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甲山岩体形成于早白垩世晚期,可划分为3个单元。电子探针分析结果表明,碱性长石主要为Na-正长石和歪长石,少量为正长石;角闪石主要为钙角闪石中的铁浅闪石,少数为铁角闪石和铁阳起石;单斜辉石属钙铁辉石和普通辉石。化学成分上,该岩体富S i、全碱、全Fe、REE、Th、Ga、Nb、Zr、H f,贫Mg、Ba、Sr、Ti,Cr、Co、N i、V等过渡元素亏损,富轻稀土,中等铕负异常,具有A型花岗岩的特点。甲山正长岩的N(87Sr)/N(86Sr)初始比值ISr=0.701 41~0.707 41,εNd(t)值为-2.27~-5.58,表明岩浆为富集的大陆岩石圈地幔部分熔融形成。岩石圈的拆沉和减薄作用是引发岩石圈地幔部分熔融的原因之一,岩石圈地幔的富集作用可能发生在中元古代晚期。
The Karst rock mass was formed in the late Early Cretaceous and can be divided into three units. The results of electron probe analysis showed that the alkaline feldspar was mainly Na-plus-feldspar and plagioclase feldspar, while the minor ones were orthoclase. The amphibole was mainly hornble amphibole in cape amphibole, Iron Yang from the stone; clinopyroxene and iron pyroxene pyroxene. In terms of chemical composition, the rock mass is rich in Si, Alkali, Fe, REE, Th, Ga, Nb, Zr, Hf, Mg, Ba, Sr, Ti, Cr, Co, Ni and V Loss, light-rich rare earth, medium-negative Eu anomaly, with the characteristics of A-type granite. The initial ratios of ISR = 0.701 41 ~ 0.707 41 and εNd (t) of N (87Sr) / N (86Sr) are between -2.27 and -5.58, indicating that the magmatic enriched continental lithosphere mantle partially melts. The delamination and thinning of the lithosphere is one of the reasons that lead to partial melting of the lithospheric mantle. The enrichment of the lithospheric mantle may occur in the late Mesoproterozoic.