Characteristics,Magma Source And Geological Significance Of Mesozoic Intrusive Rocks From Xiuyan Area,Eastern Liaoning Province

In this paper,zircon LA-ICP-MS U-Pb dating is used to determine the emplacement age of Mesozoic Magmatic Rocks in Xiuyan area,Eastern Liaoning Province.Based on their petrological,chronological and geochemical characteristics,their magma source and tectonic setting are discussed.Based on the regional distribution characteristics and properties of Mesozoic intrusive rocks,the geological significance of Mesozoic Magmatic activities and tectonic evolution in Xiuyan area is further discussed.Zircon LA-ICP-MS U-Pb dating results show that the Mesozoic magmatism in Xiuyan area can be divided into three stages:Late Triassic,late Jurassic and early Cretaceous.The magmatic emplacement ages of the Huanghuagou,Hedong and manjiapu plutons in the Late Triassic are 229 ± 1 Ma,216±1 Ma and 210±2 Ma,respectively;the Sandaogou,Hongshilazi and Luotuolazi plutons in the Late Jurassic are 160 ± 1 Ma,152±5 Ma and 148 ± 7 Ma,respectively;the Wangjiabaozi,Hadabei,Lijiabaozi,Shimiao plutons in the Early Cretaceous are 128±1 Ma?127 ± 2 Ma?125±1 Ma and 123 ± 1 Ma,respectively.In the Late Triassic intrusive rocks,Huanghuagou monzonitic granite has geochemical characteristics of "C" type adakites and TDM2=3.29?3.53 Ga,which originated from the partial melting of the Paleoarchean material in the thickened ancient lower crustal.The Hedong gabbro shows geochemical characteristics of mantle derived magma,with negative ?Hf(t)anomaly,low Rb/Sr and high Nb/Ta,Nb/U ratios,indicating that Hedong gabbro magma is originated from partial melting of enriched mantle which formed by subduction plate,and the magma was contaminated by crustal materials during the rising process;The ratios of Zr/HF and Nb/TA are higher than those of the crust source rocks.The high MgO content and Mg#value indicate that the Manjiabao diorite is the product of partial melting of basaltic lower crust and mixed with some mantle materials.Compared with Hedong gabbro,the Manjiabao diorite is more enriched in Nb,TA and HREE,indicating that the mantle material is derived from the asthenosphere mantle which is more depleted.The Late Jurassic Sandaogou,Hongshilazi and Luotuolazi intrusive rocks have geochemical characteristics of "C"adakites,which originated from partial melting of basic rocks at the bottom of thickened continental crust.However,Hongshilazi and luoluolazi monzogranite are more depleted in Nb and Ta,Cr,Ni,Co,Yb and Sr than Sandaogou monzogranite,?Eu and ?Ce show negative anomalies and Mg>45,indicating that they are contaminated by asthenosphere mantle material and oceanic material.The Early Cretaceous Wangjiabaozi,Hadabei and Lijiabaozi intrusive rocks are I-type granites with adakitic characteristics which originated from partial melting of basaltic lower crust materials,and the magma is contaminated by mantle materials.The Hadabei pluton TDM2=2.21?2.02 Ga,indicates that the magmatic source is older than that of Wangjiabaozi and Lijiabaozi intrusions.The Shimiao pluton is aluminous A-type granite with TDM2=1.989?2.164Ga,Mg#=6?13,MgO=0.05%?0.11,indicating that it originated from partial melting of the ancient felsic continental crust.The Late Triassic Huanghuagou pluton was formed in the collisional compressional orogenic environment,the Hedong and Manjiabao intrusive rocks were formed in the post collisional extensional tectonic environment;the Late Jurassic intrusive rocks were formed in the collision compression orogenic environment;the Early Cretaceous intrusive rocks were formed in the post collisional extensional tectonic environment.Based on the pluton characteristics,magma sources and tectonic environment of Mesozoic,magmatic activity and tectonic evolution in Late Triassic were related to the collage subduction of Yangtze plate,and that of Late Jurassic and Early Cretaceous was related to the subduction of Pacific plate.The appearance of Shimiao pluton wihch belong to A1 type granite in Early Cretaceous,indicates that the subduction of the Pacific plate has disappeared at 123Ma The magma activity at this time is related to asthenosphere upwelling.The destruction and thinning of the North China Craton is a process,which is not accomplished overnight.It is the result of multiple magmatic-tectonic events.According to the magmatic activity and tectonic evolution of Mesozoic intrusive rocks in Xiuyan area,the destruction and thinning of the North China Craton began in the Late Triassic(216 Ma).The lithosphere was destroyed and thinned in a small scale due to the thermal erosion,mechanical denudation and stretching caused by the collision and collage of the Yangtze plate to the North China Craton.In the Late Jurassic(160 Ma),the Yangtze plate tectonic domain has been ended,and the Pacific tectonic domain began.The subduction of the Pacific plate resulted in crustal thickening and eclogitization,until the early Cretaceous(128 Ma)delamination,until 123 Ma asthenosphere upwelling,through partial melting of lithospheric mantle and decompression melting of upwelling asthenosphere,the activity of superplume occurred,which made the destruction and thinning of North China Craton reach a peak.