Igneous Origin Research Articles

Mineralogy and Mineral Chemistry of Dioritic Dykes, Quartz Diorite Enclaves and Pyroxene of the Sungun Cu-Mo Porphyry Deposit, East Azerbaijan, Iran

The Sungun Cu-Mo porphyry deposit forms part of the Ahar–Arasbaran Magmatic Belt (AAMB). Its host Miocene porphyry stock is quartz monzonitic in composition and is cut by intermediate dykes that post-date mineralization. These dykes contain pyroxene and enclaves of ambiguous origin. Dykes of microdiorite are observed within quartz diorite dykes, whereas later diorite dykes contain three different kinds of enclaves (diorite, quartz diorite and hornfels) of sizes between 1 and 10 cm. Enclaves consist of plagioclase, hornblende and biotite, with accessory sphene, quartz and apatite. Chlorite compositions in microdiorite are within the chamosite range, whereas they are within the clinochlore range in diorite enclaves. Microprobe analyses of pyroxene indicate an augitic composition (Fs13.38-22.79Wo29.1-33.57En48.53-56.61), consistent with an igneous origin. Hornblende of the diorite enclaves formed at pressures ranging between 3 and 5.3 kilobars and temperatures between 714 and 731 °C. Average oxygen fugacity during rock formation is −14.75. Such high oxygen fugacities suggest that the diorite formed near the boundaries of a convergent margin. Amphibole compositions suggest that the diorite enclaves are sub-alkaline to mildly alkaline, consistent with reported whole-rock chemistry of the Sungun magmas. Pyroxenes were formed at pressures ranging between 11 and 15 kilobars (33–45 km) and temperatures between 1100 and 1400 °C. The amount of Fe3+ in clinopyroxene is also consistent with high oxygen fugacity within their environment of crystallization. Overall, these results have implications for our understanding of the origin of the Sungun Cu-Mo porphyry magmas and their mineral deposits in a lower-crustal setting.

Medieval Quarry Near the Koksa Bay (Krasnoyarsk Reservoir) as the Evidence of Possible Migration of the Yenisei Kyrgyz from the Sayan Mountains to the Middle Yenisei

Purpose. The results of archaeological survey in 2021 along the western shore of the Krasnoyarsk reservoir in the Koksa Bay area are presented in the process of field research. Previously unknown cultural and historical objects were revealed – a quarry on Mount Bol’shoi Togurtag, presumably of medieval times, and mounds in the form of rounded stone objects at the foot of the mountain 1 250 m from the Koksa bay.Results. The material extracted from the quarry was used in the construction of these mounds, located at the foot of the mountain. This assumption is evidenced by a similar type of rock in the quarry and on the mounds (they are of magmatic origin). Previously, similar objects for this territory were not mentioned in the scientific literature. Is the technological originality in stone processing techniques evidence of the migration to this territory of any mobile group of the population from the outside, where such technology was traditional? For example, medieval Kyrgyz kurgans in the Usinsk valley of the Western Sayan, where there are many rocks of igneous origin, are similar to them in their appearance and composition of the building material. Therefore, it is logical to assume that here, on the Middle Yenisei, some group of “Usintsy” migrated, which was quite likely as part of the process of returning to their homeland of the Yenisei Kyrgyz after the Great Power era. An exhaustive answer to this question can be given in the future only after an archaeological study of the rounded stone structures located here, similar to medieval “сhaatas” and “suukter” mounds, but composed, as indicated, of material of magmatic origin, unusual for this territory, in the form of large and medium-sized blocks of “torn” forms.Conclusion. The quarry on Bol’shoi Togurtag Mount demonstrates more labor-intensive process of obtaining stone material in comparison even with the extraction of “slabs” from layers of Devonian sandstone for the construction of mounds of the Tagar culture. All of the above and determines the originality of this object among those known in Khakassia. In this regard, their further study seems to be very relevant and expedient for the formation of a complete picture of the origin of medieval archaeological sites on the left bank of the Yenisei.

The Origin and Discrimination of High-Ti Magnetite in Magmatic-Hydrothermal Systems: Insight from Machine Learning Analysis

AbstractHigh-titanium (high-Ti, more than 1 wt % Ti) magnetite, commonly containing ilmenite exsolution, has long been attributed to an igneous origin and has been used as the most critical factor in previously developed discriminant diagrams. However, recent studies have shown that high-Ti magnetite can be present in high-temperature hydrothermal deposits, suggesting a probable hydrothermal origin. This also calls for reconsideration and necessary modification of the currently available discriminant diagrams. This high-Ti magnetite issue is particularly acute in iron oxide-apatite (IOA) deposits and raises controversy in the discussion of the origin of the high-Ti magnetite.With statistical analysis and machine learning techniques, this study applies two unsupervised dimensionality reduction methods—principal component analysis (PCA) and t-distributed stochastic neighbor embedding (t-SNE)—on a compiled data set consisting of 876 laser ablation-inductively coupled plasma-mass spectrometry analyses of primary high-Ti magnetite from high-temperature ore-forming systems worldwide. Three models are built with different element combinations to identify magnetite of different origins. The models were further evaluated by the support vectors machine (SVM) and receiver operating characteristic (ROC) curves and proved to be able to describe the characteristics of trace element compositions of high-Ti magnetite of different origins. Our models suggest that Mg, Mn, Al, Ti, V, and Co from 59 analyzed trace elements show promising properties as effective discriminators, and on this basis, a new discrimination diagram of lg(Al) + lg(Ti) + lg(V) versus lg(Mn)/[lg(Co) + lg(Mg)] is developed for distinguishing high-Ti magnetite of igneous and hydrothermal origin. Our results also show that the high-Ti magnetite in the IOA deposits has chemical compositions similar to those of high-temperature hydrothermal deposits, including the iron oxide copper-gold and porphyry deposits, but significantly distinct from the igneous magnetite. Our study, hence, implies a magmatic-hydrothermal origin for the magnetite in IOA deposits.

Subsurface structure of the Mazatlán basin, southeastern Gulf of California, Mexico, from seismic reflection and well data

The structure of the southeastern Gulf of California rifted margin is only partly known because of the thick sedimentary cover of the continental shelf and coastal areas of Sinaloa and Nayarit. Here we report the subsurface structure and probable age of the Mazatlán basin, one of the largest buried basins, based on interpretation of reprocessed by multichannel 2D reflection seismic profiles and an exploratory well drilled by Petroleos Mexicanos (PEMEX) between 1979 and 1980, as well as gravimetric data. The Mazatlán basin is located just north of the active subduction zone of the Rivera plate and west of the new oceanic crust accreted since the Pliocene at the mouth of the Gulf. The basin is bounded to the west by a high of the Late Cretaceous batholiths exposed in the Tres Marias Islands and in the normal faults bounding the Nayarit Troughs, and to the east by the late Oligocene-early Miocene extensional faults bounding the Sierra Madre Occidental. Based on the characteristics of the seismic profiles, the basin can be divided into three main sectors. The transition between the northern and central sectors is defined by an abrupt deepening of the basement that corresponds to the westward prolongation of ENE-WSW trending accommodation zones separating opposite tilted domains in the Sierra Madre Occidental. The acoustic basement is clearly defined in the central sector by a set of high-amplitude reflectors suggesting an igneous origin. The deepest part of the basin is located toward the coastal plain of Nayarit and coincides with a gravimetric minimum. We identify several high amplitude reflectors interpreted as mafic sills, which become more abundant toward the south. At least part of them can be correlated with the widespread mafic volcanism emplaced at 9–12 Ma along the eastern margin of the Gulf of California rift. In the northern and central sectors we identified three main stratigraphic boundaries (L1, L2, and L3) within the basin filling, which define seismo-stratigraphic sequences. The shallower sequences, limited by the L1 and L2 boundaries and attributed to the Pleistocene and part of the Pliocene, lack evidence of significant deformation. The sequence above L3 boundary, can be assigned to the earliest Pliocene and the Miocene since they are intruded by a ~ 10 Ma basaltic sill cut by the Huichol-1 exploratory well. The lower part of the basin is characterized by high amplitude reflectors that pinches out against the acoustic basement and correspond to volcanic tuffs and sedimentary deposits correlative with the lower member of the Comondú group exposed in Baja California, which includes ~23 to ~19 Ma distal part of ignimbrites sourced from the Sierra Madre Occidental in Nayarit. Faults with the most significant displacements have a listric geometry and dip from the E to NE. The maximum sediment thickness reported in the Huichol-1 well is 2800 m, with a two-way travel time of 2.7 s, but it reaches 3.7 TWTT in some areas. Based on sedimentation rates, the minimum age for the onset of sedimentation in the basin is ~19 Ma, which is consistent with the regional tectonic evolution of the margin.

A report on radon emission from bauxitic material in Perth, Manchester, Jamaica

Bauxitic soils in Jamaica are enriched with rare earth elements and other heavy minerals/elements by up to two orders of magnitude relative to bedrock. Geochemical evidence supports the origin of Jamaican bauxite as volcanic ash fall-out from Central America and windblown dust from West Africa. Jamaican bauxite, by virtue of its possible igneous origins, is suspected of being a source of radioactive material. The potential concentration and mobility of radon gas from bauxite waste is an environmental health and safety risk. Therefore, this paper investigates the theoretical radon concentrations and exposure rates in the bauxite mining community in Perth, Manchester. Results from the study show that the exposure rates in the Perth community are all below the recommended 1 WLM/yr. Therefore, radon from the bauxite waste is not a concern for radiation exposure and could be a potential recycled material for brick and other low-income housing materials in Jamaica.

Organic carbon concentrations in 3.5-billion-year-old lacustrine mudstones of Mars

The Sample Analysis at Mars instrument stepped combustion experiment on a Yellowknife Bay mudstone at Gale crater, Mars revealed the presence of organic carbon of Martian and meteoritic origins. The combustion experiment was designed to access refractory organic carbon in Mars surface sediments by heating samples in the presence of oxygen to combust carbon to CO2. Four steps were performed, two at low temperatures (less than ∼550 °C) and two at high temperatures (up to ∼870 °C). More than 950 μg C/g was released at low temperatures (with an isotopic composition of δ13C = +1.5 ± 3.8‰) representing a minimum of 431 μg C/g indigenous organic and inorganic Martian carbon components. Above 550 °C, 273 ± 30 μg C/g was evolved as CO2 and CO (with estimated δ13C = -32.9‰ to -10.1‰ for organic carbon). The source of high temperature organic carbon cannot be definitively confirmed by isotopic composition, which is consistent with macromolecular organic carbon of igneous origin, meteoritic infall, or diagenetically altered biomass, or a combination of these. If from allochthonous deposition, organic carbon could have supported both prebiotic organic chemistry and heterotrophic metabolism at Gale crater, Mars, at ∼3.5 Ga.

Miocene Crustal Anatexis of Paleozoic Orthogneiss in the Zhada Area, Western Himalaya

AbstractGranitic gneiss (orthogneiss) and Himalayan leucogranite are widely distributed in the Himalayan orogen, but whether or not the granitic gneiss made a contribution to the Himalayan leucogranite remains unclear. In this study, we present the petrological, geochronological and geochemical results for orthogneisses and leucogranites from the Zhada area, Western Himalayas. Zhada orthogneiss is composed mainly of quartz, plagioclase, K‐feldspar, biotite and muscovite, with accessory zircon and apatite. Orthogneiss zircon cathodoluminescence (CL) images show that most grains contain a core with oscillatory zoning, which indicates an igneous origin. Sensitive high‐resolution ion microprobe (SHRIMP) U‐Pb dating of the zircon cores in the orthogneiss shows a weighted 206Pb/238U age of 515 ± 4 Ma (early Paleozoic), with spongelike zircon rims of 17.9 ± 0.5 Ma (Miocene). Zhada leucogranite shows 206Pb/238U ages ranging from 19.0 ± 0.4 Ma to 12.4 ± 0.2 Ma, the weighted average age being 16.2 ± 0.4 Ma. The leucogranites have a low Ca content (<1 wt%), FeOt content (<1 wt%), Rb content (67.0–402 ppm), Sr content (<56.6 ppm), Ba content (3.35–238 ppm) and Rb/Sr ratio (0.5–14.7), which are similar to the geochemical characteristics of the Himalayan leucogranite derived from muscovite dehydration partial melting of metasediments and representative of most Himalayan leucogranites. The highly variable Na2O + K2O (4.33 wt%–9.13 wt%), Al2O3 (8.44 wt%–13.51 wt%), ∑REE (40.2–191.0 ppm), Rb (67.0–402 ppm) and Nb (8.23–26.4 ppm) contents, 87Sr/86Sr(t) ratios (0.7445–0.8605) and εNd(t) values (–3.6 to –8.2) indicate that the leucogranite is derived from a heterogenetic source. The nonradiogenic Nd isotope values of the studied Zhada leucogranite and orthogneiss range from –8.2 to –3.6 and from –8.7 to –4.1, respectively. Therefore, the general mixing equation was used to perform the Sr and Nd isotope mixing calculations. The results indicate that the heterogenetic source was the Tethyan Himalayan Sequence (THS)/Higher Himalayan Crystalline (HHC) metasediments and Zhada orthogneiss. The Zhada area experienced crustal anatexis during the Miocene and the heterogenetic source of the orthogneiss and metasediment may have experienced crustal anatexis controlled by muscovite dehydration. The Zhada leucogranite inherited not only the geochemical characteristics of the Himalayan metasediment (muscovite dehydration melting), but also the trace elements and Sr‐Nd isotopic characteristics of the Zhada orthogneiss. These results indicate that the Paleozoic Zhada orthogneiss was involved in crustal anatexis at 17.9 ± 0.5 Ma (Miocene) and that the muscovite dehydration of the metasediments in the heterogenetic source produced fluid, which may have caused the orthogneiss solidus lines to decline, triggering a partial melting of the Zhada orthogneiss. It is therefore proposed that Himalayan leucogranite is a crust‐derived granite rather than a S‐type granite, as previously hypothesized.

The Analysis of Cones within the Tianwen-1 Landing Area

On 15 May 2021, the Zhurong rover of China’s first Mars mission, Tianwen-1 (TW-1), successfully landed in southern Utopia Planitia on Mars. Various landforms were present in the landing area, and this area recorded a complex geological history. Cones are one of the typical landforms in the landing area and Utopia Planitia, and they have a great significance to the local geological processes due to the diversity of their origins. Using High-Resolution Imaging Camera (HiRIC) images collected by the TW-1 orbiter, we identified a total of 272 well-preserved circular cones in the landing area. Detailed surveys of their spatial distribution, morphological characteristics, and morphometric parameters were conducted. A preliminary analysis of the surface characteristics of these cones also provides additional information to strengthen our understanding of them. The results of the high-resolution topographic analysis show that the cone heights are in the range of 10.5–90.8 m and their basal diameters range from 178.9–1206.6 m. We compared the morphometric parameters of the cones in the landing area with terrestrial and Martian analogous features and found that our measured cones are consistent with the ranges of mud volcanoes and also a small subset of igneous origin cones. However, the result of spatial analysis is more favorable to mud volcanoes, and the lower thermal inertia of the cones in the landing area compared to their surrounding materials is also a typical characteristic of mud volcanoes. Based on current evidence and analysis, we favor interpreting the cones in the TW-1 landing area as mud volcanoes.

Mineralogy, geochemistry, and 40Ar/39Ar dating of hornblendite/amphibolite pods in Penjween Ophiolite of northeastern Iraq: Implications for petrogenesis and tectonics

Penjween ophiolite is one of the ophiolitic complexes of northeastern Iraq. The serpentinites within the Penjween Ophiolite hosts many pods of hornblendite and amphibolite, and dikes of diorite among many other igneous bodies. These pods have very sharp contacts with the surrounding mantle serpentinized harzburgites. The hornblendites and amphibolites are usually intimately intergrown together as extremely hard, dark green to black colored, fine-to medium-grained pods with ∼2 x ∼2 x ∼(0.5–1) m dimensions. This study presents petrography, mineral chemistry, whole-rock major and trace element geochemistry, and electron probe microanalyses (EPMA) for the major minerals in the studied rocks. The hornblendite is composed entirely of amphiboles (>99% vol.), meanwhile the amphibolite consists of comparable amounts of amphibole and plagioclase which occasionally occurs as layered rocks with banded texture. The diorite dikes are white in color and consist dominantly of coarse-grained plagioclase and less amphiboles. The amphiboles of these rocks belong to pargasite (Mg# 0.69–0.77) ─ edenite (Mg# 0.74–0.79) endmembers where pargasite is by far the predominant mineral; meanwhile the plagioclase is albite (Ab93.4An6.4Or0.2). The amphiboles are replacement products of pyroxenes indicated from the relict pyroxene within their crystals. The amphiboles are abnormally rich in various dust-like inclusions of transparent minerals like REE-rich epidote, rutile, zircon, apatite, titanite, and ore minerals like ilmenite, and pyrrhotite, oriented along the crystallographic axes and form distinct zones in the core of amphibole crystals. The geochemical characteristics of the studied hornblendite (MgO = 13.07%, Ni = 260 ppm, Mg# = 66.57) as well as the high Sc (33 ppm) and V (254 ppm) concentrations are collectively consistent with a mantle-derived, igneous origin. The primitive-mantle normalized trace elements spidergram showed enrichment (hump) in Ba, Th, U, La, Ce, Pb, and Sr, and depletion (trough) in Nb, Ta, K, and Ti. The chondrite-normalized REE diagram showed enrichment of LREE relative to HREE, indicated from the smooth and steady decrease in the negative slope from LREE towards HREE with a negligible Eu-anomaly. Various tectonic discriminating diagrams showed that the studied hornblendite, amphibolite pods and diorite dikes are of igneous fore-arc origin, formed from calc-alkaline and/or tholeiitic magma within an active continental margin setting. The 40Ar/39Ar laser age of hornblendite is late Paleocene (Thanetian) (57.8 ± 5.1 Ma) which might represent an event during the obduction between the oceanic fore-arc Island and the Arabian Plate during the Late Cretaceous/Paleocene period.

Carbonatite metasomatism, the key to unlocking the carbonatite-phoscorite-ultramafic rock paradox

One of the features of carbonatite-phoscorite complexes that has received comparatively little attention is that many of them are surrounded by large bodies of ultramafic rocks. Although it is generally assumed that all the rocks are of igneous origin, there is disagreement over whether the carbonatites and phoscorites are genetically related to the ultramafic rocks. This is despite the fact that in complexes where they have been dated, these three suites of rocks are identical in age. A major challenge for any igneous hypothesis is the paradox posed by the observation that the ultramafic and carbonatitic magmas are the products of very high and very low degrees of partial melting of the mantle, respectively. We resolve this paradox by proposing a hypothesis, in which the ultramafic rocks are metasomatic in origin. According to this hypothesis, a carbonatitic magma, generated by partial melting of carbonated mantle, acts as the agent of metasomatism. The interaction of this magma with quartz-rich rocks, including granites and gneisses, transforms them into ultramafic rocks. This is made possible by the extremely low viscosity of the magma that allows it to pervasively infiltrate the wall rocks. As a result, Mg, Ca and other components are transferred to the host, leading to the crystallisation of minerals such as olivine, clinopyroxene and biotite, and the loss of CO2 from the system. Because of its low viscosity, the carbonatitic magma is emplaced as numerous intrusions, ranging in width from the micron to the metre scale, that progressively transform the host rocks into ultramafic rocks. As this metasomatism proceeds, the Na concentration of the magma gradually increases and eventually becomes high enough to permit large scale assimilation of Si (and Al) and the generation of an alkaline silicate magma that is emplaced at the margins of complexes, forming ijolites. The metasomatism and assimilation are envisaged as a front that moves progressively from the conduit to the limits of the complex, producing an outward zonation from dunite through clinopyroxenite to ijolite or from clinopyroxenite to ijolite directly. Whether the zonation is fully developed or dominated by a single zone, e.g., dunite or clinopyroxenite, depends on the initial composition of the carbonatitic magma and/or the degree of progress of the metasomatic reaction. The processes described above constitute the “silicate stage” of carbonatite-phoscorite-ultramafic rock complex development and are marked by the complete consumption of the carbonatitic magma. During the waning stages of the formation of these complexes, metasomatism by new batches of carbonatitic magma is restricted to remnants of reactive wall rocks adjacent to the magma conduit. Consequently, the magma is only partially consumed. This results in a residual liquid that is enriched in phosphate and iron and crystallises phoscorite. We refer to this as the “phoscorite stage” of carbonatite-phoscorite-ultramafic rock complex development. The final, “carbonatite stage”, is marked by the cessation of metasomatic activity and the crystallisation of carbonatites from batches of magma that are unaffected by interaction with the wall rocks and are compositionally identical to those that initiated the “silicate stage”. This model explains the spatial association of the different rock types, in which the complexes are zoned outwards from a core of carbonatite, through a zone enriched in phoscorite, into a broad halo of ultramafic/ultrabasic rocks. In so doing, the model accounts for the many features of these complexes that have not been adequately explained in previous genetic models.

Petrotectonic framework of Siwalik Group in Khairi Murat-Kauliar area, Potwar Sub-Basin, Pakistan

The Khairi Murat-Kauliar area lies between the Salt Range Thrust (SRT) in the south whereas Main Boundary Thrust (MBT) in the north which is the part of the Potwar Sub Basin. Eocene to Recent succession is exposed in the study area. The selected siliciclastic Siwalik Group display various facies in a fluviatile environment, with different lithologies, and sedimentary features. The petrographic studies of Siwalik Group delineate different microfacies including feldspathic litharenite, litharenite and sub arkose. The provenance study of sandstones depicted the terrane of dissected arc and recycled orogeny, indicating that the detritus was received from sedimentary, metamorphic, plutonic and volcanic rocks from the northern domain of Indian Plate, Karakoram Ranges and Kohistan Island arc. The Siwalik sandstone also contains heavy mineral assemblage such as tourmaline, garnet, epidote, hornblende and chlorite. This heavy detritus assemblage depicted that the deposits were received from metamorphic and igneous origin. A modified dynamic depositional stages of the Siwalik Group with respect to Himalayan orogeny is further built using outcrop data, microfacies and heavy minerals analysis. According to this concept, the group was deposited along Himalayan uprising and thrusting, on the depository in targeted area. The Siwalik Group depicted different phase of Himalayan tectonics and these molasse sequence were deposited in a subsiding foreland basin under the conditions of rapid erosion and quick deposition.

Gamma‐CaSO4 With Abnormally High Stability From a Hyperarid Region on Earth and From Mars

AbstractOrdinary γ‐CaSO4 is a metastable calcium sulfate, while γ‐CaSO4 from the hyperarid region on Earth and from Mars has been found with abnormally high stability. In this study, we used multiple microanalyses to characterize the chemical and structural properties of two such γ‐CaSO4: one from Atacama soil (#10‐d30) and the other from Martian meteorite MIL03346,168. Silicon was determined to be quasi‐homogeneously distributed in Atacama γ‐CaSO4, while both silicon and phosphorus were detected in Martian γ‐CaSO4. We found the abnormally high stability of those γ‐CaSO4 from hyperarid environments was due to the chemical impurities which filled their structural tunnels and blocked the entrance of atmospheric H2O, with non‐detectable structural distortion. We propose that the γ‐CaSO4 with Si or Si and P impurities could have igneous origin or evaporative origin. Due to the extreme similarity in the structures of bassanite and γ‐CaSO4, their XRD patterns are almost non‐distinguishable; thus some martian “bassanite” minerals identified by Curiosity's CheMin instrument at Gale crater can actually be γ‐CaSO4. The structural tunnels in γ‐CaSO4 would allow ions and ionic groups to fill, thus providing meaningful insights about the geological and geochemical processes experienced by it during the formation and transformation. The Raman spectrometer carried by the Perseverance and by ExoMars rovers will help the selection of samples enriched in γ‐CaSO4 at Jezero Crater and Oxia Planum, which should be sampled for in‐depth analysis on Mars and back to Earth.

Distribuição de recursos agrominerais no tempo e no espaço – uma perspectiva geológica global

Abstract Agromineral resources are minerals and rocks used to improve soil productivity and health. These resources can be applied: indirectly, by extracting and concentrating one or more minerals by industrial processes for the production of conventional, highly soluble fertilizers; and directly, without processing, except fine grinding, for direct soil application. Agromineral resources include sedimentary phosphates, limestones/dolostones, potash and glauconite-bearing rocks of sedimentary origin, basaltic rocks, phonolites, kamafugites, and glass-rich mafic rocks of igneous origin. Among metamorphic agromineral resources, marble and biotite schist stand out. However, agromineral resources are not equally distributed on Earth’s surface, occurring more in one area than in another, and have accumulated in various geotectonic settings related to plate tectonics, being formed in specific geological time periods in Earth’s history. Therefore, these resources occur in specific “agromineral provinces” and were formed during specific “agromineral epochs”. This paper provides a conceptual framework for agromineral resource distribution in time and space. Agrominerals have a high potential to be used as directly applied soil amendments and soil remineralizers for new and innovative farming strategies, provided the amendments are low or free of contaminants.

Sedimentary environment and tectonic setting of the clastic formation of the Tanjianshan Group in the Tuomoerrite area, North Qaidam

柴北缘构造带断续出露的寒武-奥陶纪滩间山群火山-沉积岩系是早古生代时期原特提斯洋俯冲造山作用的产物，也是中国西部块状硫化物和造山型金矿床的重要含矿岩系。前人已对滩间山群火山岩组开展了大量的地球化学和同位素年代学研究，而碎屑岩组的沉积序列和沉积相研究相对薄弱。我们在柴北缘托莫尔日特地区地质填图过程中，对该地区的滩间山群碎屑岩组开展了系统的沉积组合序列和沉积相研究。托莫尔日特地区滩间山群碎屑岩组是由富含火山碎屑物质的含砾砂岩、砂岩、粉砂岩、泥岩、沉凝灰岩、硅质凝灰岩、硅质岩及少量砾岩共同组成。可分为下岩性段和上岩性段，其中下岩性段为一套形成于海底扇外扇环境以沉凝灰岩为主的沉积组合；上岩性段包含海底扇内扇、中扇和外扇沉积，且以中扇环境的沉积为主。垂向上，它们呈现出粒度向上逐渐变细特征；空间上，具有向北西方向火山物质成分逐渐增多、砾岩和砂岩厚度变薄且砾岩消失的变化特征。砂岩主要为岩屑长石杂砂岩，其中岩屑主要是安山岩和少量玄武岩、英安岩、凝灰岩；长石主要为斜长石；石英碎屑相对缺失。砾岩中砾石以安山岩和硅质岩为主，并含有少量灰岩和凝灰岩砾石。底冲刷面、正粒序、平行层理和波纹层理等沉积构造普遍发育，呈现出典型的浊流沉积特征；同时在局部露头见有滑塌构造和波痕。区域上，这套沉积组合序列位于寒武-奥陶纪岛弧火山岩的南侧；古水流分析显示，它们的碎屑物质主要来自于其北东方向。这些结果表明，柴北缘构造带东段的滩间山群碎屑岩组是一套成熟度极低且与寒武-奥陶纪岛弧火山活动密切相关的沉积组合。;Volcano-sedimentary system of the Cambrian-Ordovician Tanjianshan Group in the northern margin of Qaidam basin was formed by the subduction of the Proto-Tethys Ocean during Early Paleozoic and hosted massive sulfides and orogenic gold deposits in western China. Much attention had been paid to geochemistry and isotopic dating of the volcanic Formation of the Tanjianshan Group, but the sedimentary sequence and facies of the associated clastic rocks received less care. Systemic studies on the sedimentary sequence and facies in the processes of the geological mapping demonstrate that the clastic Formation in the Tuomoerrite area consists of pebbly sandstone, sandstone, siltstone, mudstone, tuffite, siliceous tuff, chert and minor conglomerate. This formation can be subdivided into two lithologic units. The lower unit is mainly dominated by tuffite deposited in the lower submarine fan environment, whereas the upper unit is deposited in the upper, mid, and lower fan environments. In contrast, the rock assemblages of the upper unit are mainly composed of the mid-fan deposits. The upper unit is characterized by fining-upward sequence and increasing abundance of volcanic composition northwestward, but the thickness of sandstones decreases and conglomerate disappears to northwest. Sandstones mainly comprise lithic greywacke. Lithic fragments contain andesite, basalt, dacite, and minor tuff and limestone. Feldspar fragments are dominated by plagioclase grains, and less monocrystalline quartz grains with an igneous origin occur in several samples. Clasts of conglomerates are dominated by angular andesite, chert and minor limestone and tuff. Irregular basal erosional surface, normal grading, parallel laminations and ripples are widespread show typical of turbidite. Slumping folds and wave marks can also be observed in the local outcrops. Regionally, volcano-clastic rocks distributed in the southern margin of Cambrian-Ordovician Keke island arc with a southwestward paleocurrent. These results demonstrate that the clastic formation is closely related to the Cambrian-Ordovician island arc.

Pressure-Temperature-Fluid Constraints for the Formation of the Halo-Shakiso Emerald Deposit, Southern Ethiopia: Fluid Inclusion and Stable Isotope Studies

ABSTRACT The Halo-Shakiso emeralds were discovered near the town of Shakiso in southern Ethiopia in 2016. They are gem quality, Cr-dominant emeralds hosted within ultramafic rocks and associated with Cambrian pegmatite intrusions of the Adola Belt. Aqueous-carbonic primary fluid inclusions hosted within emerald have a composition of approximately 3.0 wt.% NaCl eq. and an XCO2 of 0.06, with minor amounts of N2, CH4, and H2S. Stable isotope thermometry of contemporaneous quartz and emerald yields temperatures in the range of 420 to 470 °C. Combined stable isotope and fluid inclusion data are consistent with emerald precipitation at pressures ranging from 2.0 to 3.0 kbar, corresponding to depths of 5.9 to 8.9 km. Additionally, emerald channel water δD and calculated δ18O isotope values are consistent with an igneous origin for the fluids responsible for emerald precipitation; these fluids are also responsible for the metasomatization of the host rocks in and near the pegmatite, forming the phlogopite schist that is host to the Halo-Shakiso emeralds. The isotopic signatures, combined with the occurrence of adjacent pegmatites, support the classification of the Halo-Shakiso emerald deposit as a Tectonic-Magmatic-Related emerald deposit.

Petrography, geochemistry and depositional model of Ispikan Conglomerate, Makran Accretionary Prism, Southwest Pakistan

Sedimentology, petrography, and geochemistry of the Ispikan Conglomerate of southwest Makran have been studied to establish its stratigraphic position, age, provenance, and depositional environment. Very thin to massive beds, poor sorting, no fabric, and poor grading are the common features. It is composed of mostly reworked, medium- to coarse-grained pebbly sandstone, siltstone, and discontinuous lenses of matrix- and clast-supported conglomerate. The sandstone is composed of angular to sub-angular, poorly sorted, immature grains having Q72F13L15 as average composition. Pebbles are of mostly metamorphic and acidic igneous origin. Large angular boulders (~1.5m) of sandstone indicate quick debris flow conditions. Geochemical discriminants suggest the derivation of Ispikan sediments from an active continental margin. The Nb and Zr/Th and Ba/Y values indicate the continental island arc setting, whereas a high K/Rb ratio points to the derivation of detritus from an acid and intermediate source. Ispikan Conglomerate is interpreted as an Eocene olistostrome formed after a localized submarine debris flow triggered by slope failure.

Evidence for carbonatite derived from the earth's crust: The late Paleoproterozoic carbonate-rich magmatic rocks in the southeast Tarim Craton, northwest China

Carbonatites are generally accepted as derived from the mantle, whereas viewpoint of carbonatitic melt formed at crust level is considered marginal. Here we document large-scale (∼17 km2) igneous carbonate-rich rocks in the southeast Tarim Craton that were formed within the crust. These rocks exhibit clear intrusive contact with the wall-rocks and contain diverse xenolith, indicating an igneous origin. Zircon U-Pb dating reveals that they were emplaced at ca. 1.94–1.92 and 1.87–1.86 Ga, respectively. δ18O values in zircons (5.7–13.7‰) are higher than those crystallized in equilibrium with mantle melt. Total REE content is 1–2 magnitude lower than that of mantle carbonatite and shows weak fractionation of HREE. REE modeling reveals that the samples cannot be produced by partial melting of carbonated MORB at mantle conditions. The studied samples have positive δ13CV-PDB values (4.2–15.7‰), which are distinct from the mantle carbonatite but comparable to sedimentary carbonates. C-O-Sr-Nd isotope modelling indicates that the compositions of the studied samples cannot be produced by evolution of mantle carbonatite. Integrating these lines of evidence, we conclude that the studied carbonate-rich magmatic rocks were derived from partial melting of impure marble at crustal level via fluid-present melting. These carbonatites probably represent the initial magmatic record of tectonic extension of the late Paleoproterozoic collisional orogenic belt in the southern margin of the Tarim craton. The positive carbon excursion recorded by the high δ13CV-PDB values probably corresponds to the global Paleoproterozoic Lomagundi-Jatuli event. Our study implies that partial melting of sedimentary carbonates is more common than previously thought, which has significant impacts on crust rheology and global carbon cycling

Role of Hydrothermal Fluids in the Formation of the Kamioka Skarn-Type Pb–Zn Deposits, Japan

The Kamioka mine, located in Gifu Prefecture in Japan, is famous for the large water Cherenkov detector system, the Super-Kamiokande. The Kamioka skarn-type Pb–Zn deposits are formed in crystalline limestone and are replaced by skarn minerals within the Hida metamorphic rocks. The Kamioka deposits mainly consist of the Tochibora, Maruyama, and Mozumi deposits. The present study focuses on the ore-forming hydrothermal fluid activity in the Kamioka deposits and the peripheral exploration area based on the carbon and oxygen isotope ratios of calcite and rare earth element (REE) analyses. The carbon and oxygen isotope ratios of crystalline limestone (as the host rock) are not homogeneous, and depending on the degree of hydrothermal activity, they decreased to various degrees because of the reaction with the ore fluids. Thus, the carbon and oxygen isotope ratios of crystalline limestone can be used as an indicator of the influence of the hydrothermal fluids for the ore mineralization. The REE contents in the ores of igneous origin are one order of magnitude higher than the limestone origin. Further, depending on the formation temperatures, calcites precipitated during ore mineralization have a stable carbon isotope ratio and a widely varying oxygen isotope ratios. The Kamioka district fracture system is likely a major control factor on ore mineralization from hydrothermal activity. In addition, the skarnization-related ore-forming fluids are mostly meteoric in origin, confirming the conclusions from previous studies.

Experimental diopsidite: Implications for natural diopsidite genesis through fluid-melt-mantle peridotite reaction

Occurrences of diopsidites, rocks made predominantly of gem-like diopside whose composition precludes a purely igneous origin, allow tracking the pathway of high-temperature fluids and fluid-saturated melts in the oceanic lithosphere in vicinity of the mantle-crust transition zone (the Moho) and the adjacent mantle in an oceanic setting. We have experimentally explored the origin of the mantle diopsidites by reacting serpentinite with synthetic haplobasaltic glass (corresponding to anorthite-diopside eutectic at 0.1 MPa pressure) at 900 and 1250 °C, and 0.2 GPa pressure for 120 h. At 900 °C, no reaction is observed in the sample; in contrast, in the experimental runs heated to 1250 °C, we distinguish two mineral associations (1) early Al-poor diopside [Mg# = Mg/(Mg + Fe) = 99 ± 1; Al2O3 = 1.9 ± 1.6 wt%] with the diopside-hosted forsterite (Fo99.2 ± 0.1) inclusions and (2) late Al-enriched diopside (Mg# = 98 ± 1; Al2O3 = 3.7 ± 2.8 wt%). Our experiments confirm that mantle diopsidites can be produced at ≥ 1100 °C in response to partial melting of hydrated peridotite (serpentinite) in the presence of haplobasaltic melt and aqueous fluid at the conditions typical of the mantle-crust transition zone and the shallow mantle beneath oceanic spreading ridges.

Stability assessment of obliquely-bedded rock cuts using multi-prong procedures – case study

The stability of vertical cuts in rocky strata, associated with the provision of the transportation infrastructure through a mountainous terrain, is always a challenge for the geotechnical engineers. The problem becomes further complex if the cuts are parallel or near parallel to the bedding planes. Such a scenario results in all sorts of slope instability scenarios, including planar, wedge, rockfall, and toppling failure. A linear project was planned to pass through the mountainous stretches of western Saudi Arabia. The rock slopes exposed at the site after the excavations constitute igneous origin Granite/Granodiorite rock present in a moderately to highly weathered state and consist of two sets of discontinuities; one running almost parallel to slope faces and another nearly orthogonal to the major set of discontinuities. Based on the orientation of the discontinuities along the cuts on both the sides of the excavation, there is a high probability of all types of slope failures, including planar, wedge, toppling, or boulder/rockfall. This paper presents details of geologic field mapping, field and laboratory testing, and the software analysis of several modes of the possible slope failure modes. The study was carried out considering all the potential triggering factors, including rainfall, under both static and dynamic/seismic conditions. The paper also discusses the slope failure prevention measures recommended based on the interpretation of the field and laboratory data, software analysis, and the construction sequence.