内蒙古红山子地区新太古代变质侵入岩年代学及地球化学特征

华北克拉通西部陆块阴山地块花岗-绿岩带中出露的花岗岩类型比较复杂,研究其类型、成因及其与绿岩带之间的联系,对于探讨花岗-绿岩带的形成和演化有重要意义。本文对内蒙古三合明铁矿西侧红山子地区的花岗-绿岩带进行了研究。其不仅包含有大量的变质科马提岩、科马提质玄武岩和拉斑玄武岩等绿岩带的表壳岩,而且发育着多种变质侵入岩。研究表明,区内与绿岩带相关的侵入岩主要有3种,即变质英云闪长岩、变质花岗闪长岩、变质花岗岩,本文对其中的变质英云闪长岩和变质花岗岩两种岩石进行了地球化学和锆石测年的研究。变质英云闪长岩是一套富铝、低钾、贫铁镁和稀土元素强烈分异的太古宙高铝型TTG岩,SHRIMP锆石U-Pb测年为(2 534±7)Ma(MSWD=1.3),与研究区南部的赞岐岩和TTG的年龄相同;而变质花岗岩具有高硅、富碱,低铁、镁、钛、锰的特点,是一套钙碱性的过铝质岩石,SHRIMP锆石U-Pb测年为(2 509±7)Ma(MSWD=1.5),野外地质现象表明变质花岗岩明显地侵入到区内的绿岩地层和变质英云闪长岩之中。研究发现变质英云闪长岩形成于板块俯冲时TTG岩系岩浆弧构造环境,而变质花岗岩成因则可能与加厚地壳中变沉积岩的熔融有关。

Chronology and Geochemistry of Neoarchean Metamorphic Intrusive Rocks in Hongshanzi,Inner Mongolia

A set of complicated granites are exposed in the Yinshan granite-greenstone belt of the western block of North China craton. The research on the types, genesis and relationship with greenstone belt is of great significance to discuss the formation and evolution of the granite-greenstone belt. The authors studied the granite greenstone belt in the red mountain area in the west side of the Sanheming iron deposit in Inner Mongolia. The greenstone belts contain not only a large amount of epi-crust rocks such as metamorphic Komatite, Komatite basalt, and tholeiite, but also a variety of metamorphic intrusive rocks. The study shows that there are mainly three types of intrusive rocks related to the greenstone belt in this area, namely metamorphic quartz diorite, metamorphic granite diorite, and metamorphic granite. The geochemistry and zircon dating of metamorphic quartz diorite and metamorphic granite were obtained in this study. Metamorphic quartz diorite is Archean high-alumina TTG rocks, with higher aluminum and potassium, lower magnesium, and strong differentiation of REEs. The SHRIMP zircon U-Pb age is 2534±7 Ma (MSWD=1.3), which is cotemporary with Sanukite and TTG in the southern part of the study area. The metamorphic granites belong chemically to a calcalkaline per-aluminous series, rich in silica and alkali, and low in iron, magnesium, titanium and manganese. The SHRIMP zircon U-Pb age is 2509±7 Ma (MSWD=1.5). The field geological phenomena show that metamorphic granite obviously intruded into greenstone strata and metamorphic quartz diorite. The study found that the metamorphic quartz-dolomite diorite was formed in TTG magmatic arc tectonic environment during plate subduction; while metamorphic granite genesis may be related to the melting of thick crust metasedimentary rocks.