Low- and high-temperature granites
Low- and high-temperature granites
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DOI：
10.1017/s0263593300000973
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发表时间：
2004-03
影响因子：
1.2
通讯作者：
B. Chappell;Adrian White;I. Williams;D. Wyborn
中科院分区：
文献类型：
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作者：
B. Chappell;Adrian White;I. Williams;D. Wyborn
I型花岗岩可分为低温组和高温组。这两类岩石之间的区别，形式上是基于一套相对基性岩中是否存在继承锆石，而这套基性岩中的SiO2含量低于68%，在许多情况下，这一区别表现在成分变化的独特模式上。低温组花岗岩是在较低的岩浆温度下，由含H_2O的地壳源岩中的单斜花岗岩组分Q_2、Ab和O_1部分熔融而成。更多的这种类型的镁铁质花岗岩具有这种特征，因为它们含有残余矿物，通常包括继承的锆石，这些锆石被夹带在更长英质的熔体中。与其他元素一样，Zr含量与SiO2呈线性相关，但有时在非常长英质的岩石中除外，并且Zr一般随着岩石变得更长英质而减少。所有S型花岗岩均明显为低温成因。在大部分或全部残余岩从岩浆中被去除后，这些花岗岩可能通过分离结晶进一步演化。高温花岗岩是由完全或大部分熔融的岩浆形成的，其中锆石晶体最初并不存在，因为熔体中的锆石晶体并不饱和。高温岩套通常通过分离结晶而在成分上演化，并且它们可能通过产生堆晶岩而延伸到更多的镁铁质成分。然而，在某些情况下，高温套组内的成分差异可能是由相似源岩不同程度的部分熔融引起的。这两类火山岩都存在，并显示出类似的差异。这两组岩石之间存在着岩石学差异，重要的矿化作用更可能与高温花岗岩有关。这两组烃源岩的不同特征与其不同的烃源岩组成有关。低温花岗岩来源于源岩，其中单斜花岗岩成分在整个部分熔融过程中都存在，而高温花岗岩的源物质缺乏其中一种成分，因此，在熔融过程中耗尽，导致熔融温度升高。
ABSTRACT I-type granites can be assigned to low- and high-temperature groups. The distinction between those groups is formally based on the presence or absence of inherited zircon in relatively mafic rocks of a suite containing less than about 68% SiO2, and shown in many cases by distinctive patterns of compositional variation. Granites of the low-temperature group formed at relatively low magmatic temperatures by the partial melting dominantly of the haplogranite components Qz, Ab and Or in H2O-bearing crustal source rocks. More mafic granites of this type have that character because they contain restite minerals, often including inherited zircon, which were entrained in a more felsic melt. In common with other elements, Zr contents correlate linearly with SiO2, except sometimes in very felsic rocks, and Zr generally decreases as the rocks become more felsic. All S-type granites are apparently low-temperature in origin. After most or all of the restite has been removed from the magma, these granites may evolve further by fractional crystallisation. High-temperature granites formed from a magma that was completely or largely molten, in which zircon crystals were not initially present because the melt was not saturated in that mineral. High-temperature suites commonly evolved compositionally through fractional crystallisation and they may extend to much more mafic compositions through the production of cumulate rocks. However, it is probable that, in some cases, the compositional differences within high-temperature suites arose from varying degrees of partial melting of similar source rocks. Volcanic equivalents of both groups exist and show analogous differences. There are petrographic differences between the two groups and significant mineralisation is much more likely to be associated with the high-temperature granites. The different features of the two groups relate to distinctive source rock compositions. Low-temperature granites were derived from source rocks in which the haplogranite components were present throughout partial melting, whereas the source materials of the high-temperature granites were deficient in one of those components, which therefore, became depleted during the melting, causing the temperatures of melting to rise.