鄂尔多斯盆地西南部三叠纪末抬升剥蚀事件及热年代学记录   总被引：1，自引：1，他引：0  

王建强  刘池洋  赵红格  张东东  ZATTIN Massimiliano  彭恒 《岩石学报》2020,36(4):1199-1212

三叠纪末期大型鄂尔多斯盆地遭受了中生代成盆以来首次较大规模的抬升剥蚀,显著改造了中晚三叠世延长期盆地面貌,并控制了侏罗纪早期沉积格局和油藏分布,对盆地演化及矿产资源分布产生了重要影响。本文利用地质及大量钻井资料揭示了该期构造事件对盆地的剥蚀改造特征,盆地及周邻地区磷灰石裂变径迹年代学记录并约束了此次构造抬升的时限与过程;综合周邻区域构造研究成果,探讨了其发育的动力学背景。结果表明,鄂尔多斯盆地三叠纪末期的剥蚀具西南强、东北弱的特点,西南部大范围内延长组地层残缺不全,剥蚀量最大可达1000余米;前侏罗纪沉积古地貌总体呈西南高、北东低的特点;其抬升时间始于205～190Ma,西南部稍早于盆地腹部,抬升速率大于1℃/Myr,可持续至中侏罗世(约160Ma)。该期抬升剥蚀事件范围可涉及至盆地西南缘更广阔的区域,与同期秦岭造山带内出现的快速抬升冷却事件具有较好的时空耦合关系,是对秦岭造山带区域构造环境转变的响应和纪录。该研究丰富和发展了三叠纪末期构造事件在华北克拉通的影响,对该区油气、煤炭资源的进一步勘探和评价提供了新的思路,具有一定的现实意义。  相似文献   

Zircon U–Pb geochronology,whole-rock geochemical,and Sr–Nd–Pb isotopic constraints on the timing and origin of Permian and Triassic mafic dykes from eastern North China Craton     

Liu  Shen  Feng  Caixia  Fan  Yan  Chen  Xiaoqing  Yang  Yuhong  Zhao  Huibo  Coulson  Ian M. 《中国地球化学学报》2020,39(6):862-886

Acta Geochimica - This work reports an important episode of extensional, mafic magmatism that impacted the North China Craton (NCC) during the Permo-Triassic and influenced the evolution of this...  相似文献   

The ~1.85 Ga carbonatite in north China and its implications on the evolution of the Columbia supercontinent     

《Gondwana Research》2019

Mantle-derived carbonatites provide a unique window in the understanding of mantle characteristics and dynamics, as well as insight into the assembly and breakup of supercontinents. As a petrological indicator of extensional tectonic regimes, Archean/Proterozoic carbonatites provide important constraints on the timing of the breakup of ancient supercontinents. The majority of the carbonatites reported worldwide are Phanerozoic, in part because of the difficulty in recognizing Archean/Proterozoic carbonatites, which are characterized by strong foliation and recrystallization, and share broad petrologic similarities with metamorphosed sedimentary lithologies. Here, we report the recognition of a ~1.85 Ga carbonatite in Chaihulanzi area of Chifeng in north China based on systematic geological, petrological, geochemical, and baddeleyite U-Pb geochronological results. The carbonatite occurs as dikes or sills emplaced in Archean metasedimentary rocks and underwent intense deformation. Petrological and SEM/EDS results show that calcite and dolomite are the dominant carbonate minerals along with minor and varied amounts of Mg-rich mafic minerals, including forsterite (with Fo > 98), phlogopite, diopside, and an accessory amount of apatite, baddeleyite, spinel, monazite, and ilmenite. The relatively high silica content together with the non-arc and OIB-like trace element signatures of the carbonatite indicates a hot mantle plume as the likely magma source. The depleted Nd isotopic signatures suggest that plume upwelling might be triggered by the accumulation of recycled crust in the deep mantle. As a part of the global-scale Columbia supercontinent, the Proterozoic tectonic evolution of the North China Craton (NCC) provides important insights into the geodynamics governing amalgamation and fragmentation of the supercontinent. The Paleo-Mesoproterozoic boundary is the key point of tectonic transition from compressional to extensional settings in the NCC. The newly identified ~1.85 Ga carbonatite provides a direct link between the long-lasting supercontinental breakup and plume activity, which might be sourced from the “slab graveyard,” continental crustal slabs subducted into asthenosphere, beneath the supercontinent. The carbonatite provides a precise constraint of the initiation of the continental breakup at ~1.85 Ga.  相似文献   

北大巴山早古生代辉绿岩地球化学特征及其地质意义     

张方毅  赖绍聪  秦江锋  朱韧之  杨航  朱毓 《岩石矿物学杂志》2020,39(1):35-46

对南秦岭北大巴山地区广泛分布的一套基性岩墙群中的辉绿岩进行采样,并进行了锆石U-Pb年代学、全岩地球化学分析。结果显示,岩石形成年龄为435~433 Ma,为早志留世晚期岩浆活动产物。这些辉绿岩具低硅、高碱、高钛的碱性岩特征。岩石微量及稀土元素具板内玄武岩特征,轻稀土元素相对富集,轻重稀土元素分异明显,富集不相容元素Ba、Nb、Ta,而K、Y、Yb相对亏损;K及Rb的负异常表明岩石源区残留角闪石或金云母,部分熔融模拟结果显示岩石起源于尖晶石角闪石岩高程度部分熔融。综合地球化学特征及前人研究结果,认为北大巴山地区在早古生代处于大规模伸展裂陷背景下,岩石圈的拉张诱发了低熔点的交代岩石圈地幔熔融,进而形成了这条碱性岩浆带。  相似文献   

中国古代牧业社会骨制品的初步考察:以新疆巴里坤石人子沟遗址为例     

李悦  马健  张成睿  刘欢  宗天宇  陈婷  黄泽贤  任萌  习通源  王建新  温睿 《第四纪研究》2020,(2):331-342

考古遗址出土骨制品的研究对于揭示古代社会的动物资源获取和利用、手工业生产、社会组织结构等问题具有重要意义.国内骨制品研究目前多集中在农业区域,这些研究为探讨新石器时代至青铜时代的动物使用及其与社会发展、早期国家形成的关系等问题作出了重要贡献.然而,针对牧业社会骨制品的考察十分缺乏.新疆哈密地区巴里坤草原分布有大量古代牧业文化遗址,石人子沟遗址(43°31′12.8″~43°34′28.9″N,93°13′44.8″~93°16′49.1″E)是其中一处青铜时代晚期至铁器时代早期的大型聚落.本文从动物考古学视角研究该遗址2006年至2011年发掘出土的426件骨制品.结果显示,石人子沟遗址骨制品的原料主要为以羊(Ovis aries/Capra hircus)、马(Equus caballus)为主的家养动物和以鹿(Cervidae)为主的野生动物,其中羊的比例最高(69.7%),鹿(13.8%)、马(2.3%)次之,这与中原地区青铜时代农业文化遗址的骨制品多以牛为原料的情况明显不同.羊在骨制品原料中占绝对多数且大量使用羊距骨制品的现象是对石人子沟遗址以牧业为主的生业经济方式的直接反映.石人子沟遗址不同类型骨制品的制作各具特点,但整体表现出"省时省力"的特点,即对使用部位细致打磨,对非使用部位仅做简单处理.与中原地区商周时期大型制骨作坊规范化、规模化、产业化的骨器生产不同,石人子沟遗址未见专门的制骨场所,骨制品生产的操作链条也并不完整.遗址的骨制品生产可能是以家庭为单元进行的,产品的专业化、精细化程度也相对较低.该研究填补了我国古代牧业文化遗址出土骨制品动物考古学专门研究的空白,为进一步探究我国古代不同区域、不同生业经济基础下的制骨手工业面貌提供了重要资料.  相似文献   

蛇纹石化和俯冲带蛇纹岩变质脱水过程中流体活动性元素的行为   总被引：1，自引：1，他引：0  

吴凯  袁洪林  吕楠  张丽鹏 《岩石学报》2020,36(1):141-153

蛇纹石是大洋岩石圈和俯冲带内水和流体活动性元素最重要的载体之一。研究蛇纹石化和蛇纹岩变质脱水过程中流体活动性元素的行为是认识俯冲带元素地球化学循环的关键。蛇纹岩是指主要由蛇纹石类矿物构成的岩石,包括利蛇纹石、纤蛇纹石和叶蛇纹石。蛇纹石化过程中会造成流体活动性元素(B、Li、As、Sb、Pb、Cs、U、Sr和Ba等)的显著富集,并且由于原岩性质、流体成分和氧逸度等条件的不同,大洋岩石圈蛇纹岩和弧前蛇纹岩的特征也略有不同。例如,弧前蛇纹岩具有相对高的As、Sb、B和相对低的U,这反映了俯冲沉积物来源流体的贡献。在俯冲带蛇纹岩的变质脱水过程中,利蛇纹石向叶蛇纹石的转变伴随着矿物内超过50%F和Cl的释放,以及一些流体活动性元素(如B和Li)的迁出;此外,蛇纹石分解形成的变质橄榄石中的流体包裹体指示,蛇纹石脱水分解所产生的流体具有高于原始地幔几个数量级的Cl、Cs、Pb、As、Sb、Ba、Rb、B、Sr、Li和U含量。由于利蛇纹石中的Fe~(3+)含量较叶蛇纹石高,这种矿物相转变过程中也伴随着俯冲通道内的一系列氧化还原过程,从而影响流体性质和新形成的叶蛇纹石的成分。蛇纹岩与岛弧岩浆在流体活动性元素富集规律上的相似性说明蛇纹岩在俯冲带元素循环中扮演着重要的角色。此外,蛇纹石矿物相转变过程中F、Cl、B等元素的释放,可能对于斑岩型金矿、蛇绿岩中的金矿和某些蛇纹岩作为赋矿围岩的硼矿的形成起到重要的作用。  相似文献   

The oldest record of Ediacaran macrofossils in Gondwana (~563 Ma,Itajaí Basin,Brazil)     

《Gondwana Research》2020

The Avalon biota (Ediacaran Period, 570–559 Ma) marks the first appearance of macroscopic and complex benthic communities in the fossil record. This assemblage is known from a few localities worldwide, mainly in Canada and England. Here, we report for the first time the presence of Ediacaran macrofossils in deposits of similar age from Gondwana (Itajaí Basin, southern Brazil). Our new radiometric date (~563 Ma) indicates that the Itajaí Basin can be chronocorrelated with the classic Avalonian deposits and thus represents one of the oldest records of the Ediacaran biota in Gondwana. We describe the presence of the Ediacaran genus Palaeopascichnus, as well as discs (Aspidella and Nimbia), and other problematic forms. Contrary to the deep-marine macroorganisms of the Avalon Assemblage, the Itajaí fossils are associated with abundant and exceptionally preserved three-dimensional microbial mats and microbially induced sedimentary structures (MISS) in relatively shallow settings (upper slope and distal delta front deposits). In this sense, the Itajaí biota could represent early adaptations of benthic macrobiota to the shallower and more photic environments that characterize the later White Sea Assemblage.  相似文献   

Zircon U–Pb ages and Hf isotope compositions of migmatites from the North Qinling terrane and their geological implications     

Q. Liu  Y.‐B. Wu  H. Wang  S. Gao  Z.‐W. Qin  X.‐C. Liu  S.‐H. Yang  H.‐J. Gong 《Journal of Metamorphic Geology》2014,32(2):177-193

Migmatites are predominant in the North Qinling (NQ) orogen, but their formation ages are poorly constrained. This paper presents a combined study of cathodoluminescence imaging, U–Pb age, trace element and Hf isotopes of zircon in migmatites from the NQ unit. In the migmatites, most zircon grains occur as new, homogeneous crystals, while some are present as overgrowth rims around inherited cores. Morphological and trace element features suggest that the zircon crystals are metamorphic and formed during partial melting. The inherited cores have oscillatory zoning and yield U–Pb ages of c. 900 Ma, representing their protolith ages. The early Neoproterozoic protoliths probably formed in an active continental margin, being a response to the assembly of the supercontinent Rodinia. The migmatite zircon yields Hf model ages of 1911 ± 20 to 990 ± 22 Ma, indicating that the protoliths were derived from reworking of Palaeoproterozoic to Neoproterozoic crustal materials. The anatexis zircon yields formation ages ranging from 455 ± 5 to 420 ± 4 Ma, with a peak at c. 435 Ma. Combined with previous results, we suggest that the migmatization of the NQ terrane occurred at c. 455–400 Ma. The migmatization was c. 50 Ma later than the c. 490 Ma ultra‐high‐P (UHP) metamorphism, indicating that they occurred in two independent tectonic events. By contrast, the migmatization was coeval with the granulite facies metamorphism and the granitic magmatism in the NQ unit, which collectively argue for their formation due to the northward subduction of the Shangdan Ocean. UHP rocks were distributed mainly along the northern margin and occasionally in the inner part of the NQ unit, indicating that they were exhumed along the northern edge and detached from the basement by the subsequent migmatization process.  相似文献   

Highly fractionated Late Triassic I-type granites and related molybdenum mineralization in the Qinling orogenic belt: Geochemical and U–Pb–Hf and Re–Os isotope constraints     

《Ore Geology Reviews》2014

We present new data on the highly fractionated Late Triassic I-type Liyuantang granite, which is located in the middle segment of the South Qinling Subzone of central China and is associated with molybdenum mineralization. Zircon U–Pb dating indicates that the granite was emplaced at 210.1 ± 1.9 Ma, with a single zircon containing an inherited core that yielded an age of 449.8 ± 7.1 Ma. Magmatic zircons from the granite have ε_Hf(t) values of − 4.0 to + 1.5, whereas the inherited zircon core has a ε_Hf(t) value of − 5.3. Calculated Hf model ages of crust formation are indicative of substantial contributions from melting of Proterozoic crust that ranges in age from 1501 to 1155 Ma. The granite contains high concentrations of Si, Al, Na, and K, is enriched in Rb, Th, and U, has elevated Rb/Sr and Ga/Al ratios, and is depleted in Ti, Fe, Mn, Mg, Ca, and P, with significantly negative Eu anomalies (δEu = 0.33–0.50), similar to other highly fractionated I-type granites. These data indicate that the magmas that formed the Liyuantang pluton were produced during partial melting of Proterozoic garnet-absent quartz amphibolites. The magmas then fractionated apatite, feldspar, Ti-bearing phases, biotite, and hornblende prior to emplacement.Re–Os isotope analysis of molybdenite from the study area yields a mineralization age of 200.9 ± 6.2 Ma, suggesting that the Liyuantang molybdenum deposit formed during a previously unrecognized mineralization event. The present results, together with previous data, demonstrate that highly fractionated I-type granites associated with the second pulse of magmatism in the South Qinling subzone should be considered highly prospective for mineral exploration, focusing on Triassic–Early Jurassic granitoids.  相似文献   

华北板块南缘中段中上三叠统软沉积变形构造的发现及其地质意义     

全晓园  刘池洋  张龙  张东东  王建强  马奂奂  冯琦  翟光麾 《现代地质》2020,34(2):333-344

豫西地区中上三叠统主要出露在济源、义马、伊川和南召一带。印支期秦岭造山运动控制和影响着邻区中上三叠统盆地属性和沉积地层展布。通过观察研究区野外露头剖面,发现中上三叠统发育一系列典型的软沉积变形构造,包括液化底辟、枕状构造、液化柱、液化卷曲变形、负载、球-枕、火焰状构造、液化角砾岩。这些软沉积变形在垂向上表现出明显的复现性,在侧向上表现为沿地层连续展布,表明该时期研究区内地层受到频繁强烈的地震影响。通过对这些软沉积现象的识别和形成机制解释,判定其触发因素为秦岭造山过程中伴生的地震。区内地层中震积岩的存在即是对秦岭造山过程中构造活动的响应。  相似文献