynamics
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DOI：
10.1016/j.lithos.2015.08.006
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发表时间：
2015-10
期刊：
影响因子：
3.5
通讯作者：
Wenjing Xu;Xi‐sheng Xu
中科院分区：
文献类型：
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作者：
Wenjing Xu;Xi‐sheng Xu
板内岩浆作用一般是非造山作用的性质，其特征是地球化学和同位素的签名，是地幔来源的指示。华南陆块早古生代陆内岩浆岩面积约2.2万km ~ 2，主要为同位素特征丰富的花岗岩类。根据矿物组合特征，将这些早古生代花岗岩类划分为三组：A组（含角闪石花岗岩类），以相对较低的初始87 Sr/86 Sr比值为特征（0.705227-0.711639），高εNd（t）值（− 7.0 ~ − 3.0），高εHf（t）值（− 8.6 ~ − 1.2，平均− 5.0）; B组（二云母花岗岩）具有高初始87 Sr/86 Sr比值（0.715335 ~ 0.715335）。721933），低εNd（t）值（− 9.4至− 7.3）和低εHf（t）值（− 15.4至− 4.4，平均− 8.7）; C组（黑云母花岗岩），其地球化学和同位素组成大致介于A组和B组之间。A组花岗岩具弱的负Eu异常，B组和C组花岗岩具中到强的负Eu异常。来自官田石英闪长质岩体（A组）的镁铁质微粒包体显示出与其寄主相似的Sr-Nd同位素特征，但εHf（t）值较高（− 2.3至− 0.2，平均− 1.1）。这些早古生代陆内花岗岩类普遍含有大量的镁铁质微粒包体，且具有不同的化学成分，表明它们更可能是幔源镁铁质岩浆与壳源长英质岩浆混合的结果，而不是完全来自地壳深熔作用，没有地幔的贡献。成岩模式表明，这些早古生代陆内长英质岩浆岩与下地壳至中地壳的深熔作用有关，由幔源岩浆的底侵作用和/或内侵作用触发。这一早古生代陆内花岗岩类省代表了大规模的地壳生长和改造，可能与该地区冈瓦纳大陆早期裂解的独特构造环境有关。
Intraplate magmatism is generally anorogenic in nature, characterized by geochemical and isotopic signatures that are indicative of mantle sources. However, the early Paleozoic intracontinental magmatic rocks in the South China Block, which cover an area of ~ 22,000 km2, are mainly granitoids with fertile isotopic signatures. Based on mineral assemblages, these early Paleozoic granitoids are divided into three groups: Group A (amphibole-bearing granitoids) characterized by relatively low initial87Sr/86Sr ratios (0.705227–0.711639), high εNd(t) values (− 7.0 to − 3.0), and high εHf(t) values (− 8.6 to − 1.2, average − 5.0); Group B (two-mica granites) that have high initial87Sr/86Sr ratios (0.715335–0. 721933), low εNd(t) values (− 9.4 to − 7.3), and low εHf(t) values (− 15.4 to − 4.4, average − 8.7); and Group C (biotite granites) that have geochemical and isotopic compositions that are roughly intermediate between those of Group A and Group B. The Group A granitoids show weak negative Eu anomalies, whereas Group B and Group C granitoids show moderate to strong negative Eu anomalies. A mafic microgranular enclave from the Guantian quartz dioritic pluton (Group A) shows Sr–Nd isotopic signatures similar to its host, but higher εHf(t) values (− 2.3 to − 0.2, average − 1.1). These early Paleozoic intracontinental granitoids generally contain considerable amount of mafic microgranular enclaves and have varied chemical compositions, indicating that they are more likely the result of mixing between mantle-derived mafic magmas and crust-derived felsic magmas, as opposed to being derived solely from crustal anatexis without any mantle contribution. Petrogenetic models suggest these early Paleozoic intracontinental felsic magmatic rocks are linked to lower- to middle-crustal anatexis, triggered by underplating and/or intraplating of mantle-derived magmas. This early Paleozoic intracontinental granitoid province represents large-scale crustal growth and reworking, possibly associated with the unique tectonic environment of the early break-up of Gondwanaland in this region.