I-TYPE AND S-TYPE GRANITES IN THE LACHLAN FOLD BELT
I-TYPE AND S-TYPE GRANITES IN THE LACHLAN FOLD BELT
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DOI：
10.1017/s0263593300007720
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发表时间：
1992-01-01
期刊：
影响因子：
--
通讯作者：
WHITE, AJR
中科院分区：
文献类型：
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作者：
CHAPPELL, BW;WHITE, AJR
利用化学和岩相学数据，可以将拉克伦褶皱带的花岗岩和相关火山岩分为几组。套组的特征反映了烃源岩的特征。套内的第一级细分是那些来自火成岩和沉积烃源岩，I型和S型。这两类烃源岩及其衍生花岗岩之间的差异是由于沉积烃源物质先前在地球表面被风化。S型花岗岩的化学成分中Na、Ca、Sr和Fe ~（3+）/Fe ~（2+）较低，Cr和Ni较高。因此，S型总是过铝的，并含有富铝矿物。略高于50%的I型花岗岩是变辉岩，这些镁铁质岩石含有角闪石。在没有伴生镁铁质岩石的情况下，较长英质和稍过铝质的I型花岗岩可能难以与长英质S型花岗岩区分。这种成分上的重叠是可以预料到的，这是由于最低温度长英质熔体的化学成分有限造成的。更多的镁铁质I-和S-型花岗岩的组合物分歧，作为一个结果，从源，无论是作为restite或更高温度的熔体的一个组件的镁铁质成分纳入。最镁铁质的I-型和S-型花岗岩的成分之间没有重叠，它们的成分最接近它们各自的源岩。同样，包体中存在的更多的镁铁质花岗岩的成分反映了他们的寄主岩石，并可能在大多数情况下，源rocks. S型花岗岩有较高的δ-O-18值和更先进的Sr和Nd同位素组成，虽然放射性同位素组成与I型重叠。虽然同位素组成接近混合曲线，但据认为，烃源岩中的混合量是有限的，并且发生在部分熔融之前。I型花岗岩被认为是来自于地壳深部的底侵作用，因此是壳下的，而不是壳上的S型源岩。长英质花岗岩熔体中的长石结晶导致更演化的I型和S型花岗岩的微量元素组成发生了明显的变化。最值得注意的是，P的丰度增加与分馏的晶体更强烈的过铝S型长英质熔体，而它的丰度减少类似的，但弱过铝，I型熔体。
Granites and related volcanic rocks of the Lachlan Fold Belt can be grouped into suites using chemical and petrographic data. The distinctive characteristics of suites reflect source-rock features. The first-order subdivision within the suites is between those derived from igneous and from sedimentary source rocks, the I- and S-types. Differences between the two types of source rocks and their derived granites are due to the sedimentary source material having been previously weathered at the Earth's surface. Chemically, the S-type granites are lower in Na, Ca, Sr and Fe3+/Fe2+, and higher in Cr and Ni. As a consequence, the S-types are always peraluminous and contain Al-rich minerals. A little over 50% of the I-type granites are metaluminous and these more mafic rocks contain hornblende. In the absence of associated mafic rocks, the more felsic and slightly peraluminous I-type granites may be difficult to distinguish from felsic S-type granites. This overlap in composition is to be expected and results from the restricted chemical composition of the lowest temperature felsic melts. The compositions of more mafic I- and S-type granites diverge, as a result of the incorporation of more mafic components from the source, either as restite or a component of higher temperature melt. There is no overlap in composition between the most mafic I- and S-type granites, whose compositions are closest to those of their respective source rocks. Likewise, the enclaves present in the more mafic granites have compositions reflecting those of their host rocks, and probably in most cases, the source rocks.S-type granites have higher delta-O-18 values and more evolved Sr and Nd isotopic compositions, although the radiogenic isotope compositions overlap with I-types. Although the isotopic compositions lie close to a mixing curve, it is thought that the amount of mixing in the source rocks was restricted, and occurred prior to partial melting. I-type granites are thought to have been derived from deep crust formed by underplating and thus are infracrustal, in contrast to the supracrustal S-type source rocks.Crystallisation of feldspars from felsic granite melts leads to distinctive changes in the trace element compositions of more evolved I- and S-type granites. Most notably, P increases in abundance with fractionation of crystals from the more strongly peraluminous S-type felsic melts, while it decreases in abundance in the analogous, but weakly peraluminous, I-type melts.