Search results for " petrology"
showing 10 items of 1353 documents
LA-ICP-MS U–Pb dating of detrital rutile and zircon from the Reynolds Range: A window into the Palaeoproterozoic tectonosedimentary evolution of the …
2014
Abstract The Palaeoproterozoic Reynolds Range of the Arunta Region, central Australia, comprises a series of shallow marine clastic sediments (Reynolds Range Group) which overlies deeper water sequences of turbidites (Lander Rock Formation) and minor sandstones (“unnamed sandstone”). U–Pb age data collected from detrital rutile and zircon in these rocks indicates these sequences contain very similar age spectra, although with a notable and important shift to younger ages within the stratigraphically younger Reynolds Range Group. Detrital zircons from the “unnamed sandstone” directly underlying the unconformity with the Reynolds Range Group contain a major age component at ca. 1860 Ma, toget…
Ba and Ni speciation in a nodule of binary Mn oxide phase composition from Lake Baikal
2007
The partitioning and incorporation mechanism of Ni and Ba in a ferromanganese nodule from Lake Baikal were characterized by X-ray microfluorescence, microdiffraction, and absorption spectroscopy. Fe is speciated as goethite, and Mn as romanechite (psilomelane) and 10 A ˚ -vernadite (turbostratic buserite) with minor 7 A ˚ -vernadite (turbostratic birnessite). Barium is associated with romanechite and Ni with vernadite in distinct and irregularly distributed layers, and each type of Mn oxide is separated from the other type by goethite. The binary Mn oxide banding pattern is interpreted by a two-mode accretionary model, in which the variation in Ba flux induced by hydrothermal water pulses d…
PRINZIPIELLE BEMERKUNGEN ZU THEORIE UND PRAXIS DER METHODE DER ZWEITEN ABLEITUNG BEI DER INTERPRETATION GRAVIMETRISCHER MESSERGEBNISSE
1957
The first part of the paper deals with theoretical considerations concerning the arithmetic mean of gravity values and its use with regard to the derivation of approximation formulae for the second derivative. In order to calculate the second derivative in practice the arithmetic mean. ḡ(r) of a continuum of gravity values on a circle of radius r is approximated by a Taylor polynomial and then replaced by the arithmetic mean gn(r) of n discrete gravity values. Because of the invariance of ġ(r) with regard to rotations of the coordinate system in the horizontal datum plane there exists a lower limit for the number n; this lower limit depends on the degree of the Taylor polynomial used in the…
A new hydrous Al-bearing pyroxene as a water carrier in subduction zones
2011
Abstract A new Hydrous Al-bearing PYroxene (HAPY) phase has been synthesized at 5.4 GPa, 720 °C in the MgO–Al2O3–SiO2–H2O model system. It has the composition Mg2.1Al0.9(OH)2Al0.9Si1.1O6, a C-centered monoclinic cell with a = 9.8827(2), b = 11.6254(2) c = 5.0828(1) A and β = 111.07(1)°. The calculated density is 3.175 g/cm3 and the water content is 6.9% H2O by weight. Its structure has been solved in space group C2/c by the recently developed automated electron diffraction tomography method and refined by synchrotron X-ray powder diffraction. HAPY is a single chain inosilicate very similar to pyroxenes but with three instead of two cations in the octahedral layer, bonded to four oxygens and…
Investigating the effects of intersection flow localization in equivalent-continuum-based upscaling of flow in discrete fracture networks
2021
Abstract. Predicting effective permeabilities of fractured rock masses is a crucial component of reservoir modeling. Its often realized with the discrete fracture network (DFN) method, whereby single-phase incompressible fluid flow is modeled in discrete representations of individual fractures in a network. Depending on the overall number of fractures, this can result in high computational costs. Equivalent continuum models (ECMs) provide an alternative approach by subdividing the fracture network into a grid of continuous medium cells, over which hydraulic properties are averaged for fluid flow simulations. While continuum methods have the advantage of lower computational costs and the pos…
VolcDeGas: A program for modelling hydrogen isotope fractionation during degassing of rhyolitic melts
2020
Magma degassing mechanisms are key determinants of explosive and effusive eruption styles. Paired measurements of H2O content and hydrogen isotopic ratios (e.g., dD) in pyroclastic and effusive products can elucidate end-member degassing mechanisms (e.g. closed and open system) during eruption. Here we present VolcDeGas, a MatLab program that models dD-H2O degassing trajectories of rhyolitic magma. Operating within an intuitive GUI, VolcDeGas calculates degassing paths based on: initial dD (in ‰), the H2O content of the melt (wt.%), degassing step size, and temperature. VolcDeGas also calculates hydrous speciation based on either empirical models or analytical data, and incorporates this…
Seismic stratigraphy of the north-westernmost area of the Malta Plateau (Sicily Channel): The Middle Pleistocene-Holocene sedimentation in a tidally …
2022
In this study we present the results of a seismic-stratigraphic analysis of sub-bottom profiles in the north-westernmost area of the Malta Plateau in order to define the depositional mechanisms for the upper Quaternary sequences. During this interval the morphology of the Malta Plateau was characterized by a ramp and bathymetries not exceeding 200 m. Two major unconformities, related to MIS 6 and MIS 2 (the latter corresponding to the Last Glacial Maximum, LGM), characterize the upper Quaternary sequences. The geometries of the recognized seismic units indicate as depositional mechanisms were controlled by subsidence and sea-level fluctuations. In detail, deposits related to the last glacia…
Mineralogical and chemical variability of fluvial sediments 2. Suspended-load silt (Ganga–Brahmaputra, Bangladesh)
2011
Sediments carried in suspension represent a fundamental part of fluvial transport. Nonetheless, largely because of technical problems, they have been hitherto widely neglected in provenance studies. In order to determine with maximum possible precision the mineralogy of suspended load collected in vertical profiles from water surface to channel bottom of Rivers Ganga and Brahmaputra, we combined Raman spectroscopy with traditional heavy-mineral and X-ray diffraction analyses, carried out separately on low-density and dense fractions of all significant size classes in each sample (multiple-window approach). Suspended load resulted to be a ternary mixture of dominant silt enriched in phyllosi…
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…
The nature of radiohaloes in biotite: Experimental studies and modeling
2001
Several micro-techniques (confocal laser-Raman microprobe, optical absorption micro-spectroscopy, high-resolution transmission electron microscopy, electron microprobe analysis) were employed in the detailed characterization of radiohaloes in biotites from two Variscan rocks from Germany. The studied biotites are intermediate members of the phlogopite-annite series with Mg/Fe 2+ ratios in the range 1.6–1.0. Radiohaloes in biotite resulted from the impact of 4 He cores (α-particles) emitted from actinide-bearing inclusions. Monte Carlo simulations yielded α ( 238 U, 235 U, and 232 Th series) penetration ranges in biotite between 12.5 and 37.3 μm, which are in reasonable agreement with the ob…