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1.
Ritesh Purohit Harsh Bhu Prakshal Mehta P. C. Avadich 《Journal of the Geological Society of India》2012,79(2):135-150
Present study reviews the tectono-stratigraphic status of Babarmal pink marble from the Aravalli Supergroup through mapping
and petrographic study of marble as well as associated lithologies. The pink marble is predominantly calcitic and characteristically
different from dolomitic carbonate rocks of the Jhamarkotra Formation, the Lower Aravalli Group. The marble is devoid of organic
matter and phosphate content unlike the Jhamarkotra dolomite. The pink marble is underlain by quartz-pebble rich conglomerate.
This assemblage represents a rare lithological association which has not been reported so far from the Aravalli Supergroup. 相似文献
2.
嘎拉勒铜金矿床位于冈底斯成矿带西段北缘,是近年来该区域发现的一个重要的典型镁质矽卡岩型铜金矿床。本文在矿区大比例尺地质填图基础上,结合前人研究资料,对该矿床地质特征和控矿条件进行了系统阐述和分析。矿区内出露地层主要为下白垩统捷嘎组白云岩和白云质灰岩,其下伏为下白垩统郎久组砂岩、粉砂岩和流纹质-英安质火山岩及火山碎屑岩。矿区内至少发生了3期构造变形,第1期形成北西向褶皱和北东向张性横断层,第2期形成北东向褶皱、北东向压性纵断层和北西向小型张性横断层,第3期形成近南北向正断层。区内自早到晚侵入有燕山晚期斑状石英闪长岩、闪长玢岩、石英闪长岩、花岗闪长岩和花岗斑岩。在石英闪长岩和花岗闪长岩与捷嘎组白云岩和白云质灰岩接触带附近形成典型镁质矽卡岩,包括早、晚两个阶段,早阶段形成由橄榄石、粒硅镁石和少量尖晶石、石榴子石、透辉石组成的干矽卡岩,晚阶段形成由蛇纹石、金云母和少量绿帘石组成的湿矽卡岩,叠加在干矽卡岩之上或其外侧,构成自岩体向外的橄榄石+尖晶石+粒硅镁石±石榴石±金云母带、金云母+蛇纹石±橄榄石±石榴石±透辉石带、蛇纹石+金云母+绿帘石±透辉石带、蛇纹石±金云母化大理岩带。矿体呈层状、似层状、团块状及不规则状主要产于蛇纹石+金云母化带内,金属矿物主要有磁铁矿、黄铁矿、黄铜矿、斑铜矿、辉铜矿、自然金等,伴有硅化、绿泥石化和碳酸盐化。成矿作用与花岗闪长岩和石英闪长岩的侵入活动密切相关,主要受北东和北西向褶皱及相关断裂控制,矽卡岩化受捷嘎组中部纹层状白云岩和砂质白云岩等有利岩性控制,矿体就位于矽卡岩带的高渗透率部位。 相似文献
3.
大别山北部超高压变质大理岩及其地质意义 总被引：3，自引：2，他引：3
岩石学研究表明 ,大别山北部镁铁 超镁铁质岩带中白云质大理岩至少经历过三期变质阶段 :(1)榴辉岩相峰期变质阶段 ,矿物组合主要为方解石 +白云石 +金红石 +镁橄榄石 +钛 斜硅镁石 +富镁的钛铁矿±文石±石榴子石 ;(2 )麻粒岩相退变质阶段 ,矿物组合主要为方解石 +白云石 +金云母 +镁橄榄石 +透辉石 +钛铁矿 +尖晶石±斜方辉石等 ;(3)角闪岩相退变质阶段 ,主要矿物组合为方解石 +白云石 +磷灰石 +磁铁矿+榍石等。它的峰期变质矿物组合 ,类似于苏 鲁超高压大理岩 ,形成压力至少大于 2 .5GPa。这进一步证明 ,大别山北部大多数高级变质岩 (包括大理岩等 )都曾经过超高压变质作用 ,应属于印支期扬子俯冲陆壳的一部分。 相似文献
4.
大理岩岩组是内蒙古大青山地区孔兹岩系3个岩组中最上部的一个岩组,该岩组是一套富镁质的大理岩系,以巨厚的、大面积分布的白云质大理岩的发育为特征,底部有少量碎屑岩沉积,矿物组成除白云石外,普遍含蛇纹石化橄榄石、透辉石、金云母等一种或多种富镁硅酸盐矿物。岩石地球化学以富CaO、MgO和LOI为特征,反映了碳酸盐岩的地球化学特征,CaO＋MgO含量达44.96%以上,且CaO/MgO比值较小（1.37～10.94）,其原岩应为一套碎屑含量极低的白云岩,以化学沉积为主。原岩建造的沉积环境：由初期的陆海过渡的三角洲相,过渡到滨海-浅海相,最后到干燥气候条件下有障蔽岛相隔的封闭海盆相。构造环境也从亚稳定状态过渡到稳定构造环境,表明该套变质沉积地层的原岩可能形成于被动大陆边缘,但更类似于中元古界长城系、蓟县系这样的克拉通内裂陷槽或裂谷沉积。 相似文献
5.
智利Copiapó附近海岸东部边缘有一宽5km、长20km的铁氧化物铜金矿床带,包括Candelaria矿床和位于其北东方向3km处的Punta del Cobre矿集区的中小型矿床。初步估计,该成矿带的铜矿石资源量可达7×108~8×10~8t(含铜量1%)。矿石矿物主要为黄铜矿、黄铁矿、磁铁矿、赤铁矿。矿石产状为脉状、角砾状、细脉状等。含矿围岩主要为Punta del Cobre组的火山岩及火山碎屑岩。该矿带中大部分大型矿脉位于北西—北北西向高角度脆性断层与块状火山岩和火山碎屑岩接触带交汇处。Candelairia矿区主要发育黑云母-钾长石±钙角闪石±绿帘石蚀变矿物组合。在Punta del Cobr矿集区,矿床深部的矿石围岩蚀变情况与Candelairia地区一致,但是浅部的矿石赋存于黑云母-钾长石或钠长石-绿泥石±方解石蚀变带中。 相似文献
6.
Manganese silicate rocks, interbanded with manganese oxide orebodies, constitute an important stratigraphic horizon in the Mansar formation of the Sausar Group of Precambrian age in India. The manganese silicate rocks of Gowari Wadhona occupy the westernmost flank of the manganese belt of the Sausar Group. These rocks are constituted of spessartite, calcium-rich rhodonite, quartz, manganoan diopside, blanfordite (manganese bearing member of diopside-acmite series), brown manganese pyroxene (manganese bearing aegirine-augite), winchite (manganese bearing richterite-tremolite), juddite (manganese bearing amphibole with richterite, tremolite, magnesioriebeckite and glaucophane molecules), tirodite (manganese bearing amphibole with richterite, cummingtonite and glaucophane molecules), manganophyllite, alurgite, piedmontite, braunite, hollandite (and other lower oxides of manganese) with minor apatite, plagioclase, calcite, dolomite and microcline. A complete mineralogical account of the manganese-bearing phases has been given in the text. It has been shown that the juxtaposition of manganese silicate rocks with dolomitic marble, regional metamorphism to almandine-amphibolite facies and assimilation of pegmatite veins cutting across the manganese formation, were responsible for the development of these manganese silicate rocks and the unusual chemical composition of some of the constituent minerals. It has been concluded that the manganese silicate rocks of Gowari Wadhona were originally laid down as sediments comprising manganese oxides admixed with clay, silica etc. and were later regionally metamorphosed to almandine-amphibolite facies. All evidences indicate that rhodochrosite was not present in the original sediment and the bulk composition of the sediments was rich in manganese. These rocks agree entirely to the detailed nomenclature of the gondites enunciated by Fermor (1909) and amplified by Roy and Mitra (1964) and Roy (1966). 相似文献
7.
桐柏蔡家凹岩片内寒武纪高肌虫的发现及其地质意义 总被引：5，自引：0，他引：5
本文描述了河南桐柏西北部蔡家凹大理岩岩丰富的高肌虫化石Ｔｏｎｇｂａｉｅｌｌａ ｘｉｎｊｉｅｎｓｉｓ ｇｅｎ．ｅｔ ｓｐ．ｎｏｖ．、Ｘｉａｎｚｈｅｅｌｌａ ｈｅｎａｎｅｎｓｉｓ ｓｐ．ｎｏｖ．和Ｍｏｎｏｎｏｔｅｌｌａ ｃｆ．ｃｈｕａｎｓｈａｎｅｎｓｉｓ Ｈｕｏ ｅｔＳｈｕ及小壳化石Ｃｏｎｏｔｈｅｃａ ｓｐ．共有４属４种。据此确定含化石地层为寒武系,属浅海沉积环境。该生物群的发现为解决桐柏大别造山带与 相似文献
8.
A. Luque M. V. Martínez de Yuso G. Cultrone E. Sebastián 《Environmental Earth Sciences》2013,68(3):833-845
Atmospheric pollution is one of the main agents of decay in monuments and other works of art located in industrialised urban centres. SO2 is a permanent and abundant component of air pollution and, although it does not have an immediate visual effect, after continuous exposure, it can cause irreversible damage to building materials. Marble is one of the most commonly used ornamental stones in historical monuments and its mineralogical composition makes it very susceptible to damage caused by exposure to SO2. To measure the chemical reactions caused on marble by the action of atmosphere rich in SO2, selected calcitic and dolomitic samples were altered by weathering accelerated test. For this, seven marble types (four calcitic and three dolomitic) were exposed to high concentration of sulphur dioxide for 24 h in a climate chamber under controlled temperature and humidity conditions (20 °C and > 90 % HR). Changes on marble surfaces caused by reactions of SO2 with calcite and dolomite were studied using two non-destructive techniques: chromatic change by means of colorimetry and chemical analysis using X-ray photoelectron spectroscopy (XPS). The development of new mineral phases was also observed by scanning electron microscopy. Colorimetric analysis revealed a decrease in lightness and chromatic parameters suggesting that these changes were due to the development of new mineral phases in all marbles. The XPS technique, which is generally used in the analysis of metals, is relatively new in the field of stone deterioration. It enabled us to recognise the development of sulphites and sulphates on marble surfaces with high precision, after just 24 h of exposure to high SO2 concentrations and to distinguish different decay paths for calcitic and dolomitic marbles. 相似文献
9.
长江中下游地区是中国成矿理论的重要发源地之一,迄今已经完成大量研究,取得了一系列重要进展,前人已进行了多次总结。文章在此工作基础上,概括总结了最新的研究进展,并提出尚待解决的一些科学问题:该带成矿过程的深化研究和新测试、新技术的应用,有望破解层状铜金矿成因难题;越来越多单独或者伴生钨矿被发现,成矿显示多样性和多期次的特点。建立了该带矽卡岩型铜金矿+金稀散金属矿床组合新模型,有望推动在斑岩-矽卡岩型铜金矿外围发现贵金属和稀散金属矿床;研究发现该带含膏盐层在矽卡岩铁矿和玢岩铁矿的成矿过程中贡献明显;利用红外和矿物原位测试技术示踪该带深部矿化中心;通过三维找矿预测和成矿过程数值模拟,为隐伏矿找矿突破增添了新路径。最后,文章提出有待进一步研究的5个方面的科学问题,以期推动深化研究和找矿新突破。 相似文献
10.
《Ore Geology Reviews》2003,22(1-2):17-39
Many talc deposits occur in the Hwanggangri Mineralized Zone (HMZ) in dolomitic marbles of the Cambro-Ordovician Samtaesan Formation within 1 km of the contact with the Cretaceous Muamsa Granite. Talc commonly forms fine-grained, fibrous aggregates, or pseudomorphs after tremolite; abundant tremolite is included as impurities in the talc ore. Talc generally was derived from tremolite in calc-silicate rock within the dolomitic marble. Calc-silicate rock, consisting mainly of tremolite and diopside, was generated from silicic metasomatism during the prograde stage, which promoted decarbonation reactions until dolomite was exhausted locally. Hydrothermal alteration of calc-silicate rock to talc is marked by the addition of Mg and Si, and the leaching of Ca; Cr, Co, and Ni were relatively immobile during the retrograde stage. Contact metamorphism related to the granite intrusion generated the successive appearance of tremolite, diopside, and forsterite, or wollastonite-bearing assemblages in the marble, depending on the bulk rock composition. The XCO2 content of the metamorphic fluids rose initially above XCO2=0.6, and decreased steadily toward a water-rich composition with increasing temperature above 600 °C in the calcitic marble, while buffered reaction of the dolomitic marble occurred at higher XCO2 conditions above 600 °C. Talc mineralization developed under metastable conditions with infiltration of large amounts of igneous fluids along a fault-shattered zone during the retrograde stage and is characterized by the loss of Ca2+ with the addition of Mg2+. Oxygen and carbon isotopic variations of carbonate and calc-silicate minerals are in agreement with theoretical relationships determined for decarbonation products of contact metamorphism. Talc formation temperatures obtained from oxygen isotope fractionation, T–XCO2 relationships, and activity diagrams range from 380 to 400 °C. 相似文献
11.
中国辽东地区超大型菱镁矿矿床的地球化学特征和成因模式 总被引：4，自引：1，他引：4
我国辽东地区早元古代大石桥组镁质碳酸盐-泥质岩建造中赋存有多个超大型菱镁矿矿床。在这些矿床中,菱铁矿矿体均只限定在大石桥组三段岩层中。该层岩石主要由白云质大理岩、菱镁质大理岩、菱镁矿和少量泥质板岩薄层组成。赋矿层位之下地层为大石桥组二段的云母片岩;其下为大石桥组一段的白云质大理岩与云母片岩夹层。在大石桥组一段中未见菱铁矿体产出。研究表明,菱铁矿的δ18O值为5.2‰~13.8‰,低于围岩大理岩的δ18O值(11.2‰~22.8‰)。但两音的δ13C值大多接近零值,其中菱镁矿δ13C值变化为-1.4‰~1.2‰,大理岩δ13C值变化为-4.5‰~4 4‰。在菱镁矿层位中发现有石膏成层和脉状产出,其δ34S值为23.9‰~26.5‰,显示海相蒸发沉积特征。菱镁矿的稀土元素分析表明存在三种不同页岩标准化配分模式。类型Ⅰ显示中稀土富集特征,类型Ⅲ显示重稀土富集和正铕异常特征,它们可能反映了不同时期成矿热液的特征。而类型Ⅱ显示与围岩大理岩相同的平坦型,反映继承了原岩沉积碳酸盐岩的特征。本文认为,辽东地区的镁质碳酸盐岩(镁方解石和白云石)可能是从蒸发的泻湖盆地中沉积的,而菱镁矿石则主要是沉积后富镁卤水下渗交代原岩碳酸盐岩形成的。由于大石桥组二段云母片岩渗透率低隔水性强,因此菱铁矿的矿化交代作用只发 相似文献
12.
二连盆地阿南凹陷下白垩统腾格尔组发育一套湖相的富含致密油云质岩段,包括云质泥岩、云质沉凝灰岩和云质砂岩,但这类云质岩中的白云石岩石学特征及成因尚不明确.通过岩心、薄片、扫描电镜及碳氧同位素分析,将云质岩中的白云石分为两类:(1) 分布在纹层状和星点状云质泥岩或云质沉凝灰岩的非平直晶面、半自形微粉晶白云石;(2) 分布在块状云质沉凝灰岩或云质砂岩的非平直-平直晶面、自形粉细晶白云石.两类白云石的成因机制不同:(1) 半自形微粉晶白云石具偏高的δ13CPDB值(平均为5.4‰),主要受产甲烷菌的代谢活动影响,其δ18OPDB值负偏移量较小(平均为-13.0‰),计算形成温度约50~75 ℃,推测为成岩早期成因白云石,Mg2+离子主要来源于富火山灰的凝灰物质大量水解.(2) 自形粉细晶白云石晶体较大、晶形好,其δ13CPDB值偏低(0.2‰~0.7‰),受产甲烷菌的代谢活动和深层有机质热催化共同影响,其δ18OPDB值较低(平均为-19.4‰),计算形成温度约119 ℃,推测为成岩晚期埋藏成因白云石,Mg2+离子可能与粘土矿物水解及深部流体上涌有关. 相似文献
13.
14.
辽河西部凹陷雷家地区古近系沙四段混合沉积特征研究 总被引：12，自引：0，他引：12
雷家地区古近系沙四段广泛发育湖相碳酸盐与陆源碎屑混合沉积。通过对研究区混合沉积的区域地质背景、岩石学特征、沉积环境等分析,认为该区混合沉积特征为结构混合和互层混合,其中结构混合（狭义的混积岩）在不同构造部位混积岩岩石成分不同,西部以内源型混合沉积为主,中东部以陆源型混合沉积为主,局部为火山岩型混积岩。混合沉积作用类型包括渐变式混合沉积和复合式混合沉积Ⅰ类,局部发育突变式混合沉积。最后,分析本区白云岩的成因,进而探讨形成混合沉积的地质条件和沉积环境。 相似文献
15.
The concept of compositional bimodality in carbonatites has become widely accepted and has been used to impose restrictions on the composition of carbonatite magmas. We agree that mineralogical bimodality exists in carbonatites (most are either calcitic or dolomitic/ankeritic), but we argue that there is no compositional bimodality. The idea of bimodality is based on the interpretation of a variety of element distribution diagrams which were compiled only from chemical analyses in which SiO2 is < 10 wt.%. All others were rejected. Even with such a restricted data set the case for compositional bimodality is extremely weak, but the inclusion of analyses with higher SiO2 content destroys it completely. Yet these more siliceous compositions must be included, for many carbonatites contain substantial amounts of Fe–Mg silicates which are an essential part of the magmatic mineralogy of the rocks. They account for much of the Mg in carbonatites that are otherwise calcitic. Many such carbonatites contain well in excess of 10 wt.% SiO2. Supporters of the bimodality concept argue that liquids having compositions between calcite and dolomite can precipitate neither calcite nor dolomite because the minimum on the solid solution loops in the system calcite–dolomite permits only a carbonate of intermediate composition. Therefore, it is argued, liquids of such intermediate composition cannot be parental to calcitic and dolomitic carbonatites; their parent magmas must be calcitic and dolomitic. This deduction is incorrect. It is well established that dolomitic liquids have calcite as the liquidus phase over substantial temperature intervals, and that this is followed by dolomite precipitation. Mixed calcite–dolomite carbonatites are explicable in this way. Therefore, dolomitic liquids can be parental to calcitic carbonatites. However, dolomitic carbonatites cannot crystallize from a calcitic liquid. We suggest that intermediate composition carbonatite magmas are probably common. Bimodality in carbonatites is solely mineralogical, not compositional. 相似文献
16.
Guangming LI Jinxiang LI Kezhang QIN Ji DUO Tianping ZHANG Bo XIAO Junxing ZHAO 《Resource Geology》2012,62(1):99-118
The Duobuza gold‐rich porphyry copper district is located in the Bangongco metallogenetic belt in the Bangongco‐Nujiang suture zone south of the Qiangtang terrane. Two main gold‐rich porphyry copper deposits (Duobuza and Bolong) and an occurrence (135 Line) were discovered in the district. The porphyry‐type mineralization is associated with three Early Cretaceous ore‐bearing granodiorite porphyries at Duobuza, 135 Line and Bolong, and is hosted by volcanic and sedimentary rocks of the Middle Jurassic Yanshiping Formation and intermediate‐acidic volcanic rocks of the Early Cretaceous Meiriqie Group. Simultaneous emplacement and isometric distribution of three ore‐forming porphyries is explained as multi‐centered mineralization generated from the same magma chamber. Intense hydrothermal alteration occurs in the porphyries and at the contact zone with wall rocks. Four main hypogene alteration zones are distinguished at Duobuza. Early‐stage alteration is dominated by potassic alteration with extensive secondary biotite, K‐feldspar and magnetite. The alteration zone includes dense magnetite and quartz‐magnetite veinlets, in which Cu‐Fe‐bearing sulfides are present. Propylitic alteration occurs in the host basic volcanic rocks. Extensive chloritization‐silicification with quartz‐chalcopyrite or quartz‐molybdenite veinlets superimposes on the potassic alteration. Final‐stage argillic alteration overlaps on all the earlier alteration. This alteration stage is characterized by destruction of feldspar to form illite, dickite and kaolinite, with accompanying veinlets of quartz + chalcopyrite + pyrite and quartz + pyrite assemblages. Cu coexists with Au, which indicates their simultaneous precipitation. Mass balance calculations show that ore‐forming elements are strongly enriched during the above‐mentioned three alteration stages. 相似文献
17.
岩性及沉积环境的差异是鄂尔多斯盆地下奥陶统马家沟组马五5亚段储层非均质性的重要因素,根据岩石类型、沉积构造及颜色等特征及其与沉积微相的关系,研究区马五5亚段可分为盆缘坪和台内盆地两个亚相及缘内（膏）云质洼地、缘内云坪、缘内灰坪、缘内云灰-灰云坪、盆地（膏）云质洼地、灰云-云灰质盆地及灰质盆地等微相。沉积微相平面上表现为,马五52时期,鄂尔多斯盆地基底抬升,中央古隆起带露出水面;北部地区发育缘内云坪-云质洼地、缘内灰云-云灰坪和灰质盆地;西部地区为缘内云坪-云质洼地、缘内灰云-云灰坪;中部地区为灰质盆地,间夹云灰盆地及盆内云质洼地;马五51时期,北部地区主要发育缘内云坪-云质洼地;西部地区为缘内云坪-云质洼地;中部地区为灰质盆地及盆内云质洼地。盆缘坪和台内盆地的低洼处有利于发生同生期后回流渗透白云化作用,对生成较大规模的泥粉晶白云岩具有重要的意义。 相似文献
18.
Holness 《Journal of Metamorphic Geology》2000,18(1):103-118
Dolerite dykes which intrude dolomitic marble in the aureole of the Beinn an Dubhaich granite on the Isle of Skye have developed metasomatized margins close to the contact with the (younger) granite in the southern part of Torrin Quarry. These margins display well-defined mineralogical zones which can be divided into two groups on the basis of composition. Chlorite-bearing margins display the sequence dolerite | diopside+spinel | chlorite+calcite+magnetite | olivine+calcite+spinel | dolomite, whereas phlogopite-bearing sequences have a phlogopite+calcite±fluorapatite layer in place of the chlorite-bearing layer. No spatial pattern is seen in the distribution of the two margin types, but textural and compositional evidence points to an importance of metasomatism by localized infiltration of magmatic fluids in the development of the phlogopite-bearing sequences. Extensive patterning of the phlogopite-bearing margins by a process of self-organization during grain growth has resulted in the formation of alternating silicate-only/calcite-only layers parallel to the dyke margin on a millimetre to centimetre scale. Early development of chlorite-bearing sequences at the dolerite–dolomite contact during contact metamorphism was followed by metasomatism-controlled growth of phlogopite and patterning at or after the peak of metamorphism associated with the expulsion of aqueous fluids from the crystallizing pluton. 相似文献
19.
Kong Gao Guanghai Shi Meili Wang Gen Xie Jian Wang Xiaochong Zhang Ting Fang Weiyan Lei Yan Liu 《地学前缘(英文版)》2019,10(4):1597-1612
The Tashisayi nephrite deposit is located in South Altyn Tagh.in Qiemo County,Xinjiang Province,northwest China.It is a recent discovery in the vast,well-known Kunlun-Altyn nephrite belt distributed along the south of the Tarim Basin,producing more than half of the nephrite from the whole belt in 2017.Field investigations revealed that it is a dolomitic marble-related(D-type)nephrite deposit,but little is known about its age of formation and relationships between the granites and marble.Here we report field investigations,petrography of the neph rite,as well as petrography,geochemistry,geochronology of the zoisite-quartz altered intrusive rock and adjacent granites.An A-type granite is identified with a SHRIMP U-Pb zircon age of 926± 7 Ma,suggesting it was emplaced in an extensional tectonic environment at that time.The altered intrusive rock has a cluster of U-Pb zircon age of 433± 10 Ma.with similar trace element features to the A-type granite,suggesting it was formed in an extensional regime at this later time.Nephrite formed because of the metasomatism of dolomite marble by hydrothermal fluids.It is inferred that Ca~(2+) was released from the dolomitic marble by metasomatism forming Ca-rich fluids,which caused alteration of both the intrusive rocks(6.00-8.22 wt.% CaO)and granite(1.76-3.68 wt.% CaO)near the nephrite ore bodies.It is also inferred that Fe2+ from the granite migrated towards the dolomite marble.The fluids gave rise to the formation of Ca-minerals.such as zoisite,in the nephrite and altered intrusive rock,and epidote in the granite.Based on the contact relationships.similarity in hydrothermal processes,and consumption of Ca~(2+),the Tashisayi nephrite is considered to have formed at the same time as the alteration of the intrusive rocks,i.e.～433 Ma.The geochronological similarity(～926 Ma.433 Ma)of South Altyn and North Qaidam may suggest that tectonically they belong to one single complex in the past,which was offset by the Altyn Tagh fault(ATF).The similar formation ages of the nephrites from Altyn Tagh(433 Ma)and the previously studied areas of West Kunlun(378-441 Ma)and East Kunlun(416 Ma)indicate that these nephrites formed during the closure of Proto-Tethys and in the accompanving post-collisional.extensional environment. 相似文献
20.
云质岩储集层是准噶尔盆地乌—夏地区一套成因特殊的、富含油气的碳酸盐岩储集层。在分析乌—夏地区二叠系构造、沉积及火山活动等地质背景的基础上,根据风城组云质岩岩心宏观产状,将云质岩分为4种类型:波纹层状云质岩、团块状云质岩、丝絮状云质岩和星散状云质岩。镜下波纹层状云质岩晶粒细小,晶形差;团块状云质岩、丝絮状云质岩、星散状云质岩中白云石晶体以粉—细晶为主,普遍发育雾心亮边、环带交代残余结构。C、O同位素及微量元素等地化分析表明:白云岩化的成岩流体来自二叠系风城组半封闭湖湾的咸化沉积地层水以及下伏二叠系佳木河组、石炭系上涌的海相卤水。包裹体测温表明,蚀变方解石的形成温度为60～70℃,白云石的形成温度为85～105℃,白云石形成晚于蚀变方解石。波纹层状云质岩是准同生成因;团块状云质岩、丝絮状云质岩、星散状云质岩是后期成岩交代成因,交代的原岩是火山物质(凝灰岩)。成岩交代云质岩的成因机理是:火山凝灰物质中的火山玻璃容易发生水解蚀变,产物为蒙脱石、长石和石英;蒙脱石转化为伊利石、长石水解蚀变均可析出大量的Ca2+,结合CO2或CO32-形成蚀变产物方解石;方解石在富Mg2+流体交代下发生强烈白云岩化作用。 相似文献