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The Eastern Manus Basin is one of the fastest expanding back − arc basins in the world and it is the site of recent volcanism and hydrothermal activity. The role of magma mixing in the origins of the volcanic rocks in this region, as well as the modeling of its magma plumbing system, are still unclear. In this study, we have clarified the magma plumbing system processes of the Eastern Manus Basin by analyzing the petrography and geochemical characteristics of whole rocks and minerals of basaltic andesite, andesite, and dacite in this region. The analyses reveal that basaltic andesite has experienced high undercooling and intense degassing, while both andesite and dacite samples have experienced magma mixing during their formation. The mineral assemblages in andesite are derived from basaltic, dacitic, and mixed melts, with the mixed melt comprising a 2:8 ratio of the former two. Dacite samples contain three mineral assemblages derived from andesitic, rhyolitic, and mixed melts, showing multiple injections of more primitive melts, as indicated by phenocryst textures and chemical zoning patterns. Moreover, they may have experienced the capture of mafic wall rocks. The performance of different mineral − based thermobarometers has been assessed by constructing the experimental datasets applicable to this study, and the best − performing thermobarometers are all from Putirka (2008). Calculations show that the pre − eruption storage temperatures for basaltic andesitic, andesitic, and dacitic magmas are 1090 ± 13 °C, 1032 ± 9 °C, and 938 ± 10 °C, respectively, with storage pressures not well constrained at 4.3 ± 1.4 kbar, 2.8 ± 1.3 kbar, and 2.5 ± 1.3 kbar, respectively. This study provides evidence that magma mixing plays a significant role in the origins of andesite and dacite from the Eastern Manus Basin and that its complex magma plumbing systems provide materials and potential heat sources for the volcanism and hydrothermal activity.

We present two robust and well‐dated paleomagnetic poles from upper Eocene and Oligocene volcanics in the Urumieh‐Dokhtar magmatic arc, Central Iran. These two poles place Iran ∼3.7°–3° of latitude south of its present position between ca. 40 and 23 Ma. Our new paleomagnetic declination data indicate that the Central Iran block may have experienced a ∼11.6° clockwise rotation since the Late Eocene. We integrated our new data with the retrodeformed margins of the Zagros collision zone and contemporaneous Arabia positions to better constrain the age and configuration of the Arabia and Eurasia assembly process. In our model, the Arabia‐Eurasia collision occurred first in the western Main Zagros suture between ca. 35 and 30 Ma and then diachronously spread eastwards. Our paleogeographic reconstruction and initial continental collision timing supports the Arabia‐Eurasia collision as a first‐order driver of global cooling, Red Sea rifting, and Mediterranean extension. Plain Language Summary The demise of the Neo‐Tethyan ocean and accompanied continent‐continent collisions created the thick crust and the low relief surfaces of the Iran Plateau and Tibetan Plateau. The onset timing and configuration in the Zagros collisional belt are critical for understanding the uplift of the Iran Plateau, tectonic evolution of the Mediterranean and Zagros regions, as well as the associated Cenozoic climate change. However, the age and configuration of the Arabia‐Eurasia continental collision are hotly debated. Previous works generated competing collision timing estimates ranging from Late Cretaceous to Pliocene, with most estimates from Eocene to Miocene. By conducting geochronology and paleomagnetism on the Eocene‐Oligocene volcanic rocks in Central Iran, we show that the Arabia‐Eurasia collision occurred first in the western Main Zagros suture at the Eocene/Oligocene boundary, and then diachronously spread eastwards. We suggest the Arabia‐Eurasia collision facilitates the slowing of Africa, the opening of the Red Sea, the extension in the Mediterranean, and the Eocene/Oligocene global cooling. Key Points Our paleomagnetic results indicate a ∼3.7°–3° of latitude south of the present position of Central Iran during ca. 40–23 Ma Central Iran has experienced ∼11.6° clockwise rotation since ca. 40 Ma Arabia‐Eurasia collision began at the Eocene/Oligocene boundary in the western Main Zagros suture and diachronously spread eastwards

We investigate the Li isotope composition and the Li concentrations of metamorphic and sedimentary rocks of the Palaeozoic (Pz) basement in the Central Andes and follow the trace of the Li in the Cenozoic volcanic rocks at the active continental margin. The average Li isotope composition of Pz-basement closely resembles global averages of upper crustal rocks with overlapping, but higher average Li content in the Pz-basement. Lithium isotope composition and content in the Cenozoic volcanic rocks of the Central Volcanic Zone (CVZ) range from mantle-like signatures to Pz-basement compositions with high δ7Li values and high Li contents. Evolutionary trends of the Li isotope composition in the CVZ volcanic rocks can be explained by assimilation of the Pz-basement. At a margin-wide scale, the abundance of Li in the CVZ volcanic rocks is higher than that of the Cenozoic volcanic rocks of the active Andean arc north and south of the CVZ. The CVZ volcanic and Pz-basement rocks are considered to be the primary source of Li in world-class Li-deposits in evaporates of the Altiplano-Puna high plateau and its western slope between ca 27° and 20° S. These deposits define the so-called “Lithium-Triangle”, between southern Bolivia, NW Argentina and NE Chile. The pivotal processes of extraction of Li from its primary rock sources and of Li migration from the source rocks to the deposits still await detailed investigation.

Arc magmas are important building blocks of the continental crust. Because many arc lavas are oxidized, continent formation is thought to be associated with oxidizing conditions. On the basis of copper's (Cu's) affinity for reduced sulfur phases, we tracked the redox state of arc magmas from mantle source to emplacement in the crust. Primary arc and mid-ocean ridge basalts have identical Cu contents, indicating that the redox states of primitive arc magmas are indistinguishable from that of mid-ocean ridge basalts. During magmatic differentiation, the Cu content of most arc magmas decreases markedly because of sulfide segregation. Because a similar depletion in Cu characterizes global continental crust, the formation of sulfide-bearing cumulates under reducing conditions may be a critical step in continent formation.

Eco-concrete is an engineered porous material, often used in pervious pavement and slope protection. Volcanic rock, due to its loose and porous structure, can absorb pollutants and improve the performance of eco-concrete. Here, this study determined the performance of eco-concrete modified with different contents of volcanic rock in sewage purification. The results showed that eco-concrete purified sewage, and that adding volcanic rock further improved the removal capacity of total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) by 34.1, 47.3, and 6%, respectively. The water purification mechanism of volcanic rock eco-concrete (VREC) was mainly physical water absorption (mechanical retention) and microbial degradation. With the increase in the content of cement slurry, the adsorption amount decreased, porosity decreased, and strength increased, gradually not meeting the engineering application requirements. Therefore, the high porosity volcanic rock eco-concrete (VREC) had the best water purification performance. The result conclude that eco-concrete should be prepared with an admixture of volcanic rock with 30% porosity for the best sewage purification results.

Volcanic rocks and magma display a wide range of porosity and vesicle size, a result of their complex genesis. While the role of porosity is known to exert a fundamental control on strength in the brittle field, less is known as to the influence of vesicle size. To help resolve this issue, here, we lean on a combination of micromechanical (Sammis and Ashby's pore-emanating crack model) and stochastic (rock failure and process analysis code) modelling. The models show, for a homogenous vesicle size, that an increase in porosity (in the form of circular vesicles, from 0 to 40 %) and/or vesicle diameter (from 0.1 to 2.0 mm) results in a dramatic reduction in strength. For example, uniaxial compressive strength can be reduced by about a factor of 5 as porosity is increased from 0 to 40 %. The presence of vesicles locally amplifies the stress within the groundmass and promotes the nucleation of vesicle-emanating microcracks that grow in the direction of the applied macroscopic stress. As strain increases, these microcracks continue to grow and eventually coalesce leading to macroscopic failure. Vesicle clustering, which promotes the overlap and interaction of the tensile stress lobes at the north and south poles of neighbouring vesicles, and the increased ease of microcrack interaction, is encouraged at higher porosity and reduces sample strength. Once a microcrack nucleates at the vesicle wall, larger vesicles impart higher stress intensities at the crack tips, allowing microcracks to propagate at a lower applied macroscopic stress. Larger vesicles also permit a shorter route through the groundmass for the macroscopic shear fracture. This explains the reduction in strength at higher vesicle diameters (at a constant porosity). The modelling highlights that the reduction in strength as porosity or vesicle size increases is nonlinear; the largest reductions are observed at low porosity and small vesicle diameters. In detail, we find that vesicle diameter can play an important role in dictating strength at low porosity but is largely inconsequential above 15 % porosity. Vesicle clustering and stress lobe interaction are implicit at high porosity, regardless of the vesicle diameter. In the case of an inhomogeneous vesicle size, the microcracks grow from the largest vesicles, and brittle strength is closer to that of the largest vesicle end-member. The results of this study highlight the important role of vesicle size, and the complex interplay between porosity and vesicle size, in controlling the brittle strength of volcanic rocks and magma.

Seismic inversion is the primary way to obtain subsurface models, lithologic and stratigraphic information. However, seismic elastic parameters inversion and ‘discrete lithofacies’ identification for complex volcanic reservoirs are usually independent during the whole inversion process. Also, the influence of reservoir lithology on elastic parameters is not always considered directly before lithofacies prediction. This paper proposes a probabilistic pre-stack seismic inversion method for lithofacies and elastic parameters of volcanic reservoirs. Under the framework of Bayesian inversion, considering that the prior probability distribution of elastic parameters of volcanic reservoirs is affected by volcanic lithofacies, a posteriori probability distribution characterized by a mixed probability model is first derived. Then, a single-point-direct sequential simulation stochastic algorithm with simultaneous optimization of multiple solutions is used to simulate the posterior probability distribution of elastic parameters and lithofacies of volcanic reservoirs, which improves the resolution of lithofacies prediction results of volcanic reservoirs. The feasibility and stability of our method are ensured through synthetic and field applications. The prediction results highly agree with logging curves and lithology logging interpretation data. We have improved the resolution of volcanic rock reservoir lithofacies prediction results. In one-dimensional tests, we achieved the prediction of lithofacies and elastic parameters for three types of volcanic lithofacies. The error compared to prior information is no higher than 15%, thereby verifying the method’s good noise resistance.

We present a new and easy‐to‐use geochemical tectono‐magmatic setting discriminator to calculate the probability of membership (the Sparse Geochemical Tectono‐magmatic setting Probabilistic membershiP discriminatoR, SGTPPR) that runs in Excel. It outputs the probability of membership for eight different tectono‐magmatic settings (mid‐ocean ridge, oceanic island, oceanic plateau, continental flood basalt province, intra‐oceanic arc, continental arc, island arc, and back‐arc basin) for a given volcanic rock sample based on major and selected trace element contents (SiO2, TiO2, Al2O3, Fe2O3, MgO, CaO, K2O, Na2O, Rb, Sr, Y, Zr, Nb, and Ba). We consider all possible ratios and multiplications of these contents, in addition to the contents themselves, which improves the discrimination accuracy. We use a statistical method called sparse multinomial logistic regression to construct a robust and predictive discrimination model. By imposing the sparsity, only a small number of essential variables are included in the model. The variables are objectively extracted from 287 possible geochemical variables, including all possible ratios and multiplications of the major and trace element contents. The constructed model exhibits a high classification ability, indicating that tectonic discrimination using major and selected trace elements yields a high classification ability when ratios and multiplications are considered. The system outputs the relative weights of the variables (i.e., contents, and ratios and multiplications of contents) of the input geochemical data to the calculated membership probabilities. This information can be used to evaluate and interpret the results. We apply the model to multiple samples of a geological unit, to determine the tectonic setting. Plain Language Summary Identifying the source geochemical characteristics of a volcanic rock is essential for understanding magma generation processes and evaluating the tectonic setting of magmatism. We constructed a geochemical discriminator that runs in Excel to characterize volcanic rocks based on their chemical composition. It outputs the probability of membership to eight tectono‐magmatic settings based on the input chemical composition of a volcanic rock sample. The analysis can be conducted with major elements and commonly analyzed six trace elements, making it applicable to a wide range of samples from mafic to silicic compositions. We used a statistical method called sparse multinomial logistic regression to construct the discriminator, in which all possible ratios and multiplications of eight major and six trace element contents were considered. This system provides the relative weights of the input variables (major and trace element contents, and their ratios and multiplications) on the final results, making it easy to interpret and discuss the output. The discriminator can also be used to characterize a geological unit and volcanic body based on multiple samples, and determine its tectonic setting of formation. Key Points We present a probabilistic geochemical tectono‐magmatic setting discriminator that runs in Excel Probabilities of the memberships of a volcanic rock sample for eight different tectono‐magmatic settings can be easily computed Discrimination using major and selected trace elements yields a high classification ability when ratios and multiplications are considered

Natural nepheline usually contains very small amounts of MgO (<0.1 wt.%), although these examples are mainly from Mg-poor alkaline igneous rocks such as nepheline syenites. However, this work shows that nepheline and kalsilite with much higher MgO concentrations can occur in the groundmass of strongly SiO 2 -undersaturated, feldspar-free, mafic volcanic rocks (i.e. olivine-rich foidites). Furthermore, a strong positive correlation is evident between their Mg and Fe contents. The occurrence of Mg-rich nepheline and kalsilite seems to be related to their derivation from Mg-rich magmas when compared to most of the host rocks investigated to date. Additionally, the physicochemical conditions of crystallisation seem to have an important role in the incorporation of ‘small’ divalent cations by these minerals. The prevalence of Mg-rich nepheline and kalsilite as late magmatic phases and the divergent Mg and Fe relationships for phenocrysts and ‘quenched’ groundmass crystals support this hypothesis. The positive correlation between Mg and Fe contents reflects their strong geochemical affinity and the entrance of Fe 3+ , Fe 2+ and Mg 2+ cations into the same crystallographic site of nepheline and kalsilite structures. The calculation of atomic formulae and stoichiometry parameters for nepheline-group minerals where data for the T 2+ cations (e.g. Mg 2+ ) are incorporated gives more reliable compositional parameters (see Paper 1). Calculated excess silica values (Si′) are affected significantly when the coupled substitution 2Al 3+ = Mg 2+ + Si 4+ is considered. Thus, specific analyses of ‘small’ divalent cations are essential to obtain more realistic values of excess Si′, in particular, for nepheline and kalsilite that crystallised from Mg-rich, Si-poor, mafic–ultramafic alkaline lavas.

This paper describes an olistostrome formation and accompanied bimodal volcanic rocks occurring in the Baiyanggou area, south of Bogda Shan. The main lithotectonic units consist of olistostrome, volcanic rocks and turbidite. The olistostrome is tectonically underlain by Upper Carboniferous limestone and sandstone along a NEE-trending detachment fault. Paleo-growth fault is locally observed. The olistostrome unit includes plenty of blocks of limestone, sandstone, rhyolite and volcaniclastic rocks, and a matrix of graywacke. Limestone blocks are dated as Pennsylvanian-Bashkirian in age by the coral and brachiopod fossils that are extensively recognized in the Upper Carboniferous strata. The volcanic unit consists of pillowed and massive basalt and rhyolite, the latter occur as an 8- to 10-meter-thick layer above the olistostrome unit. The turbidite unit is mainly composed of chert, siliceous mudstone and sandstone, within which the Bouma sequence can be locally recognized. Meter-wide gabbro and diabase dykes intrude these three units. Geochemically, rhyolites are characterized by high ACNK value of >1.1, depletion of Ba, Nb and Sm, and enrichment in Rb, Th and Zr. Basaltic rocks are rich in K 2 O, they show a LREE-enriched pattern and depletion in Ba, Nb and Zr, and enrichment in Ti, Ce and Hf, similar to continental rift-type tholeiite series. A gabbro porphyrite intruding the olistostrome was dated at 288 ± 3 Ma by a sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb method, and a rhyolite at 297 ± 2 Ma by a laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) zircon U–Pb method. The Baiyanggou olistostrome and accompanying bimodal volcanic series are linked to an extensional setting that developed in the south of the Bogda Shan. Several lines of evidence, e.g. occurrence of large-scale strike-slip shear zones, large number of mantle-derived magmatic rocks and available geochronological data, demonstrate a significant geodynamic change from convergence to extension in the Chinese Tianshan belt, even in the whole Central Asian Orogenic Belt. The extension in the Chinese Tianshan belt is initiated at ca. 300 Ma, i.e. around Carboniferous–Permian boundary times, and the peak period of intra-plate magmatism occurred in the interval of 300–250 Ma.