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1.
蛇绿岩型金刚石和铬铁矿深部成因 总被引：5，自引：0，他引：5
地球上的原生金刚石主要有3种产出类型,分别来自大陆克拉通下的深部地幔金伯利岩型金刚石、板块边界深俯冲变质岩中超高压变质型金刚石,和陨石坑中的陨石撞击型金刚石。在全球5个造山带的10处蛇绿岩的地幔橄榄岩或铬铁矿中均发现金刚石和其他超高压矿物的基础上,我们提出地球上一种新的天然金刚石产出类型,命名为蛇绿岩型金刚石。认为蛇绿岩型金刚石普遍存在于大洋岩石圈的地幔橄榄岩中,并提出蛇绿岩型金刚石和铬铁矿的深部成因模式。认为早期俯冲的地壳物质到达地幔过渡带(410~660 km深度)后被肢解,加入到周围的强还原流体和熔体中,当熔融物质向上运移到地幔过渡带顶部,铬铁矿和周围的地幔岩石以及流体中的金刚石等深部矿物一并结晶,之后,携带金刚石的铬铁矿和地幔岩石被上涌的地幔柱带至浅部,经历了洋盆的拉张和俯冲阶段,最终在板块边缘就位。 相似文献
2.
《International Geology Review》2012,54(6):494-507
The Jurassic Mayari-Baracoa ophiolite belt and associated Cretaceous volcanic rocks form the Zaza zone of eastern Cuba. This zone has been traditionally considered allochthonous and overrides a passive continental margin, the Cuban foreland. The ophiolites consist of mantle tectonites and cumulates, overlain by a volcanicarc sequence including porphyritic basalts and andesitic lavas. These are, in turn, overlain by a sequence of tuffs and epiclastic sedimentary rocks. There are two ophiolitic massifs in the belt, the Mayari-Cristal Massif (MCM) and the Moa-Baracoa Massif (MBM). The MCM consists of harzburgites and dunites with abundant high-Cr podiform chromitites and dikes of gabbro and pyroxenite. The MBM, on the other hand, is composed of harzburgites with abundant high-Al podiform chromitites, cut by troctolite dikes. The two ophiolitic massifs have different REE and PGE patterns and contents. The mantle sequence in the MCM is more depleted than that in the MBM. We suggest that the MCM formed beneath a volcanic island arc and the MBM beneath a nascent spreading center in a back-arc basin. The two massifs form a paired ophiolite belt. 相似文献
3.
The Haji‐Abad ophiolite in SW Iran (Outer Zagros Ophiolite Belt) is a remnant of the Late Cretaceous supra‐subduction zone ophiolites along the Bitlis–Zagros suture zone of southern Tethys. These ophiolites are coeval in age with the Late Cretaceous peri‐Arabian ophiolite belt including the Troodos (Cyprus), Kizildag (Turkey), Baer‐Bassit (Syria) and Semail (Oman) in the eastern Mediterranean region, as well as other Late Cretaceous Zagros ophiolites. Mantle tectonites constitute the main lithology of the Haji‐Abad ophiolite and are mostly lherzolites, depleted harzburgite with widespread residual and foliated/discordant dunite lenses. Podiform chromitites are common and are typically enveloped by thin dunitic haloes. Harzburgitic spinels are geochemically characterized by low and/or high Cr number, showing tendency to plot both in depleted abyssal and fore‐arc peridotites fields. Lherzolites are less refractory with slightly higher bulk REE contents and characterized by 7–12% partial melting of a spinel lherzolitic source whereas depleted harzburgites have very low abundances of REE and represented by more than 17% partial melting. The Haji‐Abad ophiolite crustal sequences are characterized by ultramafic cumulates and volcanic rocks. The volcanic rocks comprise pillow lavas and massive lava flows with basaltic to more‐evolved dacitic composition. The geochemistry and petrology of the Haji‐Abad volcanic rocks show a magmatic progression from early‐erupted E‐MORB‐type pillow lavas to late‐stages boninitic lavas. The E‐MORB‐type lavas have LREE‐enriched patterns without (or with slight) depletion in Nb–Ta. Boninitic lavas are highly depleted in bulk REEs and are represented by strong LREE‐depleted patterns and Nb–Ta negative anomalies. Tonalitic and plagiogranitic intrusions of small size, with calc‐alkaline signature, are common in the ophiolite complex. The Late Cretaceous Tethyan ophiolites like those at the Troodos, eastern Mediterranean, Oman and Zagros show similar ages and geochemical signatures, suggesting widespread supra‐subduction zone magmatism in all Neotethyan ophiolites during the Late Cretaceous. The geochemical patterns of the Haji‐Abad ophiolites as well as those of other Late Cretaceous Tethyan ophiolites, reflect a fore‐arc tectonic setting for the generation of the magmatic rocks in the southern branch of Neotethys during the Late Cretaceous. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
4.
Timothy M. Kusky Xiachen Zhi Jianghai Li Qiongxia Xia Tsilavo Raharimahefa Xiongnan Huang 《Gondwana Research》2007,12(1-2):67
Podiform chromitites are diagnostic but rare features of Phanerozoic ophiolites, and often contain the most pristine textural, chemical and isotopic record of convective upper mantle conditions extant during ophiolite genesis. Ophiolitic podiform chromitites, owing to their high Os concentrations and low Re/Os ratios provide the best evidence for the Os-isotopic evolution of oceanic mantle, but established records of ophiolitic chromites from bona fide Archean ophiolites are still lacking. We report Re–Os isotopic compositions of the world's oldest known ophiolitic podiform chromites from the 2.5 billion year old Dongwanzi–Zunhua ophiolite, North China. This provides the oldest Os isotope composition for the convective upper mantle yet obtained from ophiolitic podiform chromitites, and reveals a chondritic Os isotopic composition of the Archean convective upper mantle. 相似文献
5.
The Antique Ophiolite Complex exposed along the western side of Panay Island, central Philippines was derived from the Jurassic to Cretaceous proto-South China Sea oceanic leading edge of the Palawan microcontinental block. The subduction and ultimate closure of this ocean basin resulted in the emplacement and exposure of this lithospheric fragment along the collisional boundary of the microcontinental block and the oceanic- to island arc-affiliated Philippine mobile belt. The ophiolite complex has volcanic rocks having normal- to transitional mid-ocean ridge basalt (MORB) to island arc tholeiitic (IAT) geochemistry consistent with the transitional MORB–IAT characteristics of its peridotites. The chromitites manifest subduction signature suggestive of the involvement of water in its generation. All of these would be consistent with generation in a supra-subduction zone environment, specifically in a subduction-related marginal ocean basin. The collision of the Palawan microcontinental block with the Philippine mobile belt along western Panay resulted, aside from ophiolite emplacement, into arc curvature, island rotation, serpentinite diapirism and thrusting along the forearc side. The offshore bathymetric expression of the microcontinental block along the collision zone shows the leading edge of this oceanic bathymetric high to have spread laterally. This is indicative of its being buoyant resulting to non-subduction as supported by available earthquake hypocenter data. 相似文献
6.
北祁连蛇绿岩的特征、形成环境及其构造意义 总被引：58，自引：1，他引：58
文中总结了北祁连蛇绿岩的特征，指出北祁连蛇绿岩大多具有ＭＯＲＢ的性质，有玻安岩产出，形成在弧后和岛弧环境。北祁连蛇绿岩大多侵位在岛弧增生楔或活动陆缘地体之上，蛇绿岩属于科迪勒拉型，早古生代的北祁连造山带属于科迪勒拉型造山带。部分蛇绿岩之上整合产出一套沉积－火山岩系，称为蛇绿岩的上覆岩系。指出蛇绿岩及其上覆岩系的枕状熔岩分别来自不同的源区，具有不同的构造意义。还讨论了北祁连早古生代板块构造格局，认为北祁连洋盆属于古亚洲洋的一部分，可能曾经是一个较大规模的洋盆。献中通常把它当成增生或俯冲杂岩带的一部分来看待〔１３，１６－１７〕；大岔大坂蛇绿岩带，其向两侧的延伸情况不清楚；九个泉（或塔墩沟）蛇绿岩带，向东可连到景泰县老虎山蛇绿岩，有人认为，向西可与榆树沟蛇绿岩相连〔２０〕。早先认为，北祁连存在新元古代、中寒武和早－中奥陶世三个时代的蛇绿岩〔２，１１〕，经过多年研究，目前大多数同意蛇绿岩主要是晚寒武－奥陶纪的〔１３，１６〕。图１北祁连早古生代蛇绿岩分布图１．前寒武纪基底；２．俯冲杂岩带；３．蛇绿岩。图中数字：１．九个泉；２．大岔大坂；３．边马沟；４．玉石沟；５．小八宝；６．百经寺；７．老虎山；８．榆树沟山２北祁连几 相似文献
7.
北补连蛇绿岩的特征,形成环境及其构造意义 总被引：23，自引：4，他引：23
文中总结了北祁连蛇绿岩的特征，指出北祁连蛇绿岩大多具有ＭＯＲＢ的性质，有玻安岩产生，形成在弧后和岛弧环境，北祁连蛇绿岩大多侵位在岛弧增生楔或活动陆缘地体之上，蛇绿岩属于科迪勒拉型，早古生代的北祁连造山带属于科迪勒拉型造山带，部分蛇绿岩之上整合产出一套沉积一火山岩系，称为蛇绿岩的上覆岩系，指出蛇绿岩及其上覆岩系的枕状熔岩分别来自不同的源区，具有不同的构造意义，还讨论了北祁连早古生代板块构造格局，认为 相似文献
8.
The Guomangco ophiolitic melange is situated in the middle part of the Shiquanhe- Yongzhu-Jiali ophiolitic melange belt （SYJMB） and possesses all the subunits of a typical Penrose- type ophiolite pseudostratigraphy. The study of the Guomangco ophiolitic melange is very important for investigating the tectonic evolution of the SYJMB. The mafic rocks of this ophiolitic melange mainly include diabases, sillite dikes, and basalts. Geochemical analysis shows that these dikes mostly have E-MORB major and trace element signatures; this is the first time that this has been observed in the SYJMB. The basalts have N-MORB and IAB affinities, and the mineral chemistry of harzburgites shows a composition similar to that of SSZ peridotites, indicating that the Guomangco ophiolitic melange probably originated in a back-arc basin. The Guomangco back-arc basin opened in the Middle Jurassic, which was caused by southward subduction of the Neo-Tethys Ocean in central Tibet. The main spreading of this back-arc basin occurred during the Late Jurassic, and the basalts were formed during this time. With the development of the back-arc basin, the subducted slab gradually retreated, and new mantle convection occurred in the mantle wedge. The recycling may have caused the metasomatized mantle to undergo a high degree of partial melting and to generate E- MORBs in the Early Cretaceous. E-MORB-type dikes probably crystallized from melts produced by about 20%-30% partial melting of a spinel mantle source, which was metasomatized by melts from low-degree partial melting of the subducted slab. 相似文献
9.
甘肃景泰县老虎山地区蛇绿岩及其上覆岩系中枕状熔岩的地球化学特征 总被引：10，自引：3，他引：10
甘肃景泰县老虎山地区蛇绿岩之上覆盖着一套镁铁质的喷出岩和沉积岩组合，位于蛇绿岩的枕状熔岩之上，不是蛇绿岩的成员，为蛇绿岩的上覆岩系。蛇绿岩的枕状熔岩具Ｎ－ＭＯＲＢ的特征，而其上覆岩系中的枕状熔岩类似Ｅ－ＭＯＲＢ。前者来自扩张脊的下部岩浆房；后者推测源于扩张脊之外的岩浆房，也是软流圈地幔中等至高程度部分熔融的产物，不过，可能有少量来自下地幔的物质的加入 相似文献
10.
The collision between the North Palawan Block (NPB) and Philippine Mobile Belt (PMB) has been the subject of studies considering its significance in help-ing define the tectonic evolution of the Philippine is-land arc system. The geology of the western Panay island reveals the presence of a continent-related block (Buruanga Peninsula) juxtaposed to an oceanic frag-ment (Antique Ophiolite Complex). Our recent work in the Buruanga Peninsula helped us define the terrane boundary between the Peninsula and the Antique Ophiolite Complex. However, considering available published data, the Antique Ophiolite Complex has never been considered to be a part of the NPB and to mark the collision zone between Palawan and the PMB. 相似文献
11.
阿尔金山北缘冰沟蛇绿混杂岩中辉长岩锆石SHRIMP U-Pb定年及其地质意义 总被引：5，自引：3，他引：2
冰沟蛇绿混杂岩是阿尔金山红柳沟蛇绿混杂岩带的东段部分,岩石组合包括蛇纹岩、方辉橄榄岩、辉石岩和辉长岩等。蛇纹岩具高Mg,Mg/Fe值大于9,低Al、Ca、Na、K为特征,从稀土元素和微量元素特征来看,基性辉长岩和洋壳以及洋中脊玄武岩极为相似,而超基性岩与原始地幔较为接近。辉长岩获得锆石SHRIMP年龄为449.5±10.9Ma。蛇绿混杂岩的围岩为一套巨厚的碎屑岩、火山碎屑岩、火山岩,以及部分碳酸盐岩构成,其中含有具有洋中脊特征的枕状构造玄武岩,以及放射虫硅质岩,放射虫时代为奥陶纪中晚期,与辉长岩的SHRIMP年龄一致。这些证据进一步证实了红柳沟一带存在早古生代洋盆的地质事实。 相似文献
12.
The geochemistry of mantle chromitites from the northern part of the Oman ophiolite: inferred parental melt compositions 总被引：2，自引：0，他引：2
Hugh Rollinson 《Contributions to Mineralogy and Petrology》2008,156(3):273-288
Chromitites from a single section through the mantle in the Oman ophiolite are of two different types. Low-cr# chromitites,
of MORB affinity are found in the upper part of the section, close to the Moho. High-cr# chromitites, with arc affinities
are found deeper in the mantle. Experimental data are used to recover the compositions of the melts parental to the chromitites
and show that the low-cr# chromitites were derived from melts with 14.5–15.4 wt% Al2O3, with 0.4 to 0.9 wt% TiO2 and with a maximum possible mg# of 0.76. In contrast the high-cr# chromitites were derived from melts with 11.8–12.9 wt%
Al2O3, 0.2–0.35 wt% TiO2 and a maximum melt mg# of 0.785. Comparison with the published compositions of lavas from the Oman ophiolite shows that the
low-cr# chromitites may be genetically related to the upper (Lasail, and Alley) pillow lava units and the high-cr# chromitites
the boninites of the upper pillow lava Alley Unit. The calculated TiO2–Al2O3 compositions of the parental chromitite magmas indicate that the high-cr# chromitites were derived from high-Ca boninitic
melts, produced by melting of depleted mantle peridotite. The low-cr# chromitites were derived from melts which were a mixture
of two end-members—one represented by a depleted mantle melt and the other represented by MORB. This mixing probably took
place as a result of melt–rock reaction.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
13.
SUPRA-SUBDUCTION ZONE ENVIRONMENT AND ECONOMIC POTENTIAL OF THE NIDAR OPHIOLITE OF INDUS SUTURE ZONE, EASTERN LADAKH,THE HIMALAYA 相似文献
14.
Diamonds have been discovered in mantle peridotites and chromitites of six ophiolitic massifs along the 1300 km‐long Yarlung‐Zangbo suture (Bai et al., 1993; Yang et al., 2014; Xu et al., 2015), and in the Dongqiao and Dingqing mantle peridotites of the Bangong‐Nujiang suture in the eastern Tethyan zone (Robinson et al., 2004; Xiong et al., 2018). Recently, in‐situ diamond, coesite and other UHP mineral have also been reported in the Nidar ophiolite of the western Yarlung‐Zangbo suture (Das et al., 2015, 2017). The above‐mentioned diamond‐bearing ophiolites represent remnants of the eastern Mesozoic Tethyan oceanic lithosphere. New publications show that diamonds also occur in chromitites in the Pozanti‐Karsanti ophiolite of Turkey, and in the Mirdita ophiolite of Albania in the western Tethyan zone (Lian et al., 2017; Xiong et al., 2017; Wu et al., 2018). Similar diamonds and associated minerals have also reported from Paleozoic ophiolitic chromitites of Central Asian Orogenic Belt of China and the Ray‐Iz ophiolite in the Polar Urals, Russia (Yang et al., 2015a, b; Tian et al., 2015; Huang et al, 2015). Importantly, in‐situ diamonds have been recovered in chromitites of both the Luobusa ophiolite in Tbet and the Ray‐Iz ophiolite in Russia (Yang et al., 2014, 2015a). The extensive occurrences of such ultra‐high pressure (UHP) minerals in many ophiolites suggest formation by similar geological events in different oceans and orogenic belts of different ages. Compared to diamonds from kimberlites and UHP metamorphic belts, micro‐diamonds from ophiolites present a new occurrence of diamond that requires significantly different physical and chemical conditions of formation in Earth's mantle. The forms of chromite and qingsongites (BN) indicate that ophiolitic chromitite may form at depths of >150‐380 km or even deeper in the mantle (Yang et al., 2007; Dobrthinetskaya et al., 2009). The very light C isotope composition (δ13C ‐18 to ‐28‰) of these ophiolitic diamonds and their Mn‐bearing mineral inclusions, as well as coesite and clinopyroxene lamallae in chromite grains all indicate recycling of ancient continental or oceanic crustal materials into the deep mantle (>300 km) or down to the mantle transition zone via subduction (Yang et al., 2014, 2015a; Robinson et al., 2015; Moe et al., 2018). These new observations and new data strongly suggest that micro‐diamonds and their host podiform chromitite may have formed near the transition zone in the deep mantle, and that they were then transported upward into shallow mantle depths by convection processes. The in‐situ occurrence of micro‐diamonds has been well‐demonstrated by different groups of international researchers, along with other UHP minerals in podiform chromitites and ophiolitic peridotites clearly indicate their deep mantle origin and effectively address questions of possible contamination during sample processing and analytical work. The widespread occurrence of ophiolite‐hosted diamonds and associated UHP mineral groups suggests that they may be a common feature of in‐situ oceanic mantle. The fundamental scientific question to address here is how and where these micro‐diamonds and UHP minerals first crystallized, how they were incorporated into ophiolitic chromitites and peridotites and how they were preserved during transport to the surface. Thus, diamonds and UHP minerals in ophiolites have raised new scientific problems and opened a new window for geologists to study recycling from crust to deep mantle and back to the surface. 相似文献
15.
J. A. Proenza F. Ortega-Gutirrez A. Camprubí J. Tritlla M. Elías-Herrera M. Reyes-Salas 《Journal of South American Earth Sciences》2004,16(8):129
The serpentinites and associated chromitite bodies in Tehuitzingo (Acatlán Complex, southern Mexico) are in close relationship with eclogitic rocks enclosed within a metasedimentary sequence, suggesting that the serpentinites, chromitites and eclogitic rocks underwent a common metamorphic history.Primary chromites from the chromitite bodies at Tehuitzingo are of refractory-grade (Al-rich) and have a chemical composition similar to that expected to be found in an ophiolitic environment. The chromite grains in chromitites and serpentinites are systematically altered to ‘ferritchromite’. The alteration trend is usually characterized by a decrease in the Al, Mg and Cr contents coupled by an increase in Fe3+ and Fe2+.The Tehutizingo chromitites have low Platinum Group Elements (PGE) contents, ranging from 102 to 303 ppb. The chondrite-normalized PGE patterns are characterized by an enrichment in the Ir-subgroup elements (IPGE=Os, Ir, Ru) relative to the Pd-subgroup elements (PPGE=Rh, Pt, Pd). In addition, all chromitite samples display a negative slope from Ru to Pd [(Os+Ir+Ru)/(Pt+Pd)=4.78−14.13]. These patterns, coupled with absolute PGE abundances, are typical of ophiolitic chromitites elsewhere. Moreover, all the analyzed samples exhibit chondrite-normalized PGE patterns similar to those found for non-metamorphosed ophiolitic chromitites. Thus, the PGE distribution patterns found in the Tehuitzingo chromitites have not been significantly affected by any subsequent Paleozoic high-pressure (eclogite facies) metamorphic event.The chondrite-normalized PGE patterns of the enclosing serpentinites also indicate that the PGE distribution in the residual mantle peridotites exposed in Tehuitzingo was unaffected by high-pressure metamorphism, or subsequent hydrothermal alteration since the serpentinites show a similar pattern to that of partially serpentinized peridotites present in mantle sequences of non-metamorphosed ophiolites.Our main conclusion is that the chromitites and serpentinites from Tehuizingo experienced no significant redistribution (or concentration) of PGE during the serpentinization process or the high-pressure metamorphic path, or during subsequent alteration processes. If any PGE mobilization occurred, it was restricted to individual chromitite bodies without changing the bulk-rock PGE composition.Our data suggest that the Tehuitzingo serpentinites and associated chromitites are a fragment of oceanic lithosphere formed in an arc/back-arc environment, and represent an ophiolitic mantle sequence from a supra-subduction zone, the chemical composition of which remained essentially unchanged during the alteration and metamorphic events that affected the Acatlán Complex. 相似文献
16.
中国铬铁矿资源的瓶颈状态已持续多年。最近,在西藏罗布莎蛇绿岩地幔橄榄岩的深部勘探发现200万t致密块状铬铁矿床,这是中国近50年来铬铁矿找矿的重大突破,对今后继续寻找同类型的铬铁矿床具有重要指导意义。蛇绿岩地幔橄榄岩中产出的豆荚状铬铁矿床是工业需求铬的重要来源。研究豆荚状铬铁矿的成矿作用和矿体围岩地幔橄榄岩地质特征,建立铬铁矿的成矿模型和找矿标志,是开展寻找同类型矿床的重要保证。随着近些年在豆荚状铬铁矿及围岩地幔橄榄岩中金刚石等深部矿物的不断发现和深入研究,人们对蛇绿岩型铬铁矿的物质来源和形成过程,有了新的认识,提出了铬铁矿的深部成因模式。研究认为深部成因铬铁矿床主要经历了4个阶段:(1)早期俯冲到地幔过渡带(410~660 km)的陆壳和洋壳物质被脱水和肢解,过渡带产生的热和流体促成了地幔的熔融和Cr的释放和汇聚;(2)铬铁矿浆在地幔柱驱动下,运移到过渡带顶部冷凝固结,并有强还原的流体进入,后者携带了深部形成的金刚石、斯石英等高压矿物,进入"塑性—半塑性地幔橄榄岩"中;(3)随着物质向上移动,深度降低,早期超高压相矿物发生相变,如斯石英转变成柯石英,高压相的铬铁矿中出溶成柯石英和单斜辉石;(4)在侵位过程和俯冲带环境下,含水熔体与方辉橄榄岩反应形成了不含超高压矿物的规模相对较小的浸染状铬铁矿及纯橄岩岩壳。进一步研究表明,同处雅鲁藏布江缝合带西段的几个大型地幔橄榄岩岩体与罗布莎岩体可以对比,经历了相同的构造背景和豆荚状铬铁矿的成矿作用,存在较大的找矿空间。 相似文献
17.
西藏吉定蛇绿岩地球化学特征及其构造指示意义 总被引：3，自引：2，他引：1
吉定蛇绿岩位于雅鲁藏布江蛇绿岩带的中段,是该带保存较好的蛇绿岩之一,通过对该岩体的研究及与附近蛇绿岩剖面的对比有助于恢复早白垩世雅鲁藏布江蛇绿岩带的演化过程。吉定蛇绿岩包括玄武岩、辉绿岩、堆晶岩及地幔橄榄岩四个岩石单元。壳层岩石岩浆结晶顺序为:橄榄石→单斜辉石→斜长石,代表湿岩浆系统分异。吉定蛇绿岩壳层熔岩(玄武岩和辉绿岩)Ti O2含量为0.87%~1.45%,平均1.1%,与印度洋N-MORB玻璃(1.19%)相似。REE配分模式具有明显的LREE亏损特征,稀土配分模式与典型的大洋中脊玄武岩相似。但其微量元素蛛网图上表现为富集LILE,而亏损HFSE,并具有较高LILE/HFSE比值特征,与俯冲带上的(SSZ)蛇绿岩相似。蛇绿岩熔岩在岩石地球化学上表现出既亲MORB,又具部分IAB的特征。结合区域上大竹卡、得几等蛇绿岩岩石及地球化学资料对比分析,提出吉定蛇绿岩形成于在洋内俯冲带上发育起来的弧后盆地,并提出日喀则地区早白垩世洋壳演化的解释模式:雅鲁藏布江中段蛇绿岩至少包含三种组分特征的蛇绿岩体,其代表性剖面分别是吉定,得村和大竹卡,分别形成于近俯冲带的弧后盆地、弧前盆地和弧后盆地,这些洋壳共同组成早白垩世时期的与特提斯洋俯冲带斜交的一条分段发育的洋中脊。 相似文献
18.
豆荚状铬铁矿:古大洋岩石圈残片的重要证据 总被引：16，自引：2，他引：16
豆荚状铬铁矿为蛇绿岩的特征性矿产 ,保留了上地幔岩浆构造作用、高温变形以及岩石成因的重要信息。它们常见于方辉橄榄岩内 ,位于大洋岩石圈莫霍面下 1～ 2km的古深度范围内。豆荚状铬铁矿常被纯橄岩薄壳围限 ,保留特征的豆状、豆壳状等构造。豆荚状铬铁矿的TiO2 含量较低 ,铂族元素 (PGE)的分布模式显示特征的负斜率。普遍认为 ,豆荚状铬铁矿形成于部分熔融条件下 ,涉及原始地幔熔体与亏损地幔橄榄岩的相互作用 ,伴随复杂的岩浆混合及结晶过程。狭窄的上地幔岩浆通道或孔穴为豆荚状铬铁矿理想的堆积部位。超俯冲带 (弧后盆地、岛弧、弧前 )、大洋中脊、转换断层均可能是豆荚状铬铁矿形成的理想环境。其中 ,洋脊扩张模式及大洋上俯冲带模式较好地解释了豆荚状铬铁矿成因。对于经历高级变质及多期变形的华北大陆基底 ,豆荚状铬铁矿是研究古老蛇绿岩最直接而有效的地质标志 ,对于研究古大洋岩石圈增生过程 ,上地幔演化 ,探索早期板块构造意义重大。 相似文献
19.
CHAN Lung Sang 《《地质学报》英文版》2019,93(Z2):9-9
Many ophiolite complexes like those of Oman and New Caledonia represent fragments of ancient oceanic crust and upper mantle generated at supra‐subduction zone environments and have been obducted onto the adjacent rifted continental margin together with the accretionary complexes and intra‐oceanic arcs. The Lajishan ophiolite complexes in the Qilian orogenic belt along the NE edge of the Tibet‐Qinghai Plateau are one of several ophiolites situated to the south of the Central Qilian block. Our geological mapping and petrological investigations suggest that the Lajishankou ophiolite complex consists of serpentinite, wehrlite, pyroxenite, gabbro, dolerite, and pillow and massive basalts that occur in a series of elongate fault‐bounded slices. An accretionary complex composed mainly of basalt, radiolarian chert, sandstone, mudstone, and mélange lies structurally beneath the ophiolite complex. The Lajishankou ophiolite complex and accretionary complex were emplaced onto the Qingshipo Formation of the Central Qilian block which shows features typical of turbidites deposited in a deep‐water environment of passive continental margin. Our geochemical and geochronological studies indicate that the mafic rocks in the Lajishankou ophiolite complex can be categorized into three distinct groups: massive island arc tholeiites, 509 Ma back‐arc dolerite dykes, and 491 Ma pillow basaltic and dolerite slices that are of seamount origin in a back‐arc basin. The ophiolite and accretionary complex constitute a Cambrian‐early Ordovician trench‐arc system within the South Qilian belt during the early Paleozoic southward subduction of the South Qilian Ocean prior to Early Ordovician obduction of this system onto the Central Qilian block. 相似文献
20.
别子型矿床最早形成于古元古代,并在显生宙海沟环境或弧前盆地广泛发育,其成矿区域发育厚层沉积岩地层,覆盖在火山岩之上,对成矿流体物质交换和金属元素富集有重要意义。别子型块状硫化物矿床下盘发育强烈的黄铁绢英岩化,而上盘仅发育微弱的绿泥石化、碳酸盐化。矿床常呈单个矿体产出或2~3个矿体连生,剖面上,由下至上表现为枕状玄武岩→块状含铜黄铁矿矿石→块状、条带状燧石黄铁矿矿石→块状碧玉岩。别子型矿床的火山岩围岩多为钙碱性系列,少量拉斑系列,与活动大陆边缘的岛弧火山岩具有相似的微量和稀土元素地球化学特征。成矿流体中的硫为幔源硫和海水硫的混合来源,成矿元素来源为幔-壳混合源。 相似文献