Sugarloaf Mountain is a 200-m high volcanic landform in central Arizona, USA, within the transition from the southern Basin and Range to the Colorado Plateau. It is composed of Miocene alkalic basalt (47.2-49.1 wt.% SiO2; 6.7-7.7 wt.% MgO) and overlying andesite and dacite lavas (61.4-63.9 wt.% SiO2; 3.5-4.7 wt.% MgO). Sugarloaf Mountain therefore offers an opportunity to evaluate the origin of andesite magmas with respect to coexisting basalt. Important for evaluating Sugarloaf basalt and andesite (plus dacite) is that the andesites contain basaltic minerals olivine (cores Fo(76-86)) and clinopyroxene (similar to Fs(9-18)Wo(35-44)) coexisting with Na-plagioclase (An(48-28)Or(1.4-7)), quartz, amphibole, and minor orthopyroxene, biotite, and sanidine. Noteworthy is that andesite mineral textures include reaction and spongy zones and embayments in and on Na-plagioclase and quartz phenocrysts, where some reacted Na-plagioclases have higher-An mantles, plus some similarly reacted and embayed olivine, clinopyroxene, and amphibole phenocrysts. Fractional crystallization of Sugarloaf basaltic magmas cannot alone yield the andesites because their similar to 61 to 64 wt.% SiO2 is attended by incompatible REE and HFSE abundances lower than in the basalts (e.g., Ce 77-105 in andesites vs 114-166 ppm in basalts; Zr 149-173 vs 183-237; Nb 21-25 vs 34-42). On the other hand, andesite mineral assemblages, textures, and compositions are consistent with basaltic magmas having mixed with rhyolitic magmas, provided the rhyolite(s) had relatively low REE and HFSE abundances. Linear binary mixing calculations yield good first approximation results for producing andesitic compositions from Sugarloaf basalt compositions and a central Arizona low-REE, low-HFSE rhyolite. For example, mixing proportions 52:48 of Sugarloaf basalt and low incompatible-element rhyolite yields a hybrid composition that matches Sugarloaf andesite well although we do not claim to have exact endmembers, but rather, viable proxies. Additionally, the observed mineral textures are all consistent with hot basalt magma mixing into rhyolite magma. Compositional differences among the phenocrysts of Na-plagioclase, clinopyroxene, and amphibole in the andesites suggest several mixing events, and amphibole thermobarometry calculates depths corresponding to 8-16 km and 850 degrees to 980 degrees C. The amphibole P-T observed for a rather tight compositional range of andesite compositions is consistent with the gathering of several different basalt-rhyolite hybrids into a homogenizing 'collection' zone prior to eruptions. We interpret Sugarloaf Mountain to represent basalt-rhyolite mixings on a relatively small scale as part of the large scale Miocene (similar to 20 to 15 Ma) magmatism of central Arizona. A particular qualification for this example of hybridization, however, is that the rhyolite endmember have relatively low REE and HFSE abundances.
Different from previous studies on effect of weathering upon geochemical variation along a single weathered profile, this paper provides a new methodology validated by comparing a weathered outcrop samples and their stratigraphic counterpart un-weathered core samples in a nearby shallow borehole. This outcrop and borehole penetrated the Ordovician-Silurian Wufeng Longmaxi shales, located in the same anticline structure in the northern part of Guizhou Province, Southern China. The mineral composition, major, trace and rare earth elements (REEs) composition and Rock-Eval parameters of outcrop and core samples were analyzed and compared. Organic matter (OM) was observed in the microscope and extracted for elements analysis. The results show that short-term weathering still has significant influence on OM, mineral and elemental composition of black shales. The elements composition shows the outcrop profile was moderately weathered. The REEs compositions do not alter much during weathering process and the REEs composition and their relative ratios still are valid for rock origin determination. The OM, mainly composed by graptolite and bitumen, even entering the highly-over thermal maturity, is still sensitive to the weathering with a systematic loss 30-50% of TOC along the outcrop profile, which suggests that the OM consumption is predominantly controlled by weathering duration and the distance from the weathering surface. In turn, OM has significant influence on the trace elements transportation behavior during weathering. Some trace elements associated with the OM such as V, Cr, Th, U, Ni and Co, change significantly in their absolute concentration during weathering, but their relative ratios do not necessarily change too much and might be still reliable proxies for paleo-environmental determination. The mobility of shale minerals during weathering is in the following order: plagioclase > potassium feldspar and dolomite > pyrite and OM. Short-term weathering can also result in considerable transportation of elements and significant variation of minerals content in black shale, which may pose potentially high environmental and engineering risk in the regions rich in black shale.
The Shalair area, which is located in northeastern Iraq, is considered to be part of the northern Sanandaj-Sirjan Zone (SaSZ) and contains several granitoid bodies. One of these bodies, the Mishao porphyritic-granite (MG), was crystallized at 111.6 +/- 2.4 Ma, based on its zircon U-Pb age. Its geochemical characteristics suggest that the MG rocks are talc-alkaline, peraluminous, I-type granites with microgranular mafic enclaves. They are enriched in SiO2, Na2O, Al2O3 and Zr and depleted in MgO, Fe2O3, Nb and Ti; in contrast, the enclave sample records lower SiO2 content and higher contents of MgO and Fe2O3. These rocks show an enrichment of LREE relative to HREE, and pronounced negative Eu anomalies implying feldspar fractionation. The isotopic and geochemical characteristics of the MG samples suggest that these rocks are evolved through fractional crystallization. In the La/Nb-Nb diagram and Sm/Nd ratios, the MG rocks and the enclave samples exhibit strong evidence for crustal contamination. The MG rocks record high initial Sr-87/Sr-86 (0.70625-0.70740) and low Nd-143/Nd-144(i) (0.51235-0.51274) ratios. These Sr-Nd isotopic data, combined with the presence of high Th/U and Rb/Sr ratios and significant depletions of Nb, Ta and Ti, show a relation of these bodies to an active continental margin regime. Based on the age and geochemical data of the MG, this study presents new information about the occurrence of Middle Cretaceous magmatic activities, which are related to the active continental margins in the SaSZ that run parallel to the Zagros Fold-Thrust Belt.
We present the results of physical properties, petrography, bulk chemistry, mineral compositions, phase relations modelling and Noble gases study of the meteorite El Pozo. The petrography and mineral compositions indicate that the meteorite is an L5 chondrite with a low shock stage of S2-S3. Heterogenous weathering was preferentially along shock structures. Thermobarometric calculations indicate thermal equilibrium conditions between 768 degrees C and 925 degrees C at similar to 4 to 6 kb, which are substantially consistent with the petrological metamorphism type 5. A pseudosection phase diagram is relatively consistent with the mineral assemblage observed and PT conditions calculated. Temperature vs. fO(2) diagram shows that plagioclase compositional stability is very sensitive to Tschermack substitution in orthopyroxene, clinopyroxene and X-An plagioclase during the high temperature metamorphic process. Based on noble gases He, Ne, Ar and K contents a cosmogenic exposure age CRE of 1.9 Myr was calculated. The Ne-21 would be totally cosmogenic, with no primordial Ne. The Ne-21/Ne-22 value (0.97) is higher than solar value. According to the cosmogenic Ne content, we argue that El Pozo chondrite originally had a pre-atmospheric mass of 9-10 kg, which would have been produced by a later collision after the recognized collision of the L-chondrite parent body similar to 470 Ma ago.
The Kaleybar, Razgah and Bozqush (KRB) intrusions were studied to better understand subduction-related Eocene-Oligocene alkaline magmatism in NW Iran. The bulk of intrusions mainly consist of Si-undersaturated rocks including fold-bearing monzonite and syenite (nepheline syenite, pseudoleucite syenite) with some foid-bearing diorite and gabbro. In addition, they are spatially associated with Si-saturated rocks ranging in composition from monzo-diorite to syeno-granite. The main mafic rock-forming minerals of the studied rocks are olivine (Fo(44)Fa(56)), clinopyroxene (diopside to augite), biotite (Mg-biotite through Fe-biotite), amphibole (ferropargasite and magnesio-hastingsite with Mg# < 0.55), and garnet (Ti-andradites). Based on whole rock geochemistry, the foid-syenites and associated rocks show mildly alkaline (shoshonitic) affinity. The content of SiO2, K2O + Na2O, and K2O/Na2O ratio ranges from 47.8 to 60.7 wt.%, 5.31 to 16.33 wt.%, and 0.6 to 3.2, respectively. The intrusions are commonly metaluminous, with an aluminum-saturation index (ASI) ranging from 0.66 to 1.01. Almost all the rocks display similar arc-related geochemical features characterized by the enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) together with the depletion in high field strength elements (HFSE). The chondrite-normalized REE patterns show no to marked negative Eu anomaly (Eu/Eu* = 0.55 to 1.12), (La/Yb)(N) = 8.16 to 31, (La/Sm)(N) = 2.80 to 10.59, and (Tb/Yb)(N) = 0.84 to 2.40. The evaluation of the REE patterns for the KRB magmas and the comparison of the trace element ratios with experimental studies indicate a chemically enriched lithospheric mantle source composed of garnet-spinel-lherzolite that have underwent a low degree of partial melting < 5% to generate the KRB intrusions. Based on the present data, we infer that the mantle source was contaminated by a subduction component and the melting of the mantle lithosphere occurred by local extension in an overall convergent regime in NW Iran. The extension regime during the Eocene is proposed to be the result of the Neo-Tethys slab roll-back and the Sevan-AkeraQaradagh (SAQ) slab break-off.
Two types of spatially and temporally associated Jurassic granitic rocks, I-type and A-type, occur as pluton pairs in several locations in southern Hunan Province, South China. This paper aims to investigate the genetic relationships and tectonic mechanisms of the co-development of distinct granitic rocks through petrological, geochemical and geochronological studies. Zircon LA-ICPMS dating results yielded concordant U-Pb ages ranging from 180 to 148 Ma for the Baoshan and Tongshanling I-type granodiorites, and from 180 to 158 Ma for the counterpart Huangshaping and Tuling A-type granites. Petrologically, the I-type granodiorites consist of mafic minerals such as hornblende whereas the A-type granites are dominated by felsic minerals (e.g., quartz, K-feldspar and plagioclase). Major and trace element analyses indicate that the I-type granodiorites have relatively low SiO2 (64.5-71.0%) and relatively high TiO2 (0.28-0.51%), Al2O3 (118-15.5%), total FeO (2.3-4.7%), MgO (1.3-2.6%) and P2O5 (0.10-0.23%) contents, and the A-type granites are characterized by high concentrations of Rb (212-1499 ppm), Th (18.3-52.6 ppm), U (11.8-33.6 ppm), Ga (20.0-36.6 ppm), Y (27.1-134.0 ppm) and HREE (20.3-70.0 ppm), with pronounced negative Eu anomalies (Eu/Eu* = 0.01-0.15). Moreover, the I-type granodiorites are classified as collision-related granites emplaced under a compressional environment, whereas the A-type granites are within-plate granites generated in an extensional setting. Zircon Hf isotopic compositions vary substantially for these granitic rocks. The I-type granodiorites are characterized by relatively young Hf model ages (T-DM1 = 1065-1302 Ma, T-DM(C) = 1589-2061 Ma) and moderately negative epsilon Hf(t) values (-5.9 to -11.5), whereas the A-type granites have very old model ages (T-DM1 = 1454-2215 Ma, T-DM(C) = 2211-2974 Ma) and pronounced negative epsilon Hf(t) values (-15.8 to -28.3). These petrochemical and isotopic characteristics indicate that the I-type granodiorites may have been derived from a deep source involving mantle-derived juvenile (basaltic) and crustal (pelitic) components, whereas the A-type granites may have been sourced from melting of meta-greywacke in the crust. This study proposes that the pressure and temperature differences in the source regions caused by combined effects of intra-plate mantle upwelling and plate subduction are the major controlling factors of the co-development of the two different types of magmas. Crustal anatexis related to litho-spheric delamination and upwelling of hot asthenosphere under a high pressure and temperature environment led to the formation of the I-type magmas. On the other hand, the A-type magmas were formed from melting of the shallower part of the crust, where extensional stress was dominant and mantle-crust interaction was relatively weak. Rifts and faults caused by mantle upwelling developed from surface to depth and successively became channels for the ascending I- and A-type magmas, resulting in the emplacement of magmas in adjacent areas from sources at different depths.
The Younger Granites of Yahmid-Um Adawi area, located in the southeastern part of Sinai Peninsula, comprise two coeval Late Neoproterozoic post-collisional alkaline (hypersolvous alkali-feldspar granites; 608-580 Ma) and calc-alkaline (transsolvous monzo- and syenogranites; 635-590 Ma) suites. The calc-alkaline suite granitoids are magnesian and peraluminous to metaluminous, whereas the alkaline ones are magnesian to ferroan alkaline to slightly metaluminous. Both granitoid suites exhibit many of the typical geochemical features of A-type granites such as enrichment in Nb ( > 20 ppm), Zr ( > 250 ppm), Zn ( > 100 ppm) and Ce ( > 100 ppm) and high 10000*Ga/Al2O3 ratios ( > 2.6) and Zr + Nb + Y + Ce ( > 350 ppm). Accessory mineral saturation thermometers demonstrated former crystallization of apatite at high temperatures prior to zircon and monazite separation from the magma for both granitoid suites. The mild zircon saturation temperatures of the studied Younger Granites (around 800 degrees C) imply low-temperature crustal fusion and incomplete melting of the largely refractory zircon. The two Younger Granite suites were semi-synchronously evolved during the post-collisional stage of the Arabian-Nubian Shield subsequent to the collision between the juvenile shield crust and the older pre-Neoproterozoic continental blocks of west Gondwana. Their parental magmas has been generated by melting of crustal source rocks with minor involvement from mantle, which might participated chiefly as a source of heat necessary for fusion of the crustal precursor. Extensive in-situ gamma-ray spectrometry revealed anomalously high radioactivity of some Younger Granite exposures along Wadi Urn Adawi (eU; 388-746 ppm and eTh; 1857-2527 ppm) and pegmatitic pockets pertaining to the calc-alkaline suite (equivalent U and Th; 212-252 ppm and 750-1757 ppm, respectively). The radioactivity of the syngenetic pegmatites arises from the primary radioactive minerals uranothorite and thorite together with the U- and/or Th-bearing minerals zircon, columbite, samarskite and monazite. The anomalously high radioactivity of some Younger Granite exposures in Wadi Urn Adawi stem from their appreciable enclosure of the epigenetic uranium minerals metatorbenite and uranophane.
This paper presents findings from a comprehensive geochemical and geophysical re-examination of known radiogenic anomalies in Tertiary limestones and (sub-)recent calcretes of southwestern Dhofar in the Sultanate of Oman. U-Th-enrichments seem to be associated with deep-rooted fault systems that cross-cut C ore -rich shales at depths of some 800-1000 m, which generally show elevated gamma-ray levels in southern Oman and act as the initial geochemical trap. Metals and radiogenic elements, such as K (max 1945 ppm), U (max 44 ppm), and Th (max 26 ppm) mobilised from these rocks and emplaced higher up in the faults must have constituted radiogenic lineaments at and near the surface (observed in a different but difficult to access location). However, successive weathering partially obscured such anomalies through further re-mobilisation/-mineralisation processes within the calcretes that also enriched Sr and V. In these carbonates, uranium correlates positively with Sr but not very well with V, while thorium shows moderate positive correlations with Sr and V. Both U and Th are also not present (i.e., below the detection limits of a few ppm) in a second sample group that represents background conditions. Being much more immobile than U, Th remained closer to the original western fault positions of the examined site (outlined by magnetics and VLF-EM during the surveys), while uranium moved down-dip over the plateau and through underlying sub-horizontal strata towards the eastern fault system. Here, supergene Sr-enriched calcite preferentially incorporated U, thus reflecting the observed U-Th fractionation.
The Sangan Magmatic complex (SMC) is, a large I-type magmatic complex, located in the northeastern Iran. Zircons extracted from the intrusive and volcanic rocks within the SMC record a similar Hf compositions and REE patterns, indicating that these chemical signatures have likely been inherited from the same source and simple history of magmatic crystallization during the evolution of the orogeny. The zircon from volcanic rocks yield Ti-in-zircon crystallization temperatures of 667-1145 degrees C with average temperatures of 934 degrees C while those from granitoids indicate crystallization temperatures of 614-898 degrees C with an average of 812 degrees C. Ti-in-zircon, Ti in biotite thermometries also indicates that the crystallization temperatures of volcanic rocks are relatively higher than those of granitoids. The biotite chemistry studies reveal that this mineral crystallized at approximately 725*-800 degrees C and 758 to 816 degrees C for granitoid and volcanic rocks, respectively, which is similar to obtained temperatures by Zir-saturation of Eq. (1). T-zicsat and T-magma trend lines on the T-SiO2 diagram cross at high silica contents of- 68 wt.%, at which temperature the magma becomes zircon-saturated and new zircons are crystallized. The zircon REE data including Ce/Ce*, Eu/Eu*, and Th/U ratios suggest that SMC igneous rocks are formed from oxidized magma. However, the zircon Th/U and Hf data suggest that the SMC became progressively more oxidized and also indicate lower temperatures from volcanic and plutonic rock with decreasing time.
The Quaternary alkaline volcanic field of Southern Turkey is characterized by infra-continental plate-type magmatic products, exposed to the north of the Iskenderun Gulf along a NE-SW trending East Anatolian Fault, to the west of its intersection with the N-S trending Dead Sea Fault zone. The Iskenderun Gulf alkaline rocks are mostly silica-undersaturated with normative nepheline and olivine and are mostly classified as basanites and alkaline basalts with their low-silica contents ranging between 43 and 48 wt.% SiO2. They display Ocean Island Basalt (OIB)-type trace element patterns characterized by enrichments in large-ion-lithophile elements (LILE) and light rare earth element (LREE), and have (La/Yb)(N) = 8.8-17.7 and (Hf/Sm)(N) = 0.9-1.6 similar to those of basaltic rocks found in intraplate suites. The basanitic rocks have limited variations Sr-Nd isotopic ratios (Sr-87/Sr-86 = 0.70307-0.70324, Nd-143/Nd-144 = 0.512918-0.521947), whereas the alkali basalts display more evolved Sr-Nd isotopic ratios (Sr-87/Sr-86 = 0.70346-0.70365, Nd-143/Nd-144 = 0.512887-0.521896). The Iskenderun Gulf alkaline rocks also display limited Pb isotopic variations with Pb-206/Pb-204 = 18.75-19.09 Pb-207/Pb-204 = 15.61-15.66 and Pb-208/Pb-204 = 38.65-39.02, indicating that they originated from an enriched lithospheric mantle source. Calculated fractionation vectors indicate that clinopyroxene and olivine are the main fractionating mineral phases. Similarly, based on Sr-Nd isotopic ratios, the assimilation and fractional crystallization (AFC) modeling shows that the alkali basalts were affected by AFC processes (r = 0.2) and were slightly contaminated by the upper crustal material. The high TiO2 contents, enrichments in Ba and Nb, and depletions in Rb can likely be explained by the existence of amphibole in the mantle source, which might, in turn, indicate that the source mantle has been affected by metasomatic processes. The modeling based on relative abundances of trace elements suggests involvement of amphibole-bearing peridotite as the source material. Iskenderun Gulf alkaline rocks can thus be interpreted as the products of variable extent of mixing between melts from both amphibole-bearing peridotite and dry peridotite.
The Shah Soltan Ali area (SSA) is located in the eastern part of the Lut Block metallogenic province. In this area different types of sub-volcanic intrusions including diorite porphyry, monzonite porphyry and monzodiorite porphyry have intruded into basaltic and andesitic rocks. Zircon U-Pb dating and field observations indicate that intermediate to mafic volcanic rocks (38.9 Ma) are older than subvolcanic units (38.3 Ma). The subvolcanic intrusions show high-K calc-alkaline to shoshonitic affinity and are metaluminous. Based on mineralogy, high values of magnetic susceptibility [(634 to 3208) x 10(-5) SI], and low initial Sr-87/Sr-86 ratios, they are classified as belonging to the magnetite-series of oxidant I-type granitoids and are characterized by an enrichment in LREEs relative to HREEs, with negative Nb, Ti, Zr and Eu anomalies. These granitoids are related to volcanic arc (VAG) and were generated in an active continental margin. Low initial Sr-87/Sr-86 ratios (0.7043 to 0.7052) and positive epsilon Nd values ( +1.48 to +3.82) indicate that the parental magma was derived from mantle wedge. Parental magma was probably formed by low degree of partial melting and metasomatized by slab derived fluids. Then assimilation and fractional crystallization processes (AFC) produced the SSA rocks. This magma during the ascent was contaminated with the crustal material. All data suggest that Middle-Late Eocene epoch magmatism in the SSA area, occurred during subduction of Neo-Tethys Ocean in east of Iran (between Afghan and Lut Blocks).
Carbon isotope (delta C-13) and rare earth element (REE) concentrations in representative samples of the shallow marine Subathu Formation, explored from the Neelkanth and Dogadda sections of Northwestern Himalaya (India) were determined to infer the palaeo-environmental condition during the late Paleocene and middle Eocene. delta C-13 values show variation of similar to 5.0 parts per thousand with maximum excursion (-27.34 parts per thousand) in calcareous sandstone at the basal part and minimum (-22 parts per thousand) in red shale towards the terminal end. Total REE concentration varies (due to lithology) from 27.23 ppm to 564.35 ppm with an average of 187.60 ppm. The chondrite and PAAS normalized patterns exhibit positive Ce anomaly (0.95-4.45), enriched LREE, and depleted HREE, medium Y/Ho ratio (similar to 30-45) along with positive correlation between Y/Dy and Y/Ho ratio. In addition, calcite veins present in some shale samples indicate redox sensitive trace elements. The overall REE abundance and distribution suggests highly oxygenated environment under the shallow marine regressive phase of deposition. The depositional setting, biostratigraphical constrained age along with delta C-13 values and lower TOC suggested an intense warm period, that might be coeval with the Paleocene-Eocene Thermal Maxima event (PETM).
In Central Iran, the mixed siliciclastic‒carbonate Nakhlak Group of Triassic age is commonly seen to have a Cimmerian affinity, although it shows considerable resemblances with the Triassic Aghdarband Group in far northeastern Iran, east of Kopeh-Dagh area, with Eurasian affinity. The Nakhlak Group is composed of the Alam (Late Olenekian‒Anisian), Baqoroq (Late Anisian‒?Early Ladinian), and Ashin (Ladinian‒?Early Carnian) formations consisting mainly of volcanoclastic sandstone and shale and fossiliferous limestone. The Baqoroq Formation contains also metamorphic detritus. Sandstone petrofacies reflect the detrital evolution from active volcanism to growing orogen and again active volcanism. Textural and modal analyses of volcanic lithic fragments from the Alam Formation reflect the eruption style and magma composition of a felsic to intermediate syn-sedimentary arc activity. The detrital modes of the Baqoroq Formation sediments suggest a recycled orogenic source followed by arc activity in a remnant fore-arc basin. The sandstone samples from the Ashin Formation demonstrate a continuity of felsic to intermediate arc activity. Major and trace element concentrations of the Nakhlak Group clastic samples support sediment supply from first-cycle material and felsic magmatic arc input. The enrichment in LREE, the negative Eu anomalies, and the flat HREE patterns indicate origination from the old upper continental crust and young arc material. The chemical index of alteration (CIA ∼51–70 for sandstone and 64–76 for shale samples) indicates medium degrees of chemical weathering at the source. Petrographical and geochemical evidence together with facies analysis constructed the following depositional conditions for the Nakhlak Group sediments: In the Olenekian, a fore-arc shallow to deep marine depositional basin developed that later was filled by recycled and arc-related detritus and changed into a continental basin in the Anisian. Ladinian extension let to a deepening of the basin. With respect to the similarities between the Nakhlak and Aghdarband (NE Iran) groups and unusual present-day position of the Nakhlak Group with no stratigraphic connection to the surrounding area, the development of first a fore-arc basin and later change into a back-arc depositional basin in close relation with the Aghdarband basin at the southern Eurasian active margin in the Triassic are here proposed. Understanding the basin development recorded in the Nakhlak Group provides constraints on the closure history of Palaeotethys and of the tectonic evolution of early Mesozoic basins at the southern Eurasian margin before the Cimmerian Orogeny.
Any progress in our understanding of low-temperature mineral assemblages and of quantitative physicochemical modeling of stability conditions of mineral phases, especially those containing toxic elements like selenium, strongly depends on the knowledge of structural and thermodynamic properties of coexisting mineral phases. Interrelation of crystal chemistry/structure and thermodynamic properties of selenium-containing minerals is not systematically studied so far and thus any essential generalization might be difficult, inaccurate or even impossible and erroneous. Disagreement even exists regarding the crystal chemistry of some natural and synthetic selenium-containing phases. Hence, a systematic study was performed by synthesizing ferric selenite hydrates and subsequent thermal analysis to examine the thermal stability of synthetic analogues of the natural hydrous ferric selenite mandarinoite and its dehydration and dissociation to unravel controversial issues regarding the crystal chemistry. Dehydration of synthesized analogues of mandarinoite starts at 56-87 degrees C and ends at 226-237 degrees C. The dehydration happens in two stages and two possible schemes of dehydration exist: (a) mandarinoite loses three molecules of water in the first stage of the dehydration (up to 180 degrees C) and the remaining two molecules of water will be lost in the second stage ( > 180 degrees C) or (b) four molecules of water will be lost in the first stage up to 180 degrees C and the last molecule of water will be lost at a temperature above 180 degrees C. Based on XRD measurements and thermal analyses we were able to deduce Fe-2(SeO3)(3)center dot(6-x)H2O (x = 0.0-1.0) as formula of the hydrous ferric selenite mandarinoite. The total amount of water apparently affects the crystallinity, and possibly the stability of crystals: the less the x value, the higher crystallinity could be expected.
Paleogene igneous rocks from similar to 600 km Quchan-Sabzevar-Torud magmatic belt include a thick pile of volcanic and pyroclastic rocks which intruded by younger felsic-mafic plutons. Various types of mineralization including Iron Oxide-Copper-Gold (e.g., Firouzeh mine) and porphyry Cu-Au deposits (e.g., Jalambadan mine) are associated with the Quchan-Sabzevar magmatism. In this study, we describe new zircon U-Pb ages and geochemicalisotopic data of the subvolcanic rocks from near the Firouzeh mine. The Firouzeh subvolcanic rocks consist of (quartz-bearing) monzosyenites, monzodiorites and monzonites. These rocks have typical talc-alkaline signature and are mainly metaluminous in nature. Subvolcanic rocks display enrichment in Light Rare Earth Elements (LREEs) with negative Eu anomaly. Enrichment in Large Ion Lithophile Elements (LILEs) and depletion in High Field Strength Elements (HFSEs) are geochemical characteristics of these rocks. The Firouzeh volcanic rocks also display talc-alkaline signature and are metaluminous to peraluminous. Volcanic rocks show both enrichment in LREEs and LILEs, associated with negative Eu anomaly. Zircon U-Pb indicates ages of 43.2 +/- 0.4, 42.1 +/- 0.4 and 41.8 +/- 0.4 Ma for monzosyenites, monzodiorites and monzonites respectively. Zircon epsilon Hf(t) shows average values of -1.49 for monzonites, +9.07 for monzodiorites and -1.06 for monzosyenites. The Hf model ages for these rocks are in the range of 850-730, 270-180 and 3150-450 Ma, respectively. Inherited zircons are abundant in monzonites and have variable Hf isotope values. The wide range of zircon eHfct) values and abundance of inherited/xenocrystic zircons suggest a multiple source(s) for the generation of the Firouzeh subvolcanic rocks, including a mantle melt and an old crustal component. Xenocrystic zircons indicate complex crustal components. We suggest the NE Iran subvolcanic rocks including the Firouzeh igneous rocks, generated above the Sabzevar subduction zone. This subduction zone was active since Late Cretaceous time.
The Cemilkoy ignimbrite is one of the voluminous ignimbrite deposits in Cappadocia. The Cemilkoy ignimbrite contains pumice and lithic clasts of volcanic and ophiolitic origin in an ash matrix. The unwelded Cemilkoy ignimbrite is distinguished from other deposits in Cappadocia by flattened pumices, elongate vesicles and a slaty fabric. The mineral assemblage of the Cemilkoy ignimbrite is plagioclase, biotite, quartz and oxides (magnetite and Ti-magnetite) and the matrix is glassy. Eutaxitic texture is dominant and all pumice clasts have a vitrophyric-porphyritic texture. The same textural properties were observed throughout the spatial distribution of CemilkOy ignimbrite. Microprobe studies reveal that plagioclase compositions range from albite through oligoclase-andesine. Estimated plagioclase-liquid temperatures (T) and pressures (P) are varying between 806 and 847 degrees C and 4.2-7.1 (kbar), and the H2O content of the melt is estimated to have been 5 wt.% from the pumice clasts. Based on geochemical data, the Cemilkoy ignimbrite is rhyolitic and calc-alkaline in character, and all pumice clasts are enriched in LIL and LRE elements relative to I-IFS elements. Negative Nb, Ta and Ti anomalies, ratios of Ba/Nb > 28 (56-77), Ba/Ta (>)450 (590-700) and Th/Yb vs. Ta/Yb are consistent with a subduction-related origin. According to the geochemical and mineralogical-petrographical data, the Cemilkoy ignimbrite originated from partial melting of a mantle source which was enriched during previous subduction processes with variable degrees of assimilation fractional crystallization (AFC) through time and Cemilkoy ignimbrite erupted from a crustal magma chamber at shallow to intermediate depth.
Acapulcoites (most ancient Hf-W ages are 4,563.1 +/- 0.8 Ma), lodranites (most ancient Hf-W ages are 4,562.6 +/- 0.9 Ma) and rocks transitional between them are ancient residues of different degrees of partial melting of a chondritic source lithology (e.g., as indicated by the occurrence of relict chondrules in 9 acapulcoites), although the precise chondrite type is unknown. Acapulcoites are relatively fine- grained (similar to 150-230 mu m) rocks with equigranular, achondritic textures and consist of olivine, orthopyroxene, Ca rich clinopyroxene, plagioclase, metallic Fe,Ni, troilite, chromite and phosphates. Lodranites are coarser grained (540-700 mu m), with similar equigranular, recrystallized textures, mineral compositions and contents, although some are significantly depleted in eutectic Fe,Ni-FeS and plagioclase- clinopyroxene partial melts. The acapulcoite-lodranite clan is most readily distinguished from other groups of primitive achondrites (e.g., winoanites/IAB irons) by oxygen isotopic compositions, although more than 50% of meteorites classified as acapulcoites currently lack supporting oxygen isotopic data. The heat source for melting of acapulcoites-lodranites was internal to the parent body, most likely Al-26, although some authors suggest it was shock melting. Acapulcoites experienced lower temperatures of similar to 980-1170 degrees C and lower degrees of partial melting (similar to 1-4 vol.%) and lodranites higher temperatures of similar to 1150-1200 degrees C and higher degrees (similar to 5 >= 10 vol.%) of partial melting. Hand-specimen and thin section observations indicate movement of Fe,Ni-FeS, basaltic, and phosphate melts in veins over micrometer to centimeter distances. Mineralogical, chemical and isotopic properties, Cosmic Ray Exposure (CRE) ages which cluster around 4-6 Ma and the occurrence of some meteorites consisting of both acapulcoite and lodranite material, indicate that these meteorites come from one parent body and were most likely ejected in one impact event. Whereas the precise parent asteroid of these meteorites is unknown, there is general agreement that it was an S-type object. There is nearly total agreement that the acapulcoite-lodranite parent body was <similar to 100 km in radius and, based on the precise Pb-Pb age for Acapulco of 4555.9 +/- 0.6 Ma, combined with the Hf/W and U/Pb records and cooling rates deduced from mineralogical and other investigations, that the parent body was fragmented during its cooling which the U/Pb system dates at precisely 4556 +/- 1 Ma. Hf-W chronometry suggests that the parent body of the acapulcoites-lodranites and, in fact, the parent bodies of all "primitive achondrites" accreted slightly later than those of the differentiated achondrites and, thus, had lower contents of Al-26, the heat producing radionuclide largely responsible for heating of both primitive and differentiated achondrites. Thus, the acapulcoite-lodranite parent body never experienced the high degrees of melting responsible for the formation of the differentiated meteorites, but arrested its melting history at relatively low degrees of similar to 15 vol.%. (C) 2017 Elsevier GmbH. All rights reserved.
The Imiter inlier at the eastern Anti-Atlas chain (Morocco) hosts a world-class epithermal Ag-Hg deposit, and several occurrences of sulfide-magnetite mineralization. These occurrences are confined to transcurrent faults that cut mildly to highly potassic I- and S-type granite intrusions (e.g., Igoudrane, Bou Teglimt, Taouzzakt and Bou Fliou). In this contribution, we present new field, petrographic and microanalytical data of the Bou Fliou sulfidemagnetite mineralization in the northwestern part of the Bou Teglimt granodiorite intrusion (567 +/- 6Ma). Field and microscopic investigations reveal pervasive silicification and potassic alteration associated with iron oxides-rich ( > 10 vol %) veins, stockworks, and breccias along NE-SW faults. The ore minerals are mainly magnetite, hematite, chalcopyrite, pyrite, sphalerite, Ag-galena, cobaltite, and less abundant Bi-sulfosalts (i.e., cosalite, galenobistmuthite, and llilanite-gustavite). The low-titanium iron oxides (magnetite and hematite), widespread iron-rich breccia, association with crustal scale fault zone, pervasive alteration, and overprinting mineral assemblages suggest a shallow level IOCG-style mineralization. High-order splays of the major fault zone could have provided effective traps for magmatic and basinal Cu and Zn-Pb hydrothermal fluids. The similar to 550 Ma intrusive phases in the region could have contributed by fluid, elements or heat in a local effective blumbing. The mineralogical and ore textural criteria reflecting ore formation at a realtively shallow crustal environment, but a fluid inclusion study is needed to characterize the ore fluids and mechanism of ore deposition.
Carbon and nitrogen elemental (C-N, wt%) and isotopic (delta C-13-delta N-15, parts per thousand) investigation has been carried out on alluvial and deltaic soils from the Padanian plain (northern Italy), an area interested by intensive agricultural activities, to refine previous inferences on depositional facies, pedogenetic processes and anthropogenic influences. Soil analysis, carried out by EA-IRMS, have been focused on inorganic and organic fractions properly speciated by a thermally-based method, whereas further insights on the organic matter constituents have been obtained by sequential fractionation. The bulk EA-IRMS analyses reveal a remarkable compositional heterogeneity of the investigated soils (TC 0.89 to 11.93 wt%, TN 0.01 to 0.78 wt%, delta C-13(TC )-1.2 to -28.2460, delta N-15 -1.2 to 10.0 parts per thousand) that has to be explained as an integration between inorganic and organic pools. The latter have been subdivided in Non-Extractable Organic Matter (NEOM, delta C-13 -16.3 to -28.6 parts per thousand) and in extractable fractions as Fulvic (FA, delta C-13 -24.7 to -27.5 parts per thousand, delta N-15 0.6 to 5.7 parts per thousand) and Humic (HA, delta C-13 -24.6 to -27.0 parts per thousand, delta N-15 1.0 to 9.7 parts per thousand) Acids, which have been used to infer soil dynamics and Soil Organic Matter (SOM) stability processes. Results indicate that SOM at depth of 100 cm was generally affected by microbial reworking, with the exception of clayey and peaty deposits in which biological activity seems inhibited. Peaty and clayey soils display an organic fraction loss of ca. 20% toward the surface, suggesting deterioration possibly induced by intensive agricultural activities. These latter may be the cause of the ubiquitous losses of organic fraction throughout the investigated area over the last seventy years, evaluated by the comparison with historical data on corresponding topsoils. The obtained insights are very important because these soils are carbon (and nitrogen) sinks that are vulnerable and can be degraded, loosing agricultural productivity and potentially contributing to greenhouse gases fluxes.
Coastal dune (CD) and beach sand samples were mineralogically and chemically studied to assess the weathering rates in a coastal area surrounded by the Trans-Mexican Volcanic Belt (TMVB). The study area is a narrow coastal plain with sub-humid warm weather and vigorous coastal dynamics located in the Western Gulf of Mexico (WGM). Our results show that the grain size parameters remain homogeneous along nine CD and beach sites, probably due to the hydrodynamic mechanisms prevailing in the area, i.e. wind deflation, longshore currents, and waves. The minerals found in the CD and beach sands are enriched in recycled, highly corroded monocrystalline quartz (Qm), with loss of plagioclase (P) and olivine (ol), with ilmenite fractions (op) especially in the northern sites. The geochemical data show that the sands are controlled by the exhumation of the TMVB rocks composed of a high volcanic lithic content with lathwork, microlithic, and negligible vitric textures. These volcanic fractions are in agreement with the presence of lavas of calc alkaline, andesite, Na-alkaline lavas, and rhyolite tuffs derived from the TMVB. Significant Spearman Rank Correlations (SRCs) resulted from high silica, titanium, iron, magnesium, calcium, vanadium, chromium, cobalt, associated with the presence of Qm, ilmenite, clinopyroxene, shell fragments, and volcanic lithics. Monocrystalline quartz enrichments, compared to a quartz dilution effect (< Qm; < Qm) at the northern and southern beach sites, reflect the vigorous coastal dynamics. The presence of ilmenite lag deposits in the northern sites indicate that high energy hydrodynamic conditions prevail at the site. The rare earth element (REE) patterns support the mineralogical and compositional framework of the CD and beach sands as part of the TMVB exhumation. We used various chemical indices such as the Chemical Index of Alteration (CIA), the Chemical Index of Weathering (CIW), the Plagioclase Index of Alteration (PIA), and the Weathering Index of Plagioclase (WIP). The WIP values reflect the depletion of mobile elements such as Ca, Na, K, and enrichment of Qm at the northern beach sites, e.g. the Istirinchia site. The CIA/WIP ratio of 2.13 indicates intermediate weathering under warm climatic conditions and recycling of CD and beach sands.
