Search results for "Igneous rock"
showing 10 items of 84 documents
Gradients in physical parameters in zoned felsic magma bodies: Implications for evolution and eruptive withdrawal
1990
Abstract Five diverse, well documented, chemically zoned magmas have been chosen from the literature to demonstrate the extent and patterns of density and viscosity gradients in zoned magma chambers. The patterns are used to assess implications for development of zonation, and withdrawal dynamics and preservation of systematic chemical variations in the final pyroclastic deposit. These examples are: Bishop Tuff, California (high-silica rhyolite); Los Humeros, Mexico (calc-alkaline rhyolite to andesite); Fogo A, Azores (trachyte); Laacher See, Eifel (phonolite) and Tenerife, Canary Islands (phonolite). It was necessary to make several simplifying assumptions in order to calculate viscosity a…
Comment on: Application of Raman Spectroscopy to Distinguish Metamorphic and Igneous Zircon (Xian et al., Anal. Lett. 2004, v. 37, p. 119)
2005
Abstract We critically discuss a recently proposed technique ((Xian et al. 2004)) used to distinguish igneous (i.e., magmatic) from metamorphic growth of the mineral zircon according to the intensity of the 1461 cm−1 band observed in those author's Raman spectra. The band evaluated by Xian et al. (2004) is actually due to laser‐induced photoluminescence of trace amounts of the trivalent rare earth element Er, which, as an analytical artefact, overlays the Raman spectrum when green Ar+ laser excitation is used. We demonstrate that this band is not a Raman band, and discuss why the intensity of Er3+ luminescence is not uniquely indicative of the geologic origin of a zircon crystal. The techni…
Ultrapotassic volcanism from the waning stage of the Neotethyan subduction: a key study from the Izmir-Ankara-Erzincan suture belt, central northern …
2016
Upper Cretaceous volcano-sedimentary successions in the Central Pontides of Turkey, related to the closure of the Tethys Ocean, include a variety of alkaline ultrapotassic igneous rocks that have been classified as leucititic, lamprophyric and trachytic based on their mineral paragenesis. Although the ultrapotassic rocks display a range of K 2 O contents (0·9–8·4 wt %) that may partly reflect alteration processes, they display subduction-related trace element signatures characterized by significant enrichment of large ion lithophile elements and light rare earth elements relative to high field strength elements and heavy rare earth elements and depletion of Nb and Ta. However, their initial…
Eclogites and garnet pyroxenites: Similarities and differences
2010
Eclogites and garnet pyroxenites are genetically linked to basaltic precursors. Traditionally garnet pyroxenites are linked to fractionation of basaltic Magmas Over a range of mantle pressures and more recently they have been implicated in the genesis of ocean islands. in contrast eclogites are linked to the subduction of slab basalt and gabbro precursors which may be hydrothermally altered. Recently this subduction paradigm has been questioned. We present mineralogical, trace element and O isotopic data for eclogites and garnet pyroxenites that reveal some similarities but also important chemical and isotopic differences that support a distinct provenance (i.e., age and process). Continent…
Determination of the porosity, permeability and diffusivity of rock in the excavation-disturbed zone around full-scale deposition holes using the -PM…
1998
Abstract Three experimental holes the size of deposition holes in a KBS-3 type repository (depth 7.5 m and diameter 1.5 m) were bored in hard granitic rock in the Research Tunnel at Olkiluoto to study, among other things, the properties of the rock in the excavation-disturbed zone. In the analysis described in this report, the porosities, effective diffusivities and permeabilities of disturbed and intact rock were determined by using two novel methods: the 14 C -polymethylmethacrylate method and the He-gas method. In addition, the structure of the rock in the excavation-disturbed zone was assessed using both scanning electron and optical microscopy.
Trace-element partitioning between amphibole and silicate melt.
2007
Knowledge of the partitioning behavior of trace elements between solid and liquid is a prerequisite for modern igneous and mantle petrology. Most of the mathematical models simulating melt generation, migration and evolution within the mantle and/or the crust require the availability of reliable solid/liquid partition coefficients for the mineral phases involved in the process. Calcic amphiboles are extremely important for the understanding of lithospheric processes because of both their common occurrence in a variety of igneous and metamorphic rocks types and their capability of hosting a large number of geochemically important trace elements. A series of studies on the partitioning behavi…
Single zircon ages for two Archean banded migmatitic gneisses from central Zimbabwe
2004
We report new single zircon ages for two Archean banded gneisses from the Shangani Batholith in central Zimbabwe. The ages of ~2.77 and ~2.84 Ga do not support previous views that the area west of the current exposure of the Tokwe Segment was part of an early- to mid-Archean (>2.95 Ga) domain (Sebakwe Proto-craton). The data correspond to ~2.9 to 2.8 Ga dates for TTG granitoids of the Chingezi Suite. Members of this suite occur as intrusions within the south-central part of the Zimbabwe Craton and are associated with contemporaneous felsic volcanic rocks. On the basis of their age distribution, isotopic characteristics and outcrop pattern with respect to the Tokwe Segment, the formation of …
Palaeomagnetic investigations of the tertiary and quaternary igneous rocks: IV The tertiary volcanic rocks of the Tokaji mountains, Hungary
1971
Measurements are reported from samples collected at twenty three sites in the Tokaj mountains of north-eastern Hungary. The simplest interpretation of the results is in terms of geomagnetic field reversals, for there is no petrological or magnetic evidence of self reversal or of correlation of oxidation state and magnetic sign. Four magnetic zones satisfy the minimum stratigraphic requirements, speculative use of these zones against theHeirtzler et al. magnetic time scale as a control suggests locating the Miocene-Pliocene boundary at 11.75 my. However it seems probable that much of the lower Sarmatian is not represented in the Tokaj samples, although the scatter of individual readings sugg…
Age and origin of granitic rocks of the eastern Vardar Zone, Greece: new constraints on the evolution of the Internal Hellenides
2005
The Vardar Zone is an integral part of the Internal Hellenides and has long been regarded as an ophiolite-decorated suture zone separating two distinct continental blocks, namely the Pelagonian Zone to the west and the Serbo-Macedonian Massif to the east. Several bodies of granites, gneisses and volcanic rocks are associated with the ophiolitic rocks and can provide additional constraints on the evolution of the suture. Single-zircon and monazite dating of felsic rocks yields accurate ages for the processes of accretion of the suture. The igneous formation ages obtained range from 155 to 164 Ma, suggesting an important magmatic phase in the Late Jurassic. The chemical and isotopic compositi…
Zircon ages of high-grade gneisses in the Eastern Erzgebirge (Central European Variscides)—constraints on origin of the rocks and Precambrian to Ordo…
2001
Abstract This study is an attempt to unravel the tectono-metamorphic history of high-grade metamorphic rocks in the Eastern Erzgebirge region. Metamorphism has strongly disturbed the primary petrological genetic characteristics of the rocks. We compare geological, geochemical, and petrological data, and zircon populations as well as isotope and geochronological data for the major gneiss units of the Eastern Erzgebirge; (1) coarse- to medium-grained “Inner Grey Gneiss”, (2) fine-grained “Outer Grey Gneiss”, and (3) “Red Gneiss”. The Inner and Outer Grey Gneiss units (MP–MT overprinted) have very similar geochemical and mineralogical compositions, but they contain different zircon populations…