Journal of The Virtual Explorer最新文献

{"title":"Crustal configuration across the north-western Himalaya as inferred from gravity and GPS aided geoid undulation studies","authors":"P. Banerjee, Wadia Satyaprakash","doi":"10.3809/JVIRTEX.2003.00073","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2003.00073","url":null,"abstract":"","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"502 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2003-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132856920","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New constraints of the timing of tectonic activity in the Archaean Central Pilbara Craton, Western Australia","authors":"K. Beintema, P. Mason, D. Nelson, S. White, J. Wijbrans","doi":"10.3809/JVIRTEX.2003.00081","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2003.00081","url":null,"abstract":"The Archaean Pilbara Craton in Western Australia has a domainal architecture which has been interpreted to reflect a history of accretion. The Tabba Tabba Shear Zone is the major division between the East and West Pilbara blocks: this interpretation is based on significant differences in the tectono-thermal histories of the bordering terranes. New laser ablation ICP-MS and SHRIMP U-Pb zircon geochronological data, coupled with trace element data for the same core parts of the sampled mineral grains, indicate a range of magmatic crystallization ages for representative igneous rocks emplaced before, during or after shearing. Results from both dating techniques agree for two separate homogeneous samples to within analytical error (2s). Our data indicate that a granodioritic suite intruded the area at about 3250 Ma, followed by gabbroic suite at 3235 Ma. The area was subsequently affected by an early dextral compressive event during which the Tabba Tabba Shear Zone was formed, and the granodiorites and gabbros were incorporated into the Tabba Tabba Shear Zone. A granitoid suite intruded the shear zone at 2940 Ma, with xenocrystic populations of 3115 Ma and 3015 Ma, a possibly West Pilbara association. The East and West Pilbara terranes may thus have been relatively close to each other between 3250 and 3115 Ma. The Tabba Tabba Shear Zone currently forms the eastern bounding fault of the Mallina Basin. The last major activity in the structure occurred during a major phase of oblique movement, corresponding to closure of the Mallina Basin. Ages of late syn-kinematic granitic intrusions indicate that this occurred at about 2940 Ma.","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2003-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129047353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cretaceous 40 Ar/39 Ar detrital mica ages in tertiary sediments, solving the debate on the Eo-Alpine evolution?","authors":"B. Carrapa, J. Wijbrans, G. Bertotti","doi":"10.3809/JVIRTEX.2003.00082","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2003.00082","url":null,"abstract":"Clastic sediments deposited in the syn-orogenic Tertiary Piedmont Basin in northwest Italy represent the depositional counterpart of the cooling/exhumation and erosion of Western Alpine rocks over the last 30- 35 Myr. 40 Ar/ 39 Ar analyses of detrital white micas from Oligocene-Miocene sediments and present-day river sands show, in addition to younger Tertiary age groups, a wide range of Cretaceous ages. Pronounced well defined Late Cretaceous (~70-90 Ma) and Early Cretaceous (~105-120 Ma) age clusters are recorded in Lower to Upper Miocene sediments, forming discrete age groups with a contribution to the total detrital population of as high as 58%. This age pattern of discrete age peaks is remarkably constant and can be followed up-sequence through different formations spanning a time interval for sedimentation of >20 Myr. Our new detrital mica ages may be the result of either excess Ar in the source rock, as commonly assumed for HP mica Ar ages from the internal western Alps, or of inherited Ar, and consequently be representative of real geological events. The first scenario would imply that incorporation of excess Ar in minerals can lead to non-random detrital age populations which could then mistakenly be interpreted as representative of real geological events. The second scenario would imply that during the last Eocene thermal event, pre-existing micas were only partially overprinted and the presence of older ages are the result of real Cretaceous metamorphic events of the Western Alpine orogen. We argue that our new data derived from the sedimentary record, in particular from the time interval from Serravallian to Present, cannot easily be explained as simply being due to incorporation of excess argon. We therefore interpret these ages to be representative of cooling following major metamorphic events in the Alpine orogen. The new argon data from the sediments in combination with the data from the rocks exposed in the orogen today point to a complex Mesozoic history of the internal Alpine orogen.","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"360 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2003-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122782395","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Palaeomagnetic studies on the dykes of Mumbai region, West coast of deccan volcanic province: implications on age and Span of the deccan Eruptions","authors":"S. Patil, B. Arora","doi":"10.3809/JVIRTEX.2003.00077","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2003.00077","url":null,"abstract":"Through detailed AF and thermal demagnetizations of 35 samples (161 specimens) collected from 6 dykes located at Murud region, south of Mumbai, we report the first mean characteristic remanent magnetization direction as D=341°; I= -42°(μ95=5.7; N=6 dykes) for the dykes intruded into the West Coast zone of the Deccan Volcanic Province. The virtual geomagnetic pole (VGP) position (44°N; 83°W; A95=5.8°; N=6 dykes) calculated from this study is compared with those of the Narmada-Tapti zone dykes and with the Deccan Super Pole, proposed by Vandamme et al. (1991). Based on the concordance of these poles and recently reported 40Ar/39Ar and 87Rb/86Sr dates on the dykes of the studied region (Murud), it is proposed that the entire Deccan flows and the associated dykes were erupted in a short interval close to the Cretaceous-Tertiary Boundary at 65.5 Ma. Thermal demagnetization spectra along with isothermal remanent magnetizations and LF test experiments indicated that the SD type titano-magnetite was the major ChRM carrying magnetic mineral in the samples. Out of the 6 studied dykes, one dolerite dyke showing the “reverse magnetic polarity”, could have acted as a feeder dyke to the Poladpur Formation flows, which host the dykes in the studied area. The remaining four dolerite dykes and one lamprophyre dyke, yielding “normal polarity” directions, might have fed to the youngest formations of Wai Subgroup flows, viz., Panhala Formation and Desur Formation, which were eroded in the studied region. INTRODUCTION It is a widely accepted view that the Deccan flood basalts of Indian sub-continent, covering at present an area of 500,000 sq.km., is the result of outburst of immense magma material from the Reunion Hot spot source that impinged on the northerly drifting Indian lithosphere in the Late Cretaceous (Morgan, 1981). The Deccan Province is traversed by three major rift zones, namely the Narmada-Tapti-Son rift, the Cambay rift and the West Coast rift, which form a triple junction at the CambayBasin (Sheth and Chandrashekharam, 1997). Over the last 30 years the Deccan Traps have attained the attention of geochronologists, palaeomagnetists, geochemists and petrologists alike with its impressive horizontal lava piles, enormous size and volume along with its rapid eruptions at the K/T boundary coinciding with the much debated mass extinctions (Sen, 2001; Subbarao, 1999a and 1999b). Palaeomagnetic investigations on the Deccan Traps have been successful in strengthening the plate-tectonic theory as well as establishing the magnetostratigraphy of the flow sequence permitting constraints on the ages and span of eruption of the flows. From the compilation of the available good quality palaeomagnetic data on the flows, Vandamme et al. (1991) proposed a normal-reversenormal polarity sequence that correspond to the chrons 30 N-29 R-29 N; a major part of the eruptions is limited to the chron 29 R. From detailed geochronological studies on the 2.5 km thick lava pile in the","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2003-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115551637","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Animation of refold structures","authors":"F. Fusseis, B. Grasemann","doi":"10.3809/JVIRTEX.2002.00059","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2002.00059","url":null,"abstract":"","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116114296","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Analogue modelling of asymmetrical back-arc extension","authors":"W. Schellart, G. Lister, M. Jessell","doi":"10.3809/JVIRTEX.2002.00046","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2002.00046","url":null,"abstract":"Back-arc extension takes place in the overriding plate in an overall convergent setting during retreat of the hinge-line of the subducting slab. A large number of back-arc basins display a geometry and internal structure that is asymmetric, i.e. where the amount of extension increases from one end of the arc to the other. We present the results of 3-dimensional analogue modelling of asymmetric back-arc extension of an overriding lithosphere with a varying initial rheology. The results show that with increasing lithospheric brittle to viscous strength (BS/VS), the fault density decreases in magnitude, while the asymmetry in deformation pattern in the back-arc region increases. The area extent of deformation is mainly dependent on the ratio of brittle strength to buoyancy force (BS/BF), i.e. the larger the ratio, the smaller the area of deformation. The experimental results have been compared with several arc - back-arc systems, which display a relatively large amount of structural asymmetry (Tonga Arc, Kuril Arc, New Hebrides Arc, Ryukyu arc) but a varying style of tectonic deformation. These differences are mainly the result of the stage of opening up of the back-arc basin, the subduction setting (ocean-ocean or ocean-continent) and difference in rheology of the overriding lithosphere.","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"52 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133228908","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"GeoBlocks 3D - Interactive 3D geologic blocks","authors":"S. Reynolds, Julia K. Johnson","doi":"10.3809/JVIRTEX.2002.00061","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2002.00061","url":null,"abstract":"","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"352 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134501945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Domain Boundary Migration at Multiple Scales in Experiment and Nature","authors":"G. Brecht, P. Bons, M. Jessell","doi":"10.3809/JVIRTEX.2000.00009","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2000.00009","url":null,"abstract":"","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125086330","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deformation microstructures in quartzo-feldspathic rocks","authors":"J. Tullis, H. Stünitz, C. Teyssier, R. Heilbronner","doi":"10.3809/JVIRTEX.2000.00019","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2000.00019","url":null,"abstract":"","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127748666","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Setting of the giant Muruntau Gold Deposit: Implications for ore genesis","authors":"A. Wilde, D. Gilbert","doi":"10.3809/JVIRTEX.2000.00004","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2000.00004","url":null,"abstract":"","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122392183","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}