论文部分内容阅读
埃塞俄比亚北部施瑞地区具有造山前、造山期和造山后3种花岗岩类型,全岩Sm-Nd等时线测年结果表明,造山前和造山后花岗岩成岩年龄分别为824.4±15.5Ma和517.9±5.8Ma.3类花岗岩主量元素和稀土微量元素成分存在明显差异,其中造山前花岗岩属于低钾过铝质花岗岩,稀土分配模式属轻稀土弱富集型,富集大离子亲石元素,亏损P和Ti高场强元素;造山期花岗岩为准铝质高钾钙碱性花岗岩,稀土分配模式属轻稀土富集型,富集大离子亲石元素和高场强元素;造山后花岗岩为弱过铝质高钾钙碱性花岗岩,稀土分配模式具强烈铕亏损的海鸥型,富集大离子亲石元素,明显亏损P和Ti高场强元素.综合研究表明:造山前和造山期花岗岩均为I型幔源花岗岩,构造环境处于被动大陆边缘-火山岛弧环境;造山后花岗岩为A2型壳源主花岗岩,是在洋盆关闭和阿拉伯-努比亚地盾成熟后,由减薄的地壳部分熔融产生.
There are three types of granitoids before orogenic, orogeny and post-orogenic in the Shire region of northern Ethiopia. The dating of Sm-Nd isochron in the whole rock shows that the diagenetic ages of the orogenic or granitic granites are 824.4 ± 15.5Ma and 517.9 ± 5.8, respectively The main elements of Ma.3 granites are obviously different from the trace elements in rare earths. The granitic rocks before the orogenic belonged to the low-K-perlite granites. The distribution patterns of REEs are light rare-earth enrichment type, enriched in LILE, loss P And Ti high-field elements; orogeny granite is quasi-aluminum high-K calc-alkaline granite, the REE distribution pattern is light rare earth enrichment, enriched in large ion lithophile elements and high field strength elements; Al-rich high-K calc-alkaline granitoid and seagull-type with a strong depletion of europium in the mode of REE distribution enrichment of large ion lithophile elements and obvious depletion of P and Ti high field strength elements.Comprehensive studies have shown that both pre-orogenic granite and I-type mantle source granite, the tectonic environment is in the passive continental margin - volcanic island arc environment; orogenic post-orogenic A2 granulite source granite, is in the ocean basin closed and Arabia - Nubian ground maturity, by the thinning of the crust unit Melting of.