论内蒙地槽西部某阿尔卑斯型岩体和铬矿床成因的基本问题

ON THE GENESIS OF THE ALPINE-TYPE ULTRAMAFIC COMPLEX AND RELATED CHROMITE DEPOSITS IN THE WESTERN PART OF THE INNER-MONGOLIA OROGENIC BELT

内蒙某斜辉辉橄岩体位于地槽褶皱带。岩体中产有豆荚状富铬铁矿，常见似脉状纯橄榄岩，属于典型的阿尔卑斯型含铬岩体。本区前人做过一些工作。过去，苏联人如Г．А．索科洛夫(Соколов)和Н．В．巴甫洛夫(Паалов)曾到矿区，他们对岩体和铬矿的成因有这样一些主要观点：1.岩体为岩浆成因。斜方辉石的定向排列代表原生带状构造，

The Alpine-type ultramafic complex refered to in this paper is mainly composed of harzburgite with minor dykelike dunite. It is in contact with Carboniferous slate and arkose-sandstone. Thermal metamorphism of the host rocks at the contact with peridotite is nearly absent, fading the rocks but with no metacrystal minerals. The main rock-forming mineral-enstatite (bastite) in harzburgite is characterized by secondary banded structure, bended crystal faces, and undulatory extinction under microscope. It is evident that the complex is a solid intrusion by plastically tectonic emplacement, and is regarded as the representative of the ultrabasic masses from the upper mantle. Based upon the mineralogical and experimental data (N. L. Bowen and 0. F. Tuttle, 1949) and the temporal and spacial association between chromite ore body and dykelike dunite, it is suggested that the latter might be the product during the late hydrothermal metasomatic stage. Podiform chromite deposits are founded in various parts of the peridotite intrusion. The sharp contact of chromite ore bodies with the host rocks and the dissection of the ore bodies by faulted planes indicate the similar origin as that of the host peridotite. In the paper, some ideas concerning 'the Theory of Magmatic Origin' advocated by G. A. Sokolov ( Γ. A. COKOJIOB ) have been critically analyzed and it has been pointed out that the concepts, such as the so called 'Primary Magmatic Flow Structure', 'Dunite Schlieren' and 'Late Magmatic Deposits' are, to a great extent, of hypothesis. And therefore, the author does not believe that the common methods in the research of igneous rocks and magmatic deposits are applicable to the research of the rules governing the distribution of the chromite deposits described in the paper, and the emphasis has been laid on the importance of 'Tectonic Exploration of Ore Deposits'.