Petrogenesis of granitic magma and its thermal history : disclosure of melting reaction from granitic suites

一种可以接受的花岗岩浆形成模式是地壳物质的部分熔融。利用模型和自然系统进行的实验研究揭示了地壳物质在下到中地壳条件下的熔融反应。变质岩中的熔融反应以前是在高级变质地体中报道的，而对火成岩中的熔融反应知之甚少。由于花岗岩套具有较高的岩浆粘度，因此有可能在花岗岩套中保存有关熔融反应的任何信息。我们在侵入越南Kontom地块麻粒岩相变质岩的花岗岩套中发现了产生花岗岩熔融的反应结构，并在日本东高变质带闪长岩杂岩中发现了变质包体。从结构和化学角度考虑，无面体石榴石中的黑云母在泥质片麻岩经脱水熔融熔融时为残留相。因此，产生花岗岩熔体的反应结构将被保存在泥质片麻岩和越南Kontom Massif的花岗岩中。在东达卡变质带中，全岩地球化学研究结合变质分析表明，闪长杂岩中的包体为花岗岩熔体释放后的残留物，东南极纳皮尔杂岩西段托纳岛三个超高温片麻岩的Sm-ND等时线年龄分别为1870±82 Ma、1897±50 Ma和1557±35 Ma。东冈瓦那包括纳皮尔杂岩、雷纳杂岩和东高止带的集合体，如果存在的话，应该在1600 Ma以前，并可能追溯到2000 Ma左右的超大陆“哥伦比亚”时代。

An acceptable model for the generation of granitic magma is partial melting of crustal materials. Experimental studies using both model and natural systems have revealed melting reactions for crustal materials under conditions of lower to middle crust. The melting reactions in metamorphic rocks were previously reported from high-grade metamorphic terranes, whereas those in igneous rocks are less understood. It is possible that any information with respect to melting reactions is preserved in granitic suites because of their high-viscosity of magma.We found reaction texture to produce granitic melt in the granite suites that intruded granulite facies metamorphic rocks in the Kontum Massif, Vietnam and also metamorphic xenoliths included in the diorite complex in the Hidaka metamorphic belt, Japan. Taking texture and chemistry into account, the biotite included in the anhedral garnet would be of a residual phase at melting of the pelitic gneiss by dehydration melting. The reaction texture producing granitic melt would therefore be preserved in the pelitic gneiss as well as the granite in Kontum Massif, Vietnam. In the Hidaka metamorphic belt, whole-rock geochemical studies combined with metamorphic analyses indicate that the xenoliths in the diorite complex are regarded as restites after releasing granitic melt.Sm-Nd internal isochron ages involving retrograde garnet determined from three ultrahigh-temperature (UHT) gneisses taken from Tonagh Island, the western part of the Napier Complex, East Antarctica gave 1870 ± 82 Ma, 1897 ± 50 Ma and 1557 ± 35 Ma. It is stressed that the assembly of East Gondwana including the Napier Complex, the Rayner Complex, and the Eastern Ghats Belt, if existed, should be before ca 1600 Ma, and may be traced back to ca 2000 Ma of the supercontinent "Columbia" era.