摘要:
中条山绛县群变质火山岩是铜矿峪铜矿的赋矿岩石,其形成的年龄期次还没有很好的限定,构造背景还存在很大的争议。本文确定了变质石英斑岩的形成年龄为(2179±7) Ma,变质酸性火山岩的形成年龄为(2142±11) Ma,建议重新划分铜矿峪变质火山岩的层序,自下而上分别为变质石英斑岩(骆驼峰组)、变质基性火山岩(西井沟组)和变质酸性火山岩(竖井沟组)。其中铜矿峪铜矿主要赋存于骆驼峰组变质石英斑岩中。变质石英斑岩具有后碰撞花岗岩的特征,形成于由挤压向伸展转变的环境,其εNd(t)值为–2.21~–2.15,两阶段Nd模式年龄TDM2为2.75~2.79 Ga。变质酸性火山岩具有A2型花岗岩的特征,其εNd(t)值为–1.59~–0.94,两阶段Nd模式年龄TDM2为2.63~2.69 Ga,与变质石英斑岩一样都是由老地壳再造而来。变质基性火山岩富集 LREE、LIL及 HFS等元素,具有 Nb、Ta的负异常,无明显的 Ti负异常,部分样品具有 Zr、Hf 的正异常,具有受陆壳混染的大陆玄武岩特征,形成于伸展的构造背景。推测中条山—吕梁山在古元古代可能为华北克拉通古陆块的边缘,具有从造山到造山后伸展的复杂演化过程。铜矿峪斑岩型铜矿形成于陆块边缘由挤压转变到伸展的构造背景。
关键词:
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中条山
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铜矿峪
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绛县群
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古元古代
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构造背景
Abstract:
of the metamorphic quartz porphyry range from –2.21 to –2.15, and the corresponding two stage model ages TDM2 are mainly between 2.75 Ga and 2.79 Ga. The metamorphic acidic volcanic rocks are of A2type granite features, withεNd(t) values being –1.59 ~ –0.94, and two stage model ages being mainly between 2.63 Ga and 2.69 Ga. It is inferred that their magmatic origin was related to partial melting of older continental crust. The metamorphic mafic volcanic rocks are enriched in LREE, LIL and HFS elements, with Nb, Ta negative anomalies but no significant negative Ti anomalies. Some samples show Zr, Hf positive anomalies. These features are consistent with geochemical features of continental basalt, with assimilation of crust materials to various degrees in an extension tectonic setting. Zhongtiao–Lüliang Mountains might be located on the margin of the North China ancient continental block and underwent complicated geological evolution from orogeny to post-orogenic extension in the Paleoproterozoic period. The Tongkuangyu porphyry copper deposit was formed on the margin of the land mass in the conversional stage from compression to extension.
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