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新疆西南天山下石炭统图尤克阿秀组火山岩地质及地球化学特征、构造环境及年代依据 总被引：1，自引：1，他引：0
西南天山下石炭统图尤克阿秀组火山岩为爆发相火山角砾(集块)岩、喷溢相致密状玄武岩、枕状杏仁状玄武岩,与沉积相结晶灰岩或放射虫硅质互层组成,其沉积相岩性在走向上相变明显.火山岩主要元素地球化学特征、稀土微量元素特征与典型的大洋岛屿玄武岩相似.岩石组合特征、岩相特征、主量元素、微量及稀土元素特征表明,该火山岩形成于板内大洋岛屿(海山)环境,具板内裂谷特征.综合硅质岩中放射虫组合和玄武岩全岩40Ar/39Ar年龄测试结果,确定火山岩形成地质时代为早石炭世. 相似文献
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新疆南天山库尔干南阿尔腾柯斯组硅质岩地层中发现了丰富的保存良好的放射虫化石,共计21属34种,11个未定种,1个未定种属。研究表明,两个样品的放射虫组合时代分别为中—晚泥盆世和早石炭世。中—晚泥盆世放射虫组合的发现,丰富了库车地区泥盆纪放射虫生物群组合,为确定阿尔腾柯斯组的时代奠定了生物化石依据。结合前人对该组生物化石的研究,该组为跨时代岩石地层单元,应予解体。而具有早泥盆世—晚石炭世放射虫硅质岩的深水海相沉积地层为古南天山洋盆的演化过程提供了地层学证据。 相似文献
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新疆南天山库尔干南阿尔腾柯斯组硅质岩地层中发现了丰富的保存良好的放射虫化石，共计21属34种，11个未定种，1个未定种属。研究表明，两个样品的放射虫组合时代分别为中-晚泥盆世和早石炭世。中-晚泥盆世放射虫组合的发现，丰富了库车地区泥盆纪放射虫生物群组合，为确定阿尔腾柯斯组的时代奠定了生物化石依据。结合前人对该组生物化石的研究，该组为跨时代岩石地层单元，应予解体。而具有早泥盆世-晚石炭世放射虫硅质岩的深水海相沉积地层为古南天山洋盆的演化过程提供了地层学证据。 相似文献
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东天山大南湖岛弧带石炭纪岩石地层与构造演化 总被引：5，自引：0，他引：5
详细的地质解剖工作表明,东天山地区大南湖岛弧带石炭纪出露4套岩石地层组合,即早石炭世小热泉子组火山岩、晚石炭世底坎儿组碎屑岩和碳酸盐岩、晚石炭世企鹅山组火山岩、晚石炭世脐山组碎屑岩夹碳酸盐岩。根据其岩石组合、岩石地球化学、生物化石、同位素资料以及彼此的产出关系,认为这4套岩石地层组合的沉积环境分别为岛弧、残余海盆、岛弧和弧后盆地。结合区域资料重塑了大南湖岛弧带晚古生代的构造格架及演化模式。早、晚石炭世的4套岩石地层组合并置体现了东天山的复杂增生过程。 相似文献
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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
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扬子地台北缘白勉峡组和三湾组火山岩形成构造环境及岩石成因的地球化学约束 总被引：5，自引：1，他引：4
依据中基性火山岩主量和微量元素地球化学特征的差异,白勉峡组可分两部分,一部分火山岩TiO_2大于1%,变质程度较高,主要分布在下段;另一部分火山岩TiO_2小于1%,变质程度较浅,主要分布在上段.下段火山岩属拉斑玄武岩系列,上段主体属钙碱系列,稀土总量高(∑REE=83.4～180.8μg/g),轻重稀土分异较低(LREE/HREE=2.17～5.85),有弱的Eu负异常(δEu=0.79～1.01),微量元素原始地幔蛛网图显示有弱的Nb、Ta亏损,具有板内火山岩的地球化学特点,形成于板内裂谷环境.上段火山岩稀土总量低(∑REE=40.3～82.4μg/g),轻重稀土分异较高(LREE/HREE=2.3～7.6),无Eu负异常(δEu=0.90～1.11),微量元素原始地幔蛛网图发育明显的Nb-Ta槽和Zr-Hf槽,Ti、Sr发育较强的低谷,具有典型岛弧玄武岩的地球化学特点,形成于岛弧或大陆边缘弧环境.三湾组玄武岩和安山岩稀土元素分配型式呈LREE亏损的左倾型或呈近平坦型,类似于N-MORB,明显不同于白勉峡组,岩石组合和地球化学特点类似于弧后盆地火山岩.火山岩及相关侵入岩LA-ICPMS锆石U-Pb定年及元素及Sr-Nd同位素地球化学研究揭示,白勉峡组下段火山岩形成时代可能为1144Ma,其源区为与洋岛玄武岩类似的软流圈地幔源区,部分熔融发生在石榴子石二辉橄榄岩稳定区,岩浆在演化过程中经历了一定分离结晶作用(分离结晶矿物为斜长石+单斜辉石)和地壳混染作用.白勉峡组上段火山岩形成时代可能为437Ma,有可能跨到晚古生代,其源区为受俯冲作用改造的富集地幔区,部分熔融亦发生于石榴子石二辉橄榄岩稳定区.三湾组中基性火山岩源于N-MORB近似的亏损地幔源区.白勉峡组下段代表中元古代末板内拉张事件的地质记录,白勉峡组上段和三湾组目前的火山岩样品可能代表了古生代同一洋陆转化的地质记录. 相似文献
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S. A. Palandzhyan 《Geotectonics》2015,49(2):135-149
The Ust-Belaya ophiolite terrane in the West Koryak Orogen, which is the largest in northeastern Asia, consists of three nappe complexes. The upper Ust-Belaya Nappe is composed of a thick (>5 km) sheet of fertile peridotites and mafic rocks (remnants of the proto-Pacific lithosphere); its upper age boundary is marked by Late Neoproterozoic plagiogranites. In the middle Tolovka-Otrozhny Nappe, the Late Precambrian lherzolite-type ophiolites are supplemented by fragments of tectonically delaminated harzburgite-type ophiolites, which make up the Tolovka rock association. The isotopic age of metadacite (K-Ar method, whole-rock sample) and zircons from plagiogranite porphyry (U-Pb method, SHRIMP) determines the upper chronological limit of the Tolovka ophiolites as 262–265 Ma ago. It is suggested that igneous rocks of these ophiolites were generated in a backarc basin during the Early Carboniferous and then incorporated into the fold-nappe structure in the Mid-Permian. This was the future basement of the Koni-Taigonos arc, where the Early Carboniferous ophiolites together with Late Neoproterozoic precursors were subject to low-temperature metamorphism and intruded by plagiogranite porphyry dikes in Permian-Triassic. The polymicte serpentinite mélange, which was formed in the accretionary complex of the Koni-Taigonos arc comprises rock blocks of the upper units of Late Precambrian ophiolites (in particular, plagiogranite), the overlying Middle to Upper Devonian and Early Carboniferous deposits, as well as Early Carboniferous (?) Tolovka ophiolites and meta-ophiolites. Mélange of this type with inclusions of Late Precambrian “oceanic” granitoids also developed in the lower Utyosiki Nappe composed of Middle Jurassic-Lower Cretaceous sedimentary and volcanic sequences, the formation of which was related to the next Uda-Murgal island-arc systems. 相似文献
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Relative contributions of crust and mantle to the generation of the Tianshan Carboniferous rift-related basic lavas, northwestern China 总被引：15，自引：0，他引：15
Lin-Qi Xia Zu-Chun Xia Xue-Yi Xu Xiang-Min Li Zhong-Pin Ma 《Journal of Asian Earth Sciences》2008,31(4-6):357-378
The Tianshan Carboniferous–Permian rift-related volcanism in northwestern China represents a newly recognized large igneous province extending over at least 1.5 × 106 km2. The volcanic successions comprise thick piles of basaltic lavas and subordinate intermediate and silicic lavas and pyroclastics, and are interpreted to result from a mantle plume head with component of εNd(t) ≈ +5, 87Sr/86Sr(t) ≈ 0.704 and La/Nb ≈ 0.9. On the basis of petrogeochemical data, the Carboniferous basic lavas can be generally incorporated into low-Ti/Y (LT, Ti/Y < 500) magma type that can be further divided into three subtypes: LT1, LT2 and LT3. The chemical evolution of the LT1, LT2 (in central Tianshan) and LT3 (in western Tianshan and Jungar) lavas is controlled by an olivine (ol) + clinopyroxene (cpx) fractionation, but gabbroic fractionation accounts for the chemical variation of the LT3 lavas from eastern Tianshan. Elemental and isotopic data suggest that the chemical variation of Tianshan Carboniferous basic lavas cannot be explained by crystallization from a common parental magma.The Sr–Nd isotopic variation of the crustally contaminated LT3 lavas is related to the nature of lithosphere through which the plume-derived melts have erupted. The involvement of an older (Precambrian) lithosphere led the LT3 lavas in western Tianshan to have lower to negative εNd(t) (−1.2 to +6.1) and variable 87Sr/86Sr(t) (0.7036–0.7061), whereas the LT3 lavas from eastern Tianshan and Jungar are characterized by high εNd(t) (+4.2 to +9.7) and low 87Sr/86Sr(t) (0.7035–0.7044), that are related to the contamination of upper crust containing early Paleozoic and Devonian arc-basin volcanic rocks and/or to a pre-Carboniferous subduction enrichment of the lithospheric mantle source region. The observed geochemical variations in the Tianshan data are consistent with an AFC process.The Tianshan Carboniferous rift-related volcanic rocks display a spatial petrogeochemical variation in which predominantly uncontaminated LT1 and less-contaminated LT2 tholeiitic lavas erupted in central Tianshan rift and predominantly the strongly contaminated LT3 tholeiites erupted in the circumjacent regions of the central Tianshan rift. The LT1 and LT2 lavas were generated by a higher degree (10–30%) of partial melting in the garnet stability field of the mantle plume compared to the LT3 lavas. The lower degree (<10%) of partial melting in the spinel–garnet transition zone of the mantle plume, as is characteristic of the LT3 lavas, may be the result of a relatively lower geotherm. 相似文献
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库车坳陷三叠系发育良好,出露齐全,主要由陆相碎屑岩组成。本文运用电子探针微区成分分析方法,对库车坳陷北部三叠系砂岩中石榴石、电气石、铬尖晶石进行了矿物化学成分分析。结果显示,碎屑石榴石主要富含铁铝榴石,其次为镁铝榴石、锰铝榴石,钙铝榴石含量较低,他们主要来自于低级-高级变质岩和花岗岩;电气石主要来自于变质沉积岩和花岗岩;铬尖晶石则主要源自岛弧玄武岩、洋岛玄武岩和与俯冲相关的橄榄岩。综合石榴石与电气石研究结果表明,上三叠统碎屑物质更多的来自于高级变质岩和花岗岩,而下三叠统碎屑物质主要源自低级变质岩和花岗岩。通过对比西天山榴辉岩、片麻岩中石榴石成分,本文所研究的高镁石榴石以低钙铝榴石含量与榴辉岩中石榴石相区别,而与片麻岩中石榴石成分相似。西天山榴辉岩在三叠纪时期可能尚未剥露至地表,但片麻岩已有相当范围的出露。上三叠统的碎屑铬尖晶石可能主要来自于中天山及南天山的岛弧岩浆岩及蛇绿岩,部分源自洋岛玄武岩,为南天山为多岛海造山提供了沉积学证据。 相似文献
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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
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Tahmineh Pirnia Emilio Saccani Ghodrat Torabi Marco Chiari Spela Gorican Edoardo Barbero 《地学前缘(英文版)》2020,11(1):57-81
The Nain and Ashin ophiolites consist of Mesozoic melange units that were emplaced in the Late Cretaceous onto the continental basement of the Central-East Iran microcontinent(CEIM).They largely consist of serpentinized peridotites slices;nonetheless,minor tectonic slices of sheeted dykes and pillow lavas-locally stratigraphically associated with radiolarian cherts-can be found in these ophiolitic melanges.Based on their whole rock geochemistry and mineral chemistry,these rocks can be divided into two geochemical groups.The sheeted dykes and most of the pillow lavas show island arc tholeiitic(IAT)affinity,whereas a few pillow lavas from the Nain ophiolites show calc-alkaline(CA)affinity.Petrogenetic modeling based on trace elements composition indicates that both IAT and CA rocks derived from partial melting of depleted mantle sources that underwent enrichment in subduction-derived components prior to melting.Petrogenetic modeling shows that these components were represented by pure aqueous fluids,or sediment melts,or a combination of both,suggesting that the studied rocks were formed in an arc-forearc tectonic setting.Our new biostratigraphic data indicate this arc-forearc setting was active in the Early Cretaceous.Previous tectonic interpretations suggested that the Nain ophiolites formed,in a Late Cretaceous backarc basin located in the south of the CEIM(the so-called Nain-Baft basin).However,recent studies showed that the CEIM underwent a counter-clockwise rotation in the Cenozoic,which displaced the Nain and Ashin ophiolites in their present day position from an original northeastward location.This evidence combined with our new data and a comparison of the chemical features of volcanic rocks from different ophiolites around the CEIM allow us to suggest that the Nain-Ashin volcanic rocks and dykes were formed in a volcanic arc that developed on the northern margin of the CEIM during the Early Cretaceous in association with the subduction,below the CEIM,of a Neo-Tethys oceanic branch that was existing between the CEIM and the southern margin of Eurasia.As a major conclusion of this paper,a new geodynamic model for the Cretaceous evolution of the CEIM and surrounding Neo-Tethyan oceanic basins is proposed. 相似文献
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Carboniferous Post-collisional Rift Volcanism of the Tianshan Mountains, Northwestern China 总被引：22，自引：0，他引：22
The Tianshan Carboniferous post-collisional rift volcanic rocks occur in northwestern China as a large igneous province. Based on petrogeochemical data, the Tianshan Carboniferous post-collisional rift basic lavas can be classified into two major magma types: (1) the low-Ti/Y type situated in the eastern-central Tianshan area, which exhibits low Ti/Y (<500), Ce/Yb (<15) and SiO2 (43-55%), and relatively high Fe2O3T (6.4-11.5%); (2) the high-Ti/Y type situated in the western Tianshan area, which has high Ti/Y (>500), Ce/Yb (>11) and SiO2 (49-55%), and relatively low Fe2O3T (5.8-7.8%). Elemental data suggest that chemical variations of the low-Ti/Y and high-Ti/Y lavas cannot be explained by fractional crystallization from a common parental magma. The Tianshan Carboniferous basic lavas originated most likely from an OIB-like asthenospheric mantle source (87Sr/86Sr(t) ≈ 0.703-0.705, εNd(t) ≈ +4 to +7). The crustal contamination and continental lithospheric mantle have also contributed significantly to the formation of the basic lavas of the Tianshan Carboniferous post-collisional rift. The silicic lavas were probably generated by partial melting of the crust. The data of this study show that spatial petrogeochemical variations exist in the Carboniferous post-collisional rift volcanics province in the Tianshan region. Occurrence of the thickest volcanics dominated by tholeiitic lavas may imply that the center of the mantle-melting anomaly (mantle plume) was in the eastern Tianshan area at that time. The basic volcanic magmas in the eastern Tianshan area were generated by a relatively high degree of partial melting of the mantle source around the spinel-garnet transition zone, whereas the alkaline basaltic lavas are of the dominant magma type in the western Tianshan area, which were generated by a low degree of partial melting of the mantle source within the stable garnet region, thus the basic lavas of the western Tianshan area might have resulted from relatively thick lithosphere and low geothermal gradient. 相似文献