山东北岩地区地幔捕虏体地球化学特征研究

发布时间：2018-01-08 13:23

  本文关键词：山东北岩地区地幔捕虏体地球化学特征研究　出处：《中国地质大学(北京)》2017年硕士论文　论文类型：学位论文

  更多相关文章： 岩石圈地幔 地幔捕虏体 Mg同位素 Hf同位素 熔/流体-岩石反应

【摘要】：自中生代以来,华北克拉通岩石圈地幔发生了显著地减薄和再富集,岩石学和地球化学观察表明地幔交代作用对于岩石圈地幔的再富集过程具有重要影响,但是地幔交代作用的机制包括熔流体的性质和来源仍然未完全厘清。为更好的理解地幔捕虏体和熔流体之间的反应过程,本论文对位于华北克拉通东部郯庐断裂带中段山东北岩地区的地幔捕虏体和寄主玄武岩进行了详细的野外调研、岩相学观察、全岩主微量元素组成、单矿物主量元素、全岩和单斜辉石Hf、Nd、Sr同位素组成、全岩Mg同位素组成研究。并在此基础上讨论了地幔交代作用与Hf-Nd耦合关系的相互作用。基于矿物组成北岩地幔捕虏体分为二辉橄榄岩、富单斜辉石二辉橄榄岩、异剥橄榄岩和橄榄单斜辉石岩四种类型。其中二辉橄榄岩的主量元素组成与深海橄榄岩相似,代表新增生的年轻岩石圈地幔的残余,且其亏损程度小于10%。含水矿物金云母、角闪石、长石以及碳酸盐矿物方解石、铁白云石和反应结构的出现表明其后期遭受了显性地幔交代作用改造。相比于二辉橄榄岩,富单斜辉石二辉橄榄岩全岩具有更低的Mg#值(85.0~89.6)、橄榄石具有较低的Fo值(86.5~89.4)、轻稀土富集、较高的稀土总量(∑REE=9.19~26.3 ppm)和较为富集的Sr-Nd-Hf同位素组成,而且富单斜辉石二辉橄榄岩BY13-08(δ26Mg=-0.03±0.07‰)和BY13-16(δ26Mg=-0.12±0.09‰)的Mg同位素组成显著重于二辉橄榄岩和正常地幔值(δ26Mg=-0.25±0.07‰)。结合北岩富单斜辉石二辉橄榄岩的高Sr/Hf比值、富集Sr、亏损Zr的微量元素特征,推断这些富单斜辉石二辉橄榄岩可能是二辉橄榄岩和流体反应的结果,而且这一反应流体继承了俯冲太平洋板片的重Mg同位素特征。与富单斜辉石二辉橄榄岩相似,相比于二辉橄榄岩,北岩异剥橄榄岩全岩Mg#值(81.2~87.3)较低,橄榄石Fo值(81.1~86.2)偏低、轻稀土富集、较高的稀土总量(∑REE=9.04~16.1 ppm)和较低的Nd-Hf同位素组成。异剥橄榄岩Mg同位素组成(δ26Mg=-0.12‰~-0.43‰)变化范围较大,样品BY13-29和BY13-33的Mg同位素组成较正常地幔值偏高,而样品BY13-03、BY13-30、BY13-31和BY13-32偏低,这与富单斜辉石二辉橄榄岩存在很大差异。岩相学观察发现北岩异剥橄榄岩记录了斜方辉石与低硅玄武质熔体反应生成单斜辉石、橄榄石和高硅熔体的反应过程。而寄主玄武岩与中国东部新生代玄武岩一样具有显著轻的Mg同位素组成,且Sr-Nd-Hf同位素组成富集,所以北岩异剥橄榄岩可能是由与寄主玄武岩组分相似的具有轻Mg同位素组成的玄武质熔体与二辉橄榄岩或富单斜辉石二辉橄榄岩反应形成,其重Mg同位素组成来源于对富单斜辉石二辉橄榄岩重Mg同位素组成的继承。北岩二辉橄榄岩(全岩:ΔεHf=-2.57~7.08,单斜辉石:ΔεHf=-0.72~6.69)和富单斜辉石二辉橄榄岩(全岩:ΔεHf=-1.91~2.66,单斜辉石:ΔεHf=0.47)Hf-Nd同位素组成均匀分布在地幔演化线两侧,说明具有重Mg同位素组成的流体交代并未导致北岩地幔捕虏体的Hf-Nd同位素发生解耦。而异剥橄榄岩(全岩:ΔεHf=-3.51~-0.90,单斜辉石:ΔεHf=-5.39~-2.22)和橄榄单斜辉石岩(全岩:ΔεHf=-2.91~-2.19,单斜辉石:ΔεHf=-4.27~-2.81)全岩和单斜辉石的Hf-Nd同位素组成均出现弱负解耦现象,这可能与具有较低Hf同位素组成的熔体交代有关。
[Abstract]:Since the Mesozoic lithospheric mantle in the North China Craton occurred significantly thinning and re enrichment, petrological and geochemical observations show that mantle metasomatism has an important influence on the lithospheric mantle and the enrichment process, but the mechanism of mantle metasomatism including the nature and origin of the melt fluid is still not entirely clear. The reaction process between enclaves and capture melting fluid for a better understanding of the mantle in the North China Craton with northern rock area through the middle part of Shandong east of the Tanlu fault mantle xenoliths and host Xuan Wuyan conducted a detailed field investigation, petrography, whole rock major and trace element compositions of single minerals, major elements, whole rock and clinopyroxene Hf Nd, Sr isotope, Mg isotope compositions of the whole rock. The research is discussed based on the interaction between mantle metasomatism and Hf-Nd coupling. Based on northern rock mineral composition Mantle xenoliths are divided into two pyroxene peridotite, rich clinopyroxene two pyroxene peridotite, wehrlite and clinopyroxenite olive four types. The main elements of two peridotite composition and peridotites are similar, the residual represents the new proliferation of young lithospheric mantle, and the loss rate of less than 10%. hydrous mineral phlogopite amphibole and feldspar and carbonate mineral of calcite, dolomite and iron reaction structure showed that the later suffered the dominant mantle metasomatism transformation. Compared to lherzolite, two rich clinopyroxene peridotite rock has low Mg# value (85.0~89.6), olivine has low Fo value (86.5~89.4), LREE enrichment, high total rare earths (sigma REE=9.19~26.3 ppm) and Sr-Nd-Hf isotopes are enriched, and rich clinopyroxene peridotite (two BY13-08 26Mg=-0.03 + 0.07 BY13-16 (8%) and 26Mg=-0.12 + 0 .09%) significantly heavier than the composition of lherzolite mantle and normal values of Mg isotope (delta 26Mg=-0.25 + 0.07%). High Sr/Hf ratio, combined with the two Northern Rock rich clinopyroxene peridotite enrichment characteristics of trace elements Sr, Zr loss, infer that these rich clinopyroxene two peridotite may be two lherzolite the rock and fluid in the reaction, and the reaction fluid inherited the heavy Mg isotope characteristics of the subduction of the Pacific plate. With rich clinopyroxene peridotite similar to two, compared to the lherzolite and wehrlite Northern Rock Rock Mg# value (81.2~87.3) is low, olivine Fo value (81.1~86.2). The total amount of rare earth, LREE enrichment, high (sigma REE=9.04~16.1 ppm) and Nd-Hf isotope lower. Wehrlite Mg isotopic composition (delta 26Mg=-0.12% ~-0.43%) of larger changes, the sample BY13-29 and BY13-33 Mg isotopic compositions of mantle value higher than normal, The sample BY13-03, BY13-30, BY13-31 and BY13-32 is low, and the two rich clinopyroxene peridotite have great differences. The petrographic observation found that Northern Rock wehrlite recorded orthopyroxene and low silicon basaltic melt reaction of clinopyroxene, olivine and high reaction process of silicon melt and host basalt like. China Cenozoic basalts from Eastern has significant Mg isotope composition of light, and Sr-Nd-Hf isotopic enrichment, so the Northern Rock wehrlite may be formed from a basaltic melt light Mg isotopic compositions of peridotite and two or two rich clinopyroxene peridotite reaction and host basalt components similar to that of its weight Mg isotopic composition from the inheritance of two rich clinopyroxene peridotite heavy Mg isotope composition. Two Northern Rock peridotite (Quan Yan: Delta epsilon Hf=-2.57~7.08, clinopyroxene: Delta epsilon Hf=-0.72~6.69) and monoclinic rich Two pyroxene peridotite (Quan Yan: Delta epsilon Hf=-1.91~2.66, clinopyroxene: Delta epsilon Hf=0.47) composition evenly distributed on both sides of the line in the evolution of mantle fluid metasomatism shows Hf-Nd isotope, Mg isotope composition did not cause the heavy Hf-Nd isotope of Northern Rock mantle xenoliths occur decoupling. And wehrlite (Quan Yan: Delta epsilon Hf=-3.51~-0.90 clinopyroxene, delta epsilon: Hf=-5.39~-2.22) and olive clinopyroxenite (Quan Yan: Delta epsilon Hf=-2.91~-2.19, clinopyroxene: Delta epsilon Hf=-4.27~-2.81) whole rock Hf-Nd isotopic composition of clinopyroxene and showed weak negative decoupling phenomenon, which may be related with low melt metasomatism of Hf isotope compositions.

【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P542.5
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本文编号：1397285