The Characteristics Of Magmatic Rocks And Discussion Of Geotectonics Evolution From Caledonian Through Hercynian To Indosinian Stage In The Baiyun'ebo-Mandula Region, Inner Mongolia

Baiyun'ebo–Mandula region of Inner Mongolia crossovers the boundary between North China Platform and Xingmeng Orogenic belt, and one of its notable characteristics is having large volume of Paleozoic-Mesozoic magmatic rocks. Based on 1/250000 regional geological survey of Baiyun'ebo and Mandula, the petrography, petrochemistry and geochemistry of Paleozoic-Mesozoic magmatic rocks are studied in detail. The geotectonic evolution in this region is discussed on the basis of igneous petrotectonic assemblages. Caledonian magmatic rocks include volcanic rocks and intrusive rocks which were erupted or intruded in Ordovician. Those rocks are subduction-related assemblages. Picrites, boninites and MORB-like basalts are identified for the first time which may relate to the extension of forearc basin and were formed in SSZ (supra-subduction zone) setting. All of those provide new clues for the early Paleozoic geotectonic evolution. Early Hercynian magmatic rocks include early Devonian Oceanic assemblages, Devonian HKCA granites and syenites. Oceanic assemblages were formed in SSZ setting, and have metamorphic peridotites, gabbros having cumulus textures, boninites and pillow basalts. The ocean has the characteristic of back arc basin. Devonian granites and syenites are HKCA series in general and may be formed in pos-collision setting. Middle Hercynian igneous include early Carbonic MKCA granodiorites, alkalifeldspar granites and late Carbonic syenites. Early Carbonic granitoids are subduction-related igneous. Late Carbonic syenites have the characteristics of within-plate or post-orogeny magmatic rock, and may have no relationship to the early Carbonic granitoids because of the...