Granitoid types and their distribution in the Lachlan Fold Belt, southeastern Australia
Granitoid types and their distribution in the Lachlan Fold Belt, southeastern Australia
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DOI：
10.1130/mem159-p21
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发表时间：
1983
期刊：
影响因子：
--
通讯作者：
A. J. White;B. Chappell
中科院分区：
文献类型：
--
作者：
A. J. White;B. Chappell
澳大利亚东南部的拉克兰褶皱带由寒武纪到泥盆纪的岩石组成。花岗岩类侵位及相关火山活动发生在志留纪和泥盆纪，在该带的最东端有少量石炭纪深成岩体发育。这条带至少有800公里宽，比环太平洋的中、新生代褶皱带宽得多。拉克兰带广泛发育花岗岩类，占东经148度以东相对暴露较好的古生代岩石的36%，这是一条宽达200公里的条带。拉克兰褶皱带中的花岗岩类可分成不同的岩套，每个岩套具有独特的化学性质，这与其来自独特成分的源岩是一致的。岩套内部的大部分变化可归因于部分熔融残留物或重铁矿与熔体的分离程度不同。岩套之间的差异是源岩成分不同的结果。岩套之间的一级划分是沉积源岩和火成岩源岩的S和I型花岗岩之间。这两类烃源岩的化学、矿物学和同位素特征反映了其物源的鲜明特征，特别是S式烃源岩在地表至少经历了一次化学风化旋回。S型花岗岩类的产状有一个东界，称为IS线，它被认为代表了厚结晶基底的东界。一组较晚形成的长英质花岗岩类，即A型，被认为是来自以前产生I型岩浆的地壳，因此源岩是先前熔融事件的残留物。
The Lachlan Fold Belt in southeastern Australia comprises rocks ranging in age from Cambrian to Devonian. Granitoid emplacement and related volcanic activity occurred in Silurian and Devonian times, with minor development of Carboniferous plutons in the most easterly part of the belt. The belt is at least 800 km wide, which is much wider than the Mesozoic and Cenozoic fold belts of the circum-Pacific. Granitoids are extensively developed in the Lachlan belt and make up 36 percent of exposed Paleozoic rocks in the relatively well-exposed easternmost part east of longitude 148 E, a strip up to 200 km wide. Granitoids in the Lachlan Fold Belt can be grouped into suites, where each suite has a distinctive chemical character, consistent with its having been derived from source rocks of unique composition. Most of the variation within suites can be ascribed to varying degrees of separation of material residual from partial melting, or restite, from melt. The differences between suites result from differences in source rock composition. The first-order subdivision between suites is between those granitoids derived from sedimentary and from igneous source rocks, the S-and I-types. These two types have chemical, mineralogical, and isotopic characters reflecting the distinctive features of their sources, specifically the fact that the S-type source rocks have been through at least one cycle of chemical weathering at the earth's surface. There is an eastern limit to the occurrence of S-type granitoids, called the IS line, which is thought to represent the eastern limit of thick crystalline basement. A late-formed group of felsic granitoids, the A-types, are thought to have been derived from crust that had previously produced I-type magmas so that the source rocks were residual from that prior melting event.