松潘—甘孜造山带南缘二叠系变质玄武岩的成因与构造意义

发布时间：2018-06-15 16:39

  本文选题：地球化学 + 岩石成因　； 参考：《地学前缘》2017年06期

【摘要】：松潘—甘孜造山带南缘的二叠系之中发育一套顺层产出的变玄武岩,岩石具有明显的变余枕状构造及气孔构造。本文对其进行了主微量元素分析,并探讨其岩石成因与成岩构造背景。变玄武岩具有低的SiO_2质量分数(47.56%~37.98%)与Nb/Zr值,其MgO(平均为18.95%)、Mg#值(平均为74.1)和Cr(平均为1 712×10~(-6))含量较高,表明原岩岩浆很可能起源于亏损地幔,主要由石榴石橄榄岩发生20%~25%的部分熔融形成。岩石MgO与Cr含量呈现良好的正相关,具有极低的La/Sm(2.86~1.02)、(Th/Yb)PM(2.42~0.56)、(Th/Ta)PM(1.21~0.43)和(La/Nb)PM(1.55~0.27)比值,说明岩浆演化过程中发生了含铬矿物的分离结晶,且没有遭受地壳物质的混染。变玄武岩稀土、微量配分型式及构造背景判别显示,岩石的化学成分与E-MORB及N-MORB相当。野外考察显示,与变玄武岩共生的岩石主要为二叠系大理岩,暗示变玄武岩原岩很可能形成于成熟的弧后盆地环境。结合二叠系还发育超基性岩的事实,本文认为该套变玄武岩可能是古特提斯洋的洋壳残余。另外成分对比显示,松潘—甘孜造山带南缘的二叠系变玄武岩并非峨眉山玄武岩浆活动的产物。
[Abstract]:In the Permian system of the southern margin of the Songpan-Ganzi orogenic belt, a set of bedding metabalts are developed. The rocks are characterized by variable occipital structure and stomatal structure. In this paper, the principal and trace elements are analyzed, and its petrogenesis and diagenetic tectonic background are discussed. The metamorphic basalts have high contents of MgO (an average of 18.95) and Cr (an average of 1,712 脳 10 ~ (-1) and Cr (an average of 1,712 脳 10 ~ (10) ~ (-6), which indicate that the magma may have originated from the depleted mantle. Mainly from garnet peridotite, 20% or 25% of partial melting. There is a good positive correlation between MgO and Cr content in rocks, with extremely low ratios of La / Sm ~ (2.86) ~ (1. 02) O ~ (2 +) ~ (2. 46) ~ (0.56) ~ (0.56) and La / N ~ (B) PMN ~ (1.55) ~ (0.27), which indicate that the chromium-bearing minerals have been separated and crystallized during the evolution of magma and have not been contaminated by crustal materials. Rare earth elements in metabalts, trace distribution patterns and tectonic background discrimination show that the chemical composition of the rocks is equivalent to that of E-MORB and N-MORB. Field investigation shows that the rocks symbiotic with metabalts are mainly Permian marble suggesting that the metabalts may have been formed in the mature back-arc basin environment. Combined with the fact that ultrabasic rocks were also developed in the Permian, it is suggested that this suite of metabalts may be a remnant of the oceanic crust of the PaleoTethys ocean. In addition, the composition comparison shows that the Permian metabalts in the southern margin of the Songpan-Ganzi orogenic belt are not the product of Black Tortoise magmatic activity in Emei Mountain.
【作者单位】： 西南石油大学地球科学与技术学院;中国地质调查局成都地质调查中心;中国地质大学(北京)地质过程与矿产资源国家重点实验室;河北省区域地质矿产调查研究所;
【基金】：西南石油大学青年教师“过学术关”项目(201499010083) 科研启航计划项目(2015QHZ009) 四川省教育厅科研项目(15ZB0058) 成都地质调查中心青年科学基金项目(所控基[2015]-05)
【分类号】：P534.46;P588.145
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本文编号：2022704