摘要
桑干构造带是一条地壳规模的复杂的逆冲构造带，位于华北克拉通北缘晋冀内蒙交界地区怀安杂岩和恒山杂岩之间。桑干带中剪切形变构造特别发育，有许多强应变带、糜棱岩化带和混合岩化带。桑干带的岩石构成极为复杂多样，但主体是英云闪长质片麻岩和麻粒岩，其地球化学特征与世界上典型地区的灰色片麻岩相似。桑干带的特征之一是高压基性麻粒岩和退变榴辉岩的包体和构造透镜体广泛分布。这些岩石代表最下部地壳，变质压力超过１．４ＧＰａ，其地球化学特征类似太古宙亏损型拉斑玄武岩。它们的大量出现表明晚太古代该区可能存在过一个基性下地壳。桑干带的另一特征是发育大量花岗岩小侵入体和花岗片麻岩。这些花岗质岩石富钾，含有高压麻粒岩和退变榴辉岩包体，与条带状混合岩共生，受剪切构造的控制，单个规模都不大，延续成带，但无较大岩基，其微量元素地球化学特征类似于显生宙碰撞型花岗岩。我们认为，桑干构造带是同一陆块内不同构造单元之间的拆离逆冲褶皱带。在太古宙末沿桑干带发生拆离导致怀安陆块向恒山陆块的逆冲，并将下地壳的岩石组合破坏，其中的一部分高压麻粒岩和榴辉岩被带到了中部地壳。桑干带的发育在２．５～２．１５Ｇａ之间，是华北克拉通构造体制由全活动状态向局部的和线性的活?
Sanggan structure zone is a crustal scale complicated thrust belt lying between Huai'an complex and Hengshan complex at the middle part of the northern border of the North China craton. It is characterized by plenty of shear zones, lenses of high pressure basic granulite and retrograde eclogite, and small granite intrusions, by which it is distinguished from the two Archaean complex on both sides. High pressure basic granulite and retrograde eclogite show differentiative trend of tholeiitic series in major element compositions, and were derived from depleted mantle in late Archaean according to trace element geochemical data and Sm/Nd isotopic data. They were subjected to metamorphism at pressure more than 1.4GPa. We infer, therefore, that they constituted the main part of the lower continental crust in this area then. Most of the small granite intrusions developed along with shear zones and are associated with migmatites. Although their major element compositions are very much alike, trace element data indicate that these granites arose from several quite different protoliths. There is no large granite batholith in the structure zone, indicating that the structure zone was merely crustal scale. The major rocks in the sructure zone are tonalitic gneiss and granulite which geochemical features are identical with typical Archaean TTG gneiss in the world.We intend to consider the Sanggan structure zone as a intracontinental detachment and thrust zone. Its development began from a detachment between the Huai'an complex and Hengshan complex in late Archaean. Then Huai'an complex thrust onto Hengshan complex. As a matter of course, Sanggan structure zone came into being during this process. The thrust destroyed some part of the lower most basic crust and transported some of the fragments into the middle and/or upper crustal level along the structure zone. However, the thrust process was limited, and the Sanggan structure zone did not evolved into a large scale continental lithosphere subduction zone. The Sanggan structure zone developed between 2.5Ga to 2.15 Ga. It was a primordial product of the changing process from overall activity regime in Archaean to plate tectonic regime after Archaean in North China craton.
出处
《岩石学报》
SCIE
CAS
CSCD
北大核心
1996年第2期193-207,共15页
Acta Petrologica Sinica
基金
国家自然科学基金
关键词
华北地区
早前寒武纪
桑干构造带
构造性质
Early Precambrian
Sanggan structure zone
Lower crust
High pressure granulite
Retrograde eclogite
