Characteristics And Geological Significance Of Basic Rocks Along The North-central Segments Of The Alxa Block, Inner Mongolia

Whether there is the mafic in the northern part of Alxa, and its structuralproperty,which is not known. Alxa block lies in the middle of Central Asia orogenicbelt, and in the top of arcuate tectonic belt of the Inner Mongolia. It undertakes theTianshan orogenic belt and the Xing-Meng orogenic belt.The mafic rocks are found to distribute in the Alxa Wuliji area by a detailed1:250000field Geological Survey, which intrude the Upper Carboniferous Amushangroup, and also intruded by latter acidic magma. The mafic is mainly considered to becomposed of gabbro and amphibolite gabbro, and the gabbro is the main. U-Pb datingof zircons from the amphibolite gabbro was made on LA-ICP-MS. The date of zirconswhich have the typical characteristics of mafic magma yield a weighted mean²⁰⁶Pb/²³⁸U age of248±1Ma, which belongs to the Early Triassic.The result of dating, combined with the regional structure, the relationshipbetween the lithology analysis show that the generate time of the mafic obviously islater than the time of the Paleo-Asian oceanic closed. It is not resulted from earlymagmatic activity during orogeny in subduction environment of Paleo-Asian oceaniccrust beneath the North China plate during the late Paleozoic, but probably be relatedto large-scale continental rifting. The gabbro of the region is generated in the regionalcontinental extensional environment Caused due to the upwelling of mantle material.