Oxford Eprints
(1.101 recursos)
Oxford E-prints is a cross-disciplinary digital archive for research articles written by Oxford University authors. The repository has been developed as part of the SHERPA (Securing a Hybrid Environment for Research Preservation and Access) project and is running on eprints.org open archives software.
Mostrando recursos 1 - 5 de 5
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The History of Granulite-Facies Metamorphism and Crustal Growth from Single Zircon U-Pb Geochronology: Namaqualand, South Africa - ROBB, L. J.; ARMSTRONG, R. A.; WATERS, D. J.
The Namaqualand Metamorphic Complex is a well-exposed, Mesoproterozoic, low-pressure, amphibolite-granulite-facies terrane flanking the Archaean Kaapvaal Craton of southern Africa. Previous isotopic dating in the region suggests an ~150 my period of prograde granulite-facies metamorphism and episodic granite emplacementin the mid-crust. In contrast, thermal modelling suggests thatsub- and superjacent magmatic accretion should not have exceeded 30 my in duration. This enigma is resolved by precise U-Pb zircon SHRIMP dating of the major orthogneissic units of the region. These data point to Kibaran crustal growth at 1220-1170 Ma, which occurred on the margins of a Palaeoproterozoic (2000-1800 Ma) continental nucleus. A later,...
(pdf ARRAY(0xd192268)) - 02-nov-2004
2.
The Role of Open-System Processes in the Development of Silicic Magma Chambers: a Chemical and Isotopic Investigation of the Fogo A Trachyte Deposit, São Miguel, Azores - SNYDER, DARIN C.; WIDOM, ELISABETH; PIETRUSZKA, AARON J.; CARLSON, RICHARD W.
The processes operating in the development of chemical zonation in silicic magma chambers have been addressed with a Sr-Nd-Pb-Hf-Th isotope study of the chemically zoned trachyte pumice deposit of the Fogo A eruption, Fogo volcano, Azores. Sr isotopic variation is observed in whole rocks, glass separates and sanidine phenocrysts (whole-rock 87Sr/86Sr: 0·7049-0·7061; glass 87Sr/86Sr: 0·7048-0·7052; sanidine 87Sr/86Sr: 0·7048-0·7062). Thorium isotopic variation is observed in glass separates, with (230Th/232Th)o ranging from 0·8737 to 0·8841, and exhibiting a negative correlation with Sr isotopes. The Nd, Pb and Hf isotopic compositions of the whole-rock trachytic pumices are invariant and indistinguishable from basalts flanking...
(pdf ARRAY(0xd166d44)) - 02-nov-2004
3.
The structural geometry, metamorphic and magmatic evolution of the Everest
massif, High Himalaya of Nepal - South Tibet - Searle, Mike
This paper presents a new geological map together with cross-sections and lateral sections of the
Everest massif. We combine field relations, structural geology, petrology, thermobarometry and geochronology
to interpret the tectonic evolution of the Everest Himalaya. Lithospheric convergence of India and Asia since
collision at c. 50 Ma. resulted in horizontal shortening, crustal thickening and regional metamorphism in the
Himalaya and beneath southern Tibet. High temperatures (.620 8C) during sillimanite grade metamorphism
were maintained for 15 million years from 32 to 16.9 0.5 Ma along the top of the Greater Himalayan slab.
This implies that crustal thickening must also have been active during this time, which...
(pdf http://eprints.ouls.ox.ac.uk/archive/00000744/01/Searle.Everest-11.pdf) - 02-nov-2004
4.
Attenuation and excision of a crustal section during extensional exhumation: the Carratraca Massif, Betic Cordillera, southern Spain - Argles, T.W.; Platt, J.P.; Waters, D.J.
Extensional dismemberment of the Betic Cordillera during Late Oligocene to Early Miocene time caused attenuation and excision of a crustal section overlying mantle peridotite. An integrated study of metapelites overlying the peridotite sheet in the Carratraca area shows truncation of a typical orogenic cycle of burial and heating by rapid exhumation and late- to post-tectonic, low-pressure metamorphism. Attenuation by a factor of five or more condensed a greenschist to granulite section to 4 km structural thickness.
Initially coaxial attenuation of the sequence, involving formation of a flat-lying foliation and conjugate shear bands, was superseded by non-coaxial deformation concentrated along low-angle, top-to-the-NE,...
(pdf http://eprints.ouls.ox.ac.uk/archive/00000769/01/geologicalsoc_waters_1999.pdf) - 02-nov-2004
5.
Neoproterozoic chemostratigraphy and correlation of the Port Askaig glaciation, Dalradian Supergroup of Scotland - Brasier, M.D.; Shields, G.
The 13C of preglacial carbonates beneath the glaciogenic Port Askaig Formation falls from +5 to negative values, while least-altered 87Sr/86Sr values are close to 0.7067. Postglacial 'cap carbonates' of the Bonahaven Formation begin with negative 13Ccarb values, jumping sharply to +11.7 near the top, which we correlate with excursions above the Elbobreen-Wilsonbreen glaciations of Svalbard and putative Sturtian (not Varanger) glaciations elsewhere, dated at c. 720 Ma. Much of the succeeding Terminal Neoproterozoic is missing in NE Svalbard and East Greenland, raising doubts about their use for global Sr and C isotope curves in the Neoproterozoic.
(pdf http://eprints.ouls.ox.ac.uk/archive/00000770/01/geologicalsoc_brasier_2000) - 02-nov-2004
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