1,721,048 research outputs found
Metallic spherules in silica glass from the Ries-Steinheim impact crater area: sign of the impactor?
No full textRiassunto presentato al V Forum italiano di Scienze della Terra, Geoitalia 2005, Spoleto, 21-23 settembre 2005
Studio sulla profondità di cristallizzazione e messa in posto dei plutoni di Rensen, Vedrette di Ries e Polland (Alpi Orientali).
No full textIl granato nelle masse intrusive di Rensen, Vedrette di Ries e Polland (Alpi orientali).
No full textAdmiralty intrusives in the southern Bowers terrane: the Collins Peak Pluton. Comparisons with the Salamander Granite Complex, Northern Victoria Land, Antarctica
No full textGrenville-age magmatism at the South Tasma Rise (Australia)
No full textA U-Pb zircon sensitive high-resolution ion microprobe age of 1119.4 6 8.5 Ma, obtained
from a quartz syenite dredged from the South Tasman Rise (Australia), provides
the first direct evidence of the presence of Grenville-age magmatic rocks along the central
part of the hypothesized Australia–East Antarctica conjugate margin of Laurentia. The
distinctive mineralogy and geochemistry of the rock and its Sm-Nd and Pb isotopic signatures
1) indicate that it represents a juvenile Grenville-age addition to the crust, 2)
support a correlation with the Grenville magmatic province of the western United States,
and 3) set a unique pivotal point for a precise reconstruction of Rodinia. The resulting
scenario implies the presence of a new magmatic province crossing the East Antarctic
craton, the extension of Proterozoic belts of southwest Laurentia to East Antarctica, and
appears consistent with the Australia–western United States (AUSWUS) model. This tectonic
setting envisages a near-local source for the ubiquitous Grenville-age detrital zircon
population in marginal Neoproterozoic to early Paleozoic Gondwanan sequences and suggests
a possible direct source for the widespread Grenville-age inherited zircon component
observed in most Paleozoic granites in northern Victoria Land (Antarctica) and east Tasmania
(Australia)
Dating Middle Paleozoic magmatism in Northern Victoria Land (Antarctica): State of the Art and future Plans
No full textThe genesis of Late Alpine plutonic bodies of Rensen and Monte Alto (Eastern Alps): inferences from major and trace elements data.
No full textPrimary trapped melt inclusions in olivine in the olivine-augite-orthopyroxene ureilite Hughes 009
No full textWe describe the first known occurrence of primary melt inclusions in a ureilite. The ureilite is Hughes 009, one of a small number of ureilites whose primary mineralogy is olivine-augite-orthopyroxene, rather than olivine-pigeonite. Hughes 009 has a coarse-grained, equilibrated texture typical of ureilites, and homogeneous primary mineral compositions: olivine - mg 87.3; augite - mg 89.2, Wo 37.0, Al2O3 = 1.6 wt.%; orthopyroxene - mg 88.3, Wo 4.9. It shows only limited secondary reduction effects and no petrographically recognizable carbon phases, which indicates that its original carbon content was lower than in most ureilites.
The melt inclusions occur in olivine crystals. They are concentrated in the central regions of their hosts, showing elongate (mostly 20-60 mum in maximum dimension), negative olivine crystal shapes and parallel alignment. These and other features indicate that they were trapped during initial growth of their hosts from a liquid, and are likely to be representative samples of that liquid. They consist of glass and single, subhedral crystals of high-Ca pyroxene, with minor Cr-rich spinel and metal-phosphide-sulfide spherules. They are surrounded by halos of olivine with rounded outlines defined by tiny bits of metal and thin arcs of glass. Pyroxenes within each inclusion show zonation patterns indicating that they nucleated at the olivine/liquid interface with compositions close to that of the primary augite, and then,grew inward with dramatically increasing Al2O3 (to 10.8 wt.%), Wo (to approximate to 50), TiO2 and Cr2O3 contents. Glasses within each inclusion are relatively homogeneous. Glasses from all inclusions show well-defined trends of CaO, TiO2, Cr2O3, Na2O and SiO2 vs. Al2O3, (16-23 wt.%) that can be modelled as resulting principally from crystallization of various amounts of the pyroxene. The halos, which represent olivine that grew from the trapped melts, are zoned in Cr and Ca with concentrations decreasing inward, reflecting cocrystallization of pyroxene; they have homogeneous Fe/Mg identical to that of the primary olivine, indicating reequilibration with the host.
We develop a petrologic model for the postentrapment history (crystallization, reaction and reequilibration) of the inclusions, based on which we reconstruct the composition of the primary trapped liquid (PTL). The PTL was saturated only with olivine. This result implies that Hughes 009 is a cumulate (consistent with the high Mn/Mg ratio of its olivine and a low abundance of graphite) and that the composition of the PTL is close to that of its parent magma. The low-pressure equilibrium crystallization sequence predicted by MAGPOX calculations for the PTL (olivine --> augite --> plagioclase --> pigeonite) is not, however, consistent with the primary mineralogy of Hughes 009. If the conditions of these calculations are, indeed, appropriate, then complex processes such as magma mixing must have been involved in the petrogenesis of this ureilite. This conclusion is consistent with other evidence that the olivine-augite-orthopyroxene ureilites record a more complex magmatic evolution than is evident in the olivine-pigeonite ureilites.
TEM investigations of microtextural features in all phases and XRD determination of Fe2+-Mg site distribution in orthopyroxene have elucidated the cooling and shock history of this ureilite. Hughes 009 experienced an extremely high cooling rate (7 +/- 5 degreesC/h at the closure T of 630 degreesC) late in its evolution, and two distinguishable shock events-the first at peak pressures of 5 to 10 GPa, resulting in mechanical polysynthetic twinning in augite and orthopyroxene and mild undulatory extinction in olivine; and the second at lower pressures, resulting only in brecciation and redistribution of metal. Its late history is similar to that of most ureilites, and probably reflects impact excavation. Copyright (C) 2001 Elsevier Science Ltd
Permo-Paleogene magmatism in the Eastern Alps
No full textThe present-day configuration of the lithosphere in the eastern Alps and more broadly in the northern Adriatic zone, records a multistage geologic evolution that was active since Precambrian times. Major evolutionary events (e.g., ocean opening, collision, subduction, etc.) were marked by the emplacement of large quantities of magmatic products. In this paper we present an overview of the field, petrographic, and geochemical characteristics of the main plutonic and volcanic bodies outcropping in the northern Adriatic zone and spanning from Permian to Cainozoic. Geochemical and petrologic study of these igneous occurrences greatly helped unraveling the geologic history of this area
Surgeon Island granite: implications for regional geological evolution of Northern Victoria Land from structural observationn and SHRIMP zircon dating
No full text- …
