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81.
82.
Roger Guérin 《Hydrogeology Journal》2005,13(1):251-254
83.
DUGGEN S.; HOERNLE K.; VAN DEN BOGAARD P.; GARBE-SCHONBERG D. 《Journal of Petrology》2005,46(6):1155-1201
Post-collisional magmatism in the southern Iberian and northwesternAfrican continental margins contains important clues for theunderstanding of a possible causal connection between movementsin the Earth's upper mantle, the uplift of continental lithosphereand the origin of circum-Mediterranean igneous activity. Systematicgeochemical and geochronological studies (major and trace element,SrNdPb-isotope analysis and laser 40Ar/39Ar-agedating) on igneous rocks provide constraints for understandingthe post-collisional history of the southern Iberian and northwesternAfrican continental margins. Two groups of magmatic rocks canbe distinguished: (1) an Upper Miocene to Lower Pliocene (8·24·8Ma), SiK-rich group including high-K (calc-alkaline)and shoshonitic series rocks; (2) an Upper Miocene to Pleistocene(6·30·65 Ma), Si-poor, Na-rich group includingbasanites and alkali basalts to hawaiites and tephrites. Maficsamples from the SiK-rich group generally show geochemicalaffinities with volcanic rocks from active subduction zones(e.g. IzuBonin and Aeolian island arcs), whereas maficsamples from the Si-poor, Na-rich group are geochemically similarto lavas found in intraplate volcanic settings derived fromsub-lithospheric mantle sources (e.g. Canary Islands). The transitionfrom Si-rich (subduction-related) to Si-poor (intraplate-type)magmatism between 6·3 Ma (first alkali basalt) and 4·8Ma (latest shoshonite) can be observed both on a regional scaleand in individual volcanic systems. SiK-rich and Si-poorigneous rocks from the continental margins of southern Iberiaand northwestern Africa are, respectively, proposed to havebeen derived from metasomatized subcontinental lithosphere andsub-lithospheric mantle that was contaminated with plume material.A three-dimensional geodynamic model for the westernmost Mediterraneanis presented in which subduction of oceanic lithosphere is inferredto have caused continental-edge delamination of subcontinentallithosphere associated with upwelling of plume-contaminatedsub-lithospheric mantle and lithospheric uplift. This processmay operate worldwide in areas where subduction-related andintraplate-type magmatism are spatially and temporally associated. KEY WORDS: post-collisional magmatism; Mediterranean-style back-arc basins; subduction; delamination; uplift of marine gateways 相似文献
84.
Late-Stage Mafic Injection and Thermal Rejuvenation of the Vinalhaven Granite, Coastal Maine 总被引:11,自引:0,他引:11
WIEBE R. A.; MANON M. R.; HAWKINS D. P.; McDONOUGH W. F. 《Journal of Petrology》2004,45(11):2133-2153
The Vinalhaven intrusive complex consists mainly of coarse-grainedgranite, inward-dipping gabbrodiorite sheets, and a fine-grainedgranite core. Small bodies of porphyry occur throughout thecoarse-grained granite. The largest porphyry body (roughly 0·5km by 2·5 km) occurs with coeval gabbro, hybrid rocks,and minor fine-grained granite in the Vinal Cove complex, whichformed during the waning stages of solidification of the coarse-grainedVinalhaven granite. Porphyry contacts with surrounding coarse-grainedgranite are irregular and gradational. Compositions of wholerocks and minerals in the porphyry and the coarse-grained graniteare nearly identical. Neighboring phenocrysts in the porphyryvary greatly in degree of corrosion and reaction, indicatingthat the porphyry was well stirred. Thermal rejuvenation ofa silicic crystal mush by a basaltic influx can explain thecomposition and texture of the porphyry. Comparable rejuvenationevents have been recognized in recent studies of erupted rocks.Weakly corroded biotite phenocrysts in the porphyry requirethat hydrous interstitial melt existed in the granite duringremelting. Field relations, along with thermal calculations,suggest that cooling and crystallization of coeval mafic magmacould have generated the porphyry by thermal rejuvenation ofgranite crystal-mush containing about 20% melt. Field relationsalso suggest that some of the porphyry matrix may representnew felsic magma that was emplaced during remelting. KEY WORDS: granite; magma chamber; mafic replenishment; rejuvenation 相似文献
85.
桂西下三叠统牙形石序列的新认识 总被引:5,自引:0,他引:5
桂西下三叠统为海相沉积,根据其岩性、厚度、化石类型等诸方面的明显差异可以分为两种类型,即作登型和太平型。本文详细研究了桂西两种类型下三叠统的牙形石,认为不同类型的下三叠统具有不同的牙形石序列。在前人工作基础上,对桂西下三叠统牙形石序列予以重新厘定。补充了作登型下三叠统的Neogondolella carinta带;指出作登型下三叠统不宜建立Platyvillosus costatus带;在太平型下三叠统Dienerian阶—Spathian阶中新建了Pachvcladina erromera带,Platyvillosus costatus带,Pachycladina obliqua-Parachirognathus delicatulus带和Neospathodus triangularis带;指出了每一个牙形石带的性质并与作登型下三叠统牙形石序列进行了对比。本文还从事件地层学和生物地层学两个角度,对桂西二叠一三叠系界线提出了新的认识。 相似文献
86.
87.
Plastic Deformation and Recrystallization of Garnet: A Mechanism to Facilitate Diffusion Creep 总被引:5,自引:0,他引:5
Elongate and deformed garnets from Glenelg, NW Scotland, occurwithin a thin shear zone transecting an eclogite body that hasundergone partial retrogression to amphibolite facies at circa700°C. Optical microscopy, back-scattered electron imaging,electron probe microanalysis and electron back-scatter diffractionreveal garnet sub-structures that are developed as a functionof strain. Subgrains with low-angle misorientation boundariesoccur at low strain and garnet orientations are dispersed, aroundrational crystallographic axes, across these boundaries. Towardshigh-strain areas, boundary misorientations increase and thereis a loss of crystallographic control on misorientations, whichtend towards random. In high-strain areas, a polygonal garnetmicrostructure is developed. The garnet orientations are randomlydispersed around the original single-crystal orientation. Somegarnet grains are elongate and Ca-rich garnet occurs on thefaces of elongate grains oriented normal to the foliation. Commonly,the garnet grains are admixed with matrix minerals, and, wherein contact with other phases, garnet is well faceted. We suggestthat individual garnet porphyroclasts record an evolution fromlow-strain conditions, where dislocation creep and recoveryaccommodated deformation, through increasing strain, where dynamicrecrystallization occurred by subgrain rotation, to higheststrains, where recrystallized grains were able to deform bydiffusion creep assisted grain boundary sliding with associatedrotations. KEY WORDS: diffusion creep; EBSD; garnet; plastic deformation; recrystallization 相似文献
88.
Sm-Nd法及其参数εNd(O)、εNd(T)、TCHURNd、εDMNd及x,是测定花岗岩形成年龄及研究花岗岩成因类型、模式年龄及地幔物质百分比的重要手段,但因其测试费用高等原因,难以广泛使用。作者提出了Rb-Sm法的相应参数εSr(O)、εSr(T)、TURSr、εDMSr及μ做为补充,在没有Sm-Nd同位素资料的情况下,Rb-Sr同位素参数基本上可以代替Sm-Nd同位素参数。经对比,求花岗岩中幔源物质百分比时,Rb-Sr法计算值与Sm-Nd法计算值相比,误差一般不超过10%。此外,作者还提出了计算花岗岩山幔源物质百分比的简化式,使该计算更为简便易行。 相似文献
89.
Residence, Resorption and Recycling of Zircons in Devils Kitchen Rhyolite, Coso Volcanic Field, California 总被引:14,自引:1,他引:14
Zircons from the Devils Kitchen rhyolite in the PleistoceneCoso Volcanic field, California have been analyzed by in situPb/U ion microprobe (SHRIMP-RG) and by detailed cathodoluminescenceimaging. The zircons yield common-Pb-corrected and disequilibrium-corrected206Pb/238U ages that predate a previously reported KArsanidine age by up to 200 kyr, and the range of ages exhibitedby the zircons is also approximately 200 kyr. Cathodoluminescenceimaging indicates that zircons formed in contrasting environments.Most zircons are euhedral, and a majority of the zircons areweakly zoned, but many also have anhedral, embayed cores, witheuhedral overgrowths and multiple internal surfaces that aretruncated by later crystal zones. Concentrations of U and Thvary by two orders of magnitude within the zircon population,and by 1020 times between zones within some zircon crystals,indicating that zircons were transferred between contrastingchemical environments. A zircon saturation temperature of 750°Coverlaps within error a previously reported phenocryst equilibrationtemperature of 740 ± 25°C. Textures in zircons indicativeof repeated dissolution and subsequent regrowth are probablycaused by punctuated heating by mafic magma input into rhyolite.The overall span of ages and large variation in U and Th concentrations,combined with calculated zircon saturation temperatures andresorption times, are most compatible with crystallization inmagma bodies that were emplaced piecemeal in the crust at Cosoover 200 kyr prior to eruption, and that were periodically rejuvenatedor melted by subsequent basaltic injections. KEY WORDS: zircon geochronology; residence time; rhyolite; ion microprobe; California 相似文献
90.
青藏高原是当今世界上最高、最大和最年轻的高原。青藏高原的地球动力学研究是一个复杂而饶有兴趣的问题。本文试图从高原的范围、地球物理特征、地震活动、构造演化和新构造运动等方面探讨其地球动力学过程。 从新构造分析,笔者着重指出,青藏高原是欧亚大陆板块中最活动的一个块体,它在造就中国乃至东亚新构造运动的格局方面,是一个十分重要的因素。 相似文献