本文選題：地球化學(xué) + 巖石成因　； 參考：《地學(xué)前緣》2017年06期

【摘要】：松潘—甘孜造山帶南緣的二疊系之中發(fā)育一套順層產(chǎn)出的變玄武巖,巖石具有明顯的變余枕狀構(gòu)造及氣孔構(gòu)造。本文對其進行了主微量元素分析,并探討其巖石成因與成巖構(gòu)造背景。變玄武巖具有低的SiO_2質(zhì)量分數(shù)(47.56%~37.98%)與Nb/Zr值,其MgO(平均為18.95%)、Mg#值(平均為74.1)和Cr(平均為1 712×10~(-6))含量較高,表明原巖巖漿很可能起源于虧損地幔,主要由石榴石橄欖巖發(fā)生20%~25%的部分熔融形成。巖石MgO與Cr含量呈現(xiàn)良好的正相關(guān),具有極低的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,說明巖漿演化過程中發(fā)生了含鉻礦物的分離結(jié)晶,且沒有遭受地殼物質(zhì)的混染。變玄武巖稀土、微量配分型式及構(gòu)造背景判別顯示,巖石的化學(xué)成分與E-MORB及N-MORB相當。野外考察顯示,與變玄武巖共生的巖石主要為二疊系大理巖,暗示變玄武巖原巖很可能形成于成熟的弧后盆地環(huán)境。結(jié)合二疊系還發(fā)育超基性巖的事實,本文認為該套變玄武巖可能是古特提斯洋的洋殼殘余。另外成分對比顯示,松潘—甘孜造山帶南緣的二疊系變玄武巖并非峨眉山玄武巖漿活動的產(chǎn)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.
【作者單位】： 西南石油大學(xué)地球科學(xué)與技術(shù)學(xué)院;中國地質(zhì)調(diào)查局成都地質(zhì)調(diào)查中心;中國地質(zhì)大學(xué)(北京)地質(zhì)過程與礦產(chǎn)資源國家重點實驗室;河北省區(qū)域地質(zhì)礦產(chǎn)調(diào)查研究所;
【基金】：西南石油大學(xué)青年教師“過學(xué)術(shù)關(guān)”項目(201499010083) 科研啟航計劃項目(2015QHZ009) 四川省教育廳科研項目(15ZB0058) 成都地質(zhì)調(diào)查中心青年科學(xué)基金項目(所控基[2015]-05)
【分類號】：P534.46;P588.145
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本文編號：2022704