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作为岩石圈伸展拉张背景侵位的特征岩石,基性岩墙群(煌斑岩、辉绿岩和辉绿玢岩等)地质和地球化学研究日益受到地质研究者的关注。研究显示,基性岩墙在全球范围主要分布在美国、加拿大、巴西、澳大利亚和中国等地区,且年代格架主要集中在前寒武纪时期(2.4Ga、2.1Ga、1.8Ga、1.4Ga、1.0Ga)。目前,国内中生代以来基性岩墙群主要出露于华北克拉通、华南、西藏和塔里木盆地。本研究基性岩墙来自山西省大同附近,对于该套岩墙,本文给出了锆石U-Pb定年、地球化学和Sr-Nd同位素证据。LA-ICP-MS锆石U-Pb年龄为293Ma,岩石具有变化较小的主元素变化特征(SiO2=50.78%~51.35%,TiO2=2.16%~2.32%,Al2O3=14.53%~15.08%,Fe2O3=12.42%~12.66%,MnO=0.13%~0.16%,MgO=5.14%~5.35%,CaO=7.93%~8.25%,Na2O=3.52%~3.78%,K2O=1.01%~1.14%和P2O5=0.24%~0.36%)。另外,基性岩墙富集轻稀土元素、大离子侵石元素(Ba,K和Sr)和高场强元素(Nb,Ta和Zr),亏损Th、Pb和Ti。同时,基性岩墙具有相对一致的(87Sr/86Sr)i比值(0.70422~0.70423),正的εNd(t)值(5.8~6.1)和变化较小的Nd模式年龄(tDM1=0.67~0.72Ga,tDM2=0.57~0.59Ga)。以上特征表明,基性岩墙来自亏损软流圈地幔的分布熔融作用,岩浆侵位过程中发生了橄榄石、辉石和含Ti相矿物的分离结晶作用,但没有受到地壳物质的混染作用影响。基性岩墙的成因上与华北克拉通和西伯利亚板块碰撞后的拉伸作用有密切联系。
Geology and geochemistry of the basic dyke swarms (lamprophyres, diabase and diabase plutons, etc.) are increasingly attracting the attention of geologists as the characteristic rocks stretching out of the lithosphere. The study shows that the basic dykes are mainly distributed in the United States, Canada, Brazil, Australia, China and other regions around the world, and the chronological framework is mainly concentrated in the Precambrian period (2.4Ga, 2.1Ga, 1.8Ga, 1.4Ga, 1.0Ga). At present, the basic dyke swarms mainly exposed in North China Craton, South China, Tibet and Tarim Basin since the Mesozoic. The basic dyke wall in this study comes from Datong, Shanxi Province. For the dyke wall, the zircon U-Pb dating, geochemistry and Sr-Nd isotopic evidence are given. The LA-ICP-MS zircon U-Pb age is 293 Ma, and the rocks have small variation of main elements (SiO2 = 50.78% ~ 51.35%, TiO2 = 2.16% ~ 2.32%, Al2O3 = 14.53% ~ 15.08%, Fe2O3 = 12.42% to 12.66%, MnO = 0.13% to 0.16%, MgO = 5.14% to 5.35%, CaO = 7.93% to 8.25%, Na2O = 3.52% to 3.78%, K2O = 1.01% to 1.14% and P2O5 = % ~ 0.36%). In addition, the basic dykes are enriched in LREE, large ion-intrusion elements (Ba, K and Sr) and high-field elements (Nb, Ta and Zr), depleting Th, Pb and Ti. At the same time, the basic dykes have a relatively uniform (87Sr / 86Sr) i ratio (0.70422-0.70423), a positive εNd (t) value of 5.8-6.1, and a slightly changed Nd mode age (tDM1 = 0.67-0.72Ga , tDM2 = 0.57-0.59Ga). The above characteristics show that the basic dykes are derived from the melt distribution of the depleted asthenosphere mantle, and the crystallization of olivine, pyroxene and Ti-bearing minerals during the magmatic emplacement has not been affected by the contamination of the crustal material . The genesis of the basic dyke is closely related to the stretching effect after the collision between the North China Craton and the Siberian plate.