Late Mesozoic Magmatism And Tectonic Significance In The Shenshuiliang Area Of The Eastern Segment Of Daqingshan Mountain,Inner Mongolia

The North China Craton(NCC)underwent significant and intense geological movements during the Mesozoic era,commonly known as Hercyn-Indosinian and Yanshanian orogenies.The collision between the Siberian Plate and the NCC,the collision between the Yangtze Craton and the NCC,and the subduction of the paleo-Pacific Plate have significantly altered the physical and chemical properties of the lithospheric mantle of the NCC.Consequently,the thinning of the Mesozoic lithosphere and the destruction of the North China Craton have emerged as prominent subjects of geological research.Metamorphic core complexes are prominent indicators of lithospheric thinning and exhibit deformation,which can reflect the deformation characteristics of deep crust.Located within the core of the Hohhot metamorphic core complex,the Shenshuiliang pluton in the Eastern Segment of Daqingshan of Inner Mongolia,along with the western part of the Yanshan orogenic belt,experienced the superposition of compressive and extensional structures in the late Mesozoic.It provides an ideal case study for examining the destruction and reduction of the Craton lithosphere in NCC and the intracontinental orogenic movement in the Yanshan region.This study comprehensively analyzes the Shenshuiliang pluton based on a detailed field geological survey and systematic sampling tests.It investigates the formation age,structural background,and macro structural deformation characteristics of various lithologies.Furthermore,this paper uncovers the interdependence between magmatism and extensional structures during the rock mass uplift.Lastly,it offers an in-depth exploration of the dynamic background of late Mesozoic extensional structures in the Eastern Segment of Daqingshan.The whole rock geochemical analysis indicates that the granites in Shenshuiliang from the early Cretaceous are classified as A-type granites,formed in a post-collision extensional tectonic environment.In contrast,the diorite and plagioclase amphibolite represent intraplate basalts formed in an extensional and tensile environment.Diorite and granitic rocks exhibit similar evolutionary trends but were formed at varying crustal depths within the same tectonic background.Geochemical calculations and the evolutionary trend of trace elements in zircon indicate a gradual decrease in the thickness of the molten crust’s source region in the study area.This suggests a transition of the forming environment to an extensional background.Field structural characteristics reveal weak deformation in the core of the Shenshuiliang pluton and strong deformation in its peripheral regions,indicative of sliding away from the periphery.Two deformation processes are observed,one transitioning from weak to strong deformation,and the other from strong to weak deformation.The Shenshuiliang pluton experienced high-temperature ductile shear between 148-140 Ma,followed by sustained mantle heating from 148-132 Ma,uplift from 134-115 Ma,and relatively shallow mesothermal ductile extensional shear from 124-115 Ma during magmatic activity.In addition,the hinge direction of the sheath fold opposes the sliding direction of the rock layer,suggesting that the rock mass is not entirely exposed by the detachment fault.Instead,it exhibits characteristics of active emplacement.The rock mass does not experience uplift through a thrust nappe structure;instead,it exhibits a tectonic setting similar to the "magmatic core complex" resulting from active emplacement within an extensional and thinning background of the thickened crust.