梅子窝钨矿加里东期花岗闪长岩的地球化学特征及岩石成因探讨

加里东期花岗岩在华南地区分布甚广,对其开展深入研究有助于加深对华南早古生代构造演化及地质背景的理解。对梅子窝钨矿的赋矿岩体-加里东期花岗闪长岩的岩石学和地球化学研究结果表明：该岩体属于偏铝质-弱过铝质的高钾钙碱性系列岩石,具有较高的SiO2含量、K2O/Na2O比值和较低的ACNK值;大离子元素明显富集,Ba、Sr、P、Ti负异常明显;在（La/Yb）N-δEu图解中,投影于S型或壳源型花岗岩范围内;在Rb/Sr-Rb/Ba和A/MF-C/MF图解中,该花岗闪长岩的源区物质为砂质岩而不是幔源基性岩。这些特征表明,梅子窝加里东期花岗闪长岩应归属于S型花岗岩;推测其形成机制可能与早古生代晚期的板内作用有关,先受区域挤压应力场影响,导致地壳加厚;稍后,由于应力场的转化,进入后碰撞伸展环境。并在减压、挥发分的加入等因素综合影响下,位于中、上地壳的低成熟度的变杂砂岩发生部分熔融,形成S型或壳源型花岗岩。

Geochemistry Features and Petrogenesis of the Caledonian Meiziwo Granodiorite in the Meiziwo Tungsten Deposit

The Caledonian granites are widely distributed in South China, which plays a significant role in advancing the understanding of the tectonic evolution and geological setting of South China during the Early Paleozoie. In this contribution, the petrology and geochemistry of the Meiziwo granodiorites reveal that the rocks are with relatively high SiO2 content, K20/Na20 ratio and low ACNK value. They belong to the metaluminous or slightly peraluminous high-K eal-alkaline granite series. They possess remarkable enrichment in large ion elements, negative anomaly in Ba, Sr, P and Ti, enrichment in LREEs and depletion in Eu. In the （La/Yb）N-δEu diagram, they are plotted in the field of S-type or crustal derived type granite. In the Rb/Sr-Rb/Ba and A/MF-C/MF diagrams, they are plotted in the partial melting source field of protolith of pasmmite, but not in that of mantle-derived mafic rocks. These characteristics indicate that granodiorites belong to S-type or crustal type granites. Genesis of the granodiorites is considered to be related with the intra-plate tectonism during the late stage of Early Paleozoie. In the early stage, the change of regional compression stress field generated the continental crust thickening. Later on, the tectonic regime converted to post-eollisional extension environment due to the transition of regional stress field, leading to partial melting of the low mature sandy rocks in the middle-upper crust, under influence of pressure reduction and addition of volatile, and formation of S-type or crustal derived type granites.