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1.
Zhaochong Zhang Gang Zhou Timothy M. Kusky Shenghao Yan Bailin Chen Li Zhao 《Gondwana Research》2009,16(2):201
The Eastern Junggar terrane of the Central Asian Orogenic Belt includes a Late Paleozoic assemblage of volcanic rocks of mixed oceanic and arc affinity, located in a structurally complex belt between the Siberian plate, the Kazakhstan block, and the Tianshan Range. The early history of these rocks is not well constrained, but the Junggar terrane was part of a Cordilleran-style accreted arc assemblage by the Late Carboniferous. Late Paleozoic volcanic rocks of the northern part of the east Junggar terrane are divided, from base to top, into the Early Devonian Tuoranggekuduke Formation (Fm.), Middle Devonian Beitashan Fm., Middle Devonian Yundukala Fm., Late Devonian Jiangzierkuduke Fm., Early Carboniferous Nanmingshui Fm. and Late Carboniferous Batamayineishan Fm. We present major element, trace element and Sr–Nd isotopic analyses of 64 (ultra)mafic to intermediate volcanic rock samples of these formations. All Devonian volcanic rocks exhibit remarkably negative Nb, Ta and Ti anomalies on the primitive mantle-normalized trace element diagrams, and are enriched in more highly incompatible elements relative to moderately incompatible ones. Furthermore, they have subchondritic Nb/Ta ratios, and their Zr/Nb and Sm/Nd ratios resemble those of MORBs, characteristics of arc-related volcanic rocks. The Early Devonian Tuoranggekuduke Fm., Middle Devonian Beitashan Fm., and Middle Devonian Yundukala Fm. are characterized by tholeiitic and calc-alkaline affinities. In contrast, the Late Devonian Jiangzierkuduke Fm. contains a large amount of tuff and sandstone, and its volcanic rocks have dominantly calc-alkaline affinities. We therefore propose that the Jiangzierkuduke Fm. formed in a mature island arc setting, and other Devonian Fms. formed in an immature island arc setting. The basalts from the Nanmingshui Fm. have geochemical signatures between N-MORB and island arcs, indicating that they formed in a back-arc setting. In contrast, the volcanic rocks from the Batamayineishan Fm. display geochemical characteristics of continental intraplate volcanic rocks formed in an extensional setting after collision. Thus, we propose a model that involves a volcanic arc formed by northward subduction of the ancient Junggar ocean and amalgamation of different terranes during the Late Paleozoic to interpret the formation of the Late Paleozoic volcanic rocks in the Eastern Junggar terrane, and the Altai and Junggar terranes fully amalgamated into a Cordilleran-type orogen during the end of Early Carboniferous to the Middle–Late Carboniferous. 相似文献
2.
The palaeontologically dated Ordovician associations of the Peloritan Mountains consist of metasilts, metapelites, calc-schists and metavolcanic rocks. These rocks form a portion of a terrigenous-volcanic-carbonate sequence of Cambro-Ordovician to Carboniferous age. This Palaeozoic sequence occupies the lower tectonic position in a Variscan orogen, affected by later Alpine deformation. The upper portion of this orogen is formed by low to high grade metamorphic rocks and some rare magmatic rocks. The Ordovician section of the sequence is divisible into a lower part (probably Arenigian), characterized by frequent and extensive within-plate alkaline metabasalts, and an upper part characterized by metadacites and metarhyolites intercalated with metasediments, commonly carbonates. The chemical characteristics of the metavolcanic rocks and the composition and structure of the metasediments indicate the persistence of tensional conditions during the Lower Ordovician. In contrast, the Upper Ordovician was marked by reducing tension, stagnation of basaltic magmas at different crustal levels, and consequent formation of dacitic and rhyolitic melts by partial melting of the surrounding crust. A comparison of the Ordovician sequences of the Peloritan Mountains with those of the Calabrian Palaeozoic basins shows several geodynamic similarities. Among other circum-Mediterranean basins, only that of north-western Bulgaria shows good analogies. 相似文献
3.
The Calabrian–Peloritan Hercynian Range includes three weakly metamorphosed Palaeozoic sequences cropping out in north-eastern Sila (Bocchigliero sequence), southern Sila, Serre and Aspromonte (Stilo sequence), and in the Peloritan Mountains (Peloritan sequence). The work reported here considers the Bocchigliero sequence and comprises part of a geological, petrological and geochemical research programme on the Palaeozoic evolution of the Calabrian–Peloritan Arc. The Bocchigliero sequence constitutes the lower tectonic unit of the Hercynian Caiabrian–Peloritan Range and is overthrusted by the metamorphic Mandatoriccio Unit. The Bocchigliero sequence is a terrigenous–carbonate–volcanic association, is affected byclow grade metamorphism, contains Cambro-Ordovician fossils and extends in age from the Cambrian to the Devonian. The terrigenous material is represented by meta-arenites and metapelites (Cambrian–Devonian); the volcanics include metatuffites (Cambrian and Ordovician), metabasalts (Cambro-Ordovician), metaandesites and metarhyolites (Ordovician and Siluro-Devonian); limestone beds are present in the Devonian. It is believed that the Palaeozoic Bocchigliero basin formed in the Cambrian on a continental crust in which the rocks constituting today's Mandatoriccio Unit were located at 3–8 km depth. The crustal thinning in the Cambro-Ordovician led to fracturing and upwelling of alkaline within-plate basaltic magmas, whereas in the Ordovician the thinning took place under conditions of higher plasticity. In this latter period an increase in temperature resulting from mantle upwelling produced crustal partial melts of andesite and rhyolite composition. In addition, this thermal uprise was responsible for regional metamorphism characterized by low pressures and by the absence of penetrative deformation. The effects of this metamorphism are well developed in the rocks of the Mandatoriccio Unit. In the Silurian and Devonian, progressive closing of the basin took place. The Palaeozoic sequence was then subjected to Variscan low pressure–low temperature metamorphism and Alpine deformation. 相似文献
4.
在东准噶尔卡拉麦里地区的五彩湾一带出露一套具磨拉石特征的火山沉积建造, 下部为具磨拉石特征的砾岩、砂岩, 上部为一套中基性的火山熔岩夹中酸性的火山凝灰岩.1:20万卡拉麦里山幅将其归入下石炭统松喀尔苏组.通过1:5万地质调查研究发现, 该火山沉积建造底部以一套粗砾岩高角度不整合于下-中泥盆统卡拉麦里组之上, 含晚泥盆世植物化石Prelepidodendron sp.(先鳞木), 中上部火山岩LA-ICP-MS锆石U-Pb年龄为346.8±3.3 Ma, 且被年龄为341.1±4.0 Ma~340.9±5.1 Ma后碰撞花岗岩侵入, 表明其形成时代为晚泥盆世-早石炭世, 时代上对应于北准噶尔地层分区的上泥盆统克安库都克组.该套地层中上部的火山岩的岩石组合为玄武岩、玄武安山岩、夹少量的流纹质凝灰岩, 岩石化学特征上属钙碱性-高钾钙碱性系列, (La/Yb)N=2.97~6.66, Nb、Ta亏损, 部分样品Zr、Ti弱显亏损, Nb/U、Ce/Pb比值分别为7.43~20.88、3.17~12.45.地球化学特征表明其兼具板内火山岩和弧火山岩的某些特点, 形成于后碰撞伸展环境, 是卡拉麦里洋盆于晚泥盆世之前闭合后后碰撞岩浆活动的产物.这一研究成果对广为关注的卡拉麦里洋盆的闭合时间进行了很好的限定. 相似文献
5.
Three Palaeozoic sequences belonging to three different basins crop out in the Calabrian–Peloritan Arc. Their age covers the time span from middle (?) Cambrian to early Carboniferous. The sequences comprise terrigenous, volcanic and carbonate rocks, and show low-grade metamorphism. The basement is of pre-middle Cambrian age, crops out in the Calabrian–Peloritan Arc, and was metamorphosed prior to the opening to the Palaeozoic basins. The Palaeozoic basins existed no later than the middle Carboniferous, with inferred maximum crustal extension in the Cambro-Ordovician. By Devonian time, the tectonic regime was compressional overall with middle Devonian island-arc type volcanic activity that continued until the closure of the basins. Approximately 330 Myr, the Palaeozoic sequences experienced low-pressure greenschist facies metamorphism and continuing subduction controlled the Variscan tectonogenesis with 280 Myr island-arc type intrusive magmas. Subduction ceased and late-stage 280–270 Myr granitic magmas were emplaced during continental collision. The crustal sector carrying the Palaeozoic basins is interpreted as comprising fragments of an active continental margin, one of the several microplates, located at the southern margin of the Euro-Asia continent which faced a large (at least 1500 km in width) ocean basin. 相似文献
6.
全区泥盆系、石炭系发育厚层海相火山建造。下大民山组（Ｄ３ｘ）火山岩为基性一中基性，属拉斑玄武岩和碱性玄武岩的过渡物，成因是地幔岩部分熔融，形成于大陆边缘孤后盆地裂谷作用的早期环境；在下大民山组顶部的岩屑凝灰岩中首次发现铁矿浆浆屑，也反映全区于中泥盆世－晚泥盆世早期为大陆边缘裂谷环境。上大民山组（Ｄ３ｓ）为基性一酸性火山岩，属岛孤钙碱性系列，为结晶分异成因，形成环境类似于安第斯山之火山弧。早石炭世火 相似文献
7.
阿尔泰山南缘晚古生代火山岩的地质地球化学特征及其对构造演化的启示 总被引：15，自引：0，他引：15
阿尔泰山南缘晚古生代火山岩十分发育,从早泥盆世到早二叠世均有发育。其中中泥盆世北塔山组为一套中基性火山岩,并且底部含有厚度超过100m的苦橄岩;中泥盆世蕴都喀拉组为一套浅海相细碎屑沉积岩夹中性、中基性火山岩;晚泥盆世江孜尔库都克组为火山碎屑岩夹中基性和中酸性火山岩组合;而晚石炭世巴塔玛依内山组以玄武岩和玄武安山岩为主,夹凝灰岩、粉砂岩和炭质页岩。对这4个组火山岩的主要元素、微量元素地球化学特征研究表明,北塔山组和蕴都喀拉组为拉斑和钙碱性系列,并且均具有大离子亲石元素(LILE)富集,而高场强元素与MORB相当,说明其为岛弧环境。江孜尔库都克组火山岩为钾玄岩系列,并且具有较高的LILE富集,表明其形成于岛弧演化的晚期阶段;巴塔玛依内山组火山岩为碱性系列,并且具有强烈富集LILE的特征,指示了其形成于大陆板内环境。因此,从火山岩的时间和空间演化来看,本区晚古生代火山岩与准噶尔洋板块向北的俯冲有关,西伯利亚板块和准噶尔板块的碰撞发生在早石炭-晚石炭世。 相似文献
8.
内蒙古敖汉旗朝吐沟组火山岩LA-ICP-MS锆石U-Pb年龄 总被引：2，自引：0，他引：2
内蒙古赤峰敖汉旗一带的朝吐沟组由变基性岩、变质酸性火山岩夹云母石英片岩组成。采用LA-ICP-MS技术,对朝吐沟组2件变流纹岩样品进行了U-Pb同位素测定,获得的锆石206Pb/238U年龄加权平均值分别为359.4±1.4Ma和360.3±1.4Ma,即晚泥盆世法门期,表明朝吐沟组形成于晚泥盆世,而非前人认为的早石炭世。朝吐沟组火山岩石组合为变玄武岩和变流纹岩,显示出典型的双峰式火山岩特征,揭示该区在晚泥盆世处于伸展构造环境。 相似文献
9.
式可布台铁矿位于西天山阿吾拉勒铁矿成矿带西段,是此矿带极具代表性的铁矿床。主要赋存于以凝灰岩为主的石炭系上统伊什基里克组火山岩中。本文通过对式可布台矿区的火山岩进行岩石地球化学和LA-ICPMS锆石U-Pb测年分析来探讨火山岩形成的构造环境与成岩时代。地球化学分析表明大多数火山岩样品显示为高钾钙碱性系列;主量元素表明矿区火山岩主要由安山岩、英安岩、流纹英安岩组成,为钙碱性系列;微量元素和稀土元素表明矿区火山岩产出的构造环境为火山岛弧;LA-ICPMS锆石U-Pb测年显示火山岩的206Pb/238U加权平均年龄分别为(301±1)Ma和(313±2)Ma,表明该区的火山岩为晚石炭世早期。结合区域地质资料,认为矿区内出露的高钾钙碱性系列火山岩可能属于俯冲过程末期大陆岛弧岩浆作用的产物,其岩石的形成与构造岛弧环境有关,主体与下石炭统大哈拉军山组火山岩岩石化学特征相似。 相似文献
10.
随着研究的不断深入,在中亚造山带(CAOB)不断有不同时代的洋岛玄武岩(OIB)被识别出来。在中亚造山带西南缘的西准噶尔地区的多条蛇绿混杂岩带中,也存在具有OIB特征的玄武岩。这些玄武岩呈枕状,与超基性岩、辉长岩、块状玄武岩、灰岩及紫红色硅质岩等紧密共生。地球化学研究表明枕状玄武岩均为碱性系列,具有较高的TiO2含量(大多>2.5%)、强烈富集轻稀土元素、无明显Nb、Ta负异常,与典型的OIB极为相似,认为其可能形成于大洋板内与地幔柱有关的海山环境。通过对海山的发展阶段分析认为,西准噶尔地区海山应该发展到爆炸海山阶段,因为其中发育大量的枕状熔岩。海山中火山岩或火山碎屑沉积物富集大离子亲石元素和高场强元素,海山的俯冲将对弧及弧后地区火山岩地球化学产生明显影响,而西准噶尔地区泥盆纪-石炭纪火山岩中恰恰存在海山的信号。因此,海山俯冲模式可能能更好地解释西准噶尔地区火山岩中存在OIB特征火山岩的成因。另外,海山俯冲还存在潜在的资源效应,因此应该寻找和研究古海山及火山岛链俯冲的迹象,将对进一步找金铜等矿提供可靠依据。 相似文献
11.
阿拉善北部地区石炭纪火山岩分布广泛, 目前对其成因和构造环境研究还很薄弱.通过对该区石炭纪火山岩岩石学和地球化学特征的分析, 探讨其岩石成因和形成时的构造背景, 为判定石炭纪盆地性质与古构造环境提供岩石地球化学约束.研究区内石炭纪火山岩主要为中-酸性火山岩, 少量基性火山岩.玄武岩、玄武安山岩的大多数样品显示亚碱性系列特征, Mg#介于0.29~0.69之间, 高场强元素Nb、Ta、Ti明显亏损, 岩石轻度富集轻稀土元素(LREE), (La/Yb)N=2.19~10.10, Eu异常不明显(δEu=0.81~1.08), 稀土配分曲线右倾较缓, εNd(t)值较高(+1.10~+6.35).总体上既显示板内构造环境特征, 又携带俯冲带地球化学印记.综合区域地质特征及前人研究结果, 认为阿拉善北部及其邻区石炭纪火山岩形成于板内裂谷环境, 且可能与地幔柱事件有关, 岩浆在上升过程中受到地壳物质不同程度的混染. 相似文献
12.
The paper reviews geological, geochronological and geochemical data from the Late Paleozoic – Mesozoic magmatic complexes of the Siberian continent north of the Mongol-Okhotsk suture. These data imply that these complexes are related to the subduction of the Mongol-Okhotsk Ocean under the Siberian continent. We suggest that this subduction started in the Devonian, prior to the peak of magmatic activity. Studied magmatic complexes are of variable compositions possibly controlled by changes of the subduction regime and by possible input from enriched mantle sources (hot spots).The oceanic lithosphere of the Mongol-Okhotsk Ocean had shallowly subducted under the Siberian continent in the Devonian. Steeper subduction in the Early – Late Carboniferous led to switching from an extensional to compressional tectonic regime resulting in fold-thrust deformation, to the development of duplex structures and finally to the thickening of the continental crust. This stage was marked by emplacement of voluminous autochthonous biotite granites of the Angara-Vitim batholith into the thickened crust. The igneous activity in the Late Carboniferous – Early Permian was controlled by the destruction of the subducted slab. The allochthonous granitoids of the Angara-Vitim batholith, and the alkaline granitoids and volcanics of the Western Transbaikalian belt were formed at this stage. All these complexes are indicative of extension of the thickened continental crust. A normal-angle subduction in the Late Permian – Late Triassic caused emplacement of various types of intrusions and volcanism. The calc-alkaline granitoids of the Late Permian – Middle Triassic Khangay batholith and Late Triassic Khentey batholith were intruded near the Mongol-Okhotsk suture, whereas alkaline granitoids and bimodal lavas were formed in the hinterland above the broken slab. The Jurassic is characterized by a significant decrease of magmatic activity, probably related to the end of Mongol-Okhotsk subduction beneath the studied area.The spatial relationship of the Late Permian – Middle Triassic granitoids, and the Late Triassic granitoids is typical for an active continental margin developing above a subduction zone. All the Late Carboniferous to Late Jurassic mafic rocks are geochemically similar to subduction-related basalts. They are depleted in Nb, Ta, Ti and enriched in Sr, Ba, Pb. However, the basaltoids located farther from the Mongol-Okhotsk suture are geochemically similar to a transition type between island-arc basalts and within-plate basalts. Such chemical characteristics might be caused by input of hot spot related enriched mantle to the lithospheric mantle modified by subduction. The Early Permian and Late Triassic alkaline granitoids of southern Siberia are of the A2-type geochemical affinities, which is also typical of active continental margins. Only the basaltoids generated at the end of Early Cretaceous are geochemically similar to typical within-plate basalts, reflecting the final closure of the Mongol-Okhotsk Ocean. 相似文献
13.
新疆甜水海地块种羊场石炭纪火山岩年代学和地球化学:岩石成因和地质意义 总被引：1，自引：1，他引：0
甜水海地块西段的种羊场地区发育一套互层状产出的玄武岩-玄武安山岩-流纹岩,本文对其进行了岩石学、同位素年代学和地球化学研究。结果表明,流纹岩LA-ICP-MS锆石U-Pb定年获得三组年龄:343.5±4.1Ma表明火山岩的形成时代为早石炭纪,2439±26Ma和1988±36Ma说明甜水海地块存在前寒武纪结晶基底。其中玄武质岩石岩性从拉斑系列、钙碱性系列向碱性系列过渡,呈现出E-MORB(OIB)、大陆板内拉张和岛弧的混合特征,与典型弧后盆地Okinawa玄武岩有一定的差异,表明其可能是异常陆缘弧后盆地拉张裂解的产物。玄武质岩石和流纹岩的主量元素、稀土元素和微量元素比值对的差异表明它们不是同源岩浆演化的产物,玄武质岩石的源区为类似E-MORB(OIB)的岩石圈地幔,且发生了部分熔融,原始岩浆上升过程中经历了矿物分离结晶和地壳混染作用。流纹岩属于高硅高碱的钙碱性火山岩,是上地壳部分熔融的产物。种羊场早石炭纪火山岩可能代表了古特提洋西端早期扩张的记录,为西昆仑-喀喇昆仑地区晚古生代多岛洋格局提供了新的证据。 相似文献
14.
Fault blocks and inliers of uppermost Silurian to Middle Devonian strata in the Yarrol Province of central coastal Queensland have been interpreted either as island-arc deposits or as a continental-margin sequence. They can be grouped into four assemblages with different age ranges, stratigraphic successions, geophysical signatures, basalt geochemistry, and coral faunas. Basalt compositions from the Middle Devonian Capella Creek Group at Mt Morgan are remarkably similar to analyses from the modern Kermadec Arc, and are most consistent with an intra-oceanic arc associated with a backarc basin. They cannot be matched with basalts from any modern continental arc, including those with a thin crust (Southern Volcanic Zone of the Andes) or those built on recently accreted juvenile oceanic terranes (Eastern Volcanic Front of Kamchatka). Analyses from the other assemblages also suggest island-arc settings, although some backarc basin basalt compositions could be present. Arguments for a continental-margin setting based on structure, provenance, and palaeogeography are not conclusive, and none excludes an oceanic setting for the uppermost Silurian to Middle Devonian rocks. The Mt Morgan gold–copper orebody is associated with a felsic volcanic centre like those of the modern Izu–Bonin Arc, and may have formed within a submarine caldera. The data are most consistent with formation of the Capella Creek Group as an intra-oceanic arc related to an east-dipping subduction zone, with outboard assemblages to the east representing remnant arc or backarc basin sequences. Collision of these exotic terranes with the continent probably coincided with the Middle–Upper Devonian unconformity at Mt Morgan. An Upper Devonian overlap sequence indicates that all four assemblages had reached essentially their present relative positions early in Late Devonian time. Apart from a small number of samples with compositions typical of spreading backarc basins, Upper Devonian basalts and basaltic andesites of the Lochenbar and Mt Hoopbound Formations and the Three Moon Conglomerate are most like tholeiitic or transitional suites from evolved oceanic arcs such as the Lesser Antilles, Marianas, Vanuatu, and the Aleutians. However, they also match some samples from the Eastern Volcanic Front of Kamchatka. Their rare-earth and high field strength element patterns are also remarkably similar to Upper Devonian island arc tholeiites in the ophiolitic Marlborough terrane, supporting a subduction-related origin and a lack of involvement of continental crust in their genesis. Modern basalts from rifted backarc basins do not match the Yarrol Province rocks as well as those from evolved oceanic arcs, and commonly have consistently higher MgO contents at equivalent levels of rare-earth and high field strength elements. One of the most significant points for any tectonic model is that the Upper Devonian basalts become more arc-like from east to west, with all samples that can be matched most readily with backarc basin basalts located along the eastern edge of the outcrop belt. It is difficult to account for all geochemical variations in the Upper Devonian basalts of the Yarrol Province by any simplistic tectonic model using either a west-dipping or an east-dipping subduction zone. On a regional scale, the Upper Devonian rocks represent a transitional phase in the change from an intra-oceanic setting, epitomised by the Middle Devonian Capella Creek Group, to a continental margin setting in the northern New England Orogen in the Carboniferous, but the tectonic evolution must have been more complex than any of the models published to date. Certainly there are many similarities to the southern New England Orogen, where basalt geochemistry indicates rifting of an intra-oceanic arc in Middle to Late Devonian time. 相似文献
15.
吐--哈盆地及周缘早二叠世火山岩地球化学特征及大地构造环境探讨 总被引：11，自引：1，他引：11
长期以来对吐—哈盆地及其周缘地区早二叠世构造环境的归属存在较大异议.通过对盆地早二叠世火山岩地球化学特征的研究,进一步厘定了火山岩的产出环境.研究表明,区内火山岩以玄武岩、玄武安山岩和流纹岩为主,具双峰式火山岩特征,大部分玄武岩相对MORB强烈富集LILE和LREE,HFSE适度富集,Th/Ta比值>5,Ta、Nb的适度亏损和陆壳的混染有关,少量玄武岩带有与消减作用有关的地球化学信息,与造山期后伸展环境下的火山岩地球化学特征相似.结合区域地质特征及邻区研究结果,认为吐—哈盆地早二叠世火山岩为造山期后伸展背景下裂谷环境的产物. 相似文献
16.
新疆西天山吐拉苏火山岩盆地浅成低温热液-斑岩型金多金属成矿系统的形成与演化 总被引：1，自引：0，他引：1
新疆西天山吐拉苏地区发育的与中酸性火山-次火山岩有关的浅成低温热液-斑岩型金多金属成矿系统,是在晚古生代北天山洋向南部伊犁-中天山板块之下俯冲消减的活动大陆边缘背景下形成的。赋矿的大哈拉军山组火山岩及相关的次火山岩形成于晚泥盆世-早石炭世,岩石总体显示钾质-高钾质、准铝质-过铝质的钙碱性-高钾钙碱性特征,其轻稀土富集、Eu负异常显著、大离子亲石元素富集和高场强元素亏损等,均显示出俯冲带岛弧岩浆作用的特点。阿希(低硫型)和京希-伊尔曼得(高硫型)浅成低温热液金矿床以及塔北、吐拉苏铅锌矿床,受大哈拉军山组火山岩中的断裂破碎带以及具高孔隙度和渗透率的岩性控制;塔吾尔别克斑岩型金矿化主要受斑岩体及火山岩中的断裂和裂隙系统控制,并很可能存在浅成低温热液型金矿化的套合或叠加。硫、铅、碳、氧同位素特征显示,成矿物质主要来自岩浆所分泌的热液和/或赋矿的火山-次火山岩。根据成矿系统形成后的保存和变化情况,认为在吐拉苏盆地内剥蚀程度较低的地区,浅成低温热液型金铅锌矿床具备良好的保存条件,同时在其深部还应注意寻找斑岩型或矽卡岩型铜金矿床。 相似文献
17.
突出山铜铁矿床赋存于上石炭统底坎尔组火山岩中, 地质特征表明矿床成因为火山热液交代型。矿区玄武岩具有高Al、Na, 贫K、P、Ti的特点, 属于钙碱性系列火山岩。岩石具有轻稀土元素、大离子亲石元素相对富集和高场强元素相对亏损的特点。微量元素特征表明岩石与俯冲带流体作用有关, 经历了橄榄石(±辉石)和铬铁矿的结晶分异作用, 形成于石炭纪弧后盆地环境, 指示铁矿床的成矿环境为弧后盆地环境。矿区闪长岩和钾长花岗岩的锆石LA-ICP-MS U-Pb谐和年龄分别为326.2±1.6 Ma与318.2±2.5 Ma, 均为石炭纪岩浆活动的产物。根据闪长岩、钾长花岗岩、矿体与底坎尔组火山岩的穿插关系, 限定矿床的铁成矿作用时间为底坎尔组火山岩的形成时代, 早于闪长岩的形成时代(326 Ma), 而铜成矿作用时间与闪长岩的形成时代相近或稍晚。 相似文献
18.
The Northern, Central, and Southern zones are distinguished by stratigraphic, lithologic, and structural features. The Northern Zone is characterized by Upper Silurian–Lower Devonian sedimentary rocks, which are not known in other zones. They have been deformed into near-meridional folds, which formed under settings of near-latitudinal shortening during the Ellesmere phase of deformation. In the Central Zone, mafic and felsic volcanic rocks that had been earlier referred to Carboniferous are actually Neoproterozoic and probably Early Cambrian in age. Together with folded Devonian–Lower Carboniferous rocks, they make up basement of the Central Zone, which is overlain with a angular unconformity by slightly deformed Lower (?) and Middle Carboniferous–Permian rocks. The Southern Zone comprises the Neoproterozoic metamorphic basement and the Devonian–Triassic sedimentary cover. North-vergent fold–thrust structures were formed at the end of the Early Cretaceous during the Chukchi (Late Kimmerian) deformation phase. 相似文献
19.
The paper reports new isotope-geochemical data on Late Paleocene-Early Eocene basalts from the central part of the Kolyuchin-Mechigmen graben, eastern Chukotka Peninsula. The distribution of the major and trace elements and trace-element ratios indicates that the basalts were formed in a marginal-continental rift setting. The peculiar feature of the basalts is a combination of depleted within-plate and suprasubduction geochemical signatures, which make the volcanic rocks from Mt. Otdel’naya different from rocks of suprasubduction volcanic belts and from tholeiites and alkaline lavas of continental rifts and oceanic islands. Extremely high 87Sr/86Sr ratios in the studied basalts as compared to those of similar volcanic rocks from extension zones are probably related to the involvement of carbonate material in the magma generation zone. 相似文献
20.
Upper Devonian continental and subaqueous sedimentary rocks and bimodal volcanic rocks of the Boyd Volcanic Complex of the south coast of New South Wales were deposited in a rapidly subsiding, 330°‐trending, transtensional basin. Structural analysis of synvolcanic and synsedimentary deformational structures indicate that basin formation is related to a 330°‐orientated subhorizontal σ1 and a 060°‐orientated subhorizontal σ3, which account for the development of the observed intrusion and fracture orientations. Rhyolitic, basaltic and associated clastic dykes are preferentially intruded along extensional 330°‐trending fractures, subordinately along sinistral, transtensional 010°‐trending fractures and along 290°‐trending fractures. One of the implications of such a palaeotectonic reconstruction is that the so called north‐trending Eden‐Comerong‐Yalwal Late Devonian rift does not represent a simple, single palaeobasin entity, but is presently a north‐trending alignment of exposures of sedimentary and volcanic rocks probably emplaced in different basins or sub‐basins, mildly folded during the Carboniferous Kanimblan compression (which also formed the north‐trending Budawang synclinorium) and then extended to the east by the Tasman Sea opening during the Jurassic. The development of scattered, rapidly subsiding, basins characterised by bimodal volcanism during the Late Devonian throughout the Lachlan Fold Belt, can be interpreted in terms of extensional collapse of a forming mountain belt contemporaneous with a sharp decrease of compressional stress after the Middle Devonian Tabberabberan orogenic event. This would promote a reorientation of σ3 and transition from a compressional to a transtensional tectonic environment, which could also favour block rotation and formation of release basins. 相似文献