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报道太行山燕山期中酸性岩体中暗色包体的锆石Hf-O同位素,并结合包体的岩石学、全岩化学和Nd-Sr同位素的研究,试图揭示暗色包体的成因.暗色包体细粒并具岩浆结构,有的被强烈拉长,但没有固态变形.这些特征表明包体和寄主岩石曾是共存的、但成分截然不同的岩浆.暗色包体含丰富的含水矿物(角闪石和黑云母),辉石普遍具有角闪石反应边,斜长石斑晶具有复杂的成分和结构不平衡.对比暗色包体和相邻寄主岩石发现,包体化学成分与相邻寄主岩石密切相关,但其εNd值通常比相邻寄主岩石高,虽然两者Sr同位素成分类似.暗色包体中锆石Hf同位素变化很大(εHf=?10～?22),指示其两种岩浆混合的特点.锆石O同位素变化也较大(δ18O=5.5‰～7.8‰),与壳幔岩浆混合的模式一致.包体成因可能是这样的:经历了橄榄石和辉石分离结晶之后的玄武质岩浆首先在地壳深部与壳源花岗质熔体发生混合形成混浆,再强力注入到上覆酸性岩浆房,并分散成小岩浆团(即形成暗色包体的岩浆).包体岩浆随后与酸性岩浆在接触边界发生斜长石等晶体的双向交换,以及流体和Na,P,Y,Nb和Pb等元素向包体内的化学扩散.
This paper reports the zircon Hf-O isotopes of dark inclusions in the intermediate-acid rocks in the Yanshanian period of the Taihang Mountains and attempts to reveal the origin of the dark inclusions in combination with the petrology, whole-rock chemistry and Nd-Sr isotope studies of the inclusions. Particulate and magmatic structures, some strongly elongated but not solidly deformed, indicate that the inclusions and host rocks were coexisting but distinctly magmatic, with dark inclusions containing abundant hydrous minerals (amphiboles and Biotite), pyroxene generally have amphibole reaction edge, plagioclase phenocrysts with complex composition and structural imbalances.Compared with dark inclusions and adjacent host rocks, the chemical composition of the inclusions is closely related to the adjacent host rocks , But its εNd value is generally higher than that of adjacent host rocks, although the two Sr isotopic compositions are similar.The Hf isotopic composition of zircons in the dark inclusions varies greatly (εHf =? 10 ~? 22), indicating the characteristics of the two magmas The δ18O = 5.5 ‰ ~ 7.8 ‰ (δ18O = 5.5 ‰ ~ 7.8 ‰) is consistent with that of crust-mantle magmatism.The genesis of the inclusions may be as follows: The basaltic magma after the crystallization of olivine and pyroxene Deep in the crust with shell source granite The melts are mixed to form a mixed slurry, which is then vigorously injected into the overlying acidic magma chamber and dispersed into small magma masses (ie, magmas forming dark enclaves). Later, the inclusion magma and plagioclase crystals Bidirectional exchange, as well as the chemical diffusion of fluids and elements such as Na, P, Y, Nb and Pb into the inclusions.