甘肃省明水地区石英闪长岩年代学、地球化学特征及其地质意义  

STUDY OF GEOCHRONOLOGY,GEOCHEMICAL CHARACTERISTICS AND GEOLOGICAL IMPLICATION OF QUARTZ DIORITE IN MINGSHUI AREA,BEISHAN,GANSU PROVINCE

作　　者：唐文轶 徐磊 费光春[1] 刘胜江 杨鱼帆 赵建国[2] 张为 TANG Wenyi;XU Lei;FEI Guangchun;LIU Shengjiang;YANG Yufan;ZHAO Jianguo;ZHANG Wei(College of Earth Science,Chengdu University of Technology,Chengdu,Sichuan 610059,China;Gansu Provincial Geological Survey Institute,Lanzhou,Gansu 730000,China)

机构地区：[1]成都理工大学地球与行星科学学院,四川成都610059 [2]甘肃省地质调查院,甘肃兰州730000

出　　处：《矿物岩石》2024年第2期30-46,共17页Mineralogy and Petrology

基　　金：自然科学基金(项目批准号:41702074);自然资源部地调项目(编号:DD20190065);成都理工大学课程教学改革项目(编号:202367)。

摘　　要：为揭示甘肃省北山明水地区石英闪长岩和似斑状石英闪长岩的成岩时代、成因和地质意义,本研究对该套岩石进行了全岩地球化学、岩石学、LA-ICP-MS锆石U-Pb年代学和Lu-Hf同位素分析。研究结果表明,该套岩石属准铝质高钾钙碱性I一型花岗岩。该套岩石总体硅含量较高ω(SiO_(2))56.88%~67.78%,富铝ω(Al_(2)O_(3))14.26%~18.15%,全碱含量中等ω(K_(2)O+Na_(2)O)4.97%~6.80%,K_(2)O/Na_(2)O的变化范围为0.78~1.46,以及具有弱过铝质的特征(A/CNK=0.90~1.03)。微量元素中,Nb,Ta,Ti,等高场强元素明显亏损,Rb,Th,K等大离子亲石元素则较富集,与典型火山弧岩浆岩的地球化学特征相似。稀土元素球粒陨石标准化曲线均呈不对称的右倾特征,轻重稀土分馏较强(LREE/HREE=8.59~23.41)和较弱的负Eu异常(δEu=0.74~0.96)。明水石英闪长岩的LA-ICP-MS锆石U-Pb年龄为晚石炭世中期(311.80±1.51Ma)。另外,石英闪长岩具有正εHf(t)(2.08~4.48),相对较小的Hf模式年龄(TDM的变化范围为746~863Ma),表明岩浆应源自幔源岩浆底侵而导致的上覆年轻地壳的部分熔融。综合研究和分析表明,明水石英闪长岩和似斑状石英闪长岩形成于海西中期俯冲作用下的大陆边缘弧,应为红石山洋向南侧俯冲背景下的直接产物。In this paper,we investigate the whole rock geochemistry,petrology,zircon U-Pb geochro-nology and Lu-Hf isotope analysis,to understand the rock formation age,genesis and geological implica-tion of quartz diorite and porphyritic quartz diorite in Mingshui area,Beishan,Gansu Province.The re-sults indicate that these rocks are quasi-aluminous,high-potassium,calc-alkaline I-type granites with high silica content(ω(SiO_(2))=56.88%-67.78%)and are rich in aluminum(ω(Al_(2)O_(3))14.26%~18.15%).The total alkali content is moderate(ω(K_(2)O+Na_(2)O)4.97%~6.80%),and the K_(2)0/Na_(2)0 ratio ran-ges from 0.78 to 1.46,which is characteristic of weakly peraluminous rocks(A/CNK=0.90-1.03).In terms of trace elements,the rocks show significant depletion in high field strength elements such as Nb,Ta,and Ti,while they are enriched in large ion lithophile elements such as Rb,Th,and K,resembling the geochemical characteristics of typical volcanic arc magmatic rocks.The chondrite-normalized rare earth element(REE)curves are asymmetrical and right-leaning,showing strong fractionation(LREE/HREE=8.59-23.41)and a weak negative Eu anomaly(δEu=0.74-0.96).LA-ICP-MS zircon U-Pb dating of the Mingshui quartz diorite indicates a Middle-Late Carboniferous age of 311.8±1.51 Ma.Additionally,the quartz diorite has a positive εHf(t)value(2.08-4.48)and a relatively young Hf model age(TDM=746-863 Ma),suggesting that the magma originated from the partial melting of the overlying young crust due to mantle magma infiltration.Our comprehensive analysis concludes that the Mingshui quartz diorite and porphyritic quartz diorite formed in a continental marginal arc environment during the subduction of the middle Hercynian period,as direct products of the southward subduction of the Hongshishan ocean.

关 键 词：石英闪长岩 锆石U-PB年代学 地球化学 地质意义 北山 

分 类 号：P581[天文地球—岩石学] P597.3[天文地球—地质学]