發(fā)布時間：2018-04-17 11:25

  本文選題：華北克拉通 + 膠-遼-吉造山帶�。� 參考：《巖石學(xué)報》2017年09期

【摘要】：大規(guī)模出露于膠-遼-吉造山帶的北遼河變基性巖(NLHmetabasicrocks)是恢復(fù)造山帶構(gòu)造演化的關(guān)鍵之一,然而,研究者們對這些變基性巖的成因和構(gòu)造環(huán)境有很大爭議,制約了對膠-遼-吉造山帶早期構(gòu)造演化的深入研究�；�于詳細的野外地質(zhì)調(diào)查,本文對北遼河變基性巖進行了系統(tǒng)的巖石學(xué)研究并提供了新的全巖地球化學(xué)數(shù)據(jù),結(jié)合前人的測試結(jié)果,我們對這些變基性巖的成因和構(gòu)造環(huán)境進行了相關(guān)探討。變基性巖侵入于北遼河群的大理巖和碎屑巖中,經(jīng)歷了一定程度的蝕變以及綠片巖相-角閃巖相變質(zhì)。巖石類型包括變質(zhì)輝長巖、變質(zhì)輝綠巖、斜長角閃巖以及石榴斜長角閃巖;前兩者具有明顯的變余輝長或者輝綠結(jié)構(gòu),可見自形斜長石,少見原生礦物單斜輝石的殘留;后兩者主要由斜長石和角閃石組成,部分含有石榴子石變斑晶;此外,巖石中出現(xiàn)大量Fe-Ti氧化物(磁鐵礦和鈦鐵礦)。地球化學(xué)研究表明,北遼河變基性巖均屬于拉斑玄武巖系列(SiO_2=44.55%~54.11%,Nb/Y=0.16~0.31),以低TiO_2(0.69%~1.99%)和低MgO(多數(shù)5.47%~7.97%)為特征,輕稀土輕微富集((La/Sm)_N=1.22~2.66;(La/Yb)_N=1.66~4.56),并具有明顯的Nb、Ta、P以及輕微的Zr、Ti虧損,巖石經(jīng)歷了橄欖石、單斜輝石和斜長石等礦物的三相結(jié)晶分異以及Fe-Ti氧化物(磁鐵礦和鈦鐵礦)的堆晶;它們的微量元素配分型式類似于E-MORB和地殼巖石,并且地球化學(xué)組成與MORB相近,而不同于弧玄武巖和板內(nèi)玄武巖;這些變基性巖的Ce/Pb(3.07~26.58)、(Ta/La)PM(0.47~1.45)以及(Hf/Sm)PM(0.91~1.15)顯示出有限的俯沖相關(guān)流體的交代作用;此外,大多數(shù)不相容元素比值(例如Th/Nb、La/Nb及Th/La等)的變化趨勢則表明北遼河變基性巖的巖漿源區(qū)不可能是大陸巖石圈地幔,并且在形成過程中經(jīng)歷了明顯的地殼物質(zhì)混染�；�于這些野外地質(zhì)調(diào)查和地球化學(xué)研究,我們認為北遼河變基性巖應(yīng)形成于相對成熟的弧后盆地,這樣一個形成環(huán)境也表明膠-遼-吉造山帶在早期存在~2.1Ga的洋殼俯沖過程,該構(gòu)造帶應(yīng)該是~1.9Ga島弧與大陸碰撞形成的一條古元古代造山帶。
[Abstract]:The North Liaohe metamorphic rocks (NL Hmetababasicrocks), which emerged in large scale in the Jiao-Liaojia-Jiaoshan orogenic belt, is one of the key factors to restore the tectonic evolution of the orogenic belt. However, the origin and tectonic environment of these altered basic rocks have been greatly disputed by researchers.It restricts the deep study of the early tectonic evolution of the Jiao-Liao-Ji orogenic belt.Based on the detailed field geological survey, a systematic petrological study of the North Liaohe metamorphic rocks has been carried out in this paper, and new geochemistry data of the whole rock have been provided.The genesis and tectonic environment of these metamorphic rocks are discussed.The metamorphic rocks intruded into the marble and clastic rocks of the North Liaohe Group and underwent a certain degree of alteration and greenschist facies-amphibolite facies metamorphism.The rock types include metamorphic gabbro, metamorphic diabase, amphibolite and pomegranate amphibolite.The latter two are mainly composed of plagioclase and hornblende, some of which contain garnet changed into porphyry, in addition, a large number of Fe-Ti oxides (magnetite and ilmenite) are found in the rocks.Geochemical studies show that the northern Liaohe metamorphic rocks belong to the tholeiite series SiO44.5554.1111, characterized by low TiO20.69I 0.99I and low MgO (most 5.477.97m). LREE are slightly enriched in La / Sm / N1.22 / 2.66 / 2.664.56T, and have a significant loss of NB / Ta-P and a slight loss of Zr-Ti, and the rocks have experienced olivine loss.The three-phase crystallization differentiation of clinopyroxene and plagioclase and the stacking of Fe-Ti oxides (magnetite and ilmenite) are similar to those of E-MORB and crustal rocks, and their geochemical composition is similar to that of MORB.In contrast to arc basalt and intraplate basalt, the ce / Pb ~ (3.07) ~ (26.58 ~ (0.47) ~ 1.45) and Hf / SmPM _ (0.91) ~ 1.15) of these basaltic rocks show a limited metasomatism of subduction-related fluids.The variation trend of most incompatible element ratios (such as Th/ NB / La / NB and Th/La etc.) indicates that the magmatic source of the North Liaohe metamorphic rocks cannot be the continental lithospheric mantle and experienced obvious crustal material mixing during the formation process.Based on these field geological and geochemical studies, we believe that the basic rocks of the North Liaohe River should be formed in the relatively mature back-arc basin. Such a forming environment also indicates that there was an oceanic crust subduction process of 2.1Ga in the early stage of the Jiao-Liaoji orogenic belt.The tectonic belt should be an ancient Gu Yuan orogenic belt formed by the collision of 1.9Ga island arc with the continent.
【作者單位】： 中國地質(zhì)科學(xué)院地質(zhì)研究所;
【基金】：國家自然科學(xué)基金重點項目(41430210) 中國地質(zhì)科學(xué)院基本科研業(yè)務(wù)費專項經(jīng)費資助(YYWF201703) 中國地質(zhì)調(diào)查局地質(zhì)調(diào)查項目(DD20160121)聯(lián)合資助
【分類號】：P542;P588.124

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