Igneous and Metamorphic Enclaves in the S-type Deddick Granodiorite, Lachlan Fold Belt, SE Australia: Petrographic, Geochemical and Nd-Sr Isotopic Evidence for Crustal Melting and Magma Mixing
Igneous and Metamorphic Enclaves in the S-type Deddick Granodiorite, Lachlan Fold Belt, SE Australia: Petrographic, Geochemical and Nd-Sr Isotopic Evidence for Crustal Melting and Magma Mixing
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DOI：
10.1093/petroj/38.7.815
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发表时间：
1997-07
影响因子：
3.9
通讯作者：
R. Maas;I. Nicholls;C. Legg
中科院分区：
文献类型：
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作者：
R. Maas;I. Nicholls;C. Legg
Deddick花岗闪长岩是Lachlan引进褶皱带中的一个镁铁质S型岩体，含有丰富的包体。大多数来自花岗岩和火山岩中的包体，可以提供高品位的泥质-砂质成分的变质沉积物，并且从其混合岩中不易获得的岩石成因信息是常见的。其中，主岩的离散碎片（Didier，1973; Didier & Barbarin，1991）。对于富含堇青石和石榴子石的黑素体，从部分实例来看，变质沉积岩包体可以制约熔融。然而，成分和Nd-Sr同位素数据表明，它们的年龄、成分和变形历史与大陆地壳内岩浆源区的熔体成分不平衡（Fleming，寄主岩浆，但可能形成了不同的光谱的一部分1991; Steele等人，1991年）。岩浆源岩形成的包体。或者，它们可能是早期斑晶（“自岩”）记录捕虏体的偶然堆积。不管它们的起源，这些包体的数据表明宿主岩浆的早期演化，而其他人的前体可能代表深埋的年龄相当于可能代表混合岩浆，并说明无处不在的奥陶纪浊积岩的拉克伦褶皱带。杂交的三种可能作用（Didier，1987）。在相对镁铁质的S型花岗岩类中，发现了一类具有火成结构的微粒包体。最常见的类型是澳大利亚东南部的小而圆的镁铁质岩，通常是多种多样的，包括丰富的英云闪长岩组成的包体。它们带有来自变质沉积岩成因的包体的捕虏晶和寄主岩浆的微粒，有些还含有来自包体的高镁辉石（菲利普斯等人，1981; Price，1983; Chen等人，镁铁质岩浆从-6到1989年，同位素数据形成具有eNd的阵列; Wyborn等人，1991年）。变质沉积岩-12，Sr/Sr为0·7130 ~ 0·7167（主岩-10和碎屑岩岩性多样，分别为片麻状-0·715）。这些包体形成为混合混合岩型和富含黑云母的“surmicaceous”型球状体。镁铁质岩浆混合，并被污染，除了他们的潜力作为地壳结构的指示长英质寄主岩浆。其他包体类型来自中断和组合物，他们是感兴趣的可能的片段同深成岩脉具有独特的同位素组成，并从源材料和/或难熔残留物，从同生边缘相的主机。产生并提取过铝熔体。通过
The Deddick Granodiorite, a mafic S-type pluton in the Lachlan INTRODUCTION Fold Belt, contains abundant enclaves. Most are derived from Enclaves in granites and volcanic rocks can provide high-grade metasediments of pelitic–psammitic composition, and petrogenetic information not readily available from their migmatites are common. Among these, discrete fragments of host rocks (Didier, 1973; Didier & Barbarin, 1991). For melanosomes rich in cordierite and garnet are restites from partial example, metasedimentary enclaves can place constraints melting. However, compositional and Nd–Sr isotopic data indicate on the age, composition and deformational history of they are not restite in equilibrium with the melt component of the magma source regions within continental crust (Fleming, host magma, but may have formed part of a spectrum of diverse 1991; Steele et al., 1991). Enclaves formed by acmagma source lithologies. Alternatively, they may be accidental cumulation of early phenocrysts (‘autoliths’) document xenoliths. Regardless of their origin, data for these enclaves suggest the early evolution of the host magma, whereas others their precursors could represent deeply buried age equivalents of the may represent commingled magmas and illustrate the ubiquitous Ordovician turbidites of the Lachlan Fold Belt. Three possible role of hybridization (Didier, 1987). types of microgranular enclaves with igneous textures are disEnclave suites in the relatively mafic S-type granitoids tinguished. The most common type are small and rounded mafic of SE Australia are often diverse, including abundant enclaves of tonalitic composition. They carry xenocrysts derived from enclaves of metasedimentary origin and microgranular the host magma, and some contain high-Mg pyroxene derived from enclaves (Phillips et al., 1981; Price, 1983; Chen et al., a mafic magma. Isotopic data form an array with eNd from –6 to 1989; Wyborn et al., 1991). The metasedimentary en–12, and Sr/Sr from 0·7130 to 0·7167 (host rock –10 and claves are lithologically diverse, including gneissic– 0·715, respectively). These enclaves formed as globules of hybrid migmatitic types and biotite-rich ‘surmicaceous’ types. mafic magma commingled with, and contaminated by, the more Apart from their potential as indicators of crustal structure felsic host magma. Other enclave types were derived from disrupted and composition, they are of interest as possible fragments syn-plutonic dykes having a distinct isotopic composition, and from of source material and/or refractory residue from which a cogenetic marginal facies of the host. peraluminous melts were generated and extracted. By