腾冲盆地阻水构造的发现     

上官德树 《云南地质》2007,26(1):71-76

腾冲来凤山北麓前缘,潜伏一段阻水构造——地下水位坡降带。从研究13个水文钻井、119口民间井、2个泉水露头地下水位特征入手,采用古水文和现代水文地质研究方法,论证此段阻水构造的存在。  相似文献   

云南茶树林铅锌矿电磁波找矿效果     

李本茂  张学良  史家良  普建林 《云南地质》2007,26(2):257-263

茶树林铅锌矿，过去认为震旦系赋矿，钻探验证未见矿。本次利用物探方法实施深部探矿。依据物探异常，结合地质规律综合分析，认为是构造控矿。布置验证坑道，沿断裂破碎带发现新的厚大、品位高铅锌矿体，收到良好的找矿效果。  相似文献   

Late Pleistocene–Holocene environments in Valle Carbajal, Tierra del Fuego, Argentina   总被引：1，自引：0，他引：1  

Ana María Borromei  Andrea Coronato  Mirta Quattrocchio  Jorge Rabassa  Silvia Grill  Claudio Roig   《Journal of South American Earth Sciences》2007,23(4):321-335

The authors discuss Late Pleistocene–Holocene depositional environments in one of the Fuegian Andes valleys on the basis of palynological, geomorphological, and sedimentological analyses from two sites located near the Beagle Channel. The results obtained at these localities reinforce and refine the Late Pleistocene–Holocene climatic pattern previously recorded there. A colder period, associated with the Younger Dryas stadial event, is suggested by low Nothofagus pollen frequency, and communities of grass, low scrub, and shrub heath expanded into the low/middle slopes (10,310 ¹⁴C yr BP). By ca. 9500 ¹⁴C yr BP, warmer and drier conditions occurred, as evidenced by the development of open-grown vegetation in the valley floors (pollen zone O-3), followed by the expansion of open Nothofagus woodland (pollen zone O-2) in the middle Holocene. The milder climate subsequently changed, as indicated by the spreading of the closed forest and mire (pollen zone O-1), to more humid and cooler conditions during the last ca. 5000 yr BP.  相似文献   

The Alleret maar (Massif Central, France): A new lacustrine sequence of the early Middle Pleistocene in western Europe     

Jean-Franois Pastre  Agns Gauthier  Sbastien Nomade  Paul Orth  Ana Andrieu  Franck Goupille  Herv Guillou  Stphane Kunesch  Stphane Scaillet  Paul Randall Renne 《Comptes Rendus Geoscience》2007,339(16):987-997

The Alleret maar (Massif Central, France) provides a long lacustrine sequence (40.6 m) attributed to the early Middle Pleistocene. Sediment, pollen and diatoms analysis of its upper part (AL2 core, 14.6 m) indicates two temperate phases marked by high lake levels, forest development and vegetation expansion. They are separated by a cold period during which lake level drops, coarse sediment input increases and steppic and xerophilous plants develop. Pollen data suggests that this sequence belongs to the upper part of the Cromerian complex. These results are in agreement with the 557 ± 3 ka (±12 ka, including all errors) ⁴⁰Ar/³⁹Ar age obtained from an interbedded tephra layer emitted by the Mont-Dore/Sancy strato-volcano and establish that this sequence probably covers the MIS 15 substages.  相似文献   

Structural framework and Mesozoic–Cenozoic evolution of Ponta Grossa Arch, Paraná Basin, southern Brazil     

Michael Strugale  Sidnei Pires Rostirolla  Fernando Mancini  Carlos Vieira Portela Filho  Francisco Jos Fonseca Ferreira  Rafael Corrêa de Freitas 《Journal of South American Earth Sciences》2007,24(2-4):203-227

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Estimation of Block Sizes for Rock Masses with Non-persistent Joints   总被引：2，自引：3，他引：2  

B. H. Kim  M. Cai  P. K. Kaiser  H. S. Yang 《Rock Mechanics and Rock Engineering》2007,40(2):169-192

Summary  Discontinuities or joints in the rock mass have various shapes and sizes. Along with the joint orientation and spacing, the joint persistence, or the relative size of the joint, is one of the most important factors in determining the block sizes of jointed rock masses. Although the importance of joint persistence on the overall rock mass strength has long been identified, the impact of persistence on rock strength is in most current rock mass classification systems underrepresented. If joints are assumed to be persistent, as is the case in most designs, the sizes of the rock blocks tend to be underestimated. This can lead to more removable blocks than actually exist in-situ. In addition, a poor understanding of the rock bridge strength may lead to lower rock mass strengths, and consequently, to excessive expenditure on rock support. In this study, we suggest and verify a method for the determination of the block sizes considering joint persistence. The idea emerges from a quantitative approach to apply the GSI system for rock mass classification, in which the accurate block size is required. There is a need to statistically analyze how the distribution of rock bridges according to the combination of joint orientation, spacing, and persistence will affect the actual size of each individual block. For this purpose, we generate various combinations of joints with different geometric conditions by the orthogonal arrays using the distinct element analysis tools of UDEC and 3DEC. Equivalent block sizes (areas in 2D and volumes in 3D) and their distributions are obtained from the numerical simulation. Correlation analysis is then performed to relate the block sizes predicted by the empirical equation to those obtained from the numerical model simulation. The results support the concept of equivalent block size proposed by Cai et al. (2004, Int. J. Rock Mech. Min. Sci., 41(1), 3–19).  相似文献   

Adakitic Dacites Formed by Intracrustal Crystal Fractionation of Water-rich Parent Magmas at Nevado de Longavi Volcano (36{middle dot}2{degrees}S; Andean Southern Volcanic Zone, Central Chile)     

RodrIguez  Carolina; Selles  Daniel; Dungan  Michael; Langmuir  Charles; Leeman  William 《Journal of Petrology》2007,48(11):2033-2061

The mid-Holocene eruptive products of Nevado de Longavívolcano (36·2°S, Chile) are the only reported occurrenceof adakitic volcanic rocks in the Quaternary Andean SouthernVolcanic Zone (33–46°S). Dacites of this volcano arechemically distinct from other evolved magmas of the regionin that they have high La/Yb (15–20) and Sr/Y (60–90)ratios and systematically lower incompatible element contents.An origin by partial melting of high-pressure crustal sourcesseems unlikely from isotopic and trace element considerations.Mafic enclaves quenched into one of the dacites, on the otherhand, constitute plausible parental magmas. Dacites and maficenclaves share several characteristics such as mineral chemistry,whole-rock isotope and trace element ratios, highly oxidizingconditions (NNO + 1·5 to >NNO + 2, where NNO is thenickel–nickel oxide buffer), and elevated boron contents.A two-stage mass-balance crystal fractionation model that matchesboth major and trace elements is proposed to explain magmaticevolution from the least evolved mafic enclave to the dacites.Amphibole is the main ferromagnesian phase in both stages ofthis model, in agreement with the mineralogy of the magmas.We also describe cumulate-textured xenoliths that correspondvery closely to the solid assemblages predicted by the model.We conclude that Nevado de Longaví adakitic dacites arethe products of polybaric fractional crystallization from exceptionallywater-rich parent magmas. These basaltic magmas are inferredto be related to an exceptionally high, but transient inputof slab-derived fluids released from serpentinite bodies hostedin the oceanic Mocha Fracture Zone, which projects beneath Nevadode Longaví. Fractional crystallization that is modallydominated by amphibole, with very minor garnet extraction, isa mechanism for generating adakitic magmas in cold subductionzones where a high flux of slab-derived fluids is present. KEY WORDS: adakite; amphibole; Andes; differentiation; Southern Volcanic Zone  相似文献   

Development of a Continental Volcanic Field: Petrogenesis of Pre-caldera Intermediate and Silicic Rocks and Origin of the Bandelier Magmas, Jemez Mountains (New Mexico, USA)     

Rowe  M. C.; Wolff  J. A.; Gardner  J. N.; Ramos  F. C.; Teasdale  R.; Heikoop  C. E. 《Journal of Petrology》2007,48(11):2063-2091

The Miocene–Quaternary Jemez Mountains volcanic field(JMVF) is the site of the Valles caldera and associated BandelierTuff. Caldera formation was preceded by > 10 Myr of volcanismdominated by intermediate composition rocks (57–70% SiO₂)that contain components derived from the lithospheric mantleand Precambrian crust. Simple mixing between crust-dominatedsilicic melts and mantle-dominated mafic magmas, fractionalcrystallization, and assimilation accompanied by fractionalcrystallization are the principal mechanisms involved in theproduction of these intermediate lavas. A variety of isotopicallydistinct crustal sources were involved in magmatism between13 and 6 Ma, but only one type (or two very similar types) ofcrust between 6 and 2 Ma. This long history constitutes a recordof accommodation of mantle-derived magma in the crust by meltingof country rock. The post-2 Ma Bandelier Tuff and associatedrhyolites were, in contrast, generated by melting of hybridizedcrust in the form of buried, warm intrusive rocks associatedwith pre-6 Ma activity. Major shifts in the location, styleand geochemical character of magmatism in the JMVF occur withina few million years after volcanic maxima and may correspondto pooling of magma at a new location in the crust followingsolidification of earlier magma chambers that acted as trapsfor basaltic replenishment. KEY WORDS: crustal anatexis; fractional crystallization; Jemez Mountain Volcanic Field; Valles Caldera; radiogenic isotopes; trace elements  相似文献   

Large-scale Mechanical Redistribution of Orthopyroxene and Plagioclase in the Basement Sill, Ferrar Dolerites, McMurdo Dry Valleys, Antarctica: Petrological, Mineral-chemical and Field Evidence for Channelized Movement of Crystals and Melt     

Bedard  Jean H. J.; Marsh  Bruce D.; Hersum  Taber G.; Naslund  H. Richard; Mukasa  Samuel B. 《Journal of Petrology》2007,48(12):2289-2326

The Jurassic Ferrar dolerite sills of the McMurdo Dry Valleys,Antarctica represent the plumbing system for flood basalt eruptionsassociated with the breakup of Gondwana. Among the Ferrar sills,the 350–450 m thick cumulate-textured Basement Sill isdifferentiated into a Lower Marginal Zone (LMZ) gabbronorite,a thick Lower Zone (LZ) orthopyroxene–plagioclase orthocumulatepyroxenite, a strongly layered mela- to leuco-gabbronorite MiddleZone (MZ), a thick Upper Zone (UZ) gabbronorite with ferrogabbroicpods, and an Upper Marginal Zone (UMZ) gabbronorite. Texturesand mineral compositions in the LZ pyroxenite and MZ–UZgabbronorites are nearly identical, the main distinction beingthe greater relative proportion of plagioclase in the MZ–UZgabbronorites, and of pigeonite in the UZ. Most orthopyroxenein the LZ, MZ and UZ occurs as sub-euhedral, normally zonedprimocrysts, commonly with rounded plagioclase inclusions. Plagioclaseis usually sub-euhedral and normally zoned, but can containsodic cores interpreted to be xenocrystic. Orthopyroxene andfeldspar compositions thoughout the sill are generally fairlyuniform, and resemble the compositions of micro-phenocrystsin the chilled margins. We infer that the sill was filled bya c. 1250°C slurry of orthopyroxene + plagioclase phenocrystsor primocrysts that subsequently unmixed in response to buoyancyforces. The LZ websterite contains numerous anorthosite to gabbronoriteschlieren, veins and pipes (< 2 m diameter), which we interpretas fossil segregation channels. Textures and mineral compositionsin these felsic channels are very similar both to UZ and MZgabbronorites, and to the groundmass separating accumulatedorthopyroxene primocrysts in the LZ and MZ. We infer that plagioclase-charged,hydrous pore melt from the pyroxenite may have segregated, pooledand ascended through these conduits to feed growth of the UZgabbronorite. Detailed mapping shows that the pipes are separatedby about 15 m on average. Calculations suggest that this numberdensity of conduits could have drained the LZ cumulates of theirinterstitial melt + plagioclase in about 8 days. Sequences (eachc. 5–10 m thick) of layered leuco-gabbronorite in theMZ could represent intra-cumulate sills that formed from plagioclase-richslurries ascending in segregation channels. Fe–Ti-richpyroxenitic veins and pods (some pegmatitic) and an unusualcoarse-grained plagioclase facies occur at the contacts betweenmassive leuco-gabbronorite layers in the MZ. Discordant ferro-pegmatitepods and dykes occur throughout the UZ. We interpret these Fe-richpegmatoidal rocks as evolved residual melts expelled from thecompacting gabbronoritic cumulates of the MZ and UZ. KEY WORDS: Ferrar; cumulates; differentiation; Antarctica; layering  相似文献   

The Role of Pressure in Producing Compositional Diversity in Intraplate Basaltic Magmas   总被引：3，自引：0，他引：3  

Whitaker  M. L.; Nekvasil  H.; Lindsley  D. H.; Difrancesco  N. J. 《Journal of Petrology》2007,48(2):365-393

Basaltic magmas found in intraplate suites appear to followmore than one differentiation trend. Many ocean island suitesfollow the ocean island tholeiitic trend, with the basalts differentiatingfrom olivine tholeiite through basaltic andesite, andesite,and dacite to sodic rhyolite. Many continental intraplate magmaticregimes, such as those of the Snake River Plain and the plutonicsequences associated with massif anorthosites, follow the potassicsilica-saturated alkalic trend, in which basalt differentiatesfrom olivine tholeiite through ferrobasalt (jotunite or ferrodiorite),Fe-rich intermediate rocks (trachybasalt or monzonite), andtrachyte (syenite) to potassic rhyolites and granites. Crystallizationexperiments on an olivine tholeiite from the Snake River Plainshow that the basaltic portions of the ocean island tholeiitictrend and the potassic silica-saturated alkalic trend (whichleads to strong alkali, P, Ti, and Fe enrichment and silicadepletion) can arise from the same ‘dry’ tholeiiticparental magma. These compositional differences are inducedby changes in phase equilibria as a function of pressure, withthe ocean island tholeiitic series arising from crystal–liquiddifferentiation at low pressure and the potassic silica-saturatedalkalic series arising via differentiation at elevated pressures. KEY WORDS: tholeiite differentiation; experimental petrology; phase equilibria; ferrodiorite; ferrobasalt  相似文献