scholarly journals GEOCHEMISTRY OF ULTRAMAFIC ROCKS FROM THE ULTRAHIGH-PRESSURE METAMORPHIC KIMI COMPLEX IN EAST RHODOPE (NE. GREECE)

2007 ◽  
Vol 40 (2) ◽  
pp. 653
Author(s):  
I. Baziotis ◽  
E. Mposkos ◽  
S. Palikari ◽  
M. Perraki
Keyword(s):  
Trace Element ◽  
Major Element ◽  
Ultrahigh Pressure ◽  
Ultramafic Rocks ◽  
Spinel Peridotite ◽  
Stability Field ◽  
Element Modelling ◽  
Melt Extraction ◽  
Geochemical Investigation

In the ultrahigh-pressure metamorphic Kimi Complex garnet-spinel metaperidotites with layers of clinopyroxenites occur. A detailed geochemical investigation using major-trace element relations and major-element modelling indicates that the peridotites represent mantle residues originated after variable melt extraction, along an adiabatic path starting from high- to ultrahigh-pressures. The clinopyroxenites represent HP clinopyroxene-rich cumulates probably formed within the garnet and/or Cr-spinel peridotite stability field.

The 1875 eruption of Askja volcano, Iceland: combined fractional crystallization and selective contamination in the generation of rhyolitic magma

1987 ◽  
Vol 51 (360) ◽  
pp. 183-202 ◽  
Author(s):  
R. Macdonald ◽  
R. S. J. Sparks ◽  
H. Sigurdsson ◽  
D. P. Mattey ◽  
D. W. McGarvie ◽  
...  
Keyword(s):  
Trace Element ◽  
Fractional Crystallization ◽  
Major Element ◽  
First Record ◽  
Isotopic Data ◽  
Rhyolitic Magma ◽  
Element Modelling ◽  
Relative Enrichment ◽  
Askja Volcano ◽  
Silicic Magmas

AbstractMajor and trace element and Sr, Nd and O isotopic data are presented for ferrobasalts, icelandites, rhyolites, mixed pumices and silicic xenoliths of the 1875 eruption of Askja. Trace element modelling and Sr and Nd data largely confirm previous major element calculations that fractional crystallization was dominant in the generation of the basalt-ferrobasalt-icelandite-rhyolite suite. Relative enrichment in Rb (and Th and U?), depletion in Cs, and low values of δ18O/16O, in the rhyolites are not explained by this mechanism alone. The silicic magmas were selectively contaminated by diffusion from partially molten granitic wall rocks, now found as xenoliths in the eruptive products, the process being particularly marked by lower δ18O and Cs/Rb ratios in the rhyolites than in the associated basalts. This is the first record of a combined fractional crystallization-selective contamination process in an Icelandic silicic complex.

Cordierite-gedrite rocks from the Central Metasedimentary Belt boundary thrust zone (Grenville Province, Ontario): Mesoproterozoic metavolcanic rocks with affinities to the Composite Arc Belt

2005 ◽  
Vol 42 (10) ◽  
pp. 1815-1828 ◽  
Author(s):  
William H Peck ◽  
Michael S Smith
Keyword(s):  
Trace Element ◽  
Major Element ◽  
Grenville Province ◽  
Melt Extraction ◽  
Oxygen Isotope Ratios ◽  
Metavolcanic Rocks ◽  
Thrust Zone ◽  
Ree Patterns ◽  
Isotope Systematics ◽  
Igneous Protoliths

Cordierite–gedrite rocks in the southern Grenville Province occur near the base of the Central Metasedimentary Belt boundary thrust zone, interpreted by some as a crustal suture between the 1.29–1.24 Ga Composite Arc Belt and >1.4 Ga rocks of Laurentia. Major and trace-element compositions of these rocks are consistent with volcanic protoliths that range in composition from basalt to dacite. These cordierite–gedrite rocks have low CaO (average 1.2 wt.%) and major element and oxygen-isotope ratios suggestive of hydrothermal alteration before metamorphism. Rare-earth element (REE) compositions also indicate igneous protoliths, although some REE patterns have been modified by local melt extraction. The trace-element compositions of cordierite–gedrite rocks, and neodymium-isotope systematics, are similar to those of metavolcanic rocks in the Composite Arc Belt and are consistent with the extension of the Composite Arc Belt to the base of the boundary thrust zone.

scholarly journals Rheological Contrast between Quartz and Coesite Generates Strain Localization in Deeply Subducted Continental Crust

Minerals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 842
Author(s):  
Kouhei Asano ◽  
Katsuyoshi Michibayashi ◽  
Tomohiro Takebayashi
Keyword(s):  
Rheological Behavior ◽  
Strain Localization ◽  
Shear Zones ◽  
Ultrahigh Pressure ◽  
Ultramafic Rocks ◽  
Crustal Material ◽  
Orientation Data ◽  
Crystallographic Preferred Orientation ◽  
Dabie Shan ◽  
Felsic Rocks

Deformation microstructures of peak metamorphic conditions in ultrahigh-pressure (UHP) metamorphic rocks constrain the rheological behavior of deeply subducted crustal material within a subduction channel. However, studies of such rocks are limited by the overprinting effects of retrograde metamorphism during exhumation. Here, we present the deformation microstructures and crystallographic-preferred orientation data of minerals in UHP rocks from the Dabie–Shan to study the rheological behavior of deeply subducted continental material under UHP conditions. The studied samples preserve deformation microstructures that formed under UHP conditions and can be distinguished into two types: high-strain mafic–ultramafic samples (eclogite and garnet-clinopyroxenite) and low-strain felsic samples (jadeite quartzite). This distinction suggests that felsic rocks are less strained than mafic–ultramafic rocks under UHP conditions. We argue that the phase transition from quartz to coesite in the felsic rocks may explain the microstructural differences between the studied mafic–ultramafic and felsic rock samples. The presence of coesite, which has a higher strength than quartz, may result in an increase in the bulk strength of felsic rocks, leading to strain localization in nearby mafic–ultramafic rocks. The formation of shear zones associated with strain localization under HP/UHP conditions can induce the detachment of subducted crustal material from subducting lithosphere, which is a prerequisite for the exhumation of UHP rocks. These findings suggest that coesite has an important influence on the rheological behavior of crustal material that is subducted to coesite-stable depths.

Provenance of basaltic tephra from Vatnajökull subglacial volcanoes, Iceland, as determined by major- and trace-element analyses

The Holocene ◽  
2011 ◽  
Vol 21 (7) ◽  
pp. 1037-1048 ◽  
Author(s):  
Bergrún Arna Óladóttir ◽  
Olgeir Sigmarsson ◽  
Gudrún Larsen ◽  
Jean-Luc Devidal
Keyword(s):  
Trace Element ◽  
Inductively Coupled Plasma ◽  
Major Element ◽  
Element Composition ◽  
Major Element Composition ◽  
Volcanic System ◽  
The Holocene ◽  
Inductively Coupled ◽  
Ice Cap ◽  
The North

The Holocene eruption history of subglacial volcanoes in Iceland is largely recorded by their tephra deposits. The numerous basaltic tephra offer the possibility to make the tephrochronology in the North Atlantic area more detailed and, therefore, more useful as a tool not only in volcanology but also in environmental and archaeological studies. The source of a tephra is established by mapping its distribution or inferred via compositional fingerprinting, mainly based on major-element analyses. In order to improve the provenance determinations for basaltic tephra produced at Grímsvötn, Bárdarbunga and Kverkfjöll volcanic systems in Iceland, 921 samples from soil profiles around the Vatnajökull ice-cap were analysed for major-element concentrations by electron probe microanalysis. These samples are shown to represent 747 primary tephra units. The tephra erupted within each of these volcanic system has similar chemical characteristics. The major-element results fall into three distinctive compositional groups, all of which show regular decrease of MgO with increasing K2O concentrations. The new analyses presented here considerably improve the compositional distinction between products of the three volcanic systems. Nevertheless, slight overlap of the compositional groups for each system still remains. In situ trace-element analyses by laser-ablation-inductively-coupled-plasma-mass-spectrometry were applied for better provenance identification for those tephra having similar major-element composition. Three trace-element ratios, Rb/Y, La/Yb and Sr/Th, proved particularly useful. Significantly higher La/Yb distinguishes the Grímsvötn basalts from those of Bárdarbunga and Rb/Y values differentiate the basalts of Grímsvötn and Kverkfjöll. Additionally, the products of Bárdarbunga, Grímsvötn and Kverkfjöll form distinct compositional fields on a Sr/Th versus Th plot. Taken together, the combined use of major- and trace-element analyses in delineating the provenance of basaltic tephra having similar major-element composition significantly improves the Holocene tephra record as well as the potential for correlations with tephra from outside Iceland.

Major Element, Trace Element, Nutrient, and Radionuclide Mobility in a Mining By-Product-Amended Soil

2012 ◽  
Vol 41 (6) ◽  
pp. 1818-1834 ◽  
Author(s):  
G. Douglas ◽  
J. Adeney ◽  
K. Johnston ◽  
L. Wendling ◽  
S. Coleman
Keyword(s):  
Trace Element ◽  
Major Element ◽  
Amended Soil

XVII.—The Major Ultrabasic and Basic Intrusions of St Kilda, Outer Hebrides

1967 ◽  
Vol 66 (17) ◽  
pp. 419-444 ◽  
Author(s):  
R. R. Harding
Keyword(s):  
Trace Element ◽  
Major Element ◽  
Layered Intrusion ◽  
Fine Grained ◽  
Outer Hebrides ◽  
Crystal Accumulation

AbstractThe structures and mineralogy of the Tertiary ultrabasic and basic intrusions are described. The ultrabasic rocks are thought to be remnants of a layered intrusion which once extended from Hirta to Boreray, and which probably formed by crystal accumulation. The eucrites may represent higher levels of this intrusion. A 350 feet-thick, fine-grained margin is described from the East Glen Bay Gabbro. The metamorphism of the ultrabasic and eucritic rocks, and the formation of the Glacan Mor Complex, probably occurred in a basic environment, before intrusion of the first acid rocks on St. Kilda. Five major-element and twenty-two trace-element analyses are presented.

Minor elements in olivine from spinel lherzolite xenoliths: implications for thermobarometry

1997 ◽  
Vol 61 (405) ◽  
pp. 257-269 ◽  
Author(s):  
Suzanne Y. O'Reilly ◽  
D. Chen ◽  
W. L. Griffin ◽  
C. G. Ryan
Keyword(s):  
Trace Element ◽  
Garnet Peridotite ◽  
Spinel Peridotite ◽  
Spinel Lherzolite ◽  
Proton Microprobe ◽  
Minor Elements ◽  
Spinel Lherzolites ◽  
Peridotite Xenoliths ◽  
Trace Element Contents ◽  
Element Contents

AbstractThe proton microprobe has been used to determine contents of Ca, Ti, Ni, Mn and Zn in the olivine of 54 spinel lherzolite xenoliths from Australian and Chinese basalts. These data are compared with proton-probe data for Ni, Mn and Zn in the olivine of 180 garnet peridotite xenoliths from African and Siberian kimberlites. Fe, Mn, Ni and Zn contents are well-correlated; because the spinel lherzolite olivines have higher mean Fe contents than garnet peridotite olivines (average Fo89.6vs. Fo90–92) they also have lower Ni and higher Mn contents. Zn and Fe are well-correlated in garnet peridotite olivine, but in spinel peridotites this relationship is perturbed by partitioning of Zn into spinel. None of these elements shows significant correlation with temperature. Consistent differences in trace-element contents of olivines in the two suites is interpreted as reflecting the greater degree of depletion of Archean garnet peridotites as compared to Phanerozoic spinel lherzolites. Ca and Ti contents of spinel-peridotite olivine are well correlated with one another, and with temperature as determined by several types of geothermometer. However, Ca contents are poorly correlated with pressure as determined by the Ca-in-olivine barometer of Köhler and Brey (1990). This reflects the strong T-dependence of this barometer: the uncertainty in pressure (calculated by this method) which is produced by the ±50°C uncertainty expected of any geothermometer is ca ± 8 kbar, corresponding to the entire width of the spinel-lherzolite field at 900–1200°C.

scholarly journals Exsolution Lamellae in Orthopyroxene of Lherzolite from the Pauza Ultramafic Rocks, Ne Iraq: Evidence of Deep Mantle Signature in the Zagros Suture Zone

2013 ◽  
Vol 2 (9) ◽  
pp. 102-115
Author(s):  
Yousif Osman Mohammad ◽  
Nabaz Rashid Hama Aziz
Keyword(s):  
High Pressure ◽  
Upper Cretaceous ◽  
Suture Zone ◽  
Ultramafic Rocks ◽  
Chromian Spinel ◽  
Spinel Peridotite ◽  
Incongruent Melting ◽  
Fine Grained ◽  
Ultra High Pressure ◽  
Deep Mantle

The Pauza ultramafic body is part of Upper Cretaceous Ophiolitic massifs of the Zagros Suture Zone, NE Iraq. The present study reveals evidence of Ultra-high pressure (UHP), and deep mantle signature of these peridotites in the Zagros Suture Zone throughout the observation of backscattered images and micro analyses which have been performed on orthopyroxen crystals in lherzolite of Pauza ultramafic rocks.Theorthopyroxen shows abundant exsolution lamellae of coarse unevenly distributed clinopyroxene coupled with the submicron uniformly distributed needles of Cr-spinel. The observed clusters of Opx–Cpx–Spl represent the decompression products of pyrope-rich garnet produced as a result of the transition from ultra-high pressure garnet peridotite to low-pressure spinel peridotite (LP). Neoblastic olivine (Fo92 – 93) with abundant multi-form Cr- spinel inclusions occurs as a fine-grained aggregate around orthopyroxene, whereas coarse olivine (Fo90-91) free from chromian-spinel is found in matrix. The similarity of the Cr-spinel lamellae orientations in both olivine and orthopyroxene, moreover, the enrichments of both Cr and Fe3+ in the Cr-spinel inclusions in neoblastic olivine relative to Cr-spinel lamellae in orthopyroxene, suggest that spinel inclusions in olivine have been derived from former Cr-spinel lamellae in orthopyroxene. Neoblastic olivine is formed by reaction of silica-poor ascending melt and orthopyroxene. It is inferred that the olivines with multi-form spinel inclusions has been formed by incongruent melting of pre-existing spinel lamellae-rich orthopyroxene.

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