The Geochronology Of Bedrock Reservoirs In The Eastern Part Of The Altun Mountains In The Qaidam Basin

In order to strengthen the scientific research on unconventional oil and gas reservoirs in the Qaidam Basin,This paper analyzes and tests the petrological,chronological and geochemical characteristics of bedrock in the eastern part of the Altun Mountains.It provides further understanding of the distribution,genesis and evolution of the bedrock in the eastern part of the Altun Mountains and a theoretical basis for reservoir research in the region.The bedrock types in the eastern part of the Altun Mountains include magmatic rocks and metamorphic rocks.A large number of granites and gneiss are exposed in the study area,and basalt,slate and quartz schist are visible in some areas.The isotope dating study shows that the formation of bedrock is divided from early to late:early Neoproterozoic,the age of the protolith in the Niu 4 well granitic gneiss is 838±7Ma;Late Ordovician,the age of the granodiorite in the Jianyan 1 well is 444±2Ma;Late Silurian-Early Devonian,the age of the rock is between 405Ma and 419Ma;Early Permian,the age of the basalt in Lengdong 1 well is 282±3Ma;Late Permian,the age of the Niubei 1 is between 253Ma and 276Ma;Middle Triassic,the age of granite in Niu 3 well is 230±3Ma;Late Triassic,the metamorphic age of slate in Dongping 1 well is 216±3Ma;Late Jurassic,the metamorphic age of quartz schist in Lengbei 1 well is 151 ± 3Ma.The analysis of geochemical elements shows that the granitoids in the eastern part of the Altun Mountains can be divided into S-type granites and I-type granites.The granodiorite exhibits quasi-aluminum,medium-potassium-calcium-alkaline and features I-type granite.The basalt belongs to the medium potassium-calcium alkaline-low potassium pull-spot series,and the source region is composed of spinel olivine peridotite.The gneiss protolith is magmatic rock and quasi-aluminum-alkaline rock,belonging to high potassium calcium alkaline-medium potassium calcium alkaline series.The slate and quartz schist protoliths are calcareous sedimentary rocks and argillaceous sedimentary rocks.The bedrock of the study area has experienced magmatism and metamorphism.The magma activity is divided into six phases,namely the plate collision stage in the early Neoproterozoic;the oceanic crust-continental subduction collision stage in the early Paleozoic;the Paleo-Tethys oceanic crust reopened and the subduction and the post-orogenic stage in the Late Paleozoic;the residual oceanic crust subduction and closure stage in the Mesozoic.Metamorphism is divided into two phases,The first period of magmatic activity generated by the Indosinian movement affects the metamorphic slate in the Late Triassic;In the second phase,quartz schist is formed due to a strong compressive stress metamorphic event by the Yanshan movement.