Enclaves and their bearing on the origin of the Cornubian batholith, southwest England
Enclaves and their bearing on the origin of the Cornubian batholith, southwest England
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DOI：
10.1180/minmag.1995.059.395.12
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发表时间：
1995-06
影响因子：
2.7
通讯作者：
J. Stimac;A. H. Clark;Yanshao Chen;S. Garcia
中科院分区：
文献类型：
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作者：
J. Stimac;A. H. Clark;Yanshao Chen;S. Garcia
摘要英格兰西南部科努比亚岩基的粗粒黑云母花岗岩中存在少量不同成因的包体。最常见的包体类型是层状的，富含黑云母、堇青石和铝硅酸盐，其结构和成分揭示了变质沉积岩源岩熔体提取的不同程度。稀有的硅线石包体代表残留物质，无论是从岩浆生成区域还是其上升路径，但大多数这样的包体可能来自接触光环接近目前的曝光水平。这些非火成包体（NIE）及其分解产物存在于所有主要岩体中，的花岗岩。除Carnmenellis外，所有主要岩体中都存在火成包体，一般含量< 1体积%。的花岗岩。最常见的类型是中间的组成，具有微粒结构，矿物成分和结构与岩浆混合的起源一致。大晶体的钾长石，斜长石和石英，常见于这些微粒包体（ME），但在NIE缺席，代表斑晶来自于岩浆混合事件，而不是产品的交代作用，如前所述。虽然在混合过程中涉及的镁铁质端员（玄武质或层状）的组合物是不受约束的，ME在花岗岩中的存在，和优势的幔源镁铁质岩石在同时代的埃克塞特火山岩，表明镁铁质岩浆注入到地壳中的一个因素，在生成的岩基。地壳下热量的平流为地壳相对较薄的地区（如英格兰西南部）的大规模地壳熔融提供了一种解释。
Abstract Enclaves of diverse origin are present in minor amounts in the coarse-grained biotite granites of the Cornubian batholith, southwest England. The most common enclave type is layered, rich in biotite, cordierite and aluminosilicates, and has textures and compositions that reveal variable degrees of melt extraction from metasedimentary source rocks. Rare sillimanite-bearing enclaves represent residual material, either from the region of magma generation or its ascent path, but most such enclaves were probably derived from the contact aureole closer to the present level of exposure. These non-igneous enclaves (NIE) and their disaggregation products are present in all major plutons, comprising from < 2 to 5 vol.% of the granites. Enclaves of igneous origin are also present in all major plutons except Carnmenellis, generally comprising < 1 vol.% of the granites. The most common type is intermediate in composition, with microgranular texture, and mineral compositions and textures consistent with an origin by magma mixing. Large crystals of K-feldspar, plagioclase and quartz, common in these microgranular enclaves (ME) but absent in NIE, represent phenocrysts derived from the silicic end-member during magma mixing events rather than products of metasomatism as suggested previously. Although the composition of the mafic end-member (basaltic or lamprophyric) involved in the mixing process is poorly constrained, the presence of ME in the granites, and the preponderance of mantle-derived mafic rocks in the coeval Exeter Volcanics, indicate that mafic magma injection into the crust was a factor in the generation of the batholith. Advection of sub-crustal heat provides an explanation for large-volume crustal melting in regions of relatively thin crust such as southwest England.