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1.
This paper presents the tectonostratigraphic evolution of the Maimará Basin and explores the relationship between the clastic sediments and pyroclastic deposits in the basin and the evolution of the adjacent orogeny and magmatic arc. The sedimentary facies in this part of the basin include, in ascending order, an ephemeral fluvial system, a deep braided fluvial system and a medial to distal ephemeral fluvial system. We interpret that Maimará Formation accumulated in a basin that has developed two stages of accumulation. Stage 1 extended from 7 to 6.4 Ma and included accelerated tectonic uplift in the source areas, and it corresponds to the ephemeral fluvial system deposits. Stage 2, which extended from 6.4 to 4.8 Ma, corresponds to a tectonically quiescent period and included the development of the deep braided fluvial system deposits. The contact between the Maimará and Tilcara formations is always characterized by a regional unconformity and, in the study area, also shows pronounced erosion.Rare earth element and other chemical characteristics of the tuff intervals in the Maimará Formation fall into two distinct groups suggesting the tuffs were erupted from two distinct late Miocene source regions. The first and most abundant group has characteristics that best match tuffs erupted from the Guacha, Pacana and Pastos Grandes calderas, which are located 200 and 230 km west of the study area at 22º-23º30′S latitude. The members the second group are chemically most similar to the Merihuaca Ignimbrite from the Cerro Galán caldera 290 km south-southwest of the studied section. The distinctive geochemical characteristics are excellent tools to reconstruct the stratigraphic evolution of the Neogene Maimará basin from 6.4 to 4.8 Ma.  相似文献   

2.
孟凡超  刘嘉麒 《地质科学》2010,45(3):807-821
松辽盆地晚中生代主要发育了两期大规模的火山活动,形成了火石岭组和营城组火山岩地层。火山活动高峰期分别为150 Ma和110 Ma,其中以营城组火山活动规模较大,持续时间较长,对油气的生成与成藏影响最大。晚中生代火山活动贯穿了火石岭组和沙河子组气源岩的主生烃期,加速了有机质的成熟和演化。火山喷发早于火山岩气藏的主成藏期,为气藏的形成提供了优质的储层和运移通道,有利于气藏的保存。营城组火山岩储层裂缝中充填大量的方解石、石英或岩浆浆屑等后期热液流体,其中粗面岩裂缝中岩浆浆屑的K-Ar全岩年龄为72.98 Ma,该期热液活动对火山岩储层的后期改造、天然气的运移及CO_2气藏的形成等具有重要作用。  相似文献   

3.
The alkaline El Chichón and calc-alkaline Tacaná volcanoes, located in southern Mexico, form parts of the Chiapanecan Volcanic Belt and Central American Volcanic Arc, respectively. El Chichón has emitted potassium-, sulphur-, and phosphorus-rich trachyandesites and trachybasalts (as mafic enclaves), whereas Tacaná has erupted basalts to dacites with moderate potassium contents, and minor high-Ti magmas (1.5–1.8 wt.% TiO2). The magmatic evolution in the two volcanoes has involved similar fractionating assemblages: Fe-Ti oxides, olivine, plagioclase, pyroxenes, amphibole, and apatite. K2O/P2O5 ratios and isotopic signatures indicate that magmas from both El Chichón and Tacaná have undergone significant crustal contamination. The volcanism at both Tacaná and El Chichón was previously related to northeastward subduction of the Cocos Plate, representing the main arc and the backarc, respectively. Although such an origin is in accord with Tacaná occurring 100 km above the Cocos Benioff Zone, it is inconsistent with: (a) the absence of a calc-alkaline belt between El Chichón and the Middle America Trench; and (b) truncation of the subducted Cocos Plate by the southwesterly dipping Yucatan slab near the Middle America Trench (i.e. the Cocos Plate does not presently underlie El Chichón). On the other hand, El Chichón and the Chiapanecan Volcanic Belt are located on the sinistral Veracruz fault zone that forms the northern boundary of the Southern Mexico block, which has been migrating relatively to the east since ca. 5 Ma. In this context, the anomalous high potassium, sulphur, and phosphorus levels in the El Chichón magmas are explicable in terms of rifting in a pull-apart system with the weak subduction fingerprint inherited from the Yucatan slab.  相似文献   

4.
Diagenetically altered volcanic ash deposits (bentonites) found in Cretaceous terrestrial and marine foreland basin sediments have the potential to be used for chronostratigraphy and subsurface correlation across Alaska's North Slope. Detailed age and geochemical studies of these volcanogenic deposits may also shed light on the tectonic evolution of the Arctic. Though these bentonites have been previously studied, there are few published results for regional bentonite ages and geochemistry due to challenges of dating weathered volcanic ash. We analyzed mineral separates from cored bentonites recovered from wells in the National Petroleum Reserve Alaska. The analyses confirm that an intense period of volcanic ash deposition on Alaska's North Slope began by the late Albian and persisted throughout the Cenomanian, an interval of rapid progradation and aggradation in the Colville basin. These results also add to a sparse record of radioisotopic ages from the Nanushuk Formation. A bentonite preserved in delta plain sediments in the upper Nanushuk Formation dates to 102.6 ± 1.5 Ma (late Albian), while a bentonite near the base of the overlying Seabee Formation was deposited at 98.2 ± 0.8 Ma, in the early Cenomanian. The two ages bracket a major flooding surface at the base of the Seabee Formation near Umiat, Alaska, placing it near the Albian-Cenomanian boundary (100.5 Ma). Several hundred feet up-section, the non-marine Tuluvak Formation contains bentonites with 40Ar/39Ar ages of 96.7 ± 0.7 to 94.2 ± 0.9 Ma (Cenomanian), several million years older than previously published K–Ar ages and biostratigraphic constraints suggest.Major and trace element geochemistry of a sub-sample of six bentonites from petroleum exploration wells at Umiat show a range in composition from andesite to rhyolite, with a continental arc source. The bentonites become more felsic from the late Albian (∼102 Ma) to late Cenomanian (∼94 Ma). A likely source for the bentonites is the Okhotsk-Chukotka Volcanic Belt (OCVB) of eastern Siberia, a continental arc which became active in the Albian and experienced episodes of effusivity throughout the Late Cretaceous. Chronostratigraphically anomalous 40Ar/39Ar ages coincide with peaks of magmatic activity in the OCVB, suggesting that these anomalously old ages may be due to magmatic contribution of xenocrysts or recycling of detrital minerals from older volcanic events. An alternative explanation for the chronostratigraphically anomalous ages is mixing of bentonites with detrital sediment derived from unroofing and erosion of metamorphic rocks in the Brooks Range, Herald Arch, and Chukotka throughout the mid to Late Cretaceous.  相似文献   

5.
Detrital volcanic and vein quartz, accompanied by felsic volcanic debris, occur as minor constituents in the Ordovician subduction‐related mafic volcanics of the Molong Volcanic Belt. In the western province of the Molong Volcanic Belt, detrital quartz is present in the three episodes of the mafic Volcanics. Volcanic quartz occurs in allochthonous limestone blocks in the Bendigonian Hensleigh Siltstone overlying the Mitchell Formation. The second volcanic episode (the Fairbridge Volcanics) commenced after a hiatus of approximately 20 million years and lasted around 10 million years from Darriwilian to Gisbornian time. Locally derived vein quartz, volcanic quartz and felsic detritus are concentrated at the bases of autochthonous Wahringa and Yuranigh Limestone Members of the volcanics and are extensive and abundant in basal beds of the regional Eastonian limestone body that transgressed over an eroded volcanic centre at Cargo. This early Eastonian debris, deposited early in an 8 million‐year volcanic hiatus preceding the final Ordovician Bolindian volcanism, establishes a pre‐Eastonian age for mineralisation at Cargo. It is inferred that the pauses in volcanism were preceded by magmatic fractionation, intrusion and hydrothermal activity and followed by erosion, subsidence and deposition of autochthonous limestones. Minor occurrences of vein and volcanic quartz are found in Bolindian volcanogenic sediments of the third volcanic phase. It is concluded that hydrothermal vein formation (and mineralisation by inference) was associated with pauses in volcanic activity throughout the Middle to early Late Ordovician over a wide area in the western province, culminating in the mineralisation at Cargo and Copper Hill near Molong. Volcanism in the eastern province of the Molong Volcanic Belt was continuous from at least Darriwilian to latest Ordovician time. Here, detrital hydrothermal vein quartz and volcanic quartz and felsic detritus are distributed through late Middle and early Late Ordovician turbidites of the Weemalla Formation. The possible existence of cycles in the source area like those of the Fairbridge Volcanics is masked by the distal nature of these deposits. Vein formation occurred in both provinces from late Middle Ordovician to early Late Ordovician, long before the formation of the world‐class mineral deposit at Cadia associated with the latest Ordovician Cadia Monzonite.  相似文献   

6.
《Gondwana Research》2001,4(3):421-426
The Rio Bonito Formation in southern Paraná basin contains a set of tonsteins interbedded with coal-seams. These tonsteins are composed mainly of kaolinite with zircon, apatite and beta-quartz paramorphs as accessory minerals, and were interpreted as volcanic ashes deposited by ash falls over pits protected by barrier islands in a barrier-lagoon system. A U-Pb dating of zircons in the tonstein A, which furnished an age of 267.1 ± 3.4 Ma (Early Permian) confirming previous age-dates based on palynology and correlating them with one of the main periods of volcanic activity in the Gondwana.The source of the pyroclastic material was attributed to the early Permian Choiyoi magmatic arc in Argentina, developed during the Sanrafaelic orogeny, and with a main peak of volcanic activity between 260 and 272 Ma.  相似文献   

7.
伊犁盆地南缘中-下侏罗统碎屑岩的物源特征,可为南天山造山带的演化提供重要证据。对其碎屑岩锆石U-Pb定年研究结果表明,伊犁盆地南缘坎乡下侏罗统八道湾组砂岩的碎屑锆石年龄集中在290~260 Ma,而下侏罗统三工河组的碎屑锆石年龄集中在350~290 Ma和460~390 Ma,中侏罗统西山窑组的碎屑锆石年龄集中在370~320 Ma和450~390 Ma。所有测试样品中前寒武纪的年龄记录非常少。这些特征表明,伊犁盆地南缘中生代碎屑沉积物主要来自于伊犁-中天山地块南部。测试样品中几乎不存在晚二叠世-中三叠世的碎屑锆石,与南天山造山带的岩浆岩记录一致,暗示在晚二叠世-中三叠世南天山地区并没有发生强烈的与碰撞或后碰撞相关的岩浆活动。该结果不支持塔里木克拉通与伊犁-中天山地块在晚二叠世-中三叠世碰撞的观点。结合高压-超高压变质岩的数据和地层记录,认为塔里木克拉通与伊犁-中天山地块的碰撞发生在晚石炭世。同时,样品中最年轻锆石的年龄数据从早侏罗世到中侏罗世逐渐增大,显示了揭顶沉积的特点。对伊犁盆地南部中生代的锆石年龄数据与同时代南天山地区的锆石年龄数据进行综合对比表明在早-中侏罗世发生构造沉积夷平的特征。  相似文献   

8.
GENESIS OF COPPER MINERALIZATION IN THE WESTERN KOHISTAN ISLAND ARC TERRANE,NW HIMALAYA—HINDUKUSH, N. PAKISTAN  相似文献   

9.
The lithostratigraphic sequence in the Rosário–Neves Corvo antiform comprises the Phyllite–Quartzite Group, whose top is of Famennian age, the Volcanic Sedimentary Complex, of Strunian to upper Visean age, and the Mértola Formation (the lower unit of the Baixo Alentejo Flysch Group) of upper Visean age. The volcanic sedimentary complex comprises a lower sequence of Strunian (Late Famennian) age and an upper sequence of lower to upper Visean age. Detailed mapping of the antiform towards NW of the Neves Corvo mine, supported by palynological dating, identified two new lithostratigraphic units: the Barrancão member (upper Famennian) ascribed to the Phyllite–Quartzite Group and made up of laminated dark shales with siliceous lenses and nodules, and the Ribeira de Cobres Formation of the Volcanic Sedimentary Complex, containing shales, siltstones and fine volcaniclastic rocks. Based on zircon U–Pb isotope dating, five discrete felsic magmatic events were identified at approximately 354, 359, 365, 373 and 384 Ma. This suggests that the volcanic activity in the area has extended for about 30 Ma, in a context of high regional heat flow as indicated by the geochemical signatures of the felsic volcanic rocks. The characteristics of magmatism and the depositional environment indicated by the sedimentary record should therefore have been highly favourable for massive sulphide formation. However, evidence of massive sulphide mineralization in the study area is still to be found. Moreover, reconstruction of the volcanic facies architecture demonstrated that the volcanic units in the Rosário area are strongly dominated by coherent facies typical of the inner part of thick lavas/domes. In fact, most of their external part, the more favourable location for possible massive sulphide mineralization, is missing. Palynological dating indicates a significant hiatus, recognised between the lower and upper sequences of the volcanic sedimentary complex, which implies erosion of the top of the volcanic centre, where VHMS deposits could possibly have formed. However, lateral areas of this volcanic centre, eventually preserved at depth, have good potential to host massive sulphide mineralization.  相似文献   

10.
大兴安岭北段诺敏河第四纪火山24座,分布于诺敏河及其支流毕拉河和甘河支流奎勒河,火山岩分布面积约600km2。诺敏河火山岩均属于钾质系列火山岩(K2O含量2%～4%,且K2O>Na2O-2%),类似于邻区五大连池-科洛钾质火山岩,具有来自类似的富钾地幔源区。但诺敏河火山岩的K2O含量明显低于五大连池-科洛火山岩的K2O含量(一般4%～6%)。东北地区和内蒙东部处于中亚造山带东段,从古生代到新生代,多重构造-岩浆活动导致火山岩源区地球化学非均一性和火山岩的多样性。根据本文提出的火山岩K-Ar年龄(2.3～0.128Ma)及火山地质特征,可将诺敏河第四纪火山岩分为四期。早期(早更新世)火山活动主要沿诺敏河和奎勒河流域分布,火山产物多被晚期沉积物或火山产物所覆盖。中更新世保留的火山锥体及熔岩流是诺敏河第四纪火山产物的主体,表明是第四纪火山活动的高潮期。晚更新世-全新世火山活动限于毕拉河流域,典型的四方山火山和马鞍山火山是该时期火山活动的代表作,保留了较完好的火山地质地貌特征。从火山产物的时空展布,推测诺敏河第四纪火山活动有从东向西发展的趋势。  相似文献   

11.
新疆东准噶尔石炭纪火山机构类型与时限   总被引：10，自引：2，他引：8  
东准噶尔卡拉麦里大气田的主要储层是石炭纪火山岩,石炭纪古火山机构的样式与组合特征,与火山岩储层展布关系密切。野外调查表明,隐爆角砾岩是东准噶尔石炭纪古火山机构最常见的标志之一。东准噶尔石炭纪古火山机构类型主要有中心式、裂隙式和裂隙-中心式等样式。中心式火山机构以大石头层状火山、柯克巴斯套锥状火山最为典型;巴塔玛依内山附近沿断裂分布的带状火山岩具有裂隙式喷发的特征;东黑山火山具有火山口串珠状排列特征,是裂隙-中心式喷发的产物。大石头地区原缪林托凯陶山组火山岩的锆石SHRIMP U-Pb年龄为345.6±7.1 Ma,而已知巴塔玛依内山组火山岩年龄是350.0±6.3Ma,因此东准噶尔火山活动的主要时期是早石炭世。  相似文献   

12.
本文对白乃庙地区徐尼乌苏组沉积特征、原岩建造、变质火山岩及变质碎屑岩的年代学和地球化学进行了研究,探讨了白乃庙地区早古生代构造演化。本次研究采集了徐尼乌苏组中具有代表性的变质含砾粗粒杂砂岩、变质英安质晶屑凝灰岩和变质长石石英细砂岩样品,进行了锆石LA-ICP-MS U-Pb年代学和岩石地球化学分析。结果显示,2个变质英安质晶屑凝灰岩锆石的加权平均年龄分别为440.9±1.8Ma(MSWD=0.10)和440.9±1.7Ma(MSWD=0.15),锆石Th/U比值为0.46~1.59,自形程度较好,发育有典型的岩浆锆石振荡环带结构,显示为岩浆成因锆石的特点,表明徐尼乌苏组的形成时代为早志留世。变质含砾粗粒杂砂岩的碎屑锆石年龄在452.0±1.3Ma~535.0±1.0Ma之间,最高峰值年龄为490Ma左右;变质长石石英细砂岩碎屑锆石年龄则在440.1±5.7Ma~3268.9±57.7Ma之间,最小谐和年龄为440.1±5.7Ma,峰值年龄为490Ma左右,另有1.0Ga、1.6Ga、1.8Ga和2.5Ga四个明显的峰值年龄。根据研究区徐尼乌苏组岩性组合与结构构造,可将该组划分为3个不同的沉积旋回。结合白乃庙地区徐尼乌苏组测年结果、岩石地球化学特征、原岩建造及区域岩浆岩资料,白乃庙弧后盆地沉积可划分为三个演化阶段:早期快速堆积阶段(452.3~440.9Ma),形成了一套成熟度较低的粗碎屑岩建造,物源主要来源于白乃庙岩浆弧中的岩浆岩;中期火山喷发阶段(440.9~440.1Ma),以火山沉积作用为主,为火山碎屑岩建造夹有碳酸盐建造和少量碎屑岩建造,碎屑物质主要来源于该时期的火山活动;晚期稳定沉积阶段(440.1Ma),形成一套细碎屑岩建造和碳酸盐建造,为浅海相稳定沉积,此时物源广泛,分别来源于华北克拉通基底、兴蒙造山带和白乃庙早古生代火山弧。根据徐尼乌苏组的沉积建造和火山建造特征,结合白乃庙火山弧岩浆活动特征,认为徐尼乌苏组形成于早古生代弧后盆地中,此时华北板块北缘属于安第斯型活动大陆边缘。  相似文献   

13.
在东昆仑山脉西段祁漫塔格山中东部的尕林格南地区发育一套火山岩,调查显示火山活动爆发相→溢流相相间的韵律周期较明显,见由玄武质含火山角砾凝灰岩→玄武岩、玄武质凝灰岩→安山岩、安山质角砾凝灰岩→安山岩,以及安山质含火山角砾凝灰岩和安山岩质凝灰岩→玄武岩组成的4个韵律。根据研究区安山质火山角砾凝灰岩的LA-ICP-MS锆石U-Pb年龄222.2±2.1Ma,将该火山岩地层由前人划分的顶志留统—下泥盆统契盖苏组火山岩段重新厘定为上三叠统鄂拉山组。岩石地球化学研究结果表明,该套火山岩属于亚碱性钙碱性系列岩石,具有富钾、同源岩浆演化的特点,并具弧火山岩和碰撞火山岩的地球化学特征,为陆内造山作用下的产物,较好地记录了东昆仑祁漫塔格造山带在晚三叠世岩浆演化的地质信息。  相似文献   

14.
R.S. Thorpe 《Tectonophysics》1977,40(3-4):T19-T26
The Mexican Volcanic Belt of active, mainly andesite volcanoes extends from the Pacific coast, through central Mexico, to the Caribbean coast. The setting of the Belt is linked with subduction of the oceanic Cocos plate below continental Mexico. The eastern-most volcano in the Belt is part of the Tuxtla volcanic area on the Caribbean coast. Volcanics from this area belong to a picrite basalt—basanitoid-alkali basalt—hawaiite association, in contrast to the calc-alkaline association of the remainder of the Volcanic Belt, and are linked with lithospheric fracturing in the tectonic setting of a destructive-type continental plate margin.  相似文献   

15.
The Oligocene to Present Wrangell Volcanic Belt (WVB) extends for ~500 km across south‐central Alaska (USA) into Canada at a volcanic arc‐transform junction. Previously, geochemistry documented mantle wedge and slab‐edge melting in <12 Ma WVB volcanic rocks; new geochemistry shows that the same processes characterized ~18–30 Ma WVB magmatism in Alaska. New 40Ar/39Ar ages demonstrate that WVB magmatism in Alaska initiated at ~30 Ma due to flat‐slab subduction of the Yakutat microplate and that the dextral Totschunda fault was active at this time. Our results, together with prior studies, show that Alaskan WVB magmatism occurred chiefly due to subduction and should be considered a volcanic arc (e.g. the Wrangell Arc). The WVB provides a long‐term geological record of subduction, strike‐slip and magmatism. Slab‐edge upwelling, flat‐slab defocused fluid‐flux and faults acting as magma conduits are likely responsible for the exceptionally large volcanoes and high eruption rates of the Wrangell Arc.  相似文献   

16.
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17.
The chemical composition of metamorphosed siliciclastic rocks in the Orlica-?nie?nik Dome (Bohemian Massif) identifies the main sources for the Neoproterozoic [the M?ynowiec Formation (MF)], Early Cambrian [the Stronie Formation (SF)] and Late Cambrian/Early Ordovician [the Goszów quartzites (GQ)] sediments. The MF developed from erosion of a Cadomian magmatic arc along the northern Gondwana margin. The variegated SF, with supra-subduction affinities, shows chemical characteristics pointing to erosion of the freshly exhumed Cadomian orogen and detritus deposition in the back-arc basin. The very different chemical features of the GQ indicate deposition in a basin sited on a passive continental margin. The explanation proposed for the observed changes in chemical composition involves three main stages: (1) The pre ~540 Ma evolution of an active continental margin and related back-arc basin ceased with the collision and accretion of the magmatic arc to the Gondwana margin; (2) Early Cambrian rift to drift transition (540–500 Ma) and development of a depositional basin filled with detritus derived from remnants of the magmatic arc; (3) Peri-Gondwana break-up leading to the formation of shallow-water passive margin depositional basins filled with quartz-rich detritus resembling Early Ordovician Armorican quartzites known from other parts of the Variscan Belt.  相似文献   

18.
对冈底斯带的研究历来聚焦于岩浆弧,对弧间盆地的较少关注导致火山—沉积序列缺乏精细化研究。冈底斯带古近纪地层划分方案是基于并沿用东段林周、南木林地区的层序格架,即林子宗群与日贡拉组垂向叠置不整合接触,在带上其他地区适用时常产生矛盾,制约了基础地质及资源评价工作。通过系统实测孔隆—达果地区古近纪地层剖面,选取剖面中火山岩进行LA-ICP-MS锆石U-Pb测年,以详实的同位素年代学数据搭建精细年代地层格架,以沉积学、地层学研究分析充填演化过程,恢复火山—沉积盆地古地理。结果显示冈底斯造山隆升剥蚀并被扇沉积体系记录的过程,从晚白垩世早期断续持续至古近纪;以火山岩和/或以沉积岩为主的盆地,发育时限均下延至约70 Ma,暗示岩浆作用与隆升剥蚀对雅鲁藏布洋俯冲的响应几乎同时启动;火山—沉积盆地发育贯穿了整个增生造弧事件,以印亚大陆初始碰撞后的沉积间断为界,分为70~56 Ma和56~40 Ma两期,火山岩与沉积岩同时发育,以时空上的负消长关系占主导地位,表现为剖面上交互或夹层,并受喷发中心、沉积中心的横向迁移约束,产生了地层发育时限的空间变化;受晚白垩世末—古近纪雅鲁藏布洋北向俯冲及印亚大陆碰撞过程影响,持续的造山隆升及岩浆活动的周期性强弱变化约束了盆地发育样式,火山—沉积序列在区域上延展不稳定,垂向序列产生多样性。因此,本文提出层型剖面上火山岩与碎屑岩垂向叠置序列关系不能普适地代表整个冈底斯带,同期火山岩与沉积岩存在空间上快速相变过渡,应使用更为精细年代格架下的空间展布关系,指导冈底斯带弧间盆地地层划分,探讨印亚大陆碰撞的火山—沉积响应过程。  相似文献   

19.
龙江盆地是新厘定的松辽盆地外围中新生代盆地之一。有关该盆地中的沉积物特征及物源区大地构造背景是亟待解决的问题之一。通过对龙江盆地中侏罗统万宝组碎屑岩的砂岩碎屑组分、重矿物组合、岩石地球化学及锆石U-Pb年代学等进行研究,可以推测出物源的相关特征:(1)砂岩碎屑组分和重矿物组合反映了万宝组母岩以中酸性岩浆岩和中低级变质岩为主、含有少量中基性岩浆岩的特点;(2)地球化学特征显示,龙江盆地万宝组沉积物轻稀土元素富集、重稀土元素亏损,配分曲线表现出平缓的右倾模式,微量元素呈规律性变化,富集高场强元素(HFSE)Cs、Th、U,亏损Nb、P和Ti,具有与上地壳相似的地球化学特征;(3)碎屑锆石显示4组年龄峰值,主要峰值为167 5Ma,次要峰值为236 4Ma、309 1Ma和363 2Ma,反映了万宝组沉积物具有多物源的特点,母岩主要来自于中侏罗世火山岩,其次来自于晚泥盆世三叠纪的岩浆活动产物。综合分析认为,龙江盆地万宝组的物源具有长英质和中性火山岩特征,大部分来自于上地壳,原岩形成于活动大陆边缘背景下的大陆岛弧环境,中侏罗世沉积演化可能受到与古太平洋板块俯冲作用和蒙古鄂霍茨克缝合带演化双重作用的影响。该研究成果可为龙江盆地沉积演化分析和古地理环境恢复提供重要依据。  相似文献   

20.
东昆仑地区物质组成复杂、构造演化历史悠久,现保存的建造物质记录了从古元古代以来该区发生的地质事件,在多次洋陆转化中中泥盆世—中三叠世造山阶段尤为重要,同时也是该区岩浆活动和成矿作用的主要时期之一,长期以来缺失二叠纪火山岩记录。最近开展的1∶25万大灶火幅区调工作新发现一套中酸性高钾钙碱性系列火山岩组合,用LA-ICP-MS技术测得次流纹英安岩锆石U-Pb年龄为254.7±0.6Ma。根据剖面研究和区域对比,将这套陆缘弧环境下喷发的火山岩命名为晚二叠世大灶火沟组,主要分布在大灶火沟—万保沟一带,地层严格受昆南断裂控制,出露面积大于74km~2。这一发现不仅为东昆仑岩浆弧长期争论的是否存在二叠纪火山岩提供了明确的证据,而且填补了东昆仑地区晚二叠世火山岩地层的空白。东昆仑地区从二叠纪开始昆南洋向北俯冲,形成了规模巨大的碰撞型花岗岩,大灶火沟组火山岩的形成标志着晚二叠世东昆仑处于区域性挤压阶段。  相似文献   

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