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浙江桃花岛碱性和普陀山铝质A型花岗岩副矿物对比研究

谢磊, 王汝成, 王德滋, 邱检生   

  1. 南京大学,内生金属矿床成矿机制研究国家重点实验室,地球科学系,南京, 210093
  • 收稿日期:2005-09-20 修回日期:2005-09-20 出版日期:2005-09-20 发布日期:2005-09-20

Contrasting Accessory Mineral Assemblages in the Taohuadao Peralkaline and Putuoshan Aluminous A-type Granites, Zhejiang Province

XlE Lei, WANG Ru-cheng, WANG De-zi, Qiu Jian-sheng   

  1. State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China
  • Received:2005-09-20 Revised:2005-09-20 Online:2005-09-20 Published:2005-09-20

摘要: 浙江舟山群岛的桃花岛和普陀山分别出露有大片中国东部沿海典型的燕山期碱性和铝质A型花岗岩,二者的岩石化学和主要造岩矿物存在明显差别。利用电子探针进行的测试分析表明,它们在副矿物组合及副矿物特征方面的差异也很显著:桃花岛碱性A型花岗岩中副矿物组合为富钍锆石、褐帘石、硅钛铈矿、钛磁铁矿和富锰钛铁矿;普陀山铝质A型花岗岩中的副矿物组合为贫钍锆石、富钍独居石、磁铁矿、金红石和红钛锰矿。二者更可从单颗粒矿物(特别是锆石)的成份和内部结构上加以区分。这些副矿物上的差异暗示了两类A型花岗岩的源区成分、结晶环境和物理化学特征存在明显不同:(1)碱性A型花岗岩的源岩相对较多地包含了来自较深部的地幔组分岩浆;(2)碱性A型花岗岩形成的温度相对较高,而铝质A型花岗岩结晶阶段的氧逸度较高;(3)碱度和磷活度的差异也是导致一些副矿物种类结晶差异的关键因素。

Abstract: Two typical East China's coastal perakaline and aluminous A-type granites are developed in Taohuadao and Putuoshan of Zhejiang Province, respectively. disfinction. Detailed electron-microprobe analyses are different. The Taohuadao's contains abundant Their geochemistry and main rock-forming minerals show a clear reveal that accessory minerals from these two granite subgroups zircons, allanite, chevkinite and Fe-Ti minerals (titanomagnetite,ilmenite and pyrophanite). By contrast, in the Putuoshan' s, the accessory-mineral assemblage is Th-poor zoned zircon, Ce-monazite and Fe-Ti oxide minerals dominated by magnetite, rutile and pyrophanite. Besides, these two granites could also be defined by internal structure and chemical composition of accessory minerals, especially zircon. Based on the above-mentioned features of accessory minerals, differences in origins, crystallization environments and physicochemical properties between these two granites could thus be inferred. Firstly, Th-rich zircon indicates a relatively high-temperature, Th-rich and deep-sourced magma for the peralkaline granites. Secondly, the presence of magnetite and ruffle suggests the high fo2 during the crystallization of aluminous A-type granite. Thirdly, the occurrence of allanite or Ce-monazite shows the differences of the alkaline index and P2O5 activity between the peralkaline and aluminous A-type magmas.