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拉鸡山造山带的蛇绿岩套及古构造环境 总被引：2，自引：3，他引：2
传统认为蛇绿岩套由超基性岩，含枕状构造的基本熔岩和硅质岩组成，是大洋岩石圈的碎片，具有完整的５个或４个层序，但经深入研究发现，蛇绿岩有不同的类型，可产在不同的构造环境区。从层序，岩性、岩性组合特征来看，拉鸡山存在蛇绿岩套。拉鸡山蛇岩套厚度小，层序不全、岩性变化大、不是大洋中脊产物，其岩石学特点与初始洋盆蛇绿岩套相同。拉鸡山 绿岩套是中寒武世陆间裂谷拉张到最宽时的小洋盆中形成的，属于陆间裂谷型小洋盆 相似文献
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《新疆地质》2019,(4)
新疆西准噶尔北部科克森套蛇绿岩由辉长岩、辉橄岩、橄辉岩、辉石岩、蛇纹岩、玄武岩、硅质岩、含放射虫硅质板岩及片岩、片麻岩组成。辉长岩化学特征表现为富Al_2O_3、CaO、MgO,贫K_2O、TiO_2特点,与岛弧玄武岩相似。稀土元素与E-MORB特征基本一致,反映岩浆来源于富集地幔。微量元素具大离子亲石元素Rb,Th,K,Sr相对富集,高场强元素Nb,Ta,Ti相对亏损特征,显示与俯冲带流体交代有关。辉长岩锆石年龄(405±4) Ma,代表洋壳形成年代。在构造环境上,科克森套蛇绿混杂岩显示富集洋脊玄武岩特征,形成于岛弧环境,与岛弧消减带扩张环境相一致,因此,科克森套蛇绿混杂岩应形成于早泥盆世。从时间、空间分布及构造环境上,科克森套蛇绿岩与库尔提蛇绿岩、沙尔布拉克蛇绿岩及布尔根蛇绿岩具相似性,为早泥盆世古亚洲洋在准噶尔北缘向西伯利亚板块俯冲所形成的沟-弧-盆体系下的弧后系统,与相邻哈萨克斯坦斋桑蛇绿岩带、蒙古比基蛇绿岩带共同构成西伯利亚与准噶尔板块间的缝合带。 相似文献
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蛇绿岩作为残留洋壳的良好记录,对于研究古板块构造及其演化具有重要意义。新发现的吐尔库班套蛇绿混杂岩位于新疆阿尔泰布尔津南部,主要由超镁铁岩、辉长岩、辉绿岩、玄武岩、复理石建造等构成。其中辉长岩和片麻状花岗岩的锆石U Pb年龄在363～355 Ma,指示蛇绿岩的形成、洋壳俯冲时代在晚泥盆世晚期。岩石地球化学特征表明,该蛇绿岩套的镁铁超镁铁岩和玄武岩属低碱、低钛、富镁的拉斑玄武岩系列,具有较典型的幔源岩石特征,玄武岩形成于类似洋中脊的构造环境。混杂岩带中的片麻状花岗岩属于钠质的低钾岩石系列,形成于火山弧或同碰撞构造环境,亦为洋壳俯冲的结果。吐尔库班套蛇绿岩与科克森套、乔夏哈拉、布尔根蛇绿岩一起构成了沿额尔齐斯分布的蛇绿混杂岩带,构成了分割西伯利亚板块和哈萨克斯坦-准噶尔板块的斋桑-科克森套-南蒙古缝合带。 相似文献
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西准噶尔的放射虫硅质岩 总被引：1，自引：0，他引：1
放射虫硅质岩是组成蛇绿岩套最有意义的成员之一。它不仅能说明蛇绿岩套产于洋壳海域,而且还标志着蛇绿岩套构造侵位前形成的上限时代及生成环境。笔者在对西准噶尔蛇绿岩套初步研究的基础上,试图专门对该区放射虫硅质岩进行探讨,并对其特征和地质意义提出一些见解。 相似文献
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新疆南天山榆树沟高压麻粒岩地体的原岩是一层序基本完整的蛇绿岩套。该岩套主要由变质橄榄岩、超镁铁质-镁铁质堆晶岩、下部洋脊拉斑玄武岩、以及上部洋脊拉斑玄武岩等四个岩石单元构成。其岩石学和REE与相对惰性微量元素的地球化学特征表明,该蛇绿岩中的玄武岩属洋脊型;结合区域地质背景分析,初步认为榆树沟蛇绿岩可能形成于具相当规模的洋盆构造环境。锆石U-Pb年龄表明其形成时代为早古生代中晚期,证实西南天山早古生代蛇绿岩确已延伸至库米什一带。榆树沟麻粒岩相蛇绿岩套的确定以及对其独特的形成和俯冲-折返过程进行深入研究,不仅对进一步探讨天山构造带的形成和演化有重要意义,而且对发展大陆动力学理论也具重要参考价值。 相似文献
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蛇绿岩套主要是基性、超基性成分的火山岩和深成岩的杂岩体。它常出现于显生宙的各个造山带中。按现代海底岩石学的研究表明,海洋地壳的岩石组成与蛇绿岩套基本一致,因而推测蛇绿岩套代表古海洋地壳和地幔顶部的残块,这就是最近十几年来,很多研究者所支持的蛇绿岩为洋壳碎块的假说。按板块构造学说,洋壳是在洋中脊形成的,以后转移到岩石圈板块聚合边界的消亡带,因此蛇绿岩主要沿两个板块的接触线附近的俯冲板块一侧分布。最近,都城秋穗根据蛇绿岩杂岩体中的火山岩,将蛇绿岩分为三类,每类都代表在不同的地质环境下形成。 相似文献
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西昆仑柯岗蛇绿岩地质地球化学特征及构造意义 总被引：3，自引：0，他引：3
柯岗蛇绿岩位于青藏高原北缘,与北部的奥依塔格蛇绿岩、南部的库地蛇及苏巴什绿岩组成青藏高原“第五缝合带”。本文对柯岗蛇绿岩中辉长岩进行了岩石学、地球化学及锆石LA-ICP-MS分析。柯岗辉长岩SiO2含量为43.65%-49.29%,在TAS分类图解上,样品主要落在辉长岩区域,与野外及镜下观察一致。柯岗辉长岩稀土元素总量较低,∑REE范围在12.12-45.45μg/g,经球粒陨石标准化的REE分布模式显示,3个样品显示轻稀土略亏损特征, Eu＊为正异常,平均为1.34,1个样品显示轻稀土富集特征, Eu＊为0.86,为岩浆分异结晶不同时期的产物。柯岗辉长岩锆石Th/U范围为0.28-0.67,且具有典型岩浆锆石的震荡环带结构或扇形结构特征。22颗锆石206Pb/238U加权平均年龄为（488.8±2.6） Ma, MSWD=0.81,代表柯岗蛇绿岩套中辉长岩结晶年龄。通过柯岗蛇绿岩中辉长岩地球化学特征和构造环境判别图解,并结合前人资料,认为柯岗蛇绿岩形成环境为岛弧或者弧前环境。 相似文献
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蛇绿岩普遍被发现在碰撞型和增生型两种造山带缝合线上,因此经常被用来确定板块边界。自从欧洲地质学家在19世纪早期提出蛇绿岩的概念以来,蛇绿岩的研究经历了几个发展阶段。早期研究认为蛇绿岩是侵入地槽的一套侵入岩;板块构造理论兴起后,蛇绿岩被认为是产生于大洋中脊的洋壳;在1972年的Penrose会议上,科学家们将蛇绿岩定义为一套从基性岩到超基性岩的,可以区分的复式岩体。此后,蛇绿岩的起源(构造背景),侵位机制,特征等研究都取得了很多进展。进入21世纪,出现了一些较好的蛇绿岩形成模式和划分方法。 相似文献
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Cousens BL 《The Journal of geology》2000,108(2):181-197
The geochemistry and isotope systematics of Archean greenstone belts provide important constraints on the origin of the volcanic rocks and tectonic models for the evolution of Archean cratons. The Kam Group is a approximately 10-km-thick pile of submarine, tholeiitic mafic, and subordinate felsic volcanic rocks erupted between 2712 and 2701 Ma that forms the bulk of the Yellowknife greenstone belt in the dominantly granite-metasedimentary Slave Province. Mafic rocks range from Normal-mid-ocean range basalt-like basalts to slightly light-rare-earth-element-enriched (LREE-enriched) but Nb-depleted basaltic andesites and andesites, whereas dacitic to rhyodacitic felsic rocks are strongly LREE-enriched and highly depleted in Nb. The varepsilonTNd range from +5 to -3 in the mafic to intermediate rocks and from 0 to -5.5 in the felsic rocks. The varepsilonTNd decreases with increasing La/Sm, SiO2 and decreasing Nb/La, suggesting that as the mafic magmas evolved they were contaminated by older basement rocks. Gneissic granitoids >2.9 Ga in age, found at the base of the Kam Group, have varepsilonTNd between -6 and -9 and are excellent candidates for the contaminant. The geochemical and isotopic data, combined with the submarine eruptive setting and field evidence for existing continental basement, support a continental margin rift model for the Kam Group. Similar geochemical-isotopic studies are required on other Slave greenstone belts in order to test evolutionary models for the Slave Province. 相似文献
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额尔古纳地块基底地质构造 总被引：15，自引：0，他引：15
额尔古纳地块是额尔古纳-马门-加格达奇拼合地块中的典型代表.研究表明,其基底由前中元古代绿岩及与之伴生的花岗质杂岩组成,它们具有地壳早期演化的地质构造特征.绿岩带为典型的变质基性-酸性火山岩及部分变质沉积岩系构成的火山-沉积建造,火山岩以拉斑玄武岩为主,向上过渡为钙碱性火山岩系列,表现为双峰态型特点.花岗岩类为TTG岩系及石英二长岩-花岗岩组合.花岗岩-绿岩地体内各岩石类型的岩石地球化学特征与国外太古宙及我国华北陆台花岗岩-绿岩带内同类岩石极为相似.双峰态型火山岩及绿岩建造组合,以及类似于TH2、FII型的变质基性火山岩和长英质火山岩特征,结合高铝型英云闪长岩-奥长花岗岩组合,指示了研究区绿岩带的形成环境类似于大陆边缘弧后裂谷型火山-沉积盆地. 相似文献
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The Ishpeming Greenstone Belt is an Archean belt in the southern part of the Canadian Shield in the Upper Peninsula of Michigan, U.S.A. Two volcanic cycles are preserved in it. The oldest formation, and basal to the first cycle (the Kitchi Schist), consists of mafic metavolcanics, has a major serpentinized ultramafic body near its base, and grades upward to a coarse felsic volcanic breccia at the top of the cycle. This unit in turn is overlain by a sequence of mafic flows that grades upward to interbedded mafic flows and exhalites of the Mona Schist. This sequence has been intruded by the Dead River Pluton.The Ishpeming Greenstone Belt probably represents the keel of a previously much more extensive Greenstone Belt.Gold mineralization occurs associated with mafic basaltic volcanic rocks and serpentinized ultramafics low in the succession, and with carbonate-rich quartz-chlorite-sericite schists and exhalites higher in the sequence. No mineral deposits are now being exploited here. 相似文献
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《International Geology Review》2012,54(12):1166-1181
Geological and isotope-geochemical studies of acid volcanics in the Verkhovtsevo greenstone belt and surrounding tonalite-trondhjemite plutons within the central Dnieper gneiss-green- stone terrain were conducted in the search for genetic relationships and increased understanding of the petrogenesis of acid melts. The acid volcanic and plutonic rocks are similar in mineral composition and form a unified calc-alkaline-like trend from dacite/tonalite to rhyolite/ trondhjemite. Dacites and tonalites have the same rare-earth element (REE) patterns with moderately fractionated light and heavy REE as well as small negative Eu anomalies. Rhyolite and trondhjemites have less-fractionated REE patterns with larger negative Eu anomalies. Whole-rock data for the acid volcanic and plutonic rocks yielded a single isochron of 3117 ± 204 Ma, εNd = +1.14 ± 0.80. The data suggest a temporal and genetic relationship between the acid volcanics of the greenstone sequences and the surrounding plutonic rocks; both appear to belong to a single suite. The positive eNd value tends to suggest that a source of their melts can be traced to mafic materials rather than to older sialic crust. Petrochemical data and REE-model calculations suggest that dacite/tonalite liquids might have formed during partial melting of a mafic source, such as Archaean tholeiite TH-1 in equilibrium with hornblende-pyroxene-plagioclase restite. Subsequent differentiation of these melts in equilibrium with titanoilmenite-pyroxene-plagioclase cumulate may have given rise to the trondhjemites and rhyolites. Such a mineralogy of the restite and cumulate phases suggests that felsic melts containing little water in the Verkhovtsevo greenstone belt were generated at depths up to 30 km, probably in the greenstone belt's mafic basement. 相似文献
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A coherent ophiolitic complex of pyroxenite, serpentinite, metagabbro, mafic volcanics, felsic volcanics and sediments crops out in NW Maine, adjacent to the Chain Lakes massif. The complex (here informally referred to as the Boil Mountain ophiolitic complex) is about 500 m.y. old. The volcanic sequence is not typical of ophiolites in that it contains a large proportion of felsic volcanics. The mafic volcanics are divided into two geochemical groups. A stratigraphically lower group is depleted in Ti, Zr, Y, Cr and REE contents similar to basalts from supra-subduction zone ophiolites. An upper mafic group has trace element contents similar to normal mid-ocean ridge basalts. The felsic volcanics are mostly rhyolitic and similar to low-K rhyolites found in the forearc of the Marianas trench and in an island arc sequence in the Klamath Mountains, California. The flat REE patterns of the felsic volcanic rocks are similar to those found in siliceous rocks in the Oman ophiolite. The presence of thick sequences of felsic volcanics, the abundance of pyroxenite, the low Ti, Zr and REE contents of some mafic rocks, the flat REE patterns of the felsic volcanics, and the composition of clinopyroxene all suggest the complex was formed in the vicinity of a subduction zone. The complex may be correlated with ophiolitic fragments in the eastern part of the Dunnage Zone in Newfoundland, rather than the main ophiolite belt of the western Appalachians. 相似文献
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Mapping carried out in the northern Murchison Terrane of the Archaean Yilgarn Craton, Western Australia, shows that correlation of units between isolated greenstone belts is very difficult and an informal stratigraphic subdivision is proposed where the greenstone sequences have been divided into a number of assemblages. The assemblages may not necessarily be time equivalent throughout the region. The lower units (Assemblages 1–3) consist of ultramafic, mafic and intermediate volcanic rocks deposited without significant breaks in volcanism. Felsic volcanic packages (Assemblage 4) are conformable with underlying units, but are spatially restricted. Discordant units of graphitic sedimentary rocks are developed along major crustal structures (Assemblage 5). SHRIMP and conventional U–Pb study of zircons reveal that felsic volcanic rocks of Assemblage 4 in the Dalgaranga Greenstone Belt were emplaced at 2747 ± 5 Ma, whereas those in the adjacent Meekatharra — Mt Magnet Greenstone Belt range in age from 2762 ± 6 to 2716 ± 4 Ma. The age of emplacement of a differentiated gabbro sill in the Dalgaranga Greenstone Belt at 2719 ± 6 Ma places a maximum age on major folding in the belt. The presence of 2.9–3.0 Ga inherited zircons in some of the felsic volcanic rocks indicates contamination with, or reworking of, underlying 3 Ga sialic crust. This distinguishes the Murchison Terrane from the central parts of the Eastern Goldfields terranes to the south, where there is no evidence for a 3 Ga imprint in zircons from volcanic or granitic rocks, and also from the Narryer Gneiss Terrane to the north and west, which is composed of older gneisses and granitoids. The ca 2.76–2.71 Ga felsic volcanism in the Murchison Terrane is significantly older than 2.71–2.67 Ga felsic volcanism in the Eastern Goldfields lending support to models advocating assemblage of the craton by terrane accretion. 相似文献
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太阳系固体星球都有类似的核-幔-壳结构,但唯独人类居住的地球具有长英质组成的大陆壳。太古宙大陆克拉通主要由英云闪长岩(Tonalite)-奥长花岗岩(Trondhjemite)-花岗闪长岩(Granodiorite)为主的TTG深成侵入体变质而成的正片麻岩和由基性-超基性酸性火山岩及少量沉积岩变质的表壳岩(绿岩)组成。已有的资料显示这些太古宙大陆岩石组合起源于大洋壳的部分熔融。大洋壳分为大洋盆地、洋中脊、岛弧和洋底高原(大洋岛)。前两者地壳的平均厚度只有5~10km,不可能成为形成太古宙TTG深成侵入体的场所。因此,长英质大陆或起源于板块构造体制下的岛弧,或起源于地幔柱体制下的洋底高原。板块构造体制下的岛弧模式能够很好地解释太古宙克拉通TTG深成岩的成因,即俯冲大洋板片部分熔融所形成的埃达克岩相当于太古宙高压(高Al2O2)型TTG,而俯冲板片脱水导致地幔楔部分熔融形成的玄武质地壳再次熔融所形成的钙碱性花岗质岩石相当于太古宙低压(低Al2O2)型TTG。然而,板块构造体制下的岛弧模式不能令人满意地解释太古宙绿岩带火山岩组合中缺少大量的安山岩、科马提岩~1600℃高温形成环境、克拉通规模近于同时侵位的TTG岩套、大规模卵形构造样式、代表性的逆时针P-T轨迹变质作用演化等诸多特征。相反,地幔柱洋底高原模式能够合理地解释太古宙绿岩双峰式火山岩组合的成因,即基性的拉斑玄武岩和超基性的科马提岩分别来自地幔柱头部部分熔融和尾柱熔浆,而酸性的英安岩、流纹质英安岩和流纹岩是地幔柱热异常导致的洋底高原底部的部分熔融物。按照地幔柱洋底高原模式,太古宙TTG岩浆是由洋底高原底部玄武质地壳的部分熔融而成,这样能够合理地解释为什么太古宙TTG能够在短时间内巨量产出并在形成时间上没有任何系统变化。地幔柱洋底高原模式还能合理地解释太古宙克拉通穹隆构造(dome-and-keel structure)样式、近等压冷却型(IBC)逆时针P-T轨迹,缺少蓝片岩和双变质带的等典型岛弧俯冲带的标志的特征。本文在对大陆起源的岛弧模式和地幔柱洋底高原模式综合评述的基础上,提出一个大陆起源于洋底高原的两阶段模式。 相似文献