三门峡高庙石英闪长玢岩的地球化学特征、LA-ICP-MS锆石U-Pb年龄及其地质意义

Geochemial Characteristics, LA-ICP-MS Zircon U-Pb Age of Gaomiao Quartz Diorite Porphyrite in Sanmenxia Area and Geological Significance

三门峡市高庙石英闪长玢岩的激光探针等离子质谱(LA-ICP-MS)锆石U-Pb同位素年代测定获得了135Ma的年龄,与华北地块南缘早白垩世岩石圈伸展和减薄事件的时间一致。高庙岩体中继承锆石的形成年龄为2768Ma,该年龄和模式年龄均与华北克拉通早期地壳演化的峰期时间一致。石英闪长玢岩的SiO2含量为62.93%～65.54%,铝指数A/CNK=0.90～1.03,属于准铝质—弱过铝质系列。富钠(Na2O/K2O=1.29～1.46)、镁指数偏低(Mg#=33.5～42.4<45),属于高钾钙碱性岩系。岩石稀土含量∑REE=197.09×10-6～234.41×10-6(平均216.00×10-6),轻重稀土明显分异[(La/Yb)N=15.86～20.55],基本不显示铕异常(δEu=0.96～1.02)。岩石富集大离子亲石元素Rb、Ba、Sr、K等和轻稀土,高Sr/Y值(Sr/Y=41.99～56.71),亏损高场强元素Nb、Ta、Ti、重稀土和Y等。该石英闪长玢岩具有较低的n(143Nd)/n(144Nd)(t)值(0.5116)和较高的n(87Sr)/n86Sr)(t)值(0.7080),εNd(t)=-19.08,εSr(t)=49.89,TDM=2.15Ga。岩石的地球化学特点反映岩体由下地壳部分熔融形成。综合分析认为,高庙石英闪长玢岩源自加厚的基性下地壳的部分熔融作用,是华北克拉通的岩石圈在早白垩世减薄和破坏作用的产物,华北克拉通早白垩世期间的岩石圈减薄和破坏作用影响到了华北克拉通中—南部一带。

Zircons from the Gaomiao quartz diorite porphyrite in Sanmenxia area are used in LA-ICP-MS U-Pb dating, yielding a weighted mean 206pb/Z3Su age of 135 Ma, which is consistent with the time of Early Cretaceous lithospheric extension and thinning of the southern margin of the North China Block. The age of inherited zircons from the Gaomiao quartz diorite porphyrite is 2768Ma. Both ages are in line with the peak time of early crustal evolution of North China Craton. The quartz diorite porphyrite contains SiO2 in the range of 62.93% - 65.54% , and A/CNK = 0. 90 - 1.03 which falls into the range of metaluminous to weakly peraluminous. It has the features of high Na （Na2O/K2O = 1.29 -1.46）, and low magnesium （Mg# = 33.5 -42. 4 〈45）, which belongs to high K ealc alkaline series. The value of REE contents of the rocks ranges from 197.09 ± 10 -6 to 234.41 × 10 -6 （ the mean value is 216 ± 10-6）, and the fractional degree of HREE and LREE is high [ （La/Yb）N = 15. 86 -20. 55 ] with no Eu anomaly （ δEu = 0. 96 - 1.02）. The rocks are enriched in LILE （Rb, Ba, Sr, K et al. ） and LREE. They are depleted in the high field strength elements Nb, Ta, Ti et al. , HREE and Y, and have a high value of Sr/Y （ Sr/ Y=41.99-56.71）. Low value of n（143Nd）/n（144Nd）（t） （0.5116） and high value of n（SVSr）/n（S6Sr）（t） （0. 7080） are also the characteristics of the Gaomiao quartz diorite porphyrite, and εNd （t） = -19. 08, εSr （t） = 49. 89, TDM =2. 15Ga. These geochemical features indicate that the Gaomiao quartz diorite porphyrite was formed by part-mehing of the lower crust. Based on the results, the Gaomiao quartz diorite porphyrite originates from the partial melting of the thickened lower crust, and is the result of lithospheric thinning and destruction of the North China Craton, such thinning and destruction happened in Early Cretaceous also affected central south part of the North China Craton.