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四川盆地西南缘的沐川生基坪剖面(PTB)是研究海陆交互相二叠系-三叠系界线的关键。本次研究对研究区P-T界线地层的岩石学与地球化学特征进行研究,探讨了研究区的岩石组合特征、沉积环境、风化作用、古气候及物源特征。还原环境的宣威组中叶肢介化石、煤线和水平层理的出现,反映了近缘的滨浅湖相沉积特征;氧化环境的飞仙关组中双向交错层理、透镜状层理和脉状层理、波痕印模和干裂构造等特征的出现,反映了浅海相沉积特征。通过研究四川盆地晚二叠世-早三叠世岩相古地理可知,研究区宣威组的浅湖相和飞仙关组的潮间-潮下相沉积环境与前人所得出的海陆交互相和滨浅海相沉积环境基本吻合,反映了海水的持续入侵,与晚二叠世-早三叠世的海平面升降事件一致,表现了峨眉山玄武岩喷发之后伴随的海侵。高CIA、CIW和PIA值和A-CN-K和A-C-N图解共同指示了沉积岩物源区经历了强烈的风化作用,并暗示宣威组与飞仙关组沉积时期可能处于温暖潮湿的沉积气候环境。根据研究区宣威组、飞仙关组岩石组合中的玄武岩碎屑特征,并结合稀土元素特征、La/Yb-ΣREE、Co/Th-La/Sc源岩判别关系可推测沐川生基坪二叠系-三叠系界线处沉积岩的物质来源主要可能为宣威组底部的峨眉山玄武岩。 相似文献
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内蒙古大青山煤田晚古生代砾岩的沉积特征 总被引：3，自引：0，他引：3
大青山煤田晚古生代地层中有 1 4层沉积砾岩。其中,晚石炭世地层中赋存 8层,二叠世 6层。通过对这些砾岩层的野外测量、室内岩矿鉴定等综合分析研究,查明晚石炭世的砾岩几乎全是稳定的单成分砾岩,石英砂岩和燧石质砾石的含量高达 93 %以上,砾石最大扁平面均向南倾,倾角在 5° - 1 0°之间,与砾岩伴生的粗粒石英砂岩发育大型低角度双向交错层理,萨胡环境判别参数等特征表明晚石炭世砾岩为滨海环境下的产物。二叠世的砾岩则主要是复杂成分的砾岩,尤其是早二叠世晚期及晚二叠世初期形成的 2层砾岩中砾石种类达 1 5种,以中酸性火山岩和火山碎屑岩砾石为主,并含较多量的变质岩和中酸性侵入岩砾石,砾岩层各种特征表明二叠世砾岩为河流相产物。大青山煤田晚古生代沉积砾岩的形成与北部造山带的隆升密切相关,它们是前陆盆地的沉积产物。 相似文献
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上扬子西南待补地区飞仙关组年代学、岩石地球化学及其对Rodinia超大陆构造演化的指示 总被引：1，自引：0，他引：1
晚二叠世以来受印支造山运动及峨眉山玄武岩喷发事件的影响,上扬子西南缘地区沉积物源及沉积模式发生了重大改变,引发学术界热议.本文以上扬子西南待补地区下三叠统飞仙关组碎屑岩为例,从岩相学、岩石地球化学和碎屑锆石U-Pb年代学等方面对飞仙关组源岩属性、物源、沉积及构造环境进行约束.飞仙关组碎屑岩整体成熟度较低,岩石风化程度中等,源区曾经历过持续的构造抬升剥蚀,并于早三叠世扬子西南缘浅海-滨海相的氧化环境中沉积.其碎屑锆石U-Pb年龄主要集中在257±2.9 Ma,与晚二叠世峨眉山玄武岩主喷发时限一致,岩石地球化学特征表现出与峨眉山高钛玄武岩高度一致,指示飞仙关组主要物源区为近源的峨眉山大火成岩省,源岩主要为板内拉张环境形成的峨眉山高钛玄武岩,并在玄武质岩浆上涌过程中混染了少量扬子陆块古老结晶基底成分.此外,康滇古陆及扬子克拉通也提供了部分物源,主要为Rodinia超大陆汇聚及裂解背景下产生的岩浆岩.年代学证据显示,Rodinia超大陆汇聚及裂解事件在区内具有较好的沉积物源响应,为全球性Rodinia超大陆汇聚及裂解事件的时限约束提供了重要参考依据. 相似文献
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峨眉山地幔柱上升的沉积响应及其地质意义 总被引：28，自引：0，他引：28
研究表明西南地区峨眉山玄武岩下伏茅口组的部分缺失是峨眉山地幔柱的快速上升及其所形成的地壳穹状隆起造成的。对该地区中、晚二叠世沉积记录的研究也支持上述结论。通过野外实地地质考察和室内综合研究发现，西南地区峨眉山玄武岩之下零星发育一套碎屑岩系，其主要分布在穹状隆起的边缘。在隆起西缘盐源平川一带，为一岩性以砾岩、砂岩为主的低位水下扇；在隆起的东北缘普格、巧家、武定一带，峨眉山玄武岩之下发育一层砾石，主要为茅口组灰岩的灰岩质砾岩；昆明西山地区的灰岩质砾岩中灰岩砾石的磨圆较好，可能代表古河谷沉积。在茅口组顶部古剥蚀面上还零星可见一层厚几米至十几米残积相碎屑岩或底砾岩。上述碎屑岩系的厘定及对其空间分布和沉积环境的研究表明，上扬子西缘峨眉山玄武岩喷发前地壳发生快速穹状抬升，碎屑岩是峨眉山地幔柱上升造成的沉积响应；地幔柱的上升还造成上扬子中、晚二叠世区域岩相古地理的突变和隆起区古喀斯特的形成。这些为峨眉山大火成岩省地幔柱形成机制提供了进一步佐证，同时深化了对晚古生代上扬子西缘构造的认识。 相似文献
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贵州威宁地区宣威组底部稀土含矿岩系的成因类型一直有较大争议.在野外实地调查的基础上,运用矿物学、岩相古地理与地球化学等手段进行了系统性研究.结果显示,区内二叠系宣威组底部稀土含矿岩系广泛分布,连续性好,含矿段厚度为2~16 m,并伴生有铌、锆、镓等元素;稀土氧化物平均品位0.15%,最高可达1.60%.主量、微量和稀土元素分析表明威宁地区稀土含矿岩系中含有来自玄武岩及火山灰的典型矿物,稀土配分模式与玄武岩相比具有继承性,研究区化学风化作用较强、成分成熟度较高代表其经过长距离搬运,遭受了改造;峨眉山玄武岩为该稀土层提供了主要物质来源,稀土层受源岩成分的控制,经历了沉积分选及再循环作用,还遭受了来自上地壳的中酸性岩浆物质源区的混染.其成因机制可能为在晚二叠世炎热、潮湿、强风化的环境中,玄武岩经过风化剥蚀后,搬运至沉积基底低洼处的三角洲平原亚相中的洪泛平原微相环境,与火山灰一同沉积沉淀,在风化和淋滤作用下稀土等元素以离子形式被解析出来,从而被吸附性强的高岭石等黏土矿物吸附于表面,或进入矿物晶格,形成富稀土层. 相似文献
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华南板块南缘二叠纪与三叠纪之交的构造属性仍存在较大争议。对新兴岩体详细的野外调查和研究发现,新兴岩体的侵位时间为晚三叠世（240~224 Ma）而非侏罗纪,其主要岩性为细中粒-细粒斑状黑云母二长花岗岩。地球化学分析显示,新兴花岗岩具有高钾钙碱性、过铝质-强过铝质花岗岩特征,具轻稀土元素富集、重稀土元素相对亏损的右倾稀土配分模式,富集大离子亲石元素（Rb、U）而亏损高场强元素（Nb、Ta、Zr、Hf、Ti）。Sr-Nd、Lu-Hf同位素分析显示,新兴花岗岩εNd（t）值介于-11.5~-10.5,εHf（t）值介于-2.9~-10.3,具有壳源源区特征。本次研究表明,粤西地区印支期构造-岩浆活动可能开始于~250 Ma,华南板块南缘海西-印支期岩浆作用自晚二叠世（大容山岩体）一直延续到晚三叠世（新兴岩体）,且晚三叠世仍存在强烈的岩浆活动。新的证据支持古特提斯洋东段分支的关闭时间在~250 Ma,而印支板块和华南板块的陆陆碰撞拼贴一直延续到240~224 Ma。 相似文献
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针对川西南美姑地区飞仙关组碎屑岩进行岩石学和地球化学方面的研究,以探究其物质来源以及构造背景。川西南美姑地区飞仙关组为一套碎屑岩,三角洲相沉积。碎屑岩主量元素中w(TFe2O3)为3.46%~11.23%,w(MgO)为2%~7.98%,w(TiO2)为1.51%~2.62%。微量元素中亲铁镁矿物元素w(Cr)为66×10^-6~426×10^-6,w(Co)为18.8×10^-6~30.6×10^-6,w(Sc)为16.9×10^-6~23.7×10^-6。REE分布模式和Al2O3/TiO2比值与峨眉山高钛玄武岩较为相似,指示着飞仙关组的物质来源于晚二叠世的峨眉山高钛玄武岩。样品的成分异变指数(ICV)值为0.95~3.49,普遍大于1,暗示着飞仙关组的物质来源大部分未经历过风化-沉积成岩的过程,为第一次循环碎屑。飞仙关组碎屑岩CIA值为60.49~72.44,反映了飞仙关组时期该地区经历了温暖、湿润环境下中等程度的化学风化作用。同时碎屑岩中的TFe2O3+MgO,TiO2,Al2O3/SiO2地球化学指标最接近大洋岛弧特征值,Th-Co-Zr/10,La-Th-Sc,Th-Sc-Zr/10图解亦指示着飞仙关组的源岩形成于大陆岛弧-大洋岛弧的构造环境中。结合飞仙关组的岩石学和地球化学特征,初步认为晚二叠世时期在大洋岛弧的构造背景下峨眉山玄武岩喷发溢流而出,而后隆升,为飞仙关组的沉积提供了充足的物质来源。同时,随着飞仙关组的不断沉积,亦逐渐有其他物源混入。 相似文献
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峨眉山大火成岩省在形成后遭受了强烈的风化剥蚀，与右江盆地构成了独特的源- 汇沉积体系，相关的碎屑沉积记录是重建峨眉山大火成岩省晚期火山序列、揭示大火成岩省岩浆演化的关键。本文对黔西南地区右江盆地北缘下三叠统下部飞仙关组开展了详细的沉积物源研究。飞仙关组泥岩由长石、石英和黏矿物等组成，具有低SiO2、高TiO2含量和低Al2O3/TiO2值的特征，具Eu的弱负异常，微弱的Nb、Ta负异常。基于Al2O3/TiO2和La/Sm物源图解分析，研究样品的主要物源由峨眉山大火成岩省的高- Ti玄武岩和少量酸性火山岩构成，这与右江盆地晚二叠世的碎屑沉积物源组成一致。碎屑锆石具有～260 Ma 的年龄峰值，对应锆石具有较低的Th/Nb和较高的Nb/Hf值，均支持峨眉山大火成岩省作为主要的沉积物源区，而同时存在的>400 Ma的碎屑锆石则对应于峨眉山玄武质岩浆上升时所捕获的华南地壳物质。与上二叠统的碎屑锆石U- Pb年龄组成和锆石化学组成对比分析表明，峨眉山大火成岩省在晚二叠世到早三叠世早期剥蚀的火山岩构成了一定的火山序列，反映了该大火成岩省晚期从强烈地壳混染到分异结晶为主的岩浆演化过程。 相似文献
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沉积物源分析是认识盆山演化的重要途径。了解四川盆地西南缘上二叠统宣威组物源,对于重建晚二叠世扬子克拉通周缘演化具有重要意义。本文对峨眉山地区宣威组顶部泥岩、砂岩开展了岩石学和全岩地球化学分析,进行了物源、沉积环境和构造背景的研究。宣威组泥岩主要成分为黏土矿物,SiO2含量(平均49.42%)中等;砂岩成分大部分为火山岩屑,含有少量石英及长石,具中等的SiO2含量(平均44.12%),属于杂砂岩系列。泥岩与砂岩均具有轻稀土元素富集、重稀土元素较右倾的稀土元素配分型式,微量元素相对大陆上地壳富集高场强元素(如Nb、Zr),亏损大离子亲石元素(如Sr、Ba)。根据地球化学分析结果结合已发表的扬子克拉通周缘二叠系沉积岩数据,认为上二叠统宣威组顶部沉积岩物源区经历了强烈的化学风化作用,沉积古环境为富氧的淡水沉积环境;宣威组顶部沉积物物源不仅来自于近源搬运的峨眉山高Ti玄武岩,还接受了扬子克拉通的补给,扬子克拉通西缘晚二叠世时期是活动大陆边缘沉积。 相似文献
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本区长兴组底部普遍发现一薄层砾岩,经酸解分析,内含丰富的牙形刺和鱼牙化石。根据化石确定,此层砾岩在不同地区为不同时代:浙江长兴煤山,砾岩时代为晚二叠世早期之末;安徽广德独山和江苏张渚园田,砾岩时代为晚二叠世晚期之初。此砾岩的出现说明本区龙潭组沉积之后有一短期侵蚀,并代表长兴组沉积的开始。因此长兴组沉积在各地不同,应是一穿时的地层单位。它始于晚二叠世早期之末至晚二叠世末。并根据岩相分析结果认为本区长兴组是一个由北东向南西展布的浅海台地到台前凹陷的低能海进沉积环境。 相似文献
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Xuanwei Formation is composed of mudstone, siltstone, and sandstone, with local conglomerate. However, its provenance and tectonic setting have been scarcely studied. In this paper, we use sedimentology, electron probe microanalysis(EPMA), and detrital zircon dating to investigate its source area and depositional tectonic setting. The facies assemblages indicate that it formed in alluvial fan and fluvial river sedimentary environments. The strata thicknesses and facies distribution indicate that the sediment supply was from the west. The results of EPMA show that chromian spinels within the sediments are characterized by high Cr# and varying Mg#. Discrimination plots suggest that these spinels were sourced from large igneous province(LIP) magmatic rocks. The laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) U–Pb chronology of detrital zircons suggests that the sediments were derived from intermediate–acid igneous rocks dating back to 251–260? Ma. We could, therefore, conclude that the provenance of the Xuanwei Formation is from Emeishan basalt and synchronous felsic igneous rocks, which is consistent with the composition of the detrital framework. The detrital zircon dates also suggest that felsic magmatism occurred during the Late Permian, not after the eruption of the Emeishan basalt. Based on the sedimentary successions and provenance analysis, the tectonic setting for Xuanwei Formation deposition was a volcanic rifted margin. 相似文献
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滇东北峨眉山玄武岩区的沉积型铜矿床 总被引：3，自引：0，他引：3
在滇东北峨眉山玄武岩分布区上二叠统宣威组中发现沉积型铜矿床。文章对此类沉积型铜矿床的地质特征和成矿作用特征进行了较系统的研究,结合矿物成分和硫同位素测试结果,探讨了矿床的形成过程和找矿前景。研究表明,区内沉积型铜矿床主要有两种矿化类型:结核状铜矿化和浸染状铜矿化,矿石矿物以辉铜矿、斑铜矿、铜蓝等为主;成矿受上二叠统宣威组沉积地层控制,与峨眉山玄武岩喷溢形成的古火山构造和古地形以及火山期后的热泉活动关系密切,有机质在成矿过程中可能发挥了作用;成矿过程可能从沉积成岩阶段一直延续到成岩期后。区域上假整合覆盖于上二叠统峨眉山玄武岩之上的宣威组沉积岩系具有良好的找矿前景。 相似文献
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Recycling and chemical weathering in tectonically controlled Mesozoic–Cenozoic basins of New Zealand
P.L. CORCORAN 《Sedimentology》2005,52(4):757-774
Sedimentation in molasse basins is controlled by tectonics, however, recycling and chemical weathering play a critical role in the compositional evolution of a sedimentary succession. The Cretaceous to Pliocene molasse deposits of Central Otago, New Zealand are excellent examples of tectonically related deposits that were governed by the effects of chemical weathering and recycling. Preserved in fault-controlled basins floored by flysch deposits of the Otago Schist, the clastic successions contain ubiquitous unconformities and lithofacies consistent with alluvial, fluvial and lacustrine depositional settings. Textural analysis of Central Otago sandstones establishes a general quartz enrichment and increased mixing of angular and well-rounded quartz varieties up-section, consistent with a history of sediment recycling. Rare earth element (REE) patterns, which reflect upper crustal compositions, are similar for the flysch-type Otago Schist (Permian–Early Cretaceous), a palaeo-weathering profile, and the overlying molasse deposits. The development of quartz arenites is also consistent with high degrees of chemical weathering, and erosion of the schist basement, which contains numerous quartz veins. Although recycling has occurred, SiO2 and TiO2 do not consistently show a negative correlation over time. This reflects erosion of previously deposited quartz-rich sediment and the Otago weathering profile, which produced an inverse stratigraphy. CIA values range from 52 for lithic-rich, coarse-grained sandstones and polymictic conglomerate matrices, to 93 for coarse-grained to pebble-rich quartz arenites. Individual samples were split into finer- and coarser-grained pairs (<2·5φ and 2·5 to −1φ) and were analysed separately. The results show that finer-grained samples contain higher REE abundances and less SiO2, but the coarser-grained Miocene–Pliocene samples have higher CIA values than their finer-grained counterparts. These coarse-grained deposits are quartz-rich and plot erratically on tectonic discrimination diagrams, implying that using SiO2-poor samples is more reliable for geochemical analysis. Overall, the petrographic and geochemical results indicate that the main factors controlling the composition of the Central Otago molasse deposits were source composition, chemical weathering and recycling. Studies of this nature can be conducted in Archaean tectonically controlled molasse basins that are affected by similar allocyclic factors. 相似文献
16.
E. C. Leitch C. L. Fergusson R. A. Henderson V. J. Morand 《Australian Journal of Earth Sciences》2013,60(4):301-310
Devonian and Carboniferous (Yarrol terrane) rocks, Early Permian strata, and Permian‐(?)Triassic plutons outcrop in the Stanage Bay region of the northern New England Fold Belt. The Early‐(?)Middle Devonian Mt Holly Formation consists mainly of coarse volcaniclastic rocks of intermediate‐silicic provenance, and mafic, intermediate and silicic volcanics. Limestone is abundant in the Duke Island, along with a significant component of quartz sandstone on Hunter Island. Most Carboniferous rocks can be placed in two units, the late Tournaisian‐Namurian Campwyn Volcanics, composed of coarse volcaniclastic sedimentary rocks, silicic ash flow tuff and widespread oolitic limestone, and the conformably overlying Neerkol Formation dominated by volcaniclastic sandstone and siltstone with uncommon pebble conglomerate and scattered silicic ash fall tuff. Strata of uncertain stratigraphic affinity are mapped as ‘undifferentiated Carboniferous’. The Early Permian Youlambie Conglomerate unconformably overlies Carboniferous rocks. It consists of mudstone, sandstone and conglomerate, the last containing clasts of Carboniferous sedimentary rocks, diverse volcanics and rare granitic rocks. Intrusive bodies include the altered and variably strained Tynemouth Diorite of possible Devonian age, and a quartz monzonite mass of likely Late Permian or Triassic age. The rocks of the Yarrol terrane accumulated in shallow (Mt Holly, Campwyn) and deeper (Neerkol) marine conditions proximal to an active magmatic arc which was probably of continental margin type. The Youlambie Conglomerate was deposited unconformably above the Yarrol terrane in a rift basin. Late Permian regional deformation, which involved east‐west horizontal shortening achieved by folding, cleavage formation and east‐over‐west thrusting, increases in intensity towards the east. 相似文献
17.
藏北羌塘盆地大规模古风化壳的发现及其意义 总被引：1，自引：0，他引：1
新的野外油气地质调查发现,在羌塘盆地中央隆起带及其两侧的南、北羌塘坳陷中,那底岗日组及其同沉积地层之下广泛发育了一古风化壳,古风化壳覆盖了石炭系、二叠系和前人已确定的三叠系肖茶卡组,具有区域性展布的特点。研究表明,不同地区古风化壳的形成时代不同：在南羌塘及中央隆起带上,风化剥蚀作用可能于晚二叠世就已开始,并经历了早、中三叠世的进一步演化;北羌塘地区的古风化壳形成时代可能为晚三叠世（或中三叠世）,至晚三叠世肖茶卡组沉积期,形成了南北羌塘统一的古风化壳,并被那底岗日组及其同沉积地层超覆。这些新发现对于重新认识羌塘盆地的沉积演化、正确评价羌塘盆地的石油地质条件具有重要意义。 相似文献
18.
根据福建九龙江河口ZK1孔及ZK7孔沉积物AMS(Accelerator Mass Spectrometry,加速器质谱测年技术) 14C测年、古地磁和剖面特征分析,进行该地区的第四纪地层划分,依据粒度特征,结合磁化率、微体古生物和Sr/Ba等环境代用指标进行沉积相分析,重建了该区晚第四纪的古环境演变历史。结果表明:(1)九龙江河口第四纪沉积时代为晚更新世中期至全新世晚期。(2)上更新统沉积可划分为下部龙海组洪冲积相和上部东山组河漫滩相沉积,中间有10 ka的沉积间断,末次冰期又再遭受风化剥蚀作用,推测有5～6 ka的风化剥蚀期。(3)全新统最早沉积年代约为14 ka BP,依次出现河口湾相、河口砂坝—分汊河道相、潮滩相沉积。(4)根据年代学数据和沉积相变化,重塑了该区晚第四纪沉积环境变化过程,为该区的第四纪研究和工程地质工作提供了参考依据。 相似文献
19.
Palynological assemblages of non-marine rocks at the Permian–Triassic boundary, western Guizhou and eastern Yunnan, South China 总被引：1，自引：0，他引：1
Yuanqiao Peng Jianxin Yu Yongqun Gao Fengqing Yang 《Journal of Asian Earth Sciences》2006,28(4-6):291-305
Marine and non-marine facies of the Permian–Triassic boundary stratigraphic set (PTBST) are well developed in South China. Palynological assemblages enable subdivision and correlation of the Permian–Triassic boundary (PTB) rocks. Three palynological assemblages are recognized across the PTBST in two terrestrial PTB sections in western Guizhou and eastern Yunnan, South China. Assemblage 1 (Xuanwei Formation) is a Late Permian palynological assemblage dominated by ferns and pteridosperms, with minor gymnosperms. Most taxa are typical long-ranging Paleozoic forms, but the appearance of Lueckisporites confirms a Late Permian age for this assemblage. Assemblage 2 (PTBST) is marked by an abrupt decrease in palynomorph abundance and diversity, and thriving fungal/algal(?) spores. Assemblage 2 is still dominated by ferns and pteridosperms, with a few gymnosperms, but is characterized by a mixed palynoflora containing both Late Permian and Early Triassic elements. Most taxa are typical Late Permian ones also found in Assemblage 1, however, some taxa of Early Triassic aspect, e.g. Lundbladispora and Taeniaesporites, appeared for the first time. In Assemblage 3 (top Xuanwei Formation and Kayitou Formation), the proportion of gymnosperm pollen increases rapidly, exceeding that of ferns and pteridosperms, but the abundance of palynomorphs is still low. Typical Early Triassic taxa (such as Lundbladispora, Aratrisporites and Taeniaesporites) are present in greater abundance and confirms an Early Triassic age for this assemblage. 相似文献
20.
内蒙古阿拉善北部好比如地区下石炭统好比如组时代修订及其地质意义 总被引：1，自引：0，他引：1
内蒙古阿拉善北部好比如地区地层研究程度较低,好比如组时代久有争议,制约了该区地层层序、沉积建造及构造演化的深入研究。测得好比如地区原定为早石炭世的好比如组碎屑岩LA-ICP-MS锆石U-Pb最小峰值年龄为279Ma,火山岩LA-ICP-MS锆石U-Pb年龄为270.3±2.2Ma,时代应修订为早二叠世空谷期—中二叠世罗德期。结合区域上岩性特征、地层对比及锆石年龄谱对比,将好比如组中段修订为船山统隆林阶—罗甸阶埋汗哈达组(P1-2m),将其上段修订为阳新统祥播阶—冷坞阶阿其德组(P2a)。好比如组的时代修订为研究区晚古生代地层层序、沉积建造及构造演化的研究提供了新的依据。 相似文献