Post-collisional potassic granitoids from the southern and northwestern parts of the Late Neoproterozoic East African Orogen: a review
Post-collisional potassic granitoids from the southern and northwestern parts of the Late Neoproterozoic East African Orogen: a review
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DOI：
10.1016/s0024-4937(98)00031-0
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发表时间：
1998-12
期刊：
影响因子：
3.5
通讯作者：
D. Küster;U. Harms
中科院分区：
文献类型：
--
作者：
D. Küster;U. Harms
富含 HFS 元素的钾质铝质花岗岩构成了与非洲东北部（苏丹、埃塞俄比亚、索马里）和马达加斯加新元古代晚期泛非造山运动有关的广泛碰撞后岩浆作用的一部分。岩体侵位于 580 Ma 至 470 Ma 之间，包括深溶线和超溶线黑云母-花岗岩、黑云母-角闪石-花岗岩、石英-二长岩和石英-正长岩。含辉石的花岗岩是次要的。二长闪长岩成分的碱性岩脉和飞地与花岗岩类岩体局部相关。位于前新元古代地壳中的花岗岩类，其 Sri 比在 0.7060 至 0.7236 之间，εNd(t) 值在 -15.8 至 -5.6 之间，而位于幼年新元古代地壳中或接近接触面的花岗岩类，具有较低的 Sri 比 (0.7036–0.7075) 和正 εNd(t) 值（4.6）。然而，钾质花岗岩不太可能仅代表地壳熔融的产物。与源自俯冲改变的富集地幔源的基性岩浆的关联强烈表明，花岗岩代表了下地壳中地幔和地壳衍生熔体相互作用和混合产生的混合岩浆。这种钾质花岗岩岩浆作用最强烈的时期发生在585Ma至540Ma之间，很大程度上与马达加斯加的高温麻粒岩相变质作用和非洲东北部（索马里、苏丹）的角闪岩相退变同时发生。花岗岩岩浆作用和高级变质作用可能都与碰撞后岩石圈减薄、岩浆底侵和地壳松弛有关。然而，钾质花岗岩的侵位持续到大约 470 Ma，这意味着与地壳隆起和冷却的不同阶段相关的几个岩浆脉冲。钾质高铝质花岗岩在时间和空间上与碰撞后高钾钙碱性花岗岩相关，除了不相容元素富集之外，它们在岩石学、地球化学和同位素方面具有许多相似之处。这种相似性表明这两个花岗岩组合的岩石成因密切相关。
Potassic metaluminous granitoids with enrichments of HFS elements constitute part of widespread post-collisional magmatism related to the Late Neoproterozoic Pan-African orogeny in northeastern Africa (Sudan, Ethiopia, Somalia) and Madagascar. The plutons were emplaced between 580 and 470 Ma and comprise both subsolvus and hypersolvus biotite–granite, biotite–hornblende–granite, quartz–monzonite and quartz–syenite. Pyroxene-bearing granitoids are subordinate. Basic dikes and enclaves of monzodioritic composition are locally associated with the granitoid plutons. Granitoids emplaced in pre-Neoproterozoic crust have Sri-ratios between 0.7060 and 0.7236 and εNd(t) values between −15.8 and −5.6 while those emplaced in, or close to the contact with, juvenile Neoproterozoic crust have lower Sri-ratios (0.7036–0.7075) and positive εNd(t) values (4.6). However, it is unlikely that the potassic granitoids represent products of crustal melting alone. The association with basic magmas derived from subduction-modified enriched mantle sources strongly suggests that the granitoids represent hybrid magmas produced by interaction and mixing of mantle and crust derived melts in the lower crust. The most intense period of this potassic granitoid magmatism occurred between 585 and 540 Ma, largely coeval with HT granulite facies metamorphism in Madagascar and with amphibolite facies retrogression in northeastern Africa (Somalia, Sudan). Granitoid magmatism and high-grade metamorphism are probably both related to post-collisional lithospheric thinning, magmatic underplating and crustal relaxation. However, the emplacement of potassic granites continued until about 470 Ma and implies several magmatic pulses associated with different phases of crustal uplift and cooling. The potassic metaluminous granites are temporally and spatially associated with post-collisional high-K calc-alkaline granites with which they share many petrographical, geochemical and isotopical similarities, except the incompatible element enrichments. The resemblance indicates a strongly related petrogenesis of both granite associations.