Geochemistry最新文献

The Aladağ ophiolite is located in the eastern Taurides, north of the city of Adana, southern Turkey and, from bottom to top, is composed of mantle peridotites, ultramafic-mafic cumulates, isotropic (massive) gabbro and diabase dykes. Mantle peridotites are represented by varying degrees of serpentinized dunite, harzburgite and lherzolite. We studied 100 lherzolite, harzburgite and dunite samples representing the entire Aladağ ophiolite mantle. Whole rock major and trace element analysis were performed for all samples, and mineral chemistry analysis were carried out on selected mineral phases.

According to geochemical characteristics, mantle peridotites are divided into two sub-groups: abisal (Group-1) and suprasubduction zone peridotites (Group-2). Group-1 mantle peridotites are represented by high clinopyroxene modal abundances, whole-rock and clinopyroxene heavy Rare Earth Element (REE) contents and low spinel Cr# values (13–47). Whole-rock heavy REE patterns indicate that these rocks are 5–18 % unhydrous partial melting residues. In contrast, Group-2 mantle peridotites are represented by lower clinopyroxene modal abundances, whole-rock and clinopyroxene heavy REE contents, and higher spinel Cr# values (44–74) than Group-1 samples, reflecting higher partial melting degrees of up to 33 %. Light REE and LILE enriched whole-rock and clinopyroxene contents of Group-2 samples reflect that, in addition to depletion, they were enriched with fluids/melts and underwent both cryptic and modal metasomatism in the subduction zone.

Aladağ peridotites have formed originally by low degree partial melting at mid-ocean spreading ridge (MOR) and later re-melted and metasomatized/refertilized in a suprasubduction zone (SSZ) environment.

The bauxites of the Payas area in the eastern Mediterranean region of Turkey occur as a stratigraphically continuous layer between Early and Late Cretaceous shallow marine carbonates. The laterites represent an in situ formation and mark a key stratigraphic layer in the region. Bauxite pockets are also present in the laterites, formed from the reworking of the laterites and accumulated in depressions in the karst terrain. Therefore, bauxite occurrences are found locally in this stratigraphic layer. The parental rock was a Ti-rich basalt that is compositionally similar to Hawaiian basalts, as indicated by petrographic features and distinctive trace element composition (Zr/TiO₂ and Nb/Y). The behavior of elements during the lateritization and bauxitization processes was interpreted using the composition of the Hawaiian basalts with the iron laterite and Ti-rich bauxites of the Payas Region. During lateritization, Fe, Al, Ti, Cr, Nb, and Ta, were largely immobilie while REE and other trace elements, except for Rb, Ni, Co, and Pb were significantly removed. Approximately 75 % of the REE were removed at the end of the bauxitization and/or transportation of the lateritic soil into the karstic depressions. REE were not equally mobile with La to Ce and Lu to Yb having a relatively lower mobility than highly mobile middle REE. During the transformation of laterite to bauxite, low mobility elements such as Ti, Nb, Th, Cr, Hf, and Sn were enriched in the bauxite phase. In comparison to other elements, Rb, As, Pb, Mo, and Ni were strongly removed from the lateritic material during the bauxitization processes. The transfer of MREE during lateritization and bauxitization would have resulted in the enrichment of both light and heavy REE (concave pattern) in contemporaneous seawater. In other words, silicate weathering periods on land should be marked by a concave REE pattern with positive Eu anomaly in marine sediments throughout the geological period.

The Kızıldere geothermal field, located at the eastern part of the Büyük Menderes graben in Western Turkey, is the most important geothermal reservoir suitable for electricity generation. Fossil fumarole fields and alteration or mineralization zones are directly related to the tectonic zones influenced by N-S directional extension. Associated to fossil geothermal activities, calcite, dolomite, strontianite, quartz, gypsum, anhydrite, celestine, kaolinite, smectite, boehmite and goethite/limonite were occurred in the form of void or crack fill within the Paleozoic metamorphic and Miocene-Quaternary clastic and carbonate host rocks. The current mineralogical composition indicates temperature conditions of 100–250 °C which close to current reservoir temperatures. Some of minerals with fossil geothermal origin, i.e. calcite, anhydrite, dolomite, celestine, amorphous silica and quartz, are compatible for mineral precipitations estimated from mineral equilibrium modeling, and scale mineralogy of wells, as well. The formation order of the most common geothermal minerals is determined as calcite → gypsum → anhydrite → quartz direction indicating that alkaline conditions were followed by acidic conditions. The blade-like/prismatic rhombohedral calcites replaced by quartz occurrences in siliceous‑carbonate veins indicate the boiling was occurred in the field. The geothermal mineral zoning determined from drilling samples is anhydrite-dolomite-calcite from shallow to deeper parts. The lateral and vertical distribution of mineral zoning is related to the fact that geothermal waters are mainly affected by host rock compositions, i.e. dissolution from the host rocks and precipitation along the cracks/fractures and bedding planes. Mineralizations in the Kızıldere geothermal field mainly represent the direct precipitations from hot geothermal waters rather than transformations of minerals in the host rocks. Si, Al, Mg, K and Na concentrations in carbonate and sulfate minerals show a positive correlation relationship and are derived from metapelites. Whereas Ca is negatively related to these elements and it is derived from metacarbonate and/or carbonate host rocks. According to the current geothermal water composition, Ca enriches in the deeper parts, while Mg and B enrichment in shallow depths near the basin edge that indicates the different composition of the host rocks where minerals precipitated. The relatively high boron contents at shallow depth indicate that it is retained by the minerals precipitated this level and causes less release to the surface.

Calc-silicate granulites constitute a relatively small part of the whole granulitic material outcrops characterizing the In Ouzzal terrane (NW Hoggar, South Algeria). However, these rocks preserve a number of spectacular reaction textures that could be effectively used to infer their pressure-temperature-fluid history. These textures are interpreted using P-T and T-X_CO2 grids in the simplified CaO-Al₂O₃-SiO₂-Vapor system. In this process, sequences of reactions have been subdivided into two distinct stages: (i) the early prograde stage that was accompanied by significant rise of temperature from about 800 °C up to 1050 °C at around10 kbar followed by (ii) the decompression stage from about 9 to 6 kbar. During the prograde stage, coarse grained wollastonites were produced according to the reaction calcite + quartz → wollastonite + CO₂. Furthermore, in the peak pressure temperature stage, the reaction producing wollastonite + scapolite from coarse primary garnet consumes CO₂ with temperature increasing from 850 °C to 1000 °C according to the reaction 3grossular + 3CO₂ → 3wollastonite + 2calcite + scapolite. The latest reactions have been occurred during the decompression stage from about 10 kbar to 5 kbar and cooling from 1000 °C to 800 °C. The growth of calcite + quartz around wollastonite besides to garnet coronas between wollastonite, calcite and scapolite are explained by the reaction: calcite + quartz → wollastonite + CO₂ and 3wollastonite + scapolite +2calcite → 3grossular + 3CO₂. The appearance of anorthite around scapolite occurs following a decrease of temperature independently to the fluids according to the reaction scapolite → 3anorthite + calcite. All reactions took place at CO₂ low pressure which was estimated between 0.04 and 0.55.

The Eastern Pontide Orogenic Belt (EPOB) hosts numerous plutonic bodies with different dimensions, compositions and ages ranging from Paleozoic to Late Eocene in NE Turkey. U-Pb zircon dating suggests that the Arslandede pluton crystallized at 44.50 ± 0.29 Ma, corresponding to the Lutetian (Middle Eocene) period. Rocks of this pluton have monzonitic character, with compositions ranging from monzodiorite to granite (SiO₂ = 49˗71 wt%). The studied monzonitic rocks have I-type, metaluminous and shoshonitic character and are enriched in large-ion lithophile elements (LILEs). The rare earth elements (REEs) have concave up shape (La_N/Yb_N = 6.64–11.57) and show negative to slightly positive Eu anomalies (Eu_N/Eu* = 0.37–1.24). ⁸⁷Sr/⁸⁶Sr_(i) values of 0.704801–0.705102 and εNd_(i) values of 1.01–1.34 correspond to the mantle series on isotope ratio diagrams. Positive εHf_(i) values (5.01–14.91) plot between the depleted mantle and the chondritic evolution lines. The petrological features of the rocks from the Arslandede pluton show that fractional crystallization with low rates of assimilation and/or magma mixing were effective during crystallization. All data show that the magma source of the pluton derived from an enriched lithospheric mantle and emplaced into the crust after differentiation in a deep seated magma chamber contaminated by relatively small proportions of crustal rocks.

Limited attention has been given to antimony present in detrital form in the different environmental compartments except for highly polluted systems related in some way to ore deposits. In highly polluted systems, the ultimate sinks of Sb may be the minerals tripuhyite (FeSbO₄) or perhaps schafarzikite (FeSb₂O₄) but how about Sb dynamics in the much more abundant, weakly polluted or ‘non-polluted’ systems? This deficiency in our knowledge is probably related to the perception that the element is mostly present ‘dissolved’ in waters and to a focus on the role of its binding to iron oxyhydroxides in solid phases. Here we evaluate the state of our knowledge in the Sb journey from geological matrices to detrital forms in soils and waters and identify key aspects that require further investigation. In high-temperature environments, Sb demonstrated its striking incompatibility by fractionation into aqueous fluids or sulfide/metallic melts, or by uptake in a few common minerals that accept this element (e.g., rutile or pyrite). In low-temperature environments, Sb enters the structures of minerals with different formation rates and solubilities, creating a confusing impression of being mobile and immobile at the same time. The estimates of Sb concentration in the upper continental crust are scattered and the Sb-bearing mineral(s) there have not yet been identified. Given that sedimentary rocks are consistently enriched in Sb, the carriers could be the clay minerals. In surface water bodies, Sb could be carried predominantly in the particulate fraction, despite the popular belief of the opposite. An important point to consider is the transport of Sb within the suspended particulate matter, not on its surface. In soils, many studies employed sequential extractions to show that Sb accumulates in the ‘residual’ fraction, without ever asking what the nature of this fraction is. Based on these facts (i.e., knowns), we have identified the unknowns regarding detrital Sb on our planet that should preferentially be addressed by future projects if our understanding is to improve.

The closure of the Neo-Tethys Ocean and the following continental collision produced extensive Eocene-aged granitic plutons in the northern margin of Gondwana. This paper deals with the geochronology and petrogenesis of the Karabiga pluton in western Sakarya Zone. The pluton comprises K-feldspar, plagioclase, hornblende, biotite, quartz and accessory minerals (e.g., titanite, zircon, apatite, opaques), and secondary minerals such as chlorite, sericite, epidote, carbonate and clay minerals. Laser ablation inductively coupled plasma mass spectrometer zircon U-Pb dating yielded perfect ages of 48.27 ± 0.21 and 47.06 ± 0.32 Ma, indicating that the pluton were emplaced in the Early Eocene. Our results indicate that Ti-in-zircon temperature (ca. 900 °C), which is consistent with zircons grew in the continental crust, are higher than zircon saturation temperatures (740–884 °C). ⁴⁰Ar/³⁹Ar dating of biotites of the pluton yielded cooling ages between 47.34 ± 0.43 Ma and 46.30 ± 0.52 Ma. These dates are interpreted as the cooling age of the Karabiga pluton. The pluton is characterized by high SiO₂ (72.40–76.48 wt%), K₂O (5.12–6.44 wt%) and Na₂O (3.26–5.55 wt%) contents and exhibit enriched LREEs, K, Rb, Th, U, and Pb, and depleted Nb, Ta, P, and Ti contents. It belongs to shoshonite series, and displays peraluminous, I-type character. ⁸⁷Sr/⁸⁶S_(i) ratios of the pluton vary between 0.703296 and 0.706654, while those of ¹⁴³Nd/¹⁴⁴Nd_(i) lie between 0.512596 and 0.512629. In conclusion, Karabiga pluton could be originated from dehydration-melting of metagreywacke and metapelites in middle-upper crust due to slab breakoff/delamination and major, trace element contents, decreasing Al₂O₃, Fe₂O₃, MgO and TiO₂ with increasing SiO₂ as well as initial Sr-Nd homogenity show that fractional crystallization played a role in the evolution of the pluton.