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Provenance and tectonic setting of Upper Triassic turbidites in the eastern Tethyan Himalaya: Implications for early-stage evolution of the Neo–Tethys

Year: 2020
Products: New Wave;
Authors: Liu, Y;Dai, J;Wang, C;Li, H;Wang, Q;Zhang, L;
Journal: Earth-Science Reviews

Upper Triassic turbidites in the eastern Tethyan Himalaya preserve archives for early–stage evolution of the Neo–Tethys. However, their provenance and tectonic setting remain controversial. Here we report petrographic, detrital zircon UPb and trace element data of newly discovered sandstones interbedded with layered basalts and whole–rock geochemical data of basalts from the Yumen mélange within Upper Triassic turbidites, and the same types of published data from associated terranes in the eastern Gondwana are compiled for comparison. The interbedded sandstones are dominated by quartz, lithics fragments and plagioclase grains, resembling those of the Langjiexue Group. All samples display similar ranges of detrital zircon UPb ages, with significant age populations at 280–210 Ma, 650–450 Ma and 1200–800 Ma, comparable to those of the Langjiexue Group and coeval turbidites from Western Myanmar and partly from Central Tethyan Himalaya, implying they should share identical provenance. Trace elements of 300–200–Ma–aged zircons indicate they were derived from a continental magmatic arc. Geochemical data from interbedded basalts display typical within–plate–basalt affinity. Synthesized with regional geological setting, the above observations suggest Upper Triassic turbidites from Eastern and part of Central Tethyan Himalaya, and Western Myanmar were deposited in a marine rift basin of Indian passive continental margin with their primary provenance from Lhasa. However, other contemporaneous turbidites from part of Central Tethyan Himalaya and Australia had distinct primary sources from Indian continent and West Papua, respectively, indicating they may have separate deposystems.

PET/MRI enables simultaneous in vivo quantification of β-cell mass and function

Year: 2020
Products: NWR213;New Wave;New Wave Research;
Authors: Michelotti, FC;Bowden, G;Küppers, A;Joosten, L;Maczewsky, J;Nischwitz, V;Drews, G;Maurer, A;Gotthardt, M;Schmid, AM;Pichler, BJ;
Journal: Theranostics

Non-invasive imaging of β-cells represents a desirable preclinical and clinical tool to monitor the change of β-cell mass and the loss of function during pre-diabetic stages. Although it is widely accepted that manganese (Mn) ions are actively gated by voltage-dependent calcium channels (VDCC) in response to glucose metabolism, little is known on its specificity in vivo for quantification of islet β-cell function using Mn and magnetic resonance imaging (MRI). On the other hand, glucagon-like-peptide-1 receptor (GLP-1R) represents a validated target for the estimation of β-cell mass using radiolabeled exendin-4 (Ex4) and positron emission tomography (PET). However, a multiparametric imaging workflow revealing β-cell mass and function quantitatively is still missing. Methods: We developed a simultaneous PET/MRI protocol to comprehensively quantify in vivo changes in β-cell mass and function by targeting, respectively, GLP-1R and VDCC coupled with insulin secretion. Differences in the spatial distribution of Mn and radiolabeled Ex4 were monitored overtime in native and transgenic pancreata, characterized by spontaneous pancreatic neuroendocrine tumor development. Follow-up with mass spectrometry imaging (MSI) and autoradiography allowed the ex vivo validation of the specificity of Mn and PET tracer uptake and the detection of endogenous biometals, such as calcium and zinc, throughout the endocrine and exocrine pancreas. Results: Our in vivo data based on a volumetric PET/MRI readout for native pancreata and insulinomas connects uptake of Mn measured at early imaging time points to high non-specific binding by the exocrine tissue, while specific retention was only found 24 h post injection. These results are supported by cross-validation of the spatial distribution of exogenous 55Mn and endogenous 44Ca and 64Zn as well with the specific internalization of the radiolabeled peptide targeting GLP-1R. Conclusion: Simultaneous PET/MR imaging of the pancreas enabled the comprehensive in vivo quantification of β-cell function and mass using Mn and radiolabeled Ex4. Most important, our data revealed that only late time-point measurements reflect the Mn uptake in the islet β-cells, while early time points detect non-specific accumulation of Mn in the exocrine pancreas.

The passive margin of northern Gondwana during Early Paleozoic: Evidence from the central Tibet Plateau

Year: 2020
Products: UP213;New Wave;
Authors: Liu, Y;Li, S;Santosh, M;Cao, H;Yu, S;Wang, Y;Guo, R;Xu, L;Zhou, J;Zhou, Z;
Journal: Gondwana Research

The central–south domain of the Tibet Plateau represents an important part of the northern segment of Gondwana during the early Paleozoic. Here we present zircon U–Pb, Lu–Hf isotope, and whole–rock geochemical data from a suite of early Paleozoic magmatic rocks from the central Tibet Plateau, with a view to gain insights into the nature and geotectonic evolution of the northern margin of Gondwana. Zircon grains in four granitic rocks yielded ages of 532−496 Ma with negative εHf(t) values (−13.7 to −0.6). Zircon grains in meta–basalt and mafic gneiss yielded ages of 512 ± 5 Ma and 496 ± 6 Ma, respectively. Geochemically, the granitic rocks belong to high–K calc–alkaline and shoshonitic S–type granite suite, with the protolith derived from the partial melting of ancient crustal components. The mafic gneiss and meta–basalt geochemically resemble OIB (Oceanic Island Basalt) and E–MORB (Enriched Mid–Ocean Ridge Basalt), respectively. They were derived from low degree (∼5–10%) partial melting of an enriched mantle (garnet and spinel lherzolite) that was contaminated by upper crustal components. The parental magmas experienced orthopyroxene–dominated fractional crystallization. Sedimentological features of the Cambrian–Ordovician formations indicate that the depositional cycle transformed from marine regression to transgression leading to the formation of parallel/angular unconformities between the Cambrian and Ordovician strata. The hiatus associated with these unconformities are coupled with the peak of the early Paleozoic magmatism in Tibet Plateau, indicating a tectonic control. We conclude that the Cambrian–Ordovician magmatic suite and sedimentary rocks formed in an extensional setting, and we correlate this with the post–peak stage of the Pan–African orogeny. The post–collision setting associated with delamination, orogenic collapse or lithospheric extension along the northern margin of Gondwana, can account for the Cambrian–Ordovician magmatism and sedimentation, rather than oceanic subduction along the external margin. We thus infer a passive margin setting for the northern Gondwana during the Early Paleozoic.

Late Neoarchean reworking of the Mesoarchean crustal remnant in northern Liaoning, North China Craton: A U–Pb–Hf–O–Nd perspective

Year: 2020
Products: UP213;New Wave;
Authors: Li, Z;Wei, C;Chen, B;Fu, B;Gong, M;
Journal: Gondwana Research

How the earth's crust formed and evolved during the Precambrian times is one of the key questions to decipher the evolution of the early Earth. As one of the few cratons containing well-preserved Eoarchean to Neoarchean basement on Earth, the North China Craton is an ideal natural laboratory to unravel the early crustal evolution. It is controversial whether the Archean tectonothermal events in this area represents reworking or growth of the continental crust. To solve this issue, we have compelled field-based mapping, zircon U–Pb dating by SHRIMP RG and LA–ICP–MS U–Pb, zircon SHRIMP SI oxygen and LA–MC–ICP–MS Hf isotope, and whole-rock Nd–O isotope analyses from the Archean granitoids in northern Liaoning, North China Craton. On the basis of zircon U–Pb isotopic dating and measured geological section investigation, two distinct magmatic suites as enclaves in the Jurassic granites are recognized, viz. a newly discovered 3.0 Ga crustal remnant and a 2.5 Ga granitoid. The Mesoarchean zircons from the 3.0 Ga granodioritic gneisses exhibit heterogeneous Hf isotopic compositions, with the most radiogenic analysis (εHf(t) = +3.8) following the depleted mantle evolution array and the most unradiogenic εHf(t) extending down to −3.4. This implies that both ancient continental crust at least as old as 3.4 Ga and depleted mantle contributed to the magma source of the protoliths of the Mesoarchean gneisses. The εHf(t) values of the Neoarchean zircons from these gneisses overlap the 3.4–3.0 Ga zircon evolution trend, indicating that the ancient crustal materials have been reworked during the late Neoarchean. The Neoarchean zircons from the 2.5 Ga granitoids have a relatively small variation in the Hf isotope and are mainly plotted in the 3.0–2.8 Ga zircon evolution field. However, taking all the εHf(t) values of the Neoarchean zircons into the consideration, we find that the Hf model age of the Neoarchean zircon does not represent the time of crustal growth or reworking but are artifacts of magma mixing. The interaction between the magmas derived from the ancient crustal materials and the depleted mantle is also supported by zircon O isotopic data and Hf–O isotopic modeling of the Neoarchean granitoids. Both Mesoarchean and late Neoarchean tectonothermal events involved synchronous crustal growth and reworking, which may be applicable to other parts of the world.

Petrological, geochemical and isotopic data of Neoproterozoic rock units from Uruguay and South Africa: Correlation of basement terranes across the South Atlantic

Year: 2020
Products: New Wave;
Authors: Will, T;Höhn, S;Frimmel, H;Gaucher, C;le Roux, P;Macey, P;
Journal: Gondwana Research

Felsic to intermediate igneous rocks from the Cuchilla Dionisio (or Punta del Este) Terrane (CDT) in Uruguay and the Várzea do Capivarita Complex (VCC) in southern Brazil were emplaced in the Tonian and experienced high-grade metamorphism towards the end of the Cryogenian. Geological and geochemical data indicate an S-type origin and formation in a continental within-plate setting by recycling of lower crustal material that was initially extracted from the mantle in the Palaeoproterozoic. Similar felsic igneous rocks of Tonian age occur in the Richtersveld Igneous Complex and the Vredefontein and Rosh Pinah formations in westernmost South Africa and southern Namibia and have been correlated with their supposed equivalents in Uruguay and Brazil. Geochemical and isotope data of the largely unmetamorphosed felsic igneous rocks in southwestern Africa imply a within-plate origin and formation by partial melting or fractional crystallization of mafic rocks that were extracted from the mantle in the Proterozoic. The parental melts of all of these Tonian igneous rocks from South America and southwestern Africa formed in an anorogenic continental setting at the western margin of the Kalahari Craton and were emplaced in, and/or contaminated by, Namaqua Province-type basement after separation from their source region. However, the source regions and the time of extractions thereof are different and, moreover, occurred at different palaeogeographical latitudes.

Transition from oceanic subduction to continental collision recorded in the Bangong-Nujiang suture zone: Insights from Early Cretaceous magmatic rocks in the north-central Tibet

Year: 2020
Products: NWR213;
Authors: Wang, W;Wang, M;Zhai, Q;Xie, C;Hu, P;Li, C;Liu, J;Luo, A;
Journal: Gondwana Research

The transition from oceanic subduction to continental collision is a key stage in the evolution of ancient orogens. We present new data for Early Cretaceous diorite and granite porphyry from north–central Tibet to constrain the evolution of the Bangong–Nujiang Tethyan Ocean (BNTO). The diorites have moderate SiO2 and high MgO contents, similar to high-Mg andesites. Zircon grains yield U–Pb ages of 128–124 Ma and positive εHf(t) values between +13.2 and + 16.3, corresponding to Hf depleted-mantle model ages (TDM) of 281–131 Ma. The high-Mg diorite was probably formed by partial melting of hydrous mantle wedge fluxed by slab-derived fluids in an oceanic subduction setting. The granite porphyries yield zircon U–Pb ages of 117–115 Ma and zircon εHf(t) values ranging from +0.1 to +4.5. Most samples have high SiO2 and Fe2O3T contents, variable FeOT/MgO and Ga/Al ratios, and are depleted in Ba, Sr, P, and Ti, similar to I- and A-type granites. The granite porphyries were most likely derived from partial melting of juvenile dioritic or granodioritic crust due to break-off of the BNTO lithosphere following collision between the Lhasa and Qiangtang blocks. The Early Cretaceous high-Mg diorite and A-type granite porphyry thus record the Early Cretaceous transition from oceanic subduction to continental collision along the Bangong–Nujiang suture zone (BNSZ).

Pore connectivity characterization of shale using integrated wood's metal impregnation, microscopy, tomography, tracer mapping and porosimetry

Year: 2020
Products: New Wave;
Authors: Zhao, J;Hu, Q;Liu, K;Jin, Z;Dultz, S;Kaufmann, J;Fan, Y;
Journal: Fuel

The pore connectivity of tight shale reservoirs plays an essential role in the movement of shale gas and oil, however, the characteristics of connected pores in shale with a multi-scale and coupled pore-fracture system are poorly constrained. Working with typical American (Barnett and Eagle Ford) and Chinese (Longmaxi) shale samples in 2D/3D spaces at nano- to mm-scales, connective pores were intruded with a molten alloy (Wood’s metal; WM) under a temperature of ~85 °C and high pressure (60, 300, and 600 MPa) conditions. After solidification of the alloy at room temperature, polished sections were used to map WM components by field emission-scanning electron microscopy (SEM), micro- and nano-X-ray tomography and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). These tests were supplemented with mercury intrusion porosimetry (MIP) for pore-fracture throat size distribution. The shale matrix is generally characterized by low pore connectivity; however, the extent of connectivity within μm-sized and dispersed organic matter (OM) particles is high, with the observed WM-filled pore space ranging from 10% to 70% (averaged at 43%) for the Barnett Shale sample. The grain-edge fractures are important channels to connect multiple OM-hosted pore systems dispersed in shale matrix. Our work illustrates that shales exhibit a dual-connectivity behavior, with the effective porosity decreasing sharply as the distance from the sample boundary increases; the good pore connectivity zone away from the edge of sample is 500 μm under a pressure of 600 MPa for the Barnett Shale sample.

Paratethys pacing of the Messinian Salinity Crisis: Low salinity waters contributing to gypsum precipitation?

Year: 2020
Products: NWR193UC;New Wave;New Wave Research;
Authors: Grothe, A;Andreetto, F;Reichart, G;Wolthers, M;Van Baak, C;Vasiliev, I;Stoica, M;Sangiorgi, F;Middelburg, J;Davies, G;Krijgsman, W;
Journal: Earth and Planetary Science Letters

During the so-called Messinian Salinity Crisis (MSC: 5.97-5.33 Myr ago), reduced exchange with the Atlantic Ocean caused the Mediterranean to develop into a “saline giant” wherein ∼1 million km3 of evaporites (gypsum and halite) were deposited. Despite decades of research it is still poorly understood exactly how and where in the water column these evaporites formed. Gypsum formation commonly requires enhanced dry conditions (evaporation exceeding precipitation), but recent studies also suggested major freshwater inputs into the Mediterranean during MSC-gypsum formation. Here we use strontium isotope ratios of ostracods to show that low-saline water from the Paratethys Seas actually contributed to the precipitation of Mediterranean evaporites. This apparent paradox urges for an alternative mechanism underlying gypsum precipitation. We propose that Paratethys inflow would enhance stratification in the Mediterranean and result in a low-salinity surface-water layer with high Ca/Cl and SO4/Cl ratios. We show that evaporation of this surface water can become saturated in gypsum at a salinity of ∼40, in line with salinities reported from fluid inclusions in MSC evaporites.

Paleoproterozoic melt-depleted lithospheric mantle in the Khanka block, far eastern Russia: Inferences for mobile belts bordering the North China and Siberian cratons

Year: 2020
Products: New Wave;
Authors: Ionov, D;Guo, P;Nelson, W;Shirey, S;Willbold, M;
Journal: Geochimica et Cosmochimica Acta

The eastern part of Asia between the North China and Siberian cratons contains orogenic belts formed by the Paleo-Asian and Pacific subduction and older continental blocks. A fundamental question regarding these and all mobile belts is the fate of the continental lithospheric mantle (CLM) during their formation, i.e. whether, or to what extent the CLM may be formed, replaced or affected during orogeny. Insights into these processes can be obtained from mantle xenoliths hosted by Cenozoic basalts in the Proterozoic Khanka block in the far eastern Russia between NE China and the Pacific coast of Asia. We report petrographic, chemical, and Os-Sr-Nd isotope data for spinel peridotite xenoliths at two Khanka sites: Sviyagin and Podgelban. The modal abundances and chemical compositions suggest that the peridotites are residues of low to moderate degrees of melt extraction from fertile mantle. They show an 187Os/188Os vs. 187Re/188Os correlation with an apparent 1.9 Ga age; the 187Os/188Os ratios are positively correlated with Al2O3 and other melt extraction indices. These results provide the first robust CLM age constraints for the eastern Central Asian Orogenic Belt (CAOB). The ages suggest that the ancient CLM of the Khanka block may be roughly coeval with reworked CLM at Hannuoba (North China craton), and that it persisted through the Phanerozoic orogenies. Moreover, despite the proximity to Phanerozoic subduction zones, the Khanka CLM shows little post-melting enrichment, e.g. the clinopyroxenes are typically LREE-depleted and have Sr-Nd isotope ratios typical of the MORB mantle. We posit that the metasomatism of the CLM, earlier proposed for North China xenolith suites and ascribed to the effects of Pacific or older subduction and related mantle upwelling, may not be widespread in the CAOB. In general, Proterozoic blocks composed of residual peridotites may be more common in the CLM of the SE Siberia and northern China, and possibly other orogenic belts, than previously thought.

Geochemical taphonomy of the Standing Rock Hadrosaur Site: Exploring links between rare earth elements and cellular and soft tissue preservation

Year: 2020
Products: New Wave;
Authors: Ullmann, P;Grandstaff, D;Ash, R;Lacovara, K;
Journal: Geochimica et Cosmochimica Acta

The Standing Rock Hadrosaur Site (SRHS) in South Dakota preserves a mass-death assemblage of the hadrosaurine dinosaur Edmontosaurus annectens in the Upper Cretaceous Hell Creek Formation. A previous study of SRHS bones found many of them to yield microstructures morphologically consistent with vertebrate osteocytes, blood vessels, and proteinaceous matrix upon demineralization with weak acid. To examine the geochemical history of these specimens in detail, we herein document the intra-bone distribution of rare earth elements (REE) within nine of these previously-examined Edmontosaurus limb bones from SRHS. Laser ablation-inductively coupled plasma mass spectrometry was used to determine the trace element composition of the specimens, which revealed the bones to possess unusually low REE concentrations for bones of Mesozoic age, consistent and steep declines in light REE concentrations with increasing cortical depth, and uniformly low concentrations of middle REE and elements with moderate and low diffusivities through the middle cortex. These attributes imply: (1) at least partial preservation of early-diagenetic trace element signatures; (2) that trace element uptake occurred primarily during a single, early-diagenetic phase, and; (3) that the duration of trace element diffusion was brief in these bones. As we previously reported, low permeability of the fine-grain host matrix and early-diagenetic cementation of portions of the host matrix by precipitation of siderite concretions impeded pore fluid replenishment; this partial hindrance of fluid flow was also likely responsible for the minimal trace element uptake observed in the nine SRHS specimens further studied herein. From a paleontological perspective, minimal trace element uptake reflects minimal chemical alteration, meaning bones from this site are predicted to be ideal candidates for preservation of original organics according to hypotheses previously advanced by geochemical studies. Because low REE concentrations reflect limited interaction with groundwaters during diagenesis, we propose that late-diagenetic overprinting of early-diagenetic REE profiles was minimal and that hydrolytic degradation of soft tissues was limited in the burial environment at SRHS. Mitigation of biomolecular decay by hydrolysis would favor ultrastructure stabilization and is therefore advanced as a partial explanation for the preservation of cells and soft tissue microstructures in these fossil bones.

Fluoride-calcium (F-Ca) melt in rhyolitic magma: Evidence from fluorite-rich rhyolites of the Nyalga Basin, Central Mongolia

Year: 2020
Products: NWR213;New Wave;New Wave Research;
Authors: Peretyazhko, I;Savina, E;
Journal: Lithos

Unusual varieties of Early Cretaceous (120 ± 3 Ma) rhyolites in the Nyalga basin (Central Mongolia) bear exceptionally high percentages of fluorite reaching 30–36 wt%. The origin of fluorite in the rhyolites does not fit the existing models of magmatic crystallization in haplogranitic melts or subsolidus postmagmatic and hydrothermal fluoritization. We suggest that the fluorite-enriched rhyolites formed after eruption of magma that contained a mixture (emulsion) of immiscible rhyolitic and F-Ca melts. The F-Ca melt separated from the rhyolitic magma as a result of fluoride-silicate liquid immiscibility when the concentration of F in the Ca-bearing subaluminous–peraluminous rhyolitic melt locally increased to 1–2 wt%. Trace and minor elements, mainly REE, Y, Sr, P, Zr, Hf, Ta and Nb partitioned between the two immiscible melts. The F-Ca melt existed in the course of rhyolitic magma evolution from the crystallization of phenocrysts in the magma source till eruption and quenching on the Earth's surface. The effective viscosity of the magma (mixed rhyolitic and F-Ca melts with fluid bubbles) may have been of the same order of magnitude as that of viscous liquid during the formation of the rhyolite matrix at 750–650°С. The quenching of the F-Ca melt formed an F-Ca phase consisting of submicrometer fluorite particles, while crystallization of rhyolitic glass produced quartz-sanidine symplectites. According to SEM EDS and LA-ICP-MS data, the F-Ca phase typically shows large ranges of O, Y, La, Ce, Nd, Sr, Sc, P, Si (wt%) and trace element (ppm) concentrations varying for orders of magnitude. The variations result from recrystallization of the F-Ca phase under the effect of a low-density (0.05–0.1 g/cm3) aqueous fluid released from the degassing rhyolitic melt. Upon interaction with the fluid, micrometer fluorite particles of the F-Ca phase liberated from impurities and transformed into larger crystalline segregations. The process occurred within the 570–780°С temperature range at a high oxygen fugacity of ΔlgfO2 Ni-NiO (0.9–1.7). The oxidized environment maintained crystallization of ferrian ilmenite, monazite-group As-bearing minerals, and cerianite, as well as replacement of titanomagnetite by hematite. The O2− → F− substitution in the fluorite structure led to the formation of O-vacancy centers responsible for luminescence of the F-Ca phase in the rhyolite matrix upon laser excitation. The compositions close to the primary F-Ca phase have preserved in relict globules existing as inclusions in the matrix and in enclosed minerals. The F-Ca melt could exist in a metastable liquid state during the eruption of rhyolitic magma at an oxygen fugacity remaining high till the subsolidus temperature of the rhyolitic melt. The fluoride-silicate liquid immiscibility with participation of an oxygenated F-Ca melt may be a common feature of F-rich silicate magmas at high oxygen fugacity. Fluorite and related mineralization in many igneous rocks and magmatic ores possibly resulted from transformation of the F-Ca melt enriched in REE, Y and other minor elements.

Initial 87Sr/86Sr as a sensitive tracer of Archaean crust-mantle evolution: Constraints from igneous and sedimentary rocks in the western Dharwar Craton, India

Year: 2020
Products: NWR193;ESI;
Authors: Ravindran, A;Mezger, K;Balakrishnan, S;Kooijman, E;Schmitt, M;Berndt, J;
Journal: Precambrian Research

Among the rocky planets of the solar system only the Earth has “granitic” continental crust. The timing and processes involved in the formation of Earth’s first extensive crust is still enigmatic. The chemical and isotope compositions of ancient crustal rocks preserve a record of their genesis. The Rb-Sr system proves to be an efficient proxy for the reconstruction of crust-mantle evolution since it can bring together information from seawater as preserved in chemical sedimentary rocks and information from magmatic rocks that can trace the time and extent of crust formation and concomitant mantle depletion during the Archaean eon. The Dharwar Craton in India preserves a suite of metamorphosed igneous and sedimentary rocks that record its early crustal evolution. To overcome the susceptibility for resetting and the difficulty in determining initial 87Sr/86Sr, the minerals barite and apatite are used to obtain precise and accurate 87Sr/86Sr, because these minerals preferentially incorporate Sr and exclude Rb and preserve the initial Sr isotope compositions at the time of their formation. Initial 87Sr/86Sr of apatite were obtained in situ using Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry. The robustness and only minor dispersion of the isotope ratios demonstrate the capability of matrix apatites in preserving initial Sr ratios. The least radiogenic value is used as the best estimate for the initial 87Sr/86Sr. The 87Sr/86Sr ratios of apatite from igneous rocks that formed from 3.5 Ga to 2.6 Ga constrain the Rb/Sr of the source over the whole time-span. A comparison of the Sr isotopes between seawater-derived barite and initial Sr isotope ratios in apatite from igneous rocks reveals that significant mafic to intermediate crust had formed by 3.2 Ga. Studying the entire Archaean time window, a dominantly mafic crust was the main source for the granitoid rocks in the Dharwar Craton from 3.5 to 3.1 Ga, whereas the rocks from 2.9 to 2.7 Ga were extracted dominantly from the depleted mantle.

Re-evaluation of Leonian and Liberian events in the geodynamical evolution of the Man-Leo Shield (West African Craton)

Year: 2020
Products: NWR193UC;ESI;
Authors: Koffi, G;Kouamelan, A;Allialy, M;Coulibaly, Y;Peucat, J;
Journal: Precambrian Research

The Leonian (3400–3100 Ma) and Liberian (2850–2700 Ma) events are important magmatic and tectono-metamorphic events in the Archean domain of the Man-Leo Shield in the southern West Africa Craton. The older Leonian event was associated with crust formation, which was variably reworked during the younger Liberian event. In the Man domain of western Côte d’Ivoire, zircon in-situ dating by LA-ICPMS of Granulitic Grey Gneisses (GGGs), the Mangouin charnockite and the Lagoulalé augen orthogneiss allows for the re-evaluation of magmatic and metamorphic activity related to the Leonian and Liberian events. We report here our findings that the GGGs represent the oldest rocks in the study area and formed during the Leonian event. The ages recorded in the GGGs in the Man area are 3156±24, 3098±19, 3093±49 and 3019±53 Ma. The ages of 3156±24 and 3098±19 Ma represent Leonian juvenile magmatism while those of 3093±49 and 3019±53 Ma represent Leonian metamorphism. The ages of the Mangouin charnockite and the Lagoulalé augen orthogneiss are 2798±8 Ma and 2795±9 Ma, respectively, and are interpreted to record peak metamorphic conditions during the Liberian event. Zircon from the augen orthogneiss includes an inherited core with an age of 3121±37 Ma, which corresponds to Leonian GGG ages. This inheritance indicates that the Mangouin charnockite and the Lagoulalé augen orthogneiss were derived either partially or completely from Leonian formations. A previously constrained Sm–Nd model age of 3250 Ma for the charnockite and augen orthogneiss agrees with such a process. The majority of Th/U is higher, indicating a magmatic origin for most zircons. The Leonian and Liberian events are proposed as two distinct events in Man-Leo Shield.

Paleoproterozoic (ca. 1.87–1.69 Ga) arc-related tectonothermal events on northcentral Yeongnam Massif, South Korea and its tectonic implications: Insights from metamorphism, geochemistry and geochronology

Year: 2020
Products: NWR193UC;ESI;
Authors: Lee, B;Oh, C;Wang, X;
Journal: Precambrian Research

The Paleoproterozoic basement of the Korean Peninsula consists of three massifs, the Nangrim, Gyeonggi and Yeongnam Massifs, from north to south. In the Muju area of the northcentral Yeongnam Massif, amphibolites intruded the Paleoproterozoic metasedimentary rocks and orthogneisses. The amphibolites can be divided into Type-I and Type-II amphibolites. The whole-rock geochemical data and zircon Lu–Hf composition of the amphibolites suggest that the Type-I and Type-II amphibolites formed in an island and continental arc tectonic setting, respectively, and both amphibolites were derived from enriched mantle sources. Zircon U–Pb dating reveals that the Type-I and Type-II amphibolites were emplaced at ca. 1.87 Ga and 1.69 Ga, respectively. The surrounding metasedimentary rock (migmatite) underwent upper amphibolite facies (720–730 °C and 7.3–7.4 kbar) metamorphism and then underwent amphibolite facies retrograde metamorphism (520–622 °C and 1.7–3.5 kbar). The zircon U–Pb dating reveals that the peak metamorphism occurred at ca. 1.87–1.86 Ga. The geothermal gradient (approximately 32 °C/km) during peak metamorphism correlates with that of the arc area, indicating that metamorphism occurred in an arc tectonic setting. These data suggest that the northcentral Yeongnam Massif underwent arc-related magmatic and metamorphic events during ca. 1.87–1.69 Ga. This finding indicates that the northcentral Yeongnam Massif does not correlate well with the Nangrim and northern Gyeonggi Massifs, which are correlated with the eastern North China Craton, because the Nangrim and Gyeonggi Massifs underwent postcollisional igneous activity during ca. 1.88–1.84 Ga.

Effects of magmatic volatile influx in mafic VMS hydrothermal systems: Evidence from the Troodos ophiolite, Cyprus

Year: 2020
Products: UP213;New Wave;New Wave Research;
Authors: Martin, A;Keith, M;Parvaz, D;McDonald, I;Boyce, A;McFall, K;Jenkin, G;Strauss, H;MacLeod, C;
Journal: Chemical Geology

The Troodos ophiolite, Cyprus is the principal on- land analogue for mafic-hosted volcanogenic massive sulfide (VMS) deposits. This study, for the first time, presents sulfur isotope (δ34S) data on a regional scale from VMS deposits and other mineralised zones across the Troodos ophiolite. In combination δ34S, Se/S ratios and trace element chemistry (e.g., Se, Cu and Au) of different hydrothermal sulfides are used to assess variations in magmatic volatile influx and the source of metals and sulfur in ancient hydrothermal systems. Sulfur isotope analyses (n = 180) across 19 mineral deposits indicate a variable source of sulfur in the Troodos VMS hydrothermal system, this in turn allows a variable source of metals to be inferred. Pyrite δ34S range from −5.5‰ to +13.2‰ with an average of +4.6‰ (n = 160) for all deposits investigated. These δ34S variations cannot only be explained by variable proportions of thermochemical seawater sulfate reduction (δ34S +18 to +19‰) and leaching of primary magmatic sulfur from igneous rocks (δ34S 0-1‰). Consequently, two processes are proposed, explaining the trace metal and δ34S variation across the Troodos ore-forming systems including, i) a variable source of metals in the sheeted dyke complex and ii) the addition of a magmatic volatile-rich phase to the VMS hydrothermal systems. Two distinct lava units exist in the Troodos stratigraphy, namely the upper and lower pillow lavas (UPL and LPL). The more primitive UPL are enriched in Au, Se and Cu relative to As, Sb and Zn that are concentrated in the LPL. Some VMS deposits pre-date the formation of the UPL (e.g., Agrokipia A) suggesting Se, Cu and Au depleted source rocks. Hence, the stratigraphic position of VMS deposits and the ratio of UPL:LPL affinity elements (e.g., As  + Zn + Sb vs. Cu + Se + Au) imply a systematic relationship between trace element distribution and stratigraphic depth; this relates to the relative proportion of UPL and LPL affinity lavas within the metal source region.

The impact of fermentation on the distribution of cadmium in cacao beans

Year: 2020
Products: NWR213;ESI;TV2;
Authors: Vanderschueren, R;De Mesmaeker, V;Mounicou, S;Isaure, MP;Doelsch, E;Montalvo, D;Delcour, JA;Chavez, E;Smolders, E;
Journal: Food Res. Int.

A large fraction of the South-American cacao production is affected by new cadmium (Cd) regulations in cacao. This work was set up to characterize the distribution and speciation of Cd within the cacao fruit and to monitor potential Cd redistribution during cacao fermentation. In cacao fruits from four locations, Cd concentrations decreased with testa > nib ~ placenta ~ pod husk > mucilage. The distribution of Cd within cacao beans was successfully visualized using laser ablation inductively coupled plasma spectrometry (LA-ICP-MS) and confirmed higher Cd concentrations in the testa than in the nib. Speciation analysis by X-ray absorption spectroscopy (XANES) of unfermented cacao beans revealed that Cd was bound to O/N-ligands in both nib and testa. Fermentation induced an outward Cd migration from the nibs to the testa, i.e. against the total concentration gradient. This migration occurred only if the fermentation was sufficiently extensive to decrease the pH in the nib to <5.0, likely as a result of increased Cd mobility due to organic acid penetration into the nibs. The change in dry weight based nib Cd concentrations during fermentation was, on average, a factor 1.3 decrease. We propose that nib Cd can be reduced if the nib pH is sufficiently acidified during fermentation. However, a balance must be found between flavor development and Cd removal since extreme acidity is detrimental for cacao flavor.

The world-class Nanling metallogenic belt (Jiangxi, China): W and Sn deposition at 160 Ma followed by 30 m.y. of hydrothermal metal redistribution

Year: 2020
Products: NWR193UC;ESI;TwoVol2;
Authors: Legros, H;Harlaux, M;Mercadier, J;Romer, R;Poujol, M;Camacho, A;Marignac, C;Cuney, M;Wang, R;Charles, N;Lespinasse, M;
Journal: Ore Geology Reviews

The W-Sn Maoping deposit and related W-Sn deposits from the world-class Nanling Range in Southeast China formed at ca. 160 Ma and experienced several phases of metal addition and metal redistribution between 160 and 130 Ma. Isotopic dating of ore mineral (wolframite) of Maoping demonstrates that W was deposited first, during a hydrothermal event at ca. 160 Ma. Successive fluid episodes, at ca. 156 Ma (Mo and Sn-rich fluid) and 152 Ma (REE-rich fluid), resulted in the formation of REE- and Fe-Cu-Zn-sulfide minerals. A last fluid event occurring at ca. 130 Ma was responsible for the deposition of Zr-REE-Nb-Ta minerals that are attributed to magmatic fluids derived from unexposed magmatic bodies. The three episodes of fluid circulation post-dating W deposition resulted in partial to complete resetting of the isotopic systems (mica, wolframite, xenotime), which are conventionally used for dating such deposits. We show that W and Sn mineralization in the Nanling Range formed during a unique fluid event at ca. 160 Ma. Later fluid episodes redistributed the previously deposited metals and sequentially introduced additional metals, including Mo-Sn, Fe-Cu-Zn, and Zr-REE-Nb-Ta. Direct dating of paragenetically well-constrained minerals is therefore critical for determining the age and the duration of mineralizing processes and for characterizing the fluid evolution of magmatic-hydrothermal systems, as exemplified in the Nanling Range.

Weakly fractionated I-type granitoids and their relationship to tungsten mineralization: A case study from the early Paleozoic Shangmushui deposit, Dayaoshan area, South China

Year: 2020
Products: UP213;NewWave;
Authors: Dang, Y;Chen, M;Mao, J;Fu, B;
Journal: Ore Geology Reviews

Tungsten deposits related to weakly fractionated granitoids are scarce worldwide. The geological significance of early Paleozoic magmatism and associated mineralization in South China remains poorly understood compared with well-documented Mesozoic magmatism and related mineralization. Early Paleozoic magmatic rocks, previously thought to be only rarely associated with mineralization, crop out widely in the Dayaoshan area, South China, and have significant prospecting potential for tungsten polymetallic deposits. Shangmushui is a newly discovered W-bearing skarn (with minor Cu) deposit in the Dayaoshan area. The zircon U–Pb age of the granodiorite that hosts the tungsten deposit is 465.4 ± 1.5 Ma, which is consistent with scheelite Sm–Nd age (466.6 ± 5.5 Ma) within the error. The present data, combined with previous findings, indicate a protracted period of magmatism and related W–Mo polymetallic mineralization during 470–420 Ma in the Dayaoshan area. Elevated zircon δ18OV-SMOW values (5.5‰ to 6.6‰) and mostly negative εHf(t) values (–9.5 to +0.7), together with TDM2 of 1.6 Ga indicate that these plutons formed via partial melting of Mesoproterozoic crust with some contributions from mantle materials. Estimates of the oxygen fugacity of the magmas show that the Shangmushui granodiorite is relatively reduced (FMQ–0.11). Shangmushui granodiorite is a weakly fractionated I-type granitoid with low differentiation index values (DI = 59.6–66.9), B contents (8.6–30.1 ppm), and Rb/Sr ratios (0.34–0.73), which are different from most highly fractionated tungsten-bearing S- and I-type granitoids globally. The low oxygen fugacity and high W contents of the granodiorites, and the close spatio-temporal relationship between the granodiorites and the tungsten ore bodies, indicate that early Paleozoic weakly fractionated I-type granitoids in the Shangmushui region have a close genetic relationship with tungsten mineralization.

Fluorite deposits in the Zhejiang Province, southeast China: The possible role of extension during the late stages in the subduction of the Paleo-Pacific oceanic plate, as indicated by the Gudongkeng fluorite deposit

Year: 2020
Products: UP213;NewWave;
Authors: Fang, Y;Zou, H;Bagas, L;Said, N;Li, Y;Liu, H;
Journal: Ore Geology Reviews

Southeast China with its widespread occurrences of Mesozoic igneous rocks, is one of the largest magmatic provinces worldwide, containing a large variety of mineral types, including hypothermal W-Sn, porphyry Cu, epithermal Au deposits. The Gudongkeng deposit is an example consisting of fluorite mineralisation trending SE over a distance of about 6 km. The major minerals in the deposit include fluorite and calcite of a hydrothermal origin and interpreted as a vein-type deposit associated with the Linghou Granite that yields a zircon U–Pb date of 100 ± 1 Ma, but intriguingly the fluorite yields an Sm–Nd isochron age of 73 ± 3 Ma, placing the genesis of the fluorite as a post-magmatic event. Fluid inclusions in the fluorite have low homogenisation temperatures of 104–195° C, salinities of 0.5 to 2.24 wt% NaCl eqv., and densities of 0.67–0.94 g/cm3. The inclusions contain NaCl–H2O–CaF2 with δDV-SMOW values between −64.3 and-50.1‰ and δ18OV-SMOW values between −7.6 and −2‰. The initial 87Sr/86Sr ratios of the fluorite range from 0.709816 to 0.710165 are characteristic of a crustal contribution. The ore-forming fluids can be mainly attributed to a NaCl–H2O–CaF2 system of moderate to low temperature, low salinity, and low density. The ore-forming fluid has a meteoric water source, with the reaction between the fluid and wallrocks being the main mechanism for fluorite precipitation at relatively low temperatures. Gudongkeng is a low temperature epithermal deposit which was formed in an extensional setting within the Cathaysia Block during the Late Cretaceous.

Multistage W-mineralization and magmatic-hydrothermal fluid evolution: Microtextural and geochemical footprints in scheelite from the Weondong W-skarn deposit, South Korea

Year: 2020
Products: UP213;New Wave;
Authors: Choi, W;Park, C;Song, Y;
Journal: Ore Geology Reviews

Weondong deposit is one of the W-skarn deposits in South Korea, and main ore mineral is scheelite (CaWO4). Scheelite occurs in both a massive skarn zone (MSZ; Type I) and a quartz porphyry fracture zone (QPFZ; Type II), forming solid solution with powellite (CaMoO4). We examined the relationship between the evolution of ore-forming fluids and formation of multistage scheelites based on microtextural and geochemical features. Type I scheelites can be divided into Type Ia and Type Ib. Type Ia scheelites are characterized by complex internal textures with oscillatory zoning. The texturally associated clinopyroxene (diopside), garnet (andradite), and magnetite strongly suggest an oxidized prograde skarn origin. They are also characterized by enriched light rare earth elements (LREEs) and a negative Eu anomaly. Type Ib scheelites are W-enriched (74–81 wt% of WO3) with no internal zoning. Relict grossular garnet, calcite, pyrrhotite, serpentine, and vesuvianite indicate its relatively reduced retrograde skarn origin. Their rare earth element (REE) pattern is flat with a negative Eu anomaly. Type II scheelites can further be divided into Types IIa and IIb based on textural and geochemical differences. The former largely exhibit patchy zoning with minor oscillatory zoning that normally occurs along microfractures in association with fluorite. Type IIa scheelites show REE fractionation between W- and Mo-enriched zones (i.e., those containing 60–71 wt% of WO3 and 15–25 wt% of MoO3, respectively). Tungsten enriched scheelites show middle rare earth element (MREE)-enriched patterns with a strong negative Eu anomaly; Mo-rich zones are MREE-depleted and show a weak negative Eu anomaly. Type IIb scheelites are W-rich and rarely have zoned texture, similar to Type Ib scheelites. Type IIb scheelites generally coexists with sulfide minerals, indicating a relatively high sulfur fugacity (fS2) retrograde conditions. The REE pattern is flat with a negative Eu anomaly. These results indicate that Type Ia and Type IIa scheelites were formed during prograde conditions at each stage, followed by Type Ib and Type IIb in retrograde conditions. Type Ia scheelites have LREE-enriched patterns, which mimic the REE profile of juvenile magmatic fluids under open systems. Type IIa scheelites have MREE-enriched fractionation patterns that likely reflect a highly evolved magmatic fluid origin in a closed system. The flat REE pattern in Type Ib and IIb scheelites is due to meteoric water in retrograde conditions. This causes changes in the trace element composition of scheelites that reflect differences in the fluid origin and stages of evolution. The geochemical characteristics of both scheelite types match well with their microtextural features and provide crucial evidence for understanding the multistage formation of the Weondong W-skarn.

The Genesis of the Giant Shuangjianzishan Epithermal Ag-Pb-Zn Deposit, Inner Mongolia, Northeastern China

Year: 2020
Products: UPfemto 266;ESI;
Authors: Zhai, D;Williams-Jones, A;Liu, J;Selby, D;Voudouris, P;Tombros, S;Li, K;Li, P;Sun, H;
Journal: Economic Geology

The newly discovered Shuangjianzishan Ag-Pb-Zn deposit, with 145 Mt of ore grading 128.5 g/t Ag (locally up to 32,000 g/t) and 2.2 wt % Pb + Zn, is located in the Great Hinggan Range metallogenic belt, northeastern China, and is currently the largest Ag deposit in Asia. The Ag-Pb-Zn orebodies occur as veins and are hosted primarily by a Permian slate. Recent drilling and core logging have identified a partially Mo mineralized granite porphyry intrusion adjacent to the Ag-Pb-Zn mineralized veins. This well-preserved magmatic-hydrothermal system therefore offers an excellent opportunity to evaluate the possible temporal and genetic relationship between Mo-mineralized porphyry intrusions and Ag-Pb-Zn veins. Three primary paragenetic stages of veining have been recognized: (I) early pyrite + quartz ± K-feldspar, (II) main ore sulfide + sulfosalt + quartz + calcite + sericite + chlorite ± epidote, and (III) post-ore quartz. The silver mineralization occurs mainly in the late paragenetic part of Stage II, in which canfieldite (Ag8SnS6), argentite (Ag2S) and freibergite [(Ag, Cu)12Sb4S13] are the dominant Ag-bearing ore minerals. A combination of ore mineral chemical and sulfur isotope geothermometers and physicochemical calculations suggest that the Ag-Pb-Zn mineralization took place at a temperature of 250° to 200°C, a pH of 6.7 to 5.6, and a Δlogfo2 (HM) of –2.4 to –8.7. A conspicuous enrichment of Sn and Se in the ore, which is represented by minerals containing the metal suite Ag-Pb-Zn-(Cu-Sn-Se-Sb), likely reflects a close genetic association between the base metal mineralization and a magma. In situ analyses show that the δ34S values of the sulfides and Ag-bearing sulfosalts from the Ag-Pb-Zn mineralized veins vary from –4.67 to +2.44‰; the mean value is –2.11 ± 1.49‰ (n = 77). The calculated mean δ34SH2S value of the ore-forming fluid is –1.65 ± 0.83‰, which is indicative of a magmatic sulfur source. In situ Pb isotope analyses of the ore minerals yielded a narrow range of values (206Pb/204Pb of 18.243–18.310, 207Pb/204Pb of 15.503–15.563 and 208Pb/204Pb of 38.053–38.203, n = 59). Comparisons to corresponding isotopic data for the various rock units in the area and sulfides from nearby ore deposits indicate that there were substantial contributions of Pb and other metals (e.g., Ag and Zn) to the Shuangjianzishan deposit from a Mesozoic granitic source. Diorite-granodiorite dikes and dacite are crosscut by the Ag-Pb-Zn veins, and therefore, predate ore formation. These rock units have zircon U-Pb ages of 250.2 ± 2.0 and 133.9 ± 1.4 Ma, respectively. A concealed, weakly Mo mineralized granite porphyry intrusion proximal to the Ag-Pb-Zn mineralized vein system yielded zircon U-Pb ages of 134.4 ± 1.0 (MSWD = 0.1) and 134.4 ± 1.0 Ma (MSWD = 0.2), for coarse- and fine-grained facies, respectively. These ages are indistinguishable within the uncertainty from the zircon ages for the dacite and a granite intrusion ~2 km north of the mineralized veins, which has a weighted mean zircon U-Pb age of 135.2 ± 1.4 Ma (MSWD = 0.78). Molybdenite from three quartz vein/veinlet samples hosted by slate immediately above the porphyry intrusion yielded Re-Os model ages from 136.3 ± 0.9 to 133.7 ± 1.2 Ma and a weighted mean Re-Os age of 134.9 ± 3.4 Ma. Finally, three pyrite samples separated from the Ag-Pb-Zn mineralized veins have a weighted mean Re-Os model age of 135.0 ± 0.6 Ma. The very similar zircon U-Pb ages for the Mo-mineralized granite porphyry and dacite, and Re-Os ages for molybdenite and pyrite in the Shuangjianzishan ore district indicate that the Mesozoic magmatic-hydrothermal activity was restricted to a relatively short time interval (~136–133 Ma). They also suggest that the weakly Mo mineralized granite porphyry was likely the source of the fluids and metals that produced the Ag-Pb-Zn mineralization. Based on our geological observations and an extensive analytical database, a model is proposed for the genesis of the giant Shuangjianzishan Ag-Pb-Zn deposit in which the ore-forming fluid and its metals (i.e., Ag, Pb, and Zn) were exsolved during crystallization of the final phase of a composite granite porphyry intrusion. This fluid transported metals to the distal parts of the system, where they were deposited in preexisting faults or fractures created by the withdrawal of magma during the waning stages of the magmatic-hydrothermal event. The present study of the Shuangjianzishan Ag-Pb-Zn deposit and those of other magmatic-hydrothermal ore deposits in the region provide compelling evidence that the widespread Mesozoic felsic magmatism and Ag-Pb-Zn mineralization in the southern Great Hinggan Range took place in an intracontinental extensional tectonic setting, which was synchronous with, and spatially associated to, Paleo-Pacific slab rollback and lithospheric delamination and thinning.

Geobarometry for spinel peridotites using Ca and Al in olivine

Year: 2020
Products: UP213;New Wave;
Authors: D’Souza, R;Canil, D;Coogan, L;
Journal: Contrib Mineral Petrol

Experiments were performed from 950 to 1250 °C and 1.5–2.4 GPa to determine the effect of pressure (P) on the temperature (T)-dependent partitioning of Al between olivine and spinel, using mixtures of natural spinel, olivine, clino- and ortho-pyroxene. When compared to 100 kPa experiments, the results show that there is no discernible effect of pressure on the Al-in-olivine thermometer at PT conditions relevant to the spinel peridotite facies. In our experiments with high-Cr spinel, we see no change in Al in olivine from starting values, likely due to the refractory nature of high-Cr spinel. Phase boundary flourescence prevented accurate quantification of Ca in olivine in the run products by electron microprobe analysis but measurements by laser ablation are consistent with the Köhler and Brey (Geochim Cosmochim Acta 54:2375–2388, 1990) Ca-in-olivine thermobarometer. The combination of Al (for T) and Ca (for P) in olivine thus has great potential for thermobarometry in spinel facies peridotites. As a test we apply this approach to published high precision Ca and Al data for olivine from the Ray Pic spinel peridotite xenoliths from the Massif Central (De Hoog et al. Chem Geol 270:196–215, 2010). Reassuringly, the calculated PT conditions (1.0–1.8 GPa; 900–1080 °C) for all samples lie beneath the Moho, within the spinel peridotite facies and fall along a geophysically constrained geotherm.

Evidence for non-lithostatic pressure in subducted continental crust

Year: 2020
Products: NWR193;New Wave;New Wave Research;ESI;
Authors: Cutts, J;Smit, M;Vrijmoed, J;
Journal: Contrib Mineral Petrol

Continental crust buried during collisional orogeny typically records pressures of 3 GPa or lower; however, pressures much higher than this are recorded locally, which would suggest burial to mantle depths. Deep continental subduction is not observed in active orogens and should be hindered by the positive buoyancy of sialic crust relative to the mantle. Non-lithostatic pressure caused by mechanical contrasts between rock types provides an alternative explanation for extreme pressures recorded in buried continental crust; however, its occurrence and significance in natural systems is debated. Mechanical pressure heterogeneities were proposed specifically to explain extreme pressures of c. 5.5 GPa obtained in enstatite eclogite veins in the archetypal subducted continental terrane, the Western Gneiss Complex (WGC) in Norway. In this study, we use Lu–Hf garnet geochronology to test when, and thus, in what part of the burial cycle of the WGC the enstatite eclogite assemblages actually equilibrated. The results show that equilibration occurred at c. 393 Ma, which is much later than the typical ages obtained from ‘normal’ eclogites in the WGC and represents a time when the terrane was already at crustal depths (< 2.5 GPa). Finite element modeling of mechanical pressure distribution demonstrates that late extreme pressure excursions are feasible for the given rock system and could explain the seemingly spurious conditions recorded in these unusual rocks. The recognition of non-lithostatic ultrahigh-pressure in deeply buried continental crust allows crucial simplification of models for continental subduction and validates the importance of rock thermo-mechanics in interpreting observations from collision zones.

Laser based analysis of transition metal boride thin films using liquid standards

Year: 2020
Products: NWR213;ESI;
Authors: Weiss, M;Riedl, H;Moares, V;Mayrhofer, P;Limbeck, A;
Journal: Microchemical Journal

In this work the use of two laser assisted direct solid sampling methods, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and laser induced breakdown spectroscopy (LIBS) for the determination of the stoichiometry of novel diboride based materials is reported. To overcome the need for certified reference materials or matrix matched standards, which were usually required for quantitative investigations with LA-ICP-MS or LIBS, in this work liquid standards are employed. For LA-ICP-MS the concept of self-aliquoting micro-grooves and for LIBS conventional dried droplets were used. As a model for application of the developed analytical procedures the ternary system W1-xTaxB2-z was used. Fabrication of W1-xTaxB2-z thin films with varying stoichiometry was performed via magnetron sputtering. Reference compositions were obtained by liquid digestion of the samples and subsequent ICP-OES measurement. Both laser-assisted methods enabled fast and spatially resolved measurements, although the LA-ICP-MS method generally yielded more accurate results. It was shown that the method can easily be adapted for the stoichiometry determination of systems with different elemental composition.

Nanoparticle enhanced laser ablation inductively coupled plasma mass spectrometry

Year: 2020
Products: NWR213;New Wave;New Wave Research;ESI;
Authors: Mangone, A;Mastrorocco, F;Giannossa, L;Comparelli, R;Dell'Aglio, M;De Giacomo, A;
Journal: Spectrochimica Acta Part B: Atomic Spectroscopy

Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LAICPMS) is a powerful and well-established analytical technique, with high sensitivity and fast response, extensively applied to investigate inorganic elements in solid specimen [1–3]. Little or no sample preparation is required and analyses can be performed on a large range of materials: conducting, non-conducting, opaque and transparent. The sample mass size required is in the order of sub-micrograms, which essentially keeps the item aspect unaltered. It can be applied to different analysis approaches: from bulk analysis and depth profiling to elemental/isotope mapping.

Exposure to geogenic lithium in ancient Andeans: Unraveling lithium in mummy hair using LA-ICP-MS

Year: 2020
Products: NWR213;
Authors: Blumenstiel, D;McDonald, M;Arriaza, B;Amarasiriwardena, D;
Journal: Journal of Archaeological Science

The ancient Andeans, who lived along the coastal region of the arid Atacama Desert in present day Chile had access to scarce freshwater via a few small rivers originating from the Andean Altiplano. Due to volcanic-derived lithium minerals and their solubility in water, the surface water in the Atacama Desert region is rich with lithium (Li); often many orders of magnitude higher than that of other rivers in the world. The goal of this study was to examine whether ancient Andean mummy individuals (n = 145) from four burial areas in northern Chile (Azapa, Camarones, Lluta and Morro) were exposed to geogenic lithium by conducting laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on a single strand of hair per individual. The resulting concentrations for Li in mummy hair [Site, Median, Range (μg/g), n: Azapa, 0.38, 0.04–2.91 μg/g, n = 98; Morro, 0.33, 0.03–0.65 μg/g, n = 14; Camarones, 0.61, 0.07–12.8 μg/g, n = 31; Lluta, 2.9, 2.7–3.1 μg/g, n = 2] had the following order: Lluta > Camarones > Azapa > Morro. Hair-Li concentration of the Andean mummies were nearly 20 times elevated when compared to concentrations of Li in the hair of contemporary populations in other regions. Exposure to Li as revealed in hair appears to be depend in part on where ancient Andeans were buried, and generally correlates well with dissolved Li in associated rivers.

The ~500 Ma Asaji ultramafic–mafic intrusion in Kyushu, southwest Japan: Implications for boninitic magmatism in a late Cambrian nascent arc

Year: 2020
Products: NWR213;New Wave;New Wave Research;
Authors: Yamasaki, T;
Journal: Journal of Asian Earth Sciences

It is thought that the continental crust that ultimately became Japan (i.e., proto-Japan) formed during the early Cambrian near the margin of the South China block following its separation from the Australian block. However, the onset of timing of subduction and details of the magmatic evolution of the region are poorly understood, due mainly to the sporadic occurrence of Cambrian rocks. A high-temperature metamorphic complex is distributed throughout eastern Kyushu island, Japan. At the northeastern end of the complex, a narrow zone of ultramafic–mafic rocks includes a late Cambrian ophiolitic assemblage, namely the Asaji ultramafic–mafic intrusion. The ultramafic cumulates in the intrusion consist of harzburgite (spinel–olivine–orthopyroxene), lherzolite–olivine websterite (olivine–orthopyroxene–clinopyroxene ± spinel), and websterite (orthopyroxene–clinopyroxene ± olivine), which formed in that order during differentiation of a parental magma. The chemical compositions of clinopyroxene and spinel from the cumulates show strongly depleted features (e.g., spinel Cr# [= atomic Cr/(Cr + Al)] ≤ 0.91 and TiO2 < 0.3 wt%, and clinopyroxene YbN < 2) and comparable to those of spinel in boninites. In addition, the calculated trace element composition of melts in equilibrium with clinopyroxene from the ultramafic rocks closely resembles the composition of the North Tongan boninite. These petrological and geochemical features suggest that the Asaji ultramafic–mafic intrusion consists of cumulates from a boninitic magma. The presence of boninitic magmatism suggests that the Asaji ultramafic–mafic intrusion was the result of subduction initiation and the infiltration of water into hot asthenosphere during the formation of nascent arc crust.

New insights into the hydrothermal evolution of skarn deposits: A case study of the Dongzhongla Pb-Zn deposit in Tibet, SW China

Year: 2020
Products: UPfemto 266;
Authors: Sun, G;Zhou, J;Luo, K;Xiang, Z;Bao, Z;Sun, T;
Journal: Journal of Asian Earth Sciences

Revealing hydrothermal evolution (from the early quartz-sulfide to the late fluorite-carbonate-sulfide stages) of skarn sulfide deposits is significant for understanding their ore formation processes, but the detailed studies are rare. In this study, we choose the Dongzhongla skarn Pb-Zn deposit (0.38 Mt Pb + Zn) located in central Lhasa, Tibet as a case study, and present detailed ore deposit geology and dataset of in situ chemical compositions of quartz, in situ Pb isotopic ratios of galena, sulfur isotopic compositions of sulfides and C-O isotopic compositions of hydrothermal calcite and wall rocks to address this issue. There are two types of hydrothermal quartz in the early stage: (1) the early phase euhedral quartz (Qz1) crosscut by quartz-sulfide veins, and (2) the late phase subhedral quartz (Qz2) coexisting with sulfides. TitaniQ thermometer of Qz1 and Qz2 limits the two phases with a temperature range of 336–427°C (mean 373°C) and 357–461°C (mean 386°C), respectively. The decreasing Al concentrations of Qz1 from core to rim suggest that magmatic fluids mixed with acidic meteoric water prevented the precipitation of sulfides during the early phase. The increasing Al and decreasing sulfur concentrations of Qz2 indicate that the increasing pH values of hydrothermal fluids made principal sulfides precipitate during the late phase.

Detrital zircons from Late Paleozoic to Triassic sedimentary rocks of the Gongshan-Baoshan Block, SE Tibet: Implications for episodic crustal growth of Eastern Gondwana

Year: 2020
Products: New Wave;
Authors: Song, Y;Su, L;Dong, J;Song, S;Allen, M;Wang, C;Hu, X;
Journal: Journal of Asian Earth Sciences

The Gongshan-Baoshan Block is a segment of the northern Sibumasu Terrane, which is a continental strip derived from Eastern Gondwana. However, the formation history of the Gongshan-Baoshan Block and its relationship with other East Gondwana-derived blocks remain unclear. Here, we present five hundred and eighty new analyses of U-Pb ages of detrital zircons from Late Paleozoic to Triassic sedimentary rocks in the Gongshan-Baoshan Block, western Yunnan. The detrital zircon age spectra show distinctive age clusters at 2500–2400 Ma, 1750–1500 Ma, 1200–900 Ma, 600–500 Ma, with a few Archean ages of 3500–2600 Ma, suggesting secular, episodic, continental growth. The age spectra are comparable to those from the Sibumasu Terrane, Australia, Lhasa Block, Qiangtang Block, Tethyan High Himalaya and Cathaysia Block. We confirm that the Gongshan-Baoshan Block and Sibumasu Terrane could have occupied a position outboard of the Lhasa Block and close to northern India, along the northwestern margin of Australia in East Gondwana. The youngest ages from the Mesozioc sediments limit the timing of subduction of the Paleo-Tethys Ocean, which initiated by ~273 Ma and finally stopped at ~223 Ma.

Timing of high-grade metamorphism in the Kontum Massif, Vietnam: Constraints from zircon–monazite multi-geochronology and trace elements geochemistry of zircon–monazite–garnet

Year: 2020
Products: UP213;New Wave;New Wave Research;
Authors: Bui, V;Osanai, Y;Nakano, N;Adachi, T;Kitano, I;Owada, M;
Journal: Journal of Asian Earth Sciences

Metamorphic rocks in the Kontum Massif, including the Kannak, Ngoc Linh and Kham Duc Complexes are characterized by amphibolite- to granulite-facies metamorphism and their mono- versus poly-metamorphic evolution is a matter of debate. In this study, we constrained on the timing of high-grade metamorphism in this massif by combining laser ablation inductively coupled plasma mass spectrometry U–Pb zircon and electron microprobe chemical U–Th–Pb monazite ages with geochemical relation of trace elements between zircon–monazite–garnet. The results indicated that the analyzed pelitic and mafic granulites in the western Kannak Complex experienced the high temperature metamorphism at ca. 250 Ma with subsequent decompression. However, in the western Ngoc Linh Complex two high-grade metamorphic events were recorded in one of analyzed pelitic gneisses. The first high temperature metamorphism began at ca. 440–450 Ma with the attainment of the peak condition at ca. 430 Ma, overprinted by the second one at ca. 240–250 Ma with following decompression and exhumation stage at ca. 230 Ma. The other pelitic gneiss and mafic granulite detected only younger single event. Pelitic gneisses in the Kham Duc Complex recorded medium pressure metamorphism occurred at ca. 240 Ma without any traces of early metamorphic event.

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