鞍山—本溪地区太古宙绿岩带的形成及演化

发布时间：2018-06-28 01:35

  本文选题：华北克拉通东北缘 + 新太古代　； 参考：《吉林大学》2016年博士论文

【摘要】：鞍山-本溪地区位于华北克拉通东北缘,区内保留了3.8Ga~2.5Ga的地质记录,是研究华北克拉通太古宙演化的理想区域。本文通过对鞍本地区太古宙变质表壳岩的年代学、岩相学、岩石地球化学、构造等进行研究,再结合前人的一些研究成果,以探讨鞍本地区绿岩带的形成与演化。鞍本地区的变质表壳岩主要由鞍山群组成,包括茨沟岩组、大峪沟岩组和樱桃园岩组。来自于茨沟岩组斜长角闪岩的岩浆锆石测年结果为2571±5.3Ma,与前人的测年结果基本一致,表明变质表壳岩的成岩时代为新太古代晚期。鞍本地区变质表壳岩的岩层层序相似:都是底部以变质基性岩为主,局部含有少量变质沉积岩;中部为条带状铁建造,夹有少量变质基性岩;顶部以变质火山岩碎屑岩、沉积岩为主。只是不同区域的绿岩带中变质基性火山岩与变质沉积岩所占比例不一样。鞍本地区绿岩带中的变质基性岩具有平坦(TH1型)或轻微右倾(TH2型)的稀土配分模式曲线,在微量元素蛛网图上,TH2型表现为较弱的Nb、Ti亏损,而TH1型则无Nb、Ti亏损。TH2型地球化学特征类似岛弧拉斑玄武岩(IAT),TH1型与洋中脊玄武岩(MORB)相似。岛弧拉斑玄武岩(IAT)和洋中脊玄武岩(MORB)的岩石组合、分布规律以及构造环境判别图解的投图结果表明鞍本地区的变质表壳岩形成于弧后盆地环境。离陆壳或火山弧较远的区域形成了以变质中基性岩为主的岩石组合(茨沟岩组、大峪沟岩组),离陆壳或火山弧较近的区域形成以变质沉积岩为主的岩石组合(樱桃园岩组)。统计华北克拉通上各地区的花岗-绿岩带的分布规律和岩石组合,然后根据以下几点对这些花岗-绿岩带进行分带:(1)是否存在老于2.55Ga的花岗质岩石;(2)绿岩带中变质中基性岩属于CAB、IAT还是MORB;(3)是否有高镁安山岩存在;(4)2.55Ga之后的新太古代花岗岩类是TTG还是钾质花岗岩;(5)变质沉积岩的碎屑物主要来源于火山弧还是由火山弧和陆壳共同提供。最终将华北克拉通东部的绿岩带划分为三个带:西部的岛弧带(辽北-辽西-冀东-五台一带,可能延伸至登封一带);中部微陆块带(以迁怀陆块和胶辽陆块为主);东部弧后盆地-陆缘带(吉南-鞍本-胶东-鲁西-舞阳-鲁山一带)。2.60Ga~2.53Ga,东部陆块西侧的洋壳向东俯冲,在东部陆块的西部边缘形成了岛弧和弧后盆地,在岛弧区形成了钙碱性玄武岩(CAB)、岛弧拉斑玄武岩(IAT)、安山岩(以高镁安山岩为典型代表)、TTG的岩石组合,而在弧后盆地之中,则主要是洋中脊玄武岩(MORB)和岛弧拉斑玄武岩(IAT)的组合,且离弧后盆地扩展中心越近,岩石地球化学特征越接近洋中脊玄武岩(MORB)。弧后盆地-陆缘(本文中的大陆边缘仅指陆块边缘,不包含弧后盆地、以及从大陆分离出去的陆缘弧)带中存在大量老于2.55Ga的花岗岩类,可能是形成弧后盆地过程中从大陆边缘拖拽出来的陆壳碎块。弧后盆地在~2.53Ga开始闭合,弧后盆地中的洋壳开始向陆壳俯冲,同时大陆边缘形成CAB、TTG和钾质花岗岩的岩性组合。2.52~2.47Ga为碰撞阶段,残留的洋壳受到挤压变形,形成一系列NW-SE向的褶皱、韧性剪切带和脆性断裂,奠定了鞍本地区绿岩带的基本构造格局。洋壳变形的同时并受到低角闪岩相-绿片岩相区域变质作用改造。第二次改造作用发生于~1.80Ga,主要受到辽吉裂谷闭合和后造山运动的影响,早期的断裂重新活化。富Mg热液沿这些断裂运移,对绿岩带中的条带状磁铁石英岩及其围岩进行改造,使磁铁石英岩发生富集,并形成了一系列的蚀变岩。
[Abstract]:The Anshan Benxi area is located on the northeastern margin of the North China Craton. The geological record of the 3.8Ga~2.5Ga is retained in the area. It is an ideal area for the study of the Archean evolution of the North China Craton. This paper has studied the chronology, petrography, petrochemistry and construction of the Archean metamorphic crust rocks in the sellar area, and then combined with some previous research results. The formation and evolution of the greenstone belt in the sellan area are discussed. The metamorphic surface rocks in the sellan area are mainly composed of Anshan groups, including the zigigite group, the dagugou rock group and the Cherry Orchard Group. The result of the magmatic zircon dating from the diagonal amphibolite from the yuziguiganyan group is 2571 + 5.3Ma, which is basically consistent with the previous survey results, indicating the formation of metamorphic case rocks. The rock age is late Neoarchean. The strata sequence of metamorphic topical rocks in the Sanben area is similar: the base is mainly metamorphic base rock with a small amount of metamorphic sedimentary rocks, the middle part is constructed with strip iron, with a small amount of metamorphic base rock, and the top is metamorphic volcanic clastic rock and sedimentary rock. The proportion of the sexual volcanic rocks is different from that of metamorphic sedimentary rocks. The metamorphic base rocks in the greenstone belt in the sellar area have a flat (TH1) or a slight right (TH2) rare-earth distribution pattern curve. On the trace element cobweb map, the TH2 type shows weak Nb, Ti loss, and TH1 type no Nb, Ti loss.TH2 type geochemical characteristics resembling island arc spots. Xuan Wuyan (IAT), TH1 type is similar to the mid ocean ridge Xuan Wuyan (MORB). The rock assemblage of the island arc pullout Xuan Wuyan (IAT) and the mid ocean ridge Xuan Wuyan (MORB), the distribution pattern and the mapping results of the tectonic setting diagram show that the metamorphic crust in the saddle area is formed in the back arc basin environment. The far areas from the continental crust or volcanic arc formed to metamorphism. The rock assemblage of the middle base rock (ditgou rock group, daku Gou rock group), the rock assemblage of metamorphic sedimentary rocks (Cherry Orchard Group) in the area near the continental crust or volcanic arc. The distribution law of granite greenstone belt in the North China Craton and the rock assemblage of the granite greenstone belt in the North China Craton are counted, and then the granite greenstone is brought into the following several points. Line Zoning: (1) whether there are granitic rocks old in 2.55Ga; (2) the metamorphic base rocks in the greenstone belt belong to CAB, IAT or MORB; (3) there are high magnesium andesite; (4) the Neoarchean granitoids after 2.55Ga are TTG or potassic granites; (5) the detritus of the metamorphic sedimentary rocks is mainly derived from the volcanic arc or the volcanic arc and the continental crust. In the end, the greenstone belt in the eastern North China Craton is divided into three zones: the western island arc belt (Liaodong - Liaoxi - Jidong - five area, possibly extending to Dengfeng), and the central micro - continental block (mainly migrating continental block and gelatin land block), and the eastern arc basin - the marginal zone (Zilin - Jiaodong Luxi Wuyang - Lushan Mountain Lushan Mountain) .53Ga, the oceanic crust on the west side of the eastern continent subducts eastward, forming island arcs and back arc basins on the western edge of the eastern continental block. In the island arc, the calc basalt (CAB), island arc tholeiite (IAT), andesite (typical of high magnesium andesite) and TTG rock assemblage, and in the back arc basin, are mainly the middle ocean ridge basalt ( MORB) and the combination of island arc pulping basalt (IAT), and the closer to the extension center of the post arc basin, the more close to the oceanic ridge basalt (MORB). The back arc basin - the continental margin (the continental margin in this article only refers to the continental margin, does not contain the back arc basin, and the continental margin arc separated from the continent) is a large number of old 2.55Ga The granitoids may be the continental crust fragments which were dragged from the continental margin in the process of the back arc basin. The back arc basin began to close in ~2.53Ga, and the oceanic crust in the back arc basin began to subduction to the continental crust, and the continental margin formed CAB, and the lithologic combination of TTG and potassic granite was.2.52~ 2.47Ga as the collision stage, and the residual oceanic crust was squeezed and deformed. The formation of a series of NW-SE folds, ductile shear zones and brittle fracture, laid the basic structural pattern of the greenstone belt in the sellar area. The deformation of the oceanic crust was simultaneously transformed by the metamorphism of the low amphibolite phase and the greenschist facies region. The second transformation occurred at ~1.80Ga, mainly influenced by the closure of the Liaoji Rift Valley and the post orogenic movement. The fracture of the period is reactivated. The rich Mg hydrothermal fluid is migrated along these faults, and the strip magnetite quartzite and its surrounding rock in the greenstone belt are reformed to enrich the magnetite quartzite and form a series of altered rocks.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P588.3
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本文编号：2076131