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为研究东乌旗晚古生代地幔性质和造山演化特征,对在东乌旗西部首次发现的超镁铁岩—辉闪橄榄岩进行系统的岩相学和元素地球化学研究。东乌旗辉闪橄榄岩主要由橄榄石、角闪石、斜方辉石及少量斜长石、单斜辉石组成,SiO_2含量介于42.84%~43.96%、MgO(24.10%~26.10%)、Na_2O+K_2O(1.52%~2.32%,小于3.5%),低m/f(3.03~3.54)比值和高FeO~T(12.67%~14.33%)的含量、高Mg~#(76.42~79.20),属铁质超镁铁岩和拉斑玄武岩系列。岩石稀土总量较高(∑REE=39.57×10~(-6)~83.32×10~(-6)),轻稀土(LREE)相对于重稀土(HREE)明显富集[(La/Yb)_N=4.04~7.66],Eu异常不明显(δEu=0.90~0.95),稀土元素球粒陨石标准化配分模式表现为轻稀土相对富集的右倾型。岩石富集大离子亲石元素(LILE)Cs、Rb、Ba、Sr、K等,相对亏损高场强元素(HFSE)Nb、Ta,具明显的Nb、Ta、Ti负异常,而又有别于强烈Nb、Ta亏损的岛弧岩浆岩;相容元素Cr(769×10~(-6)~2480×10~(-6))、Ni(454×10~(-6)~901×10~(-6))含量较高;低Th/U(2.54~3.03)、Nb/U(3.40~12.85)比值和高La/Nb(2.60~3.63)、Ba/Nb(43.11~72.52)、Zr/Y(5.45~7.83)比值。综上,结合区域最新研究成果,我们认为辉闪橄榄岩来源于受俯冲流体交代的尖晶石相地幔橄榄岩部分熔融,上升过程中受地壳物质不同程度的混染,形成于早二叠世板内伸展构造体制,与古亚洲洋闭合之后板内非造山作用有关。这一认识填补了早二叠世幔源岩浆事件和非造山阶段超镁铁质岩石记录的空白。
In order to study the characteristics of the Late Paleozoic mantle and the orogenic evolution in the Dongwuqi, systematic petrography and elemental geochemistry of the ultramafic-diterite peridotites first discovered in the west of Dongwuqi were studied. The dolomite of Dongwu County consists mainly of olivine, amphibole, orthopyroxene and a small amount of plagioclase and clinopyroxene with SiO 2 content ranging from 42.84% to 43.96% and MgO (24.10% -26.10%), (1.52% ~ 2.32%, less than 3.5%), low m / f (3.03 ~ 3.54) and high FeO ~ T content of 12.67% ~ 14.33% , Is a ferrous ultramafic and tholei basalt series. (LREE) is obviously enriched [(La / Yb)) relative to heavy rare earth elements (HREE) due to the high content of rare earth elements (ΣREE = 39.57 × 10-6 ~ 83.32 × 10-6) _N = 4.04 ~ 7.66]. The Eu anomalies are not obvious (δEu = 0.90 ~ 0.95). The normalized distribution patterns of REE chondrites are characterized by the relative enrichment of LREE. The rocks are enriched in LILEs such as Cs, Rb, Ba, Sr, K and so on. Relatively depleted HFSE Nb and Ta have significant Nb, Ta and Ti negative anomalies, In the arc magmatic rocks with strong depletion of Nb and Ta, the contents of Cr (769 × 10 -6 ~ 2480 × 10 -6), Ni (454 × 10 -6 ~ 901 × 10 6) (2.5 ~ 3.03), Nb / U (3.40 ~ 12.85), high La / Nb (2.60 ~ 3.63), Ba / Nb / Y (5.45 ~ 7.83) ratio. In summary, based on the latest research results in the region, we believe that diorite peridotites originated from the partial melting of the spinel-derived mantle peridotites that were subducted by subduction fluids and mixed up to varying degrees during the uplifting process and formed in the Early Permian Plate extensional structure system, and the closure of the ancient Asian continent non-orogenic role. This understanding fills the gaps recorded in the Early Permian mafic magmatic events and ultra-mafic rocks in the non-orogenic stages.