摘要:
卡拉麦里钾质火山岩位于准噶尔盆地的东北缘下石炭统巴塔玛依内山组内。这些火山岩以粗面玄武岩和玄武质粗面安山岩为主，SiO2含量稳定（46.29%~51.56%），具有较高的碱含量（K2O+Na2O=5.39%~6.96%）以及高K2O/Na2O比值（K2O/Na2O=0.5~1.4），TiO2含量相对稳定（0.94%~1.21%），显示钾玄质岩石特征。岩石地球化学表明，钾玄岩强烈富集LILE（如K、Rb和Sr）和LREE（（La/Yb）N=4.39~6.25），Eu正异常明显（δEu=1.3~1.7），相对亏损HFSE（如Zr、Hf），Ta、Nb和Ti呈明显的“TNT”负异常，及较高Ba/Nb和Ba/Ta比值（分别为38~93，574~1470），显示典型岛弧岩浆特征，而Nd-Sr同位素显示亏损地幔源区特征。不相容元素(Nb/La)N和Ba/La比值（分别为0.33~0.41，11.07~18.82）以及高Nb含量（4.45×10-6~7.76×10-6），表明这些岩石来自一个交代作用富集的地幔源区。通过钾质火山岩环境的梯次判别图研究，发现巴塔玛依内山组钾玄岩形成于后碰撞环境，显示岛弧的岩石地球化学特征。在后碰撞期，由于陆内调整和均衡作用，东准噶尔东北缘的岩石圈伸展减薄，随着岩石圈地幔的减薄，前期交代富集的下部地幔楔（金云母和/或钾质角闪石-尖晶石相二辉橄榄岩）发生低度部分熔融形成钾玄质母岩浆，诱发了后碰撞型钾玄质岩浆活动（具有弧火山岩岩石地球化学特征），形成了卡拉麦里巴塔玛依内山组钾质玄武岩。
Abstract:
Kalamaili potassic basaltic rocks occur within the Lower Carboniferous Batamayineishan Formation, NE margin of the Junggar Basin. The potassic basaltic rocks mainly composed of trachybasalt and basalic trachyandesite, have moderate SiO2 (46.29%~51.56%) values, relatively high alkali (K2O+Na2O=5.39%~6.96%), TiO2 (0.94%~1.21%) contents and K2O/Na2O ratios (K2O/Na2O=0.5~1.4), displaying characteristics of shoshonitic basalts series. Through researching petrogeochemistry, showing the rocks enriched in LILE (such as K, Rb and Sr) and LREE ((La/Yb)N=4.39~6.25), possess positive Eu anomalies (δEu=1.3~1.7), relatively depleted in HFSE (such as Zr, Hf), with strong negative Ta, Nb and Ti “TNT” anomalies, high Ba/Nb and Ba/Ta ratios (38~93, 574~1470 respectively), indicating typical island-arc characteristics, and Nd-Sr isotopes show a depleted mantle source. The ratios of incompatible element (Nb/La)N and Ba/La (0.33~0.41, 11.07~18.82 respectively), and high Nb (4.45×10-6~7.76×10-6) contents, suggesting that these potassic basaltic rocks were derived from a metasomatized, phlogopite- and/or amphibole-bearing mantle source. Through hierachical set of discrimination diagrams of tectonic settings for Kalamaili potassic basalt, indicating Batamayineishan Formation shoshonitic basalts formed in the post-collisional arc-type surroundings. Due to intracontinental adjustment in the post-collisional period, lithosphere extended and thinned, with this process, the mantle wedge (phlogopite and/or potassic amphibole-spinel facies lherzolite) metasomatized by fluid in earlier stage melted partially under decompression and high temperature, forming shoshonitic basaltic magma, leading to post-collisional type magma movement (characteristics by arc volcanic rocks in geochemistry), the erupted lavas became the Batamayineishan Formation shoshonitic basalts.
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