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浙江青田花岗岩中岩石包体特征及成因
The Features and Origin of the Enclaves in the Qingtian Granite,Zhejiang Province
  
中文关键词:寄主花岗岩 岩石包体 淬冷包体 岩浆混合作用
英文关键词:host granite  enclaves  quenched enclaves  magma mingling
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作者单位
董传万  
彭亚鸣  
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中文摘要:
      浙江青田燕山晚期黑云母花岗岩中有许多石英闪长质岩石包体,它们大小不一,形态各异,以微细粒结构、具冷凝边构造、并发育针状磷灰石为特征。岩石包体与寄主花岗岩的主要氧化物、微量元素的变化趋势呈线性关系。岩石学、矿物学、岩石化学及地球化学等特征的研究表明,石英闪长质岩石包体属淬冷包体,由玄武质岩浆和花岗质岩浆通过不均匀的混合作用而形成。
英文摘要:
       There are a lot of microgranular enclaves in the late Yanshanian Qingtian biotite granite in southeast Zhejiang Province. The enclaves are generally round or sub-round with diameters from 10 to 20 cm. They are usually scattered but some of them occur in groups in the granite. The enclaves are often gray or dark-gray in colour. Generally, there are clear boundaries between the enclaves and host granite, but some show diffusion contact. A few of enclaves show fine-grained margins, i. e. chilled margins. The enclaves are mainly composed of plagioclase(An=37), hornblende, biotite, quartz, and K-feldspar. The plagioclase is zoned. Quartz and K-fel-dspar fill in the interval betWeen plagioclase, or enclose the microcrystal plagioclase and hornblendes to form intergranular texture which is similar to that of dolerite, or poikilitic texture. The accessory minerals include magnetite, ilmenite, apatite, sphene, etc. The apatite is very long with the ratio of length to width up to 30:1, and has clear basal cleavage. According to Wylie this kind of apatite is formed by sudden cooling of the magmaoc-existing with the apatite. Chemically, the enclaves belong to the calc-alkline rock serieswith SiO2=60-68%, Na2O>K2O, and A/NKC<1.In comparison to the host granite,the quartz-dioritic enclaves have higher contents of Ti, V, Cr, Co, Ni, Zr,Sr, Ca, Mg and REE. On the variation diagrams of major oxides versus SiO2 of the enclaves and the host granite, the plots show linear trends, and so do some pairs of trace-elements divided hy other trace-elements. There are different hypotheses about the origin of microgranular enclave in granitic rocks. The enclave may be regarded as xenolith, or the relict phase of partial melting of basement rocks, or a product of magma mixing,and so on. Based on field observations and petrological, geochemical, and mineralogical features of enclaves, the authors believe that magma mixing theory is most suitable for explaining the characteristics of the quartz-dio-ritic enclaves in the Qingtian biotite granite, namely, they were the products of mechanical mingling between basaltic or intermediate-basic magma and granitic magma.
董传万,彭亚鸣,1992,浙江青田花岗岩中岩石包体特征及成因[J].岩石矿物学杂志,11(1):21~31.
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