scholarly journals Multi-stage Reactive Formation of Troctolites in Slow-spreading Oceanic Lithosphere (Erro–Tobbio, Italy): a Combined Field and Petrochemical Study

2019 ◽  
Vol 60 (5) ◽  
pp. 873-906 ◽  
Author(s):  
Valentin Basch ◽  
Elisabetta Rampone ◽  
Laura Crispini ◽  
Carlotta Ferrando ◽  
Benoit Ildefonse ◽  
...  
Keyword(s):  
Fractional Crystallization ◽  
Oceanic Lithosphere ◽  
Rock Interaction ◽  
Crystallographic Preferred Orientation ◽  
Compositional Evolution ◽  
Fine Grained ◽  
Interaction Processes ◽  
Multi Stage ◽  
Mineral Compositions ◽  
Melt Composition

Abstract Many recent studies have investigated the replacive formation of troctolites from mantle protoliths and the compositional evolution of the percolating melt during melt–rock interaction processes. However, strong structural and geochemical constraints for a replacive origin have not yet been established. The Erro–Tobbio impregnated mantle peridotites are primarily associated with a hectometre-size troctolitic body and crosscutting gabbroic dykes, providing a good field control on melt–rock interaction processes and subsequent magmatic intrusions. The troctolitic body exhibits high inner complexity, with a host troctolite (Troctolite A) crosscut by a second generation of troctolitic metre-size pseudo-tabular bodies (Troctolite B). The host Troctolite A is characterized by two different textural types of olivine, corroded deformed millimetre- to centimetre-size olivine and fine-grained rounded undeformed olivine, both embedded in interstitial to poikilitic plagioclase and clinopyroxene. Troctolite A shows melt–rock reaction microstructures indicative of replacive formation after percolation and impregnation of mantle dunites by a reactive melt. The evolution of the texture and crystallographic preferred orientation (CPO) of olivine are correlated and depend on the melt/rock ratio involved in the impregnation process. A low melt/rock ratio allows the preservation of the protolith structure, whereas a high melt/rock ratio leads to the disaggregation of the pre-existing matrix. The mineral compositions in Troctolite A define reactive trends, indicative of the buffering of the melt composition by assimilation of olivine during impregnation. The magmatic Troctolite B bodies are intruded within the pre-existing Troctolite A and are characterized by extreme textural variations of olivine, from decimetre-size dendritic to fine-grained euhedral crystals embedded in poikilitic plagioclase. This textural variability is the result of olivine assimilation during melt–rock reaction and the correlated increase in the degree of undercooling of the percolating melt. In the late gabbroic intrusions, mineral compositions are consistent with the fractional crystallization of melts modified after the reactive crystallization of Troctolites A and B. The Erro–Tobbio troctolitic body has a multi-stage origin, marked by the transition from reactive to fractional crystallization and diffuse to focused melt percolation and intrusion, related to progressive exhumation. During the formation of the troctolitic body, the melt composition was modified and controlled by assimilation and concomitant crystallization reactions occurring at low melt supply. Similar processes have been described in ultraslow-spreading oceanic settings characterized by scarce magmatic activity.

scholarly journals Mineralogical Evidence for Partial Melting and Melt-Rock Interaction Processes in the Mantle Peridotites of Edessa Ophiolite (North Greece)

Minerals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 120 ◽  
Author(s):  
Aikaterini Rogkala ◽  
Petros Petrounias ◽  
Basilios Tsikouras ◽  
Panagiota Giannakopoulou ◽  
Konstantin Hatzipanagiotou
Keyword(s):  
Partial Melting ◽  
Mantle Wedge ◽  
Oceanic Lithosphere ◽  
Upper Jurassic ◽  
Northern Greece ◽  
Rock Interaction ◽  
Oceanic Spreading ◽  
Mantle Peridotites ◽  
Mineral Compositions ◽  
Ocean Ridge

The Edessa ophiolite complex of northern Greece consists of remnants of oceanic lithosphere emplaced during the Upper Jurassic-Lower Cretaceous onto the Palaeozoic-Mesozoic continental margin of Eurasia. This study presents new data on mineral compositions of mantle peridotites from this ophiolite, especially serpentinised harzburgite and minor lherzolite. Lherzolite formed by low to moderate degrees of partial melting and subsequent melt-rock reaction in an oceanic spreading setting. On the other hand, refractory harzburgite formed by high degrees of partial melting in a supra-subduction zone (SSZ) setting. These SSZ mantle peridotites contain Cr-rich spinel residual after partial melting of more fertile (abyssal) lherzolite with Al-rich spinel. Chromite with Cr# > 60 in harzburgite resulted from chemical modification of residual Cr-spinel and, along with the presence of euhedral chromite, is indicative of late melt-peridotite interaction in the mantle wedge. Mineral compositions suggest that the Edessa oceanic mantle evolved from a typical mid-ocean ridge (MOR) oceanic basin to the mantle wedge of a SSZ. This scenario explains the higher degrees of partial melting recorded in harzburgite, as well as the overprint of primary mineralogical characteristics in the Edessa peridotites.

scholarly journals Thermodynamic Stabilities of U(VI) Minerals: Estimated and Observed Relationships

1996 ◽  
Vol 465 ◽  
Author(s):  
Robert J. Finch
Keyword(s):  
Gibbs Energy ◽  
Reaction Pathways ◽  
Free Energies ◽  
Fine Grained ◽  
Surface Energies ◽  
Stability Diagrams ◽  
Activity Diagrams ◽  
Mineral Stability ◽  
Mineral Compositions

ABSTRACTGibbs free energies of formation (ΔG°ƒ) for several structurally related U(VI) minerals are estimated by summing the Gibbs energy contributions from component oxides. The estimated ΔG°f values are used to construct activity-activity (stability) diagrams, and the predicted stability fields are compared with observed mineral occurrences and reaction pathways. With some exceptions, natural occurrences agree well with the mineral stability fields estimated for the systems Sio2-Cao-Uo3-UOH2O and Co2-caO-UO3-H2O providing confidence in the estimated thermodynamic values. Activity-activity diagrams are sensitive to small differences in ΔG°f values, and mineral compositions must be known accurately, including structurally bound H2O. The estimated ΔG°f values are not considered reliable for a few minerals for two major reasons: (1) the structures of the minerals in question are not closely similar to those used to estimate the ΔG°f* values of the component oxides, and/or (2) the minerals in question are exceptionally fine grained, leading to large surface energies that increase the effective mineral solubilities.

Relative roles of source composition, fractional crystallization and crustal contamination in the petrogenesis of Andean volcanic rocks

1984 ◽  
Vol 310 (1514) ◽  
pp. 675-692 ◽  
Keyword(s):  
Subduction Zone ◽  
Continental Crust ◽  
Fractional Crystallization ◽  
Magma Mixing ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
Alkaline Basalt ◽  
Complex Process ◽  
Heterogeneous Mantle

There are well established differences in the chemical and isotopic characteristics of the calc-alkaline basalt—andesite-dacite-rhyolite association of the northern (n.v.z.), central (c.v.z.) and southern volcanic zones (s.v.z.) of the South American Andes. Volcanic rocks of the alkaline basalt-trachyte association occur within and to the east of these active volcanic zones. The chemical and isotopic characteristics of the n.v.z. basaltic andesites and andesites and the s.v.z. basalts, basaltic andesites and andesites are consistent with derivation by fractional crystallization of basaltic parent magmas formed by partial melting of the asthenospheric mantle wedge containing components from subducted oceanic lithosphere. Conversely, the alkaline lavas are derived from basaltic parent magmas formed from mantle of ‘within-plate’ character. Recent basaltic andesites from the Cerro Galan volcanic centre to the SE of the c.v.z. are derived from mantle containing both subduction zone and within-plate components, and have experienced assimilation and fractional crystallization (a.f.c.) during uprise through the continental crust. The c.v.z. basaltic andesites are derived from mantle containing subduction-zone components, probably accompanied by a.f.c. within the continental crust. Some c.v.z. lavas and pyroclastic rocks show petrological and geochemical evidence for magma mixing. The petrogenesis of the c.v.z. lavas is therefore a complex process in which magmas derived from heterogeneous mantle experience assimilation, fractional crystallization, and magma mixing during uprise through the continental crust.

Magnetite Redistribution during Multi-stage Serpentinization: Evidence from the Taishir massif, the Khantaishir Ophiolite, Western Mongolia

2021 ◽  
Author(s):  
Otgonbayar Dandar ◽  
Atsushi Okamoto ◽  
Masaoki Uno ◽  
Noriyoshi Tsuchiya
Keyword(s):  
Hydrogen Generation ◽  
Mantle Peridotite ◽  
Oceanic Lithosphere ◽  
Ultramafic Rocks ◽  
Western Mongolia ◽  
Fluid Infiltration ◽  
Multi Stage ◽  
Fe Content ◽  
Coarse Grains ◽  
Modal Abundance

<p>Magnetite commonly forms during serpentinization of mantle peridotite, involving the hydrogen generation within the oceanic lithosphere. Although magnetite is concentrated in veins, the mobility of iron during serpentinization is still poorly understood. The completely serpentinized ultramafic rocks (originally dunite) within the Taishir massif in the Khantaishir ophiolite, western Mongolia, include abundant magnetite + antigorite veins, which manifest novel distribution of magnetite. The serpentinite records the multi-stage serpentinization, in order of (1) Al-rich antigorite + lizardite mixture with hourglass texture (Al<sub>2</sub>O<sub>3</sub> = 0.46-0.69 wt%; Atg+Lz), (2) Al-poor antigorite composed of thick veins and their branches (Atg), and (3) chrysotile that cut all previous textures. The Mg# (= Mg/ (Mg + Fe<sub>total</sub>)) of Atg+Lz (0.94-0.96) is lower than Atg (0.99) and chrysotile (0.98). In the region of Atg+Lz, magnetite occurs as the arrays of fine grains (<50 μm) around the hourglass texture. In the Atg veins replacing Atg+Lz, magnetite disappears and re-precipitated as coarse grains (100-250 μm) in the center of some veins. As the extent of replacement of Atg+Lz by Atg veins increases, both modal abundance of magnetite and the bulk Fe content decrease. These characteristics indicate that hydrogen generation mainly occurred at the stage of Atg+Lz formation, and magnetite distribution was largely modified via dissolution and precipitation in response to later fluid infiltration associated with the Atg veins. This also indicates the high iron mobility within the serpentinized peridotites even after the primary stage of magnetite formation.</p>

scholarly journals Preliminary chemical characterization of groundwater in the Rome Municipality

2015 ◽  
Author(s):  
Luca Pizzino ◽  
Daniele Cinti ◽  
Monia Procesi ◽  
Alessandra Sciarra
Keyword(s):  
Chemical Elements ◽  
Central Italy ◽  
Chemical Characterization ◽  
Mineral Waters ◽  
Measured Temperature ◽  
Large Variability ◽  
Rock Interaction ◽  
Interaction Processes ◽  
Two Samples ◽  
Water Rock Interaction

In summer 2015 a geochemical survey on groundwater was carried out at 31 sampling points (wells and piezometers) belonging to the new “Official monitoring groundwater network of Rome Municipality” (GMNR). The following parameters were measured: temperature, pH, electrical conductivity (i.e. salinity) and alkalinity; these data were used to compute partial pressure of CO2 (pCO2). Furthermore, samples were collected to characterise waters from a chemical point of view (major elements). To implement our data - base, chemical analyses of 6 CO2 - rich mineral waters of Rome were considered. Hydrochemical survey was mainly devoted to: i) classify waters in chemical facies; ii) investigate the main water-rock interaction processes governing the water’s chemical evolution, also affected by variable amounts of dissolved CO2 and iii) define the pCO2 level in groundwater in the frame of the knowledge so far acquired in the Tyrrhenian sector of central Italy.. Groundwater shows a dominant Ca-HCO3 chemistry; some samples belong to Na-HCO3, Na-Cl and CaCl2 hydrochemical facies. In the dominant facies waters show a large variability in the abundance of chemical elements, in their salinity (ranging between 0.46 e 3.83 g/l) and pH (in the interval 5.87-7.22); these features are mainly due to different water-rock interaction processes together with the presence of variable CO2 contents. Na-HCO3 waters show the lowest salinity values (TDS up to 0.32 g/l) and strongly alkaline pH; cation exchange processes with clays, causing Na enrichment and Ca and Mg removal from solution, can be invoked to justify the observed chemistry. Waters of the Castel Fusano Natural Reserve (CFNR) belong to the Na-Cl and Ca-Cl2 facies; the different chemistry reflects the geochemical processes going on in the considered coastal aquifers such as: i) mixing between freshwater and saline waters of marine origin (fossil waters, seawater intrusion) and ii) cationic exchanges with clays that make up the less permeable sediments of the area. Two samples of the CFNR group have Ca-HCO3 chemistry and represent aquifers not affected by salinization processes. Calculated pCO2 distribution is highly variable, from low (0.03 bar) to high values (0.72 bar), implying different CO2 input (and origin) in the studied aquifers. Highest levels of carbon dioxide are linked to the degassing processes going on in the Tyrrhenian sector of Central Italy.

scholarly journals Multi-stage arc magma evolution recorded by apatite in volcanic rocks

Geology ◽  
2020 ◽  
Vol 48 (4) ◽  
pp. 323-327 ◽  
Author(s):  
Chetan L. Nathwani ◽  
Matthew A. Loader ◽  
Jamie J. Wilkinson ◽  
Yannick Buret ◽  
Robert H. Sievwright ◽  
...  
Keyword(s):  
Fractional Crystallization ◽  
Volcanic Rocks ◽  
Explosive Volcanism ◽  
Ore Deposits ◽  
Magma Evolution ◽  
Arc Magmas ◽  
Deep Crust ◽  
Multi Stage ◽  
Novel Approach ◽  
Arc Magma

Abstract Protracted magma storage in the deep crust is a key stage in the formation of evolved, hydrous arc magmas that can result in explosive volcanism and the formation of economically valuable magmatic-hydrothermal ore deposits. High magmatic water content in the deep crust results in extensive amphibole ± garnet fractionation and the suppression of plagioclase crystallization as recorded by elevated Sr/Y ratios and high Eu (high Eu/Eu*) in the melt. Here, we use a novel approach to track the petrogenesis of arc magmas using apatite trace element chemistry in volcanic formations from the Cenozoic arc of central Chile. These rocks formed in a magmatic cycle that culminated in high-Sr/Y magmatism and porphyry ore deposit formation in the Miocene. We use Sr/Y, Eu/Eu*, and Mg in apatite to track discrete stages of arc magma evolution. We apply fractional crystallization modeling to show that early-crystallizing apatite can inherit a high-Sr/Y and high-Eu/Eu* melt chemistry signature that is predetermined by amphibole-dominated fractional crystallization in the lower crust. Our modeling shows that crystallization of the in situ host-rock mineral assemblage in the shallow crust causes competition for trace elements in the melt that leads to apatite compositions diverging from bulk-magma chemistry. Understanding this decoupling behavior is important for the use of apatite as an indicator of metallogenic fertility in arcs and for interpretation of provenance in detrital studies.

scholarly journals Geochemistry of Garga-Sarali intrusive granitoids (central domain of the central African fold belt in Cameroon): petrological implication

2020 ◽  
Vol 8 (1) ◽  
pp. 33
Author(s):  
Daama Isaac ◽  
Mbowou Gbambie Isaac Bertrand ◽  
Yamgouot Ngounouno Fadimatou ◽  
Ntoumbe Mama ◽  
Ngounouno Ismaïla
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Partial Melting ◽  
Fractional Crystallization ◽  
Coarse Grained ◽  
Geochemical Analysis ◽  
Fold Belt ◽  
Volcanic Arcs ◽  
Fine Grained ◽  
Incompatible Elements

The Garga-Sarali granitoids outcrop in form of large slabs and undistorted large blocks, into a schisto-gneissic basement. These rocks contain mainly muscovite and microcline, followed by K-feldspar, quartz, biotite, pyroxene, zircon and oxides, with coarse-grained to fine-grained textures. Geochemical analysis show that it belongs to differentiated rocks group (granodiorite-granite) with high SiO2 (up to 72 wt%) contents. Their genesis was made from a process of partial melting and fractional crystallization. These rocks are classified as belonging to I- and S-Type, meta-peraluminous, shoshonitic granites; belonging to the domain of volcanic arcs. The rare earth elements patterns suggest a source enriched of incompatible elements. The Nb-Ta and Ti negative anomalies from the multi-element patterns are characteristics of the subduction domains.  

Quantitative texture analysis of small domains with synchrotron radiation X-rays

1999 ◽  
Vol 32 (5) ◽  
pp. 841-849 ◽  
Author(s):  
F. Heidelbach ◽  
C. Riekel ◽  
H.-R. Wenk
Keyword(s):  
Synchrotron Radiation ◽  
European Synchrotron Radiation Facility ◽  
Polymer Fibers ◽  
Polycrystalline Materials ◽  
X Rays ◽  
Bone Material ◽  
Experimental Procedure ◽  
Crystallographic Preferred Orientation ◽  
Fine Grained ◽  
Steel Wires

Quantitative analysis of crystallographic preferred orientation (texture) of very small volumes in fine-grained polycrystalline materials has been carried out with a monochromatic X-ray microbeam (≤30 µm) at the microfocus beamline of the European Synchrotron Radiation Facility (ESRF). The experimental procedure is described and illustrated with textures of rolled aluminium, aluminium and steel wires, polymer fibers and natural bone material (apatite).

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