Study Of The Precambrian Metamorphic Plutonic In Alatengaobao Region Of Aixa Youqi, Inner Mongolia

This paper is to study the Bijiertai gneisses and Dabusu Hill gneiss in theAlatengaobao. We did the protolith recovery of the two gneiss by using Petrology,petrochemistry, geochemistry, and discussed their formation age and tectonicbackground.The Bijiertai gneisses are mainly biotite plagioclase gneiss, enriched apatite,sphene, zircon minerals in rocks, a few rocks contain metamorphic mineralsgarnet. Thegeochemical characteristics show that the constant element of high silicon, lowcalcium, in general K₂O less than the Na₂O Characteristics, rich in REE and highfield strength elements, the loss of P, Ti. Rittmann index is less than3.3, so the rockbelongs to the calc-alkaline series, the original rock isa tonalite rocks-granodioriteportfolio. These features indicate that the Bi-level Seoul Taiwan gneiss is the productof partial melting of crustal material in the higher maturity. The Bijiertaigneissprotolith formed in front of the plate collision-after an active continentalmargintectonic setting of the same collision–collision.Dabusu Hill gneisses are mainly two-mica two-feldspar gneiss rocks, enriched inapatite, zircon, sphene, minerals and enriched in garnet, andalusite, tourmalineandother metamorphic minerals. The geochemical characteristics show high-silicon-richpotassium, high potassium poor of aluminum, magnesium, calcium characteristics,Rich in REE and high field strength elements, the loss of Sr, P, Ti, Eu, and the10000Ga/Al value, FeO^T/MgO values are higher. These features show that Dabusu Hillgneisses are the result of crust partial melting in the higher maturity. The result of theDabusu Mountain gneiss zircon LA-ICP-MS U-Pb isotopic dating is830.7±2.8Ma,indicating that they are the product of the Jinning magmatic events. Dabusu Hill gneissic protolith rocks may form the post-orogenic extensional environment.According to two sets of gneiss protolith formation age and the formation of theenvironment, we can determine the area occurred in a collision in the Neoproterozoic.Alxa microland mass and north China plate collision collage in the Neoproterozoic.Research area and north China plate should belong to different tectonic units in theMiddle Proterozoic.