华北克拉通东北部新太古代晚期岩浆作用和地壳增生:锆石U-Pb-Hf同位素、微量元素和地球化学制约

辽西-辽南地区新太古代花岗质岩石的锆石LA-ICP-MS U-Pb年代学和微量元素及全岩地球化学和锆石Hf同位素研究为探讨华北克拉通东北部前寒武纪地壳生长和演化提供了制约。结果表明,辽西地区钓鱼台二长花岗岩和辽南地区城子坦片麻状石英闪长岩、安波花岗质片麻岩中锆石均发育岩浆生长环带,结合相对高的Th/U比值(0.24~1.75)和锆石稀土元素特征,暗示它们均为岩浆锆石。定年结果显示,钓鱼台二长花岗岩、城子坦片麻状石英闪长岩和安波花岗质片麻岩的原岩分别形成于2519±9Ma、2505±10Ma和2519±11Ma,即它们均形成于新太古代晚期。辽西-辽南地区新太古代花岗质岩石均具有高SiO2(61.85%~73.38%)、低MgO(0.36%~2.83%)、富Na2O+K2O(7.64%~10.86%)的特征,为准铝质-弱过铝质的高钾钙碱性系列岩石;富集轻稀土元素和大离子亲石元素,亏损重稀土元素和高场强元素,发育弱的Eu负异常和Sr、P、Ti的亏损。岩浆锆石均具有正的εHf(t)值,介于0.4~5.9之间,tDM1变化于2595~2798Ma之间,峰值年龄为2740Ma,与华北克拉通最重要的一次地壳增生事件相一致。辽西-辽南地区新太古代花岗质岩石形成于板块俯冲的弧构造环境下新增生下地壳物质的部分熔融。

Late Neoarchean magmatism and crustal growth in northeastern North China Craton: Constraints from zircon U-Pb-Hf isotope, trace elements and whole rock geochemistry

LA-ICP-MS zircon U-Pb geochronology and their trace elements,as well as whole rock geochemistry and zircon Hf isotope studies on Neoarchean granitic rocks in western and southern Liaoning regions have been provided,aimed to constrain the Precambrian crustal growth and evolution in the northeastern North China Craton(NCC).The results show that zircons from Diaoyutai monzogranite in western Liaoning,Chengzitan gneissic quartz diorite and Anbo granitic gneiss in southern Liaoning all developed magmatic growth zone,and show relatively high Th/U ratios(0.24~1.75)and typical rare earth element patterns,which indicate that their magmatic origin.Zircon U-Pb dating results show that the Diaoyutai monzogranite,the original rocks of the Chengzitan gneissic quartz diorite and Anbo granitic gneiss were formed at 2519±9Ma,2505±10Ma and 2519±11Ma,respectively,i.e.the Late Neoarchean.The Neoarchean granitic rocks in western and southern Liaoning regions are characterized by high SiO2(61.85%~73.38%),low MgO(0.36%~2.83%)and high Na2O+K2O(7.64%~10.86%)contents,typical of metaluminum to weak peraluminum and high potassium calc-alkaline granites.They were characterized by enrichment in light rare earth elements and large-ion lithophile elements and depletion in heavy rare earth elements and high field strength elements,as well as weakly negative Sr,P,Ti and Eu anomalies.Magmatic zircons all have positiveεHf(t)values ranging from 0.4 to 5.9,and their tDM1 ages vary from 2595 to 2798Ma with a peak age of 2740Ma,which is consistent with the most important Neoarchean crustal accretion event in the NCC.Moreover,relatively low TZr values of the Chengzitan gneissic quartz diorite and Anbo granitic gneiss indicate participation of subduction fluids in the source area.Combined with the characteristics of regional tectonic evolution,we suggest that the Neoarchean granitic rocks in western and southern Liaoning region were derived from partial melting of the juvenile lower crustal materials and formed in the arc environment related to the plate subduction.