苏鲁超高压变质带北缘古-新元古代浅变质基性岩的构造属性及其意义  

The tectonic affinity of the Meso-Neoproterozoic low-grade metamorphic mafic rocks in the northern margin of the Sulu UHP metamorphic belt and its tectonic significance

作　　者：宋明春 周建波[3] 林少一 李杰 李世勇 宋英昕 王斌 刘鹏瑞 SONG MingChun;ZHOU JianBo;LIN ShaoYi;LI Jie;LI ShiYong;SONG YingXin;WANG Bin;LIU PengRui(Shandong Provincial No.6 Exploration Institute of Geology and Mineral Resources,Weihai 264209,China;Key Laboratory of Gold Mineralization Processes and Resources Utilization Subordinated to the Ministry of Nature and Resources,Jinan 250013,China;College of Earth Sciences,Jilin University,Changchun 130061,China;College of Resources,Hebei GEO University,Shijiazhuang 050031,China;Shandong Institute of Geophysical and Geochemical Exploration,Jinan 250013,China;Institute of Geological Sciences of Shandong Province,Jinan 250013,China)

机构地区：[1]山东省地质矿产勘查开发局第六地质大队,威海264209 [2]自然资源部金矿成矿过程与资源利用重点实验室,济南250013 [3]吉林大学地球科学学院,长春130061 [4]河北地质大学资源学院,石家庄050031 [5]山东省物化探勘查院,济南250013 [6]山东省地质科学研究院,济南250013

出　　处：《岩石学报》2020年第2期315-332,共18页Acta Petrologica Sinica

基　　金：山东省重点研发计划(2017CXGC1604);山东省泰山学者建设工程专项经费(ts201511076)联合资助

摘　　要：苏鲁超高压变质带北缘发育的少量以浅变质基性杂岩为代表的非超高压变质岩片,为深入探讨造山带的大陆深俯冲作用及板块缝合线位置提供了重要的制约。1∶5万区域填图表明,浅变质基性杂岩分布于从家屯、胡家和海眼口等地,它们以石门-薛家庄韧性剪切带与超高压变质带分界。同位素测年结果指示,胡家斜长角闪岩时代为古元古代末(1790±27Ma、1853±15Ma),而从家屯斜长角闪岩时代为新元古代(797±11Ma、782±16Ma)。地球化学分析表明,从家屯和胡家斜长角闪岩的SiO2、TiO2、Fe2OT 3和MgO含量分别为47.20%~52.60%、0.98%~3.30%、9.31%~16.78%和3.76%~7.13%,为拉斑玄武岩成分。岩石的稀土总量介于45.8×10^-6~289.0×10^-6之间,LREE/HREE=1.29~11.6,(La/Yb)N=0.45~17.3,稀土配分曲线较平坦,无铕异常(δEu=0.75~1.37)。微量元素相对富集Ba、Rb和Sr,亏损Zr、Hf、Th和Nb。从家屯斜长角闪岩的地球化学特征与E型洋中脊玄武岩相似,而胡家斜长角闪岩则具有洋岛玄武岩特点。综合分析认为,从家屯和胡家斜长角闪岩分别与扬子板块和华北板块具有构造亲缘性,在三叠纪扬子板块向华北板块俯冲碰撞过程中,这些不同大地构造位置和性质的基性岩被刮削叠置于板块缝合线附近,构成了大陆板块俯冲的加积杂岩。同时认为,分布在超高压变质带与非超高压变质岩片之间的石门-薛家庄韧性剪切带为一条重要的板块缝合线。The non-UHP tectonic slices,epically the low-grade metamorphic mafic rocks,located in the northern margin of Sulu ultra-high-pressure(UHP)metamorphic belt,are the key issue to understanding the continental deep subduction and the location of subduction suture in the Sulu area.According to the 1∶50000 regional geologic mapping,the low-grade metamorphic mafic rocks crop out in Congjiatun,Hujia and Haiyankou area.They are separated from the Sulu UHP belt by the Shimen-Xuejiazhuang ductile shear zone.LA-ICPMS U-Pb zircon dating indicates that weighted mean ages of the amphibolites from Hujia and Congjiatun are in the end of Paleoproterozoic(1790±27Ma,1853±15Ma)and Neoproterozoic(797±11Ma,782±16Ma),respectively.The geochemical data show that the contents of SiO2,TiO2,Fe2OT 3 and MgO of Hujia and Congjiatun low-grade metamorphic mafic rocks are 47.20%~52.60%,0.98%~3.30%,9.31%~16.78%and 3.76%~7.13%respectively,which are components of tholeiite.The total amount of REE is from 45.8×10^-6 to 289.0×10^-6,LREE/HREE=1.29~11.6,(La/Yb)N=0.45~17.3.The REE distribution pattern is relatively flat,and shows none-Eu anomaly(δEu=0.75~1.37).Trace element Ba,Rb and Sr are comparatively enriched,and Zr,Hf,Th and Nb are depleted.The geochemical characteristics of the Congjiatun amphibolites were similar to those of the E-MORB affinity,and the Hujia amphibolites is characterized by OIB affinity.The new evidence from this study,suggests that Congjiatun and Hujia amphibolites have the tectonic affinity with the Yangtze Plate and North China Plate respectively.These mafic rocks located on a different tectonic location were formed as accretionary complexes when the Yangtze Plate subduction-collision during the Triassic.Therefore,we suggest that Shimen-Xuejiazhuang ductile shear zone is the suture zone between the North China and Yangtze plates and not the Wulian-Rongcheng fault as previously suggested.

关 键 词：浅变质基性杂岩 斜长角闪岩 拉斑玄武岩 苏鲁超高压变质带 锆石U-Pb年龄 俯冲加积杂岩 

分 类 号：P588.145[天文地球—岩石学] P597.3[天文地球—地质学]