Chloritoid–hornblende assemblages in quartz–muscovite pelitic rocks of the Central Metasedimentary Belt, Grenville Province, Canada     

P.H. THOMPSON  A.D. LECLAIR 《Journal of Metamorphic Geology》1987,5(3):415-436

Abstract Chloritoid–hornblende occurs in quartz–muscovite pelitic schist derived from sediment in a volcaniclastic sequence of the Grenville Supergroup and from reworked sedimentary and regolithic material above the unconformity at the base of the Flinton Group. Comparison of these samples with other pelitic rocks on triangular composition diagrams and in the ACNF and ACFM tetrahedra indicates that the presence of hornblende cannot be explained by unusually high CaO content. The rare assemblage is attributed to a combination of relatively low Al₂O₃ and high K₂O with high CaO/(CaO+Na₂O) and FeO/(FeO+MgO).
On two qualitative reaction grids derived from AFM diagrams projected through CaO and plagioclase, respectively, the P–T stability field of chloritoid–hornblende overlaps the first appearance of staurolite–biotite in normal pelitic rocks in the kyanite field. Staurolite–hornblende overlaps chloritoid–hornblende and extends to the higher temperatures and pressures of the kyanite–hornblende field.
The phase relations in these rocks provide a link between the conventional hornblende-absent grids for pelitic rocks and those for K₂O-poor (muscovite-absent) pelitic and mafic amphibolitic rocks.  相似文献   

超导岩样磁力仪的研制          下载免费PDF全文

何仁汉  薛寿清 《地球物理学报》1987,30(5):504-513

超导岩样磁力仪是以超导量子干涉器（SQUID）为磁传感器用来测量岩样剩磁的仪器,是研究岩石磁学和古地磁学的重要手段。它比常规的古地磁仪器--无定向磁力仪、旋转磁力仪具有灵敏度高、响应时间短、动态范围大、又可三分量同时测量等优点,满足了弱磁岩样测量的要求。本文叙述了超导测磁的理论基础,仪器的组成,原理,研制情况及实测结果。  相似文献   

The crustal structure of the Guayana Shield, Venezuela, from seismic refraction and gravity data   总被引：1，自引：0，他引：1  

Michael Schmitz  Daniel Chalbaud  Jesús Castillo  Carlos Izarra   《Tectonophysics》2002,345(1-4)

We present results from a seismic refraction experiment on the northern margin of the Guayana Shield performed during June 1998, along nine profiles of up to 320 km length, using the daily blasts of the Cerro Bolívar mines as energy source, as well as from gravimetric measurements. Clear Moho arrivals can be observed on the main E–W profile on the shield, whereas the profiles entering the Oriental Basin to the north are more noisy. The crustal thickness of the shield is unusually high with up to 46 km on the Archean segment in the west and 43 km on the Proterozoic segment in the east. A 20 km thick upper crust with P-wave velocities between 6.0 and 6.3 km/s can be separated from a lower crust with velocities ranging from 6.5 to 7.2 km/s. A lower crustal low velocity zone with a velocity reduction to 6.3 km/s is observed between 25 and 25 km depth. The average crustal velocity is 6.5 km/s. The changes in the Bouguer Anomaly, positive (30 mGal) in the west and negative (−20 mGal) in the east, cannot be explained by the observed seismic crustal features alone. Lateral variations in the crust or in the upper mantle must be responsible for these observations.  相似文献   

西沙群岛星虫类研究Ⅲ——石管星虫属Lithacrosiphon     

李凤鲁 《中国海洋大学学报(自然科学版)》1987,(2)

本文连续报道南海西沙群岛星虫类的第三部分即石管星虫属(Lithacrosiphon)。本属系1902年由Shipley氏订立。据文献记载属中的种均分布于热带海,通常钻孔于珊瑚石中。作者仅鉴定了马岛石管星虫(Lithac-rosiphon maldivensis Shipley)一种。本属在中国海是首次记载。  相似文献   

TBM in the Future of China     

Yang Lu  Ji-Ming Ma  Qian-Jun Xu  Mo-Ning Han 《Marine Georesources & Geotechnology》2004,22(3):185-193

China is arguably one of the countries where the most tunneling and underground projects are being performed. Recently in China, it has often been necessary to construct tunnels under many types of conditions and to develop new techniques. Currently, some advanced construction techniques cannot be appropriately applied to different types of underground conditions, and many traditional methods are still often used. However, because of the progress in tunnel boring machines (TBM), innovations are required for the construction method. This article introduces the current situation of TBM both in western countries and in China, and examines the future of TBM in China.  相似文献   

Interrelations between coeval mafic and A-type silicic magmas from composite dykes in a bimodal suite of southern Israel, northernmost Arabian–Nubian Shield: Geochemical and isotope constraints     

Y. Katzir  B.A. Litvinovsky  B.M. Jahn  M. Eyal  A.N. Zanvilevich  J.W. Valley  Ye. Vapnik  Y. Beeri  M.J. Spicuzza 《Lithos》2007,97(3-4):336-364

Late Neoproterozoic bimodal dyke suites are abundant in the Arabian–Nubian Shield. In southern Israel this suite includes dominant alkaline quartz porphyry dykes, rare mafic dykes, and numerous composite dykes with felsic interiors and mafic margins. The quartz porphyry chemically corresponds to A-type granite. Composite dykes with either abrupt or gradational contacts between the felsic and mafic rocks bear field, petrographic and chemical evidence for coexistence and mixing of basaltic and rhyolitic magmas. Mixing and formation of hybrid intermediate magmas commenced at depth and continued during emplacement of the dykes. Oxygen isotope ratios of alkali feldspar in quartz porphyry (13 to 15‰) and of plagioclase in trachydolerite (10–11‰) are much higher than their initial magmatic ratios predicted by equilibrium with unaltered quartz (8 to 9‰) and clinopyroxene (5.8‰). The elevation of δ¹⁸O in alkali feldspar and plagioclase, and extensive turbidization and sericitization call for post-magmatic low-temperature (≤ 100 °C) water–rock interaction. Hydrous alteration of alkali feldspar, the major carrier of Rb and Sr in the quartz–porphyry, also accounts for the highly variable and unusually high I(Sr) of 0.71253 to 0.73648.

The initial ¹⁴³Nd/¹⁴⁴Nd ratios, expressed by ε_Nd(T) values, are probably unaltered and show small variation in mafic and felsic rocks within a narrow range from + 1.4 to + 3.3. The Nd isotope signature suggests either a common mantle source for the mafic and silicic magmas or a juvenile crustal source for the felsic rocks (metamorphic rocks from the Elat area). However, oxygen isotope ratios of zircon in quartz porphyry [δ¹⁸O(Zrn) = 6.5 to 7.2‰] reveal significant crustal contribution to the rhyolite magma, suggesting that mafic and A-type silicic magmas are not co-genetic, although coeval. Comparison of ¹⁸O/¹⁶O ratios in zircon allows to distinguish two groups of A-type granites in the region: those with mantle-derived source, δ¹⁸O(Zrn) ranging from 5.5 to 5.8‰ (Timna and Katharina granitoids) and those with major contribution of the modified juvenile crustal component, δ¹⁸O(Zrn) varying from 6.5 to 7.2‰ (Elat quartz porphyry dykes and the Yehoshafat alkaline granite). This suggests that A-type silicic magmas in the northern ANS originated by alternative processes almost coevally.  相似文献   

盾构掘进过程土体变形特性数值模拟   总被引：5，自引：0，他引：5  

张利民  李大勇 《岩土力学》2004,25(Z1):75-78

运用三维有限差分软件FLAC3D对盾构掘进工程进行了数值仿真,仿真过程中考虑了盾构机、注浆压力、土仓压力等因素,得到了地表沉降槽和土体纵向变化规律,并与实测结果进行了对比,结果表明,吻合较好。  相似文献   

盾构近距离穿越相邻隧道施工的数值解析   总被引：10，自引：5，他引：10  

廖少明  余炎  彭芳乐 《岩土力学》2004,25(Z2):223-226

近距离穿越施工时盾构对周围地层位移场的影响明显不同于常规施工.结合上海地铁隧道近距离穿越工程实例,运用边界单元法模拟分析了掘进施工过程中盾构对已建建筑的影响,同时对施工参数进行了理论探讨.结果表明,盾构壳体是影响周围地层的主要因素,而且其影响具有滞后性和累积特性,在施工中需要超前控制.  相似文献   

盾构隧道管片衬砌荷载模式比较分析   总被引：5，自引：0，他引：5  

胡志平  罗丽娟  蔡志勇 《岩土工程技术》2004,18(1):19-22,42

地下结构的荷载分布计算是非常复杂的 ,针对上海某越江盾构隧道 ,采用梁—弹性铰—地基系统计算模型 ,就水土压力合算与分算、侧向土压力和水压力的分布形式等设计了几种荷载模式 ,并分别计算分析比较了管片衬砌结构在这些荷载模式作用下的内力分布和变形特性 ,并从中得出了一些有价值的结论。  相似文献   

Geology and mineral potential of Ethiopia: a note on geology and mineral map of Ethiopia   总被引：1，自引：0，他引：1  

Solomon Tadesse  Jean-Pierre Milesi  Yves Deschamps   《Journal of African Earth Sciences》2003,36(4):273-313

This work presents a geoscientific map and database for geology, mineral and energy resources of Ethiopia in a digital form at a scale of 1:2,000,000, compiled from several sources. The final result of the work has been recorded on CD-ROM in GIS format so that the map and the database could be available to users on a personal computer.Metallic resources (precious, rare, base and ferrous–ferroalloy metals) are widely related to the metamorphic meta-volcano-sedimentary belts and associated intrusives belonging to various terranes of the Arabian–Nubian Shield, accreted during the East and West Gondwana collision (Neoproterozoic, 900–500 Ma).Industrial minerals and rock resources occur in more diversified geological environments, including the Proterozoic basement rocks, the Late Paleozoic to Mesozoic sediments and recent (Cenozoic) volcanics and associated sediments.Energy resources (oil, coal, geothermal resources) are restricted to Phanerozoic basin sediments and Cenozoic volcanism and rifting areas.  相似文献