Journal of The Virtual Explorer最新文献

{"title":"Detrital zircon U-Pb data from the Hellenic south Aegean belts: Constraints on the age and source of the South Aegean basement","authors":"A. Marsellos, D. Foster, G. Kamenov, K. Kyriakopoulos","doi":"10.3809/JVIRTEX.2011.00284","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2011.00284","url":null,"abstract":"U-Pb analyses of 595 zircons from 10 metasedimentary rocks collected from the forearc and volcanic arc in the South Aegean, Greece constrain the provenance of the widespread Phyllite-Quartzite unit (PQU) above the retreating Hellenic subduction zone in the South Aegean. Zircons from Miocene metamorphic rocks in the forearc on the islands of Peloponnese, Kythera, and Crete all give pre-Cenozoic U-Pb crystallization ages. Metamorphic rocks exposed within the volcanic arc on Milos and Santorini also lack zircons grown during the recent phase of Hellenic subduction. Samples of clastic sedimentary rocks that were affected by the Miocene metamorphism show zircon crystallization ages that range fromca.80 to 2937 Ma. Sandstone collected from the upper plate of the Kythera Detachment fault, which was not affected by Miocene metamorphism based on Jurassic-Cretaceous zircon fission-track data, yields detrital zircon ages that range fromca.202 to 3487 Ma. Zircons with Archean crystallization ages are absent in the metamorphosed detrital rocks from Crete, Kythera, Peloponnese, Milos and Santorini. This is most likely because metamorphism caused the breakdown and/or recrystallization of any ancient zircons with substantial radiation damage. Mean U-Pb ages (206Pb/238U or207Pb/206Pb) of distinct populations of 534 concordant zircons are about 316, 639, 994, 1954, 2598 and 3325 Ma. These populations are consistent with parts of the detritus that now makes up the South Aegean basement having a source within orogenic belts of North African or other parts of Gondwana.","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125098478","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":"Field Trip 1 - Geology and petrology of Ocean Continent Transition (OCT) zones metamorphosed under eclogite facies conditions","authors":"A. V. Brovarone, J. Malavieille, M. Beltrando, G. Molli, R. Compagnoni","doi":"10.3809/JVIRTEX.2011.00300","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2011.00300","url":null,"abstract":"CorseAlp 2011 was held in April 2011. A link to the website is here: CorseAlp 2011. The CorseAlp field trips were designed to introduce the participants to the general features of the geology of Alpine Corsica and to recent specific discoveries. Field trip 1 focused on the geology of the Ocean-Continent Transition preserved in the Monte San Petrone, in Central Corsica, which was subducted to eclogite facies conditions during the Alpine orogeny. Field Guide 1 itinerary: Bastia, Golo Valley, Piedicroce, M.S.Petrone and S.Florent.","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114635389","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":"Visualisation of active normal fault scarps in the Apennines, Italy: A key to assessment of tectonic strain release and earthquake rupture","authors":"G. Roberts","doi":"10.3809/JVIRTEX.2008.00197","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2008.00197","url":null,"abstract":"Active normal fault scarps that offset 12-18 ka landforms in the Apennines, Italy, have been mapped into Google Earth to provide precise locations for structures responsible for tectonic strain release and earthquake rupture. Climate change at the end of the last glacial maximum (12-18 ka) reduced erosion and sedimentation rates below a critical threshold allowing preservation of displacements produced by surface ruptures to palaeoearthquakes. The resultant fault scarps, which record the surface displacements from multiple earthquakes, allow determination of the spatial variation in the rates of fault slip, a parameter critical to assessment of how long-term strain release recorded in the geomorphology (104 years) relates to short-term strain release recorded by earthquake catalogues and geodesy (102-3 years). Spatial variation in fault slip occurs at a scale of tens of kilometres, whilst fault scarps have offsets of <20-40 metres and a geomorphic expression that can only be visualised on topographic images with spatial resolution approaching the metre-scale. Thus, until now, debate has surrounded the exact positions of scarps at least in part due to problems of visualising both the detailed geomorphic features and their regional variation. Provision of complete SPOT image coverage and topography within Google Earth allows individual scarps visited during fieldwork to be visualised at a regional scale within an easily-accessible interface. The resultant maps are used to comment on tectonic strain release and earthquake rupture.","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134265996","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":"Late Neoproterozoic palaeogeography: The Laurentia-Baltica puzzle","authors":"S. Pisarevsky, Peter A. Cawood","doi":"10.3809/JVIRTEX.2006.00150","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2006.00150","url":null,"abstract":"","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126591007","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":"An Elle-based 2-D model for cation exchange reaction between garnet and biotite","authors":"Youngdo Park, Dal Yong Park, L. Evans, Jin-Han Lee","doi":"10.3809/JVIRTEX.2004.00093","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2004.00093","url":null,"abstract":"We have developed a model for diffusion zoning development in garnet employing a numerical modeling system, Elle [Jessell et al. 2001]. The Elle system simulates textural development at thin section scale with an assumption that long term textural changes can be achieved by adding incremental processes. Many numerical models have been developed for the diffusion zoning pattern of garnet, but these models considered only lattice diffusion without allowing grain boundary diffusion. However, our model simulates the diffusion zoning in garnets by considering not only lattice diffusion but also grain boundary/lattice reaction and grain boundary diffusion. Sub-processes for our garnet-biotite system include (1) lattice diffusion, (2) grain-boundary diffusion, and (3) grain boundary/lattice reaction. The finite difference explicit method was used for the numerical calculation of lattice and boundary diffusion. For diffusion calculation, chemical concentrations of individual nodal points are used to calculate the amount of transported cations with diffusion coefficients determined from experiments. For lattice/boundary reaction, the lowest energy compositions of garnet and biotite were calculated using the distribution coefficient. Experimental runs were performed to test the consistency and reproducibility of the results. The results demonstrate the consistency and reproducibility, but show somewhat different zoning from that of Spear (1991), due to reduced dimension (3D in nature vs 2D in our model) and the arbitrarily chosen reaction constant. In spite of these limitations, we feel that the model presented here is at least a good starting point for diffusive mass transfer in a material with grain boundary structure. Journal of the Virtual Explorer, 2004 Volume 15 Paper 6 http://virtualexplorer.com.au/ An Elle-based 2-D model for cation exchange reaction between garnet and biotite Page 2 Journal of the Virtual Explorer, 2004 Volume 15 Paper 6 http://virtualexplorer.com.au/ An Elle-based 2-D model for cation exchange reaction between garnet and biotite Page 3","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128054483","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":"Structural mapping of the Eagle Crater outcrop on Mars: New Challenges for the Extraterrestrial Field Geologist","authors":"D. Paor, B. Brenton, K. Cox, S. Duplantis, P. T. Egan, D. Kowalewski, P. Lancaster, C. A. Masaric-Johnson, H. Melanson, A. Orlando, L. M. Sauer, C. M. Witkowski","doi":"10.3809/JVIRTEX.2004.00087","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2004.00087","url":null,"abstract":"We report the results of a structural analysis of the outcrop at Eagle Crater, Meridiani Planum, Mars, which was carried out as an undergraduate class project at Boston University. The outcrop exposes an approximately 20-meter-diameter, semi-circular section of the crater rim in the prevailing down-wind direction. Sedimentary units dip radially outwards on the whole, consistent with an impact origin, though there is some evidence of local folding. Many rock slabs are only slightly out of place, forming a quasi-broken formation that accounts for a sizable portion of the exposure. Geometric features in and around the crater include inclined bedding, cross bedding, undeformed \"blueberry\" concretions, fracture cleavage, faults, fractures, undeformed crystal vugs, and striations. Observed structures are consistent with an origin by impact cratering and/or wrinkle ridge tectonics. Oblique panorama imagery presented unusual challenges which we overcame with new analytical techniques. Our approach may prove useful for professors and students aiming to understand new forms of field data using the classical techniques of structural analysis.","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131600473","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":"Final stages of the Brasiliano Orogenesis in SE Brazil: U-Pb and 40Ar/39Ar evidence for overprinting of the Brasília Belt by the Ribeira Belt Tectonics","authors":"P. Hackspacher, A. Fetter, W. Teixeira, E. Dantas, H. D. Ebert, R. Trouw, P. Vasconcelos","doi":"10.3809/JVIRTEX.2004.00108","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2004.00108","url":null,"abstract":"Around the southern margins of the Sao Francisco Craton, there is a zone of tectonic interference between the Brasilia belt to the west and the younger Ribeira belt to the east. U-Pb monazite and Ar/Ar cooling age determinations carried out in the area reveal the cooling histories of these belts and the timing of tectonic overprint, unraveling the final stages of Brasiliano Orogeny in SE Brazil. The U-Pb monazite data from migmatized paragneisses and late-stage pegmatites in the Socorro-Guaxupe Nappe System of the southern Brasilia belt show that migmatization peaked between ca. 613±1 and 607±3 Ma. Ar/Ar biotite and muscovite ages of paragneisses and schists in this area indicate that the northern high-grade core of the Nappe System (Guaxupe Domain) was uplifted and cooled through the 350°C isotherm between 599±1 and 587±1 Ma. In contrast, samples from the southern high-grade core of the Nappe System, the Socorro Domain, south of the Jacutinga shear zone, yields a broader and younger spectrum of Ar/Ar biotite ages between 571±1 and 562±1 Ma, attributed to a later uplift and cooling of the crust. The cooling ages can be assigned to local resetting of the Ar/Ar system during transpressive tectonic overprint due to reactivation as a result of collision of the Ribeira belt. A younger group of Ar/Ar mica ages (537±1 to 521±1Ma) in schists of the Socorro Domain, are associated with transpressional structures of the Ribeira belt. Rock samples from the Jacutinga and Tres Coracoes shear zones, yield Ar/Ar biotite-muscovite ages around 520 Ma. These are typical cooling ages of the Ribeira belt, and are interpreted to mark the western limit of the Ribeira belt transpressional regime within the Brasilia belt. The youngest biotite-muscovite cooling ages in schists of the Socorro Domain, between 510±2 and 491±1 Ma, mark the final cooling and exhumation of that part of the Brasilia belt.","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127130835","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":"Rotation of Prismatic Rigid Porphyroblasts and Development of Internal Foliation: Results from Pixel-based Modelling Study","authors":"Youngdo Park, Jin-Han Lee, Won-Sun Jung","doi":"10.3809/JVIRTEX.2004.00094","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2004.00094","url":null,"abstract":"","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"91 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129459287","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":"Structural and geochronological studies of the Médio Coreaú domain, NE Brazil: Constraints on Brasiliano/Pan-African tectonic evolution in the NW part of the Borborema Province","authors":"T. J. D. dos Santos, A. Fetter, P. Hackspacher, W. Van Schmus, J.A. Nogueira Neto","doi":"10.3809/JVIRTEX.2004.00112","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2004.00112","url":null,"abstract":"Instituto de Geociencias Universidade Estadual de Campinas (UNICAMP), Caixa Postal: 6152, CEP 13081-970, Campinas, SP","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132106275","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":"Numerical simulation of disequilibrium structures in solid- melt systems during grain-growth","authors":"J. Becker, D. Köhn, N. Walte, M. Jessell, P. Bons, C. Passchier, L. Evans","doi":"10.3809/JVIRTEX.2004.00089","DOIUrl":"https://doi.org/10.3809/JVIRTEX.2004.00089","url":null,"abstract":"","PeriodicalId":201383,"journal":{"name":"Journal of The Virtual Explorer","volume":"34 11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133971952","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}