Eclogites preserved as pebbles in Jurassic conglomerate, Dabie Mountains, China   总被引：9，自引：0，他引：9  

Qingchen Wang  Renwei Li  Daoxuan Wang  Shuangying Li 《Lithos》2003,70(3-4):345-357

Two types of eclogite pebbles were discovered in Middle to Upper Jurassic conglomerates from the Hefei Basin north of the Dabie ultrahigh-pressure (UHP) terrain, China. Type A eclogite pebbles are characterized by idioblastic garnet with well preserved chemical zonation. Si content in phengite is lower than 3.5 per formula unit (pfu). The maximum metamorphic pressure is lower than 2.5 GPa, and the temperature is below 600 °C. Type B eclogite pebbles contain coesite pseudomorphs in xenoblastic garnet. Si content in phengite is higher than 3.5 pfu. The maximum metamorphic pressure is 2.8–4.0 GPa at 700 °C indicating UHP metamorphism.

Types A and B eclogite pebbles are comparable with eclogites occurring in the southern portion of the Dabie UHP terrain. Based on the petrologic similarities and northeastwards directed paleocurrents, we infer that the eclogite pebbles were eroded from the Dabie UHP terrain. Sandstones containing detrital phengite with Si content higher than 3.5 pfu are also derived from UHP rocks. These petrologic and stratigraphic data place time constraints on exhumation and erosion history of the Dabie UHP terrain.  相似文献   

钙质砂物理力学性质初探   总被引：14，自引：4，他引：10  

刘崇权  汪稔 《岩土力学》1998,19(1):32-37

钙质砂是一种含CaCO3超过50％以上的粒状材料。其特殊的组构特征,导致了独特的力学和工程性状。文中综述了钙质砂在压缩、剪切等方面的表现及其机理,指出钙质砂力学及工程性能的研究必须综合考虑颗粒破碎、剪胀及颗粒重排列。  相似文献   

A new conglomerate test in palaeomagnetism   总被引：2，自引：0，他引：2  

Stanislav V. Shipunov  Anton A. Muraviev  & Mikhail L. Bazhenov 《Geophysical Journal International》1998,133(3):721-725

The conglomerate test is widely used in palaeomagnetism to date components of natural remanent magnetization with respect to deposition of conglomerates. It has been demonstrated, however, that this test may be positive even if the data are strongly contaminated by a secondary remanence, especially for the commonly used small number of clasts Starkey & Palmer 1970). Here we show with the aid of numerical simulations that different statistical procedures employed in this test have similar low sensitivities to remagnetization. We suggest a new conglomerate test which incorporates additional information on the direction of a secondary palaeomagnetic component which is isolated from either clasts themselves or their host rocks. Numerical simulations show that this new test is about twice as sensitive to remagnetization as the previous procedures and is robust with respect to small errors in the direction of a secondary component.  相似文献   

山东蓬家夼金矿的基本地质特征及其找矿方向   总被引：47，自引：10，他引：37  

沈远超  谢宏远 《地质与勘探》1998,34(5):3-7,13

通过工作,认为该区中生代构造体系以走滑构造为主,走滑以在蓬家夼地区转换为拉张,在白垩纪莱阳组砾岩与下无古界荆山群变质杂岩之间一剥离断层,蓬家夼金矿产于该剥离断层内,为区内火山活动期间在大气水参一下形成的层间滑动角砾岩型金矿。通过对区内地质体变形特征的研究,认为蓬有夼金矿在三维空间上的应呈倾向１５５°±１０°、倾角４５°±１０°的大的复式透镜体,可望成为大型金矿。  相似文献   

黑龙江小金山砾岩型金矿地质特征及成矿机理   总被引：1，自引：1，他引：0  

王之彬  王亮义 《黄金地质》1998,4(3):30-34

叙述了产于上侏罗统砾岩型金矿的矿床地质特征,赋存与富集规律,金的物质来源和砾岩金的成矿机理,侧重阐明了“底流”对砾岩金形成的作用。  相似文献   

川西前陆盆地南部中新生代砾岩的构造意义   总被引：1，自引：0，他引：1  

曾宜君  杨学俊  李云泉  谢启兴  朱兵  郝雪峰 《四川地质学报》2004,24(4):198-201

通过对龙门山前缘川西前陆盆地南部中新生代地层中砾岩的岩石学特征、年代及分布规律的对比研究，认为五龙沟砾岩、大溪砾岩及大邑砾岩是龙门山造山运动的沉积响应；龙门山的崛起是一个多阶段性的持续过程，其发生的时限依次对应于燕山早期、燕山晚期-喜马拉雅初期、喜马拉雅晚期。  相似文献   

Impact de la vie benthique sur la genèse de nodules calcaires dans les black shales     

Jean-Gabriel Bréhéret  Micheline Hanzo  Abderrazzak El Albani  Agnès Iatzoura 《Comptes Rendus Geoscience》2004,336(15):1355-1362

The study of calcareous nodules from four organic-rich black shale series allows us to suggest a prominent part for benthic organisms in creating heterogeneities in the sediment, thus favouring microbially mediated early diagenesis based on organic matter consumption. To cite this article: J.-G. Bréhéret et al., C. R. Geoscience 336 (2004).  相似文献   

Middle Miocene to Pleistocene magneto-biostratigraphy of ODP Sites 1150 and 1151, northwest Pacific: Sedimentation rate and updated regional geological timescale     

Isao Motoyama  Nobuaki Niitsuma  Toshiaki Maruyama  Hiroki Hayashi  Shin-ichi Kamikuri  Masamichi Shiono  Toshiya Kanamatsu  Kaori Aoki  Chikako Morishita  Kyoko Hagino  Hiroshi Nishi  Motoyoshi Oda 《Island Arc》2004,13(1):289-305

Abstract Shipboard and shore‐based investigation on siliceous and calcareous microfossil biostratigraphy, magneto‐stratigraphy and tephrostratigraphy identified numerous datum events from the sedimentary sequences of Sites 1150 and 1151 drilled on the forearc basin of northern Japan by the Ocean Drilling Program Leg 186. Some 83 datum events were selected to construct new age–depth models for the sites. Based on the reliable magneto‐stratigraphy from the Pleistocene to the Upper Miocene, which were correlated to the standard geomagnetic polarity timescale, and on excellent records of diatom and radiolarian biostratigraphy throughout the sequences, the shipboard age model was revised. Major revisions referred to stratigraphic position of the Miocene–Pliocene boundary that has been shifted more than 200 m downward in each sequence. The age–depth relations of the forearc sites represent drastic changes in the sedimentation rate—extremely high (40 cm/k.y. on average) in the Early Pliocene and low (less than 2 cm/k.y. on average) in the Middle Miocene—and several hiatuses exist throughout the sequence. The drastic changes can be related mostly to changes in diatom sedimentation and the tectonics of the Japanese Island Arc. Local ages for some foraminiferal, calcareous nannofossil and radiolarian bioevents are estimated from the age–depth models at each site. These newly calibrated bioevents and biozones as well as established diatom biostratigraphy are incorporated into the updated magneto‐biochronologic timescale, which will contribute to an improvement in biochronologic accuracy of Neogene sediments in northern Japan and adjacent areas.  相似文献   

我国咸化湖泊沉积中钙质超微化石特征及其地质意义   总被引：7，自引：2，他引：7       下载免费PDF全文

孙镇城  杨革联  乔子真  杨藩  李东明  景民昌 《古地理学报》2002,4(2):56-63

对我国西北和东北（内蒙古东部）36个地点的新生代-现代陆相咸化湖泊沉积中的433块标本进行了采样分析，在其中15个地点38块标本中发现钙质超微化石10个属：Coccolithus, Reticulofenestra, Cyclicargolithus,Quadrum, Discoaster, Gephyrocapsa, Calcidiscus, Umbilicasphaera,Cotonocyclus, Watznaueria等，多数为原地沉积，也有一部分属于再沉积来源。由此可见，不能笼统地把所有钙质超微化石的发现都当作海相或海侵的证据。陆相咸化湖泊沉积中钙质超微化石的特点是：丰度低，数量稀少；属种分异度低；常与陆相喜盐水生生物共生。第四系和现代陆相咸化湖泊沉积中发现的钙质超微化石属种往往是海相第四系或现代海洋中常见类型。在青海柴达木盆地七个泉构造七心1井中-上始新统下干柴沟组上段岩心中，发现Reticulofenestra bisecta。这是海相中始新世-渐新世沉积中标志化石。看来，利用钙质超微化石进行海、陆相地层对比探索已取得一定进展，但离“统”一级的地层对比还有很大距离。  相似文献   

西藏文部一姆错丙尼地区早二叠世拉嘎组——兼述杂砾岩形成环境与成因     

李晓勇  谢国刚  袁建芽  肖业斌  黄传冠 《地质通报》2002,21(11)

通过1∶250000邦多区幅和措麦区幅区域地质调查,对西藏文部—姆错丙尼地区的早二叠世拉嘎组进行了地层古生物及杂砾岩特征的研究,发现赋存于滑塌块体中的生物化石反映的地质时期为早二叠世Sakmarian—Artinskian期,而滑塌块体的“基质”地层时代应稍晚于早二叠世Sakmarian—Artinskian期;沉积特征表明杂砾岩成因具冰海相和水下块体重力流的复合(双重)性质。  相似文献