共查询到20条相似文献，搜索用时 171 毫秒
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
南极乔治王岛化石山剖面的化石山组主要由沉积火山碎屑岩（包括沉火山角砾岩和沉凝灰岩）组成，上部夹正常沉积岩和两层薄煤层，形成从粗到细的两个沉积旋回。第１旋回的沉火山角砾岩和沉凝灰岩由不同粒级的火山岩岩屑、斜长石晶屑和细火山尘基质组成，火山碎屑物质含量在９０％以上，沉积特征显示从火山碎屑流（？）到低密度流的快速堆积性质。其中第１、２层沉凝灰岩受强烈的沸石化（浊沸石和方沸石）作用，而泥级沉凝灰岩夹层的细火山尘物质多已变成绿泥石－蒙脱石规则混层矿物；因为这种混层矿物也常常被沸石化，故其形成应在沸石化作用之前。Ｘ－衍射分析显示较多钠长石的存在。钠长石和方沸石的钠可能来自中长石被浊沸石化后释放出的Ｎａ＋。第２旋回由沉火山角砾岩、沉凝灰岩夹岩屑长石杂砂岩和薄煤层组成，显示正常沉积物经常被携入沉积盆地。第３、４层的泥级沉凝灰岩以显著的蒙皂石化为特征，沸石化作用不发育；其中的斜长石主要是中长石和（或）拉长石。化石山组泥级沉凝灰岩的微量元素组分及含量与下伏玛瑙滩组顶部安山岩的相当，但第２～３层间有某些元素迁移和富集，这可能与层间热水溶液的活动有关。Ｂ含量特别低（＜１×１０－６），不仅指示背景值低，而且也说明沉积环境与海水没有关 相似文献
12.
本文对菲尔德斯半岛群的划分提出了一个新的方案 ,时代从晚白垩世一直延续到中新世早期 ;新建立的半三角组系湖相沉积 ,孢粉及同位素年龄数据 (71 .3 +0 .3 Ma)均指示属晚白垩世后期 ,是目前所知菲尔德斯半岛出露最早的岩层 ,也是南极仅知的晚白垩世陆相沉积地层 ;据岩层区域分布、岩相及含古生物组分的差别 ,始新统化石山组可进而划分为上、下两部分 ,层型剖面仅代表该组下部地层 ,上部在别林斯高晋站油库附近出露较好 ;文中命名“苏菲尔角火山岩”以表示菲尔德斯半岛更新时代的火山活动 ,但尚需深入研究。 相似文献
13.
14.
本文根据四次南极考察所取资料,对西南极乔治王岛菲尔德斯半岛长城站地区第三纪火山岩进行了全面和系统的总结,在火山岩地层的划分、岩相学和矿物学特点、岩浆的生成演化等问题上提出了新的认识。 长城站所在的菲尔德斯半岛出露有一套层状的熔岩、火山碎屑岩和火山碎屑沉积岩,是第三纪岛弧火山作用的产物。长城组包括碧玉山段和玛瑙滩段,由熔岩和正常火山碎屑岩组成,同位素年龄测定证明其形成于古新世至始新世。化石组主要形成于渐新世,其下部化石山段的含有植物化石的火山碎屑沉积岩不整合在玛瑙滩段岩层之上,上部的岩块山段以集块熔岩、角砾熔岩为主体,火山活动可能持续到了中新世早期。整个半岛的火山活动有两个高潮,两次较强烈的火山作用之间是较长的喷发间断,造成半岛岩石被风化剥蚀和火山碎屑沉积岩的出现。次火山岩以岩颈、岩墙、岩脉和规模较小的岩株等形式产出,并受到古火山机构和基底断裂的控制,沿着北西西-南东东的方向有规律地分布。从火山喷发中心和火山岩分布特点分析,该区火山活动有从西向东逐渐迁移的趋势。 熔岩以高铝玄武岩和玄武安山岩为主,安山岩、英安岩数量较少。斜长石和普通辉石是最主要的造岩矿物。高铝玄武岩和玄武安山岩中斜长石斑晶的核部往往为倍长石或钙长石,边缘成份与 相似文献
15.
根据植物化石证据,在早第三纪早、中期,南极乔治王岛地区曾出现过温暖、潮湿的气候,作者认为,当时南半球各板块的相对位置以及由此而引起的洋流的变化,很可能是造成这种温暖气候的主要原因。 相似文献
16.
Tectonic inversion models predict that stratigraphic thickening and local facies patterns adjacent to reactivated fault systems should record at least two phases of basin development: (1) initial extension‐related subsidence and (2) subsequent shortening‐induced uplift. In the central Peloncillo Mountains of southwestern New Mexico, thickness trends, distribution, and provenance of two major stratigraphic intervals on opposite sides of a northwest‐striking reverse fault preserve a record of Early Cretaceous normal displacement and latest Cretaceous–Paleogene reverse displacement along the fault. The Aptian–Albian Bisbee Group thickens by a factor of three from the footwall to the hanging‐wall block, and the Late Cretaceous?–Eocene Bobcat Hill Formation is preserved only in the footwall block. An initial episode of normal faulting resulted in thickening of upper Aptian–middle Albian, mixed siliciclastic and carbonate deposits and an up section change from coarse‐grained deltas to shallow‐marine depositional conditions. A second episode of normal faulting caused abrupt thickening of upper Albian, quartzose coastal‐plain deposits across the fault. These faulting episodes record two events of extension that affected the northern rift shoulder of the Bisbee basin. The third faulting episode was oblique‐slip, reverse reactivation of the fault and other related, former normal faults. Alluvial and pyroclastic deposits of the Bobcat Hill Formation record inversion of the Bisbee basin and development of an intermontane basin directly adjacent to the former rift basin. Inversion was coeval with latest Cretaceous–Paleogene shortening and magmatism. This offset history offers significant insight into extensional basin tectonics in the Early Cretaceous and permits rejection of models of long‐term Mesozoic shortening and orogen migration during the Cretaceous. This paper also illustrates how episodes of fault reactivation modify, in very short distances (<10 km), regional patterns of subsidence, the distribution of sediment‐source areas, and sedimentary depositional systems. 相似文献
17.
干旱区石羊河终闾湖泊孢粉组合中云杉圆柏属环境指示意义探讨 总被引：8，自引：3，他引：8
河西走廓东段、石羊河终闾湖泊边缘的三角城剖面下部全新世早期至末次冰消期的292-600cm处155个样孢粉组合显示云杉、圆柏属含量极高，两者之和达40%-60%左右，且百分比互为消长，通过对云杉、圆柏属生态习性、传播性能、与其它组分关系、当地特殊的自然地理条件和表土花粉记录的综合分析，笔者认为剖面中高含量的云杉、圆柏属来自流域上游祁连山，是石羊河搬运的结果，两者含量与区域有效湿度关系密切，云杉丰值指示湿润，圆柏丰值指示干旱。 相似文献
18.
以K-Ar,(39)~Ar-(40)~Ar和Rb-Sr法对菲尔德斯半岛的火山岩进行了同位素测年。实验结果表明,半岛的火山作用从晚古新世开始,可能一直延续至中中新世的早期。其间,碧玉山段的岩石分别以Rb-Sr和(39)~Ar-(40)~Ar法测定了形成年龄,年龄值为54Ma和55Ma,属于晚古新世;岛上广泛分布的玛瑙滩段熔岩的K-Ar年龄区间为45～50Ma,为早始新世;化石山段从中始新世到渐新世;而最晚形成的岩块山段的时代为中中新世的早期。这些数据,与地质和古生物证据一起,对了解该区地层的相互关系和讨论火山作用提出了正确的认识。 相似文献
19.
Timing of Late Cretaceous shortening and basin development,Little Hatchet Mountains,southwestern New Mexico,USA – implications for regional Laramide tectonics 
下载免费PDF全文
下载免费PDF全文 Laser ablation‐multi collector‐inductively coupled mass spectrometry U‐Pb geochronology, detailed field mapping and stratigraphic data offer improved insights into the timing and style of Laramide deformation and basin development in the Little Hatchet Mountains, southwestern New Mexico, USA, a key locality in the ‘southern Laramide province.’ The Laramide synorogenic section in the northern Little Hatchet Mountains comprises upper Campanian to Maastrichtian strata consisting of the Ringbone and Skunk Ranch formations, with a preserved maximum thickness of >2400 m, and the correlative Hidalgo Formation with a total thickness >1700 m. The Ringbone Formation and superjacent Skunk Ranch Formation are each generally composed of (1) a basal conglomerate member; (2) a middle member consisting of lacustrine shale, limestone, sandstone, and interbedded ash‐fall tuffs; and (3) an upper sandstone and conglomerate member. Basaltic andesite flows are intercalated with the upper member of the Ringbone Formation and the middle member of the Skunk Ranch Formation. The Hidalgo Formation, which crops out in the northern part of the range, is dominantly composed of basaltic andesite breccias and flows equivalent to those of the Ringbone and Skunk Ranch formations. The Laramide section was deposited in an intermontane basin partitioned across intrabasinal thrust structures, which controlled growth‐stratal development. U‐Pb zircon ages from five tuffs indicate that the age range of the Laramide sedimentary succession is ca. 75–70 Ma. U‐Pb detrital‐zircon age data (n = 356 analyses) from the Ringbone Formation and a Lower Cretaceous unit indicate sediment contribution from uplifted Lower and Upper Cretaceous rocks adjacent to the basin and the contemporary Tarahumara magmatic arc in nearby northern Sonora, Mexico. The new ages, combined with published data, indicate that uplift, basin development, and magmatism in the region proceeded diachronously northeastwards as the subducting Farallon slab flattened under northern Mexico and southern New Mexico from Campanian to Palaeogene time. 相似文献
20.
从南极半岛南设得兰群岛地区的４３个采样点采集了３３４个定向火山岩样品进行古地磁研究。火山岩层的地质时代为早第三纪。火山岩样品的古地磁学研究表明，早第三纪时，南设得兰群岛及南极半岛已经处于或接近于现今的地理位置。早第三世以来，本区未有明显的相对运动。古地磁资料还表明，古新世南极半岛的北缘出现了小规模的逆时针转动（约１５°）。这与南美板块与南极板块的相对移动有关。随着南大西洋的扩张，南美板块向西漂移，南极半岛北部受此西向漂移的带动，出现了小规模的逆时针转动 相似文献