本文關(guān)鍵詞：山東北巖地區(qū)地幔捕虜體地球化學(xué)特征研究　出處：《中國(guó)地質(zhì)大學(xué)(北京)》2017年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 巖石圈地幔 地幔捕虜體 Mg同位素 Hf同位素 熔/流體-巖石反應(yīng)

【摘要】：自中生代以來(lái),華北克拉通巖石圈地幔發(fā)生了顯著地減薄和再富集,巖石學(xué)和地球化學(xué)觀察表明地幔交代作用對(duì)于巖石圈地幔的再富集過(guò)程具有重要影響,但是地幔交代作用的機(jī)制包括熔流體的性質(zhì)和來(lái)源仍然未完全厘清。為更好的理解地幔捕虜體和熔流體之間的反應(yīng)過(guò)程,本論文對(duì)位于華北克拉通東部郯廬斷裂帶中段山東北巖地區(qū)的地幔捕虜體和寄主玄武巖進(jìn)行了詳細(xì)的野外調(diào)研、巖相學(xué)觀察、全巖主微量元素組成、單礦物主量元素、全巖和單斜輝石Hf、Nd、Sr同位素組成、全巖Mg同位素組成研究。并在此基礎(chǔ)上討論了地幔交代作用與Hf-Nd耦合關(guān)系的相互作用�；诘V物組成北巖地幔捕虜體分為二輝橄欖巖、富單斜輝石二輝橄欖巖、異剝橄欖巖和橄欖單斜輝石巖四種類型。其中二輝橄欖巖的主量元素組成與深海橄欖巖相似,代表新增生的年輕巖石圈地幔的殘余,且其虧損程度小于10%。含水礦物金云母、角閃石、長(zhǎng)石以及碳酸鹽礦物方解石、鐵白云石和反應(yīng)結(jié)構(gòu)的出現(xiàn)表明其后期遭受了顯性地幔交代作用改造。相比于二輝橄欖巖,富單斜輝石二輝橄欖巖全巖具有更低的Mg#值(85.0~89.6)、橄欖石具有較低的Fo值(86.5~89.4)、輕稀土富集、較高的稀土總量(∑REE=9.19~26.3 ppm)和較為富集的Sr-Nd-Hf同位素組成,而且富單斜輝石二輝橄欖巖BY13-08(δ26Mg=-0.03±0.07‰)和BY13-16(δ26Mg=-0.12±0.09‰)的Mg同位素組成顯著重于二輝橄欖巖和正常地幔值(δ26Mg=-0.25±0.07‰)。結(jié)合北巖富單斜輝石二輝橄欖巖的高Sr/Hf比值、富集Sr、虧損Zr的微量元素特征,推斷這些富單斜輝石二輝橄欖巖可能是二輝橄欖巖和流體反應(yīng)的結(jié)果,而且這一反應(yīng)流體繼承了俯沖太平洋板片的重Mg同位素特征。與富單斜輝石二輝橄欖巖相似,相比于二輝橄欖巖,北巖異剝橄欖巖全巖Mg#值(81.2~87.3)較低,橄欖石Fo值(81.1~86.2)偏低、輕稀土富集、較高的稀土總量(∑REE=9.04~16.1 ppm)和較低的Nd-Hf同位素組成。異剝橄欖巖Mg同位素組成(δ26Mg=-0.12‰~-0.43‰)變化范圍較大,樣品BY13-29和BY13-33的Mg同位素組成較正常地幔值偏高,而樣品BY13-03、BY13-30、BY13-31和BY13-32偏低,這與富單斜輝石二輝橄欖巖存在很大差異。巖相學(xué)觀察發(fā)現(xiàn)北巖異剝橄欖巖記錄了斜方輝石與低硅玄武質(zhì)熔體反應(yīng)生成單斜輝石、橄欖石和高硅熔體的反應(yīng)過(guò)程。而寄主玄武巖與中國(guó)東部新生代玄武巖一樣具有顯著輕的Mg同位素組成,且Sr-Nd-Hf同位素組成富集,所以北巖異剝橄欖巖可能是由與寄主玄武巖組分相似的具有輕Mg同位素組成的玄武質(zhì)熔體與二輝橄欖巖或富單斜輝石二輝橄欖巖反應(yīng)形成,其重Mg同位素組成來(lái)源于對(duì)富單斜輝石二輝橄欖巖重Mg同位素組成的繼承。北巖二輝橄欖巖(全巖:ΔεHf=-2.57~7.08,單斜輝石:ΔεHf=-0.72~6.69)和富單斜輝石二輝橄欖巖(全巖:ΔεHf=-1.91~2.66,單斜輝石:ΔεHf=0.47)Hf-Nd同位素組成均勻分布在地幔演化線兩側(cè),說(shuō)明具有重Mg同位素組成的流體交代并未導(dǎo)致北巖地幔捕虜體的Hf-Nd同位素發(fā)生解耦。而異剝橄欖巖(全巖:ΔεHf=-3.51~-0.90,單斜輝石:ΔεHf=-5.39~-2.22)和橄欖單斜輝石巖(全巖:ΔεHf=-2.91~-2.19,單斜輝石:ΔεHf=-4.27~-2.81)全巖和單斜輝石的Hf-Nd同位素組成均出現(xiàn)弱負(fù)解耦現(xiàn)象,這可能與具有較低Hf同位素組成的熔體交代有關(guān)。
[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.

【學(xué)位授予單位】：中國(guó)地質(zhì)大學(xué)(北京)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P542.5
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本文編號(hào)：1397285