Petrological Studies Research Articles

Why Did Red Ereño Limestone Go Red? Linking Scientific Knowledge and Geoheritage Story-Telling (Basque Country, Spain)

Red Ereño is a red-stained ornamentaland construction limestone with characteristic white fossil shells. Although exploited since Roman times, marketed worldwide and that the rock itself and its outcrop areas have been included in geological heritage inventories, the origin of its characteristic reddish colour remained unresolved. The aim of this work is to deepen the scientific knowledge of Red Ereño as a basis for understanding the characteristics of this stone and to make this information available for geoconservation actions. The mineralogical and petrological study, mainly based on optical and electron microscopy, X-ray diffraction, and rock magnetism and paleomagnetic techniques, concluded that the red-staining mineral is pigmentary hematite. Moreover, the analysis stated that hematite precipitated after sedimentation but prior to burial diagenesis and before alpine inversion. Based on palaeomagnetic studies, it can be stated that mineralisation occurred during the Late Cretaceous. This work illustrates how scientific research on this potential heritage stone provides key information for geoconservation.

The efficacy of high frequency petrological investigation at open-conduit volcanoes: The case of May 11 2019 explosions at southwestern and northeastern craters of Stromboli

Petrological studies of active volcanoes typically focus on eruptive phenomena occurring over long timescales of the order of days to years, aiming at identifying major changes in the physico-chemical state of magma during ascent towards the surface. Exceptionally, we present results from an integrated petrological and statistical approach based on the compilation of ∼5300 major and trace element data for glass and crystals, in combination with volcanological data on eruptive events occurred over timescales of minutes at Stromboli volcano (Sicily). On May 11, 2019, we had the rare opportunity to collect individual fresh fallout ash products from eighteen mostly consecutive explosions, erupted in a 2-h time span and, at the same time, to acquire continuous high frequency (50 Hz) infrared thermal data of the same explosions. Through video analysis, we observe that explosions were more frequent and ash-dominated at the southwestern crater area (SCA, 8–10 events/h) than at the northeastern crater area (NCA, 3–5 events/h), where coarser material was ejected. The statistical analysis of glass and plagioclase compositions reveals differences in the products erupted from the two crater areas. SCA explosions tapped less differentiated magmas (Mg#∼42–46, ∼257–365 LaN, ∼0.7–0.9 Eu/Eu*) in equilibrium with more anorthitic plagioclase cores (An∼72–88), whereas NCA area explosions are more differentiated (Mg#∼40–44, ∼286–387 LaN, ∼0.6–0.8 Eu/Eu*) and in equilibrium with less anorthitic plagioclase cores (An∼68–82). Thermometric calculations based on major and trace element clinopyroxene-plagioclase-melt equilibrium modeling highlight that the SCA explosions were statistically fed by hotter magmas in comparison to NCA explosions. Plagioclase-based diffusion modeling also indicates longer timescales for the dynamic ascent of NCA magmas, leading to preferential groundmass crystallization at the conduit walls and transition from sideromelane to tachylite groundmass textures. The final emerging picture is that in May 2019, concurrent normal eruptions from different crater areas at Stromboli were heralds of compositionally and thermally diverse magmas rising at different rates within the uppermost branched part of the conduit region. High frequency petrological investigations aided by statistical treatment of data have the potential to constrain dynamic conduit processes related to transient, explosive eruptions in persistently active volcanoes, thereby offering new insights on the interplay between magma dynamics, ascent timescales, and eruptive behavior.

Galaxy of Green

Olivine occurs across the galaxy, from Earth to extraterrestrial bodies including the Moon, Mars, and asteroids, to particles of comet dust and distant debris disks. The mineral is critical to our understanding of early Solar System chronology, planetary formation processes (e.g., magma ocean solidification), crustal evolution (e.g., volcanic eruptions), and surface weathering. Olivine’s ability to shed light on these processes lies in the linkage of small, physical samples and satellite-derived data. Laboratory spectra become the basis for olivine detection and compositional interpretation in remotely sensed spectra ranging from high-resolution planetary maps to single extra-solar datapoints. In turn, petrologic studies of olivine underpin the geologic interpretations of these spectral datasets. Finally, olivine chemistry records Solar System formation conditions and relative chronology. Olivine is our bridge across time and space.

Hide and Seek—Trace Element Incorporation and Diffusion in Olivine

Olivine, once overlooked as a host of trace elements, is becoming increasingly important for our understanding of the kinetic and equilibrium behaviour of these elements. Much of our understanding of trace element substitution and diffusion in geological materials comes as a result of experimental and petrological studies of olivine. Here, we consider trace element concentrations and incorporation mechanisms, and how these relate to diffusive behaviour. If we understand trace element behaviour in olivine, we have a powerful tool kit that can be directly applied to address many problems in petrology and volcanology. Perhaps more importantly, what we have learned from olivine can be applied to other minerals and aid us in addressing other far-reaching questions from across the Earth sciences.

On unusual conditions for the exhumation of subducted oceanic crustal rocks: How to make rocks hotter than models

The thermal structure of subduction zones controls many important processes such as metamorphic devolatilization, arc magmatism, and seismicity. However, the thermal state of subducted oceanic slab predicted by subduction zone thermal models down to ∼80 km depth is systematically cooler than inferred from exhumed metamorphic slab rocks, raising questions about the current understanding of subduction dynamics portrayed by these models. Upon synthesizing previous petrological studies and estimating slab ages of ancient subduction zones from metamorphic terranes, we think that exhumation of subducted oceanic metamorphic rocks is extremely rare and likely requires unusual processes that are not an integral component of normal subduction dynamics. We construct simple numerical scenarios to illustrate how the thermal regime under some unusual conditions at the beginning and ending stages of a subduction margin may deviate from the normal subduction process. At the beginning stage of subduction, a shallow maximum decoupling depth (MDD) between the slab and mantle wedge enables viscous mantle wedge flow to reach a shallow depth, bringing heat to make slab rocks warmer than in a mature subduction zone. At the ending stage of subduction, if subduction cessation is in the form of slab stalling and if the stalled slab is not immediately exhumed, the slab rocks can be warmed up by the heat from the warm mantle wedge and underlying asthenosphere. In either situation, the slab rocks can be much warmer than normal before they are exhumed by other dynamic processes. Observed exhumed rocks are not expected to represent the normal subduction process and should not be directly compared with thermal models that are designed for the normal process. To extract important information about general geodynamic processes from these rocks, we must first understand the processes these rocks went through.

Magma ascent and degassing processes of the 2011 and 2017–18 eruptions of Shinmoedake in Kirishima volcano group, Japan, based on petrological characteristics and volatile content of magmas

The eruption activity of Shinmoedake in the Kirishima volcanic group of Japan resumed in 2017–18, following a quiet period during 2011–17. Subplinian eruptions preceded lava effusion in 2011; however, no subplinian eruption occurred during 2017–18. Petrological studies and melt inclusion analyses were conducted to investigate the ascent and degassing of the magma to understand the cause of the different eruption styles. Chemical analysis of the melt inclusions from the 2011 eruption indicates that mafic magma with high volatile content (6.2 wt% H2O, 0.25–1.4 wt% CO2) ascended into the shallow felsic magma (1.9–3.7 wt% H2O, 0.025–0.048 wt% CO2) at depths of 5–6 km. Calculations indicate that the mafic magmas were of lower density (1717–1835 kg m−3) than the felsic magma (2264–2496 kg m−3) at 125 MPa and that the two magmas were mixed. The 2011 mixed magma with high volatile content (4.0 wt% H2O, 0.14–0.70 wt% CO2) had a bubble volume of approximately 50 vol% at 50 MPa, which is likely to have caused the subplinian eruption. The whole-rock and chemical compositions of the plagioclase, clinopyroxene, and orthopyroxene phenocryst cores from 2018 and 2011 were similar, suggesting that the 2018 magma was a remnant of the 2011 magma. Chemical analyses of the groundmass from 2018 and the MELTS calculation indicate that the magma approached chemical equilibrium during 2011–18. Melt inclusion analyses and volcanic gas observation noted a lower bulk volatile content in the 2018 magma (2.1–3.0 wt% H2O, 0.087–0.10 wt% CO2) than that in the 2011 magma. Comparison of the degassed-magma volumes estimated from the S and Cl contents of the melt inclusions, SO2 flux and volcanic gas composition, and erupted-magma volume indicates that excess degassing has been occurring in the magma due to convection since February 2011, which may have decreased the volatile content of the magma. The relatively low volatile content meant that the 2018 magma could not erupt explosively and lava was instead erupted via effusion.Graphical

Generation of continental intraplate alkaline basalts by edge-driven convection: Insights from the Cenozoic basalts beyond the Big Mantle Wedge

Continental intraplate basalts are widespread across Central-East Asia, and their melting mechanisms are poorly known. Herein, we present integrated studies of petrology, elemental-isotope systematics, and thermodynamic modeling of Cenozoic Liangcheng basalts, a representative volcanic field of the vast intracontinental basaltic magmatic province covering Central-East Asia, with the aim of constraining the source characteristics and melting dynamics in this intraplate setting. These basalts have moderate-to-low silica (45.2 to 49.0 wt%), high Fe2O3T (10.0 to 12.2 wt%), and alkali (Na2O + K2O, 4.27 to 7.38 wt%) contents with ocean-island basalt (OIB) -like trace-element patterns and moderately depleted to slightly enriched Sr–Nd–Pb–Hf isotopes (87Sr/86Sr = 0.703924–0.705176, 143Nd/144Nd = 0.512540–0.512861, 206Pb/204Pb = 17.2752–17.9180, 207Pb/204Pb = 15.4860–15.7383, 208Pb/204Pb = 37.6995–38.3599, and 176Hf/177Hf = 0.282852–0.282999). The major elements (e.g., high Fe/Mn, low CaO) and olivine chemistry (e.g., high Ni, Zn/Fe, and low Mn/Zn) favor derivation from a silica-deficient pyroxenite-bearing source, while the trace-element and isotope systematics suggest the involvement of recycled components including oceanic slab and sediment (both terrigenous and pelagic). A grid search with a thermodynamic melting model using incompatible trace elements was carried out to impose quantitative constraints on the mantle source. The modeling results show that the source of the Liangcheng basalt contains 80% primitive mantle peridotite and 20% silica-deficient pyroxenite. This exercise and geobarometric calculation using major elements suggest that melting occurs at a potential temperature of 1380 °C underneath a thinned continental lithosphere with a basal pressure of ∼2GPa, consistent with the source characteristics and melting conditions estimated for many other volcanic fields in the vast Central-East Asia magmatic province. By combining these results with the regional geology and tectonic history, we can suggest that these basalts were formed by decompression melting owing to mantle convection driven by lithospheric thickness variations (edge-driven convection). We suggest that such a melting scenario is ubiquitous beneath Central-East Asia and may have played a vital role in the formation of widespread intraplate continental alkaline basalts.

Tracing the human movements of three thousand years ago by volcanic grinding tools in the Final Bronze Age settlement of Monte Croce Guardia (Arcevia-Marche Region, central Italy)

Volcanic rocks were among the most sought-after materials to produce grinding tools in antiquity because lavas lithologies, either mafic or felsic, ensured good wear resistance and grinding capacity with respect to many other kinds of rocks. The interest in findings made of vesciculated lavas, referable to parts of querns, mortars, and/or pestles of the Final Bronze Age site of Monte Croce Guardia (Arcevia) lies in the fact that this settlement was built upon limestones belonging to the sedimentary sequence of the Marche-Umbria Apennines (central Italy) and far away from potential raw materials of volcanic rocks. A petrologic study of 23 grinding tool fragments clearly indicates a provenance from the volcanic provinces of central Italy: Latium and Tuscany Regions. Few leucite tephrites (5) and one leucite phonolite lavas have a clear magmatic affinity with the high-K series of the Roman Volcanic Province (Latium) whereas the most abundant volcanic lithotype (17 samples) is represented by shoshonites (K-series) whose thin section texture, modal mineralogy and major-trace elements contents closely match with the shoshonite lavas from the Radicofani volcanic centre in the Tuscan Magmatic Province. At Radicofani (a volcanic neck in the eastern sector of Tuscany) a Final Bronze Age site coeval to that of Arcevia is present and a potential pathway corridor from that site towards Arcevia (air-line distance of ca. 115 km) is dotted with many settlements of the same age. Through analytical algorithms based on the slope and the different human-dependent cost-functions which can be applied to determine non-isotropic accumulated cost surface, least-cost paths and least-cost corridors, the best route from Radicofani to Monte Croce Guardia, approximately 140 km long, was simulated, with a walking time of 25–30 h, possibly using pack animals and wheel chariots. Three thousand years ago the Apennine Mountains did not thus constitute a barrier for human movements. This study also shed light on some other possible patterns of interactions between Final Bronze Age communities of central Italy through the present-day regions of Tuscany, Umbria and Marche, aimed towards the best performance of strategic economic activities at that time such as that of the transformation of cereals, and accompanied to cultural and social reasons.

Redefinition of the Petersburg batholith and implications for crustal inheritance in the Dinwiddie terrane, Virginia, USA

Field relations as well as geochemical and petrologic studies of meta-igneous rocks assigned to the Pennsylvanian–Permian Petersburg batholith identify at least two distinct rock types: foliated metagranitoid gneiss and massive to porphyritic granite. Foliated metagranitoid gneiss of mostly granodioritic composition is geochemically distinct from associated massive and porphyritic granitic rocks. These gneissic rocks yield radiometric ages from ca. 425 Ma to ca. 403 Ma and document that many of the rocks assigned to the late Paleozoic Petersburg batholith are 100 m.y. older than the youngest portions of the composite batholith and are part of an earlier infrastructural terrane. Two samples of massive equigranular granite southwest of Petersburg, Virginia, yield ages of ca. 321 Ma and ca. 317 Ma, which are 15–20 m.y. older than ca. 300 Ma ages for porphyritic granite, massive granite, and monzodiorite near Richmond, Virginia. Geologic mapping shows that the Early Pennsylvanian granite southwest of Petersburg is separated from Late Pennsylvanian to early Permian granite near Richmond by a map-scale septum of Silurian–Devonian foliated metagranitoid gneiss, referred to herein as the informal Pocoshock Creek gneiss. Laser ablation–inductively coupled plasma–mass spectrometry data from one sample of a quartz-muscovite felsic schist xenolith show a peak age mode of ca. 529 Ma that we interpret to be the maximum depositional age. Inherited zircons from foliated metagranitoid gneiss and massive equigranular granite range from ca. 631 Ma to ca. 376 Ma, but many are Cambrian. Neoproterozoic–Cambrian quartz-muscovite felsic schist and amphibolite, Silurian–Devonian Pocoshock Creek gneiss, and Pennsylvanian–Permian granite comprise a fault-bounded terrane referred to herein as the Dinwiddie terrane. Ages of inherited cores in zircon from igneous rocks and limited detrital zircon geochronology suggest the terrane is of peri-Gondwanan affinity. U/Pb ages of healed fractures in zircon grains from foliated metagranitoid gneiss indicate low-grade deformation of the gneiss at ca. 378–376 Ma, while ca. 320–280 Ma rims on many grains record intrusion of late Paleozoic granite. The temperature-time-deformation history of the Dinwiddie terrane is distinct from the adjacent Goochland and Roanoke Rapids terranes. Orogen-scale dextral transpression likely translated the Dinwiddie terrane southward during the Alleghanian orogeny, at which time they were intruded by Pennsylvanian to Permian granite.

Presence of infratrappean Gondwana sediments below Deccan volcanic covered 1993 Killari earthquake region, Maharashtra (India) and geodynamical instability of the south Indian craton

KLR‐1 scientific deep borehole, drilled in the 1993 Killari earthquake region of Maharashtra (India), penetrated 8 m thick infratrappean sediments below a 338 m‐thick column of Deccan volcanics that rested over Neoarchean amphibolite to granulite facies mid‐crustal basement. Detailed palynological studies revealed the presence of characteristic Gondwana palynomorphs in sedimentary succession that includePlicatipollenites indicus,P. trigonalis,Parasaccites korbaensis,P. diffusus,Microbaculispora indica,Cyclobaculisporites minimus,Cyclogranisporites barakarensis,C. gondwanensis,Jayantisporites pseudozonatus,Leiosphaeridia bokaroensis,Latosporitessp.,Verrucosisporitessp., cf.V. ambiplicatusandStriatopodocarpites gondwanensis.Qualitative analyses of palynomorphs would suggest an Asselian age (298–295 Ma) for their formation and burial in dysoxic to anoxic conditions. Recorded palynological assemblages correlate well with continental Lower Gondwana (Early Permian) sediments of India, as well as other Gondwana continents, indicating a larger extent of Gondwana sedimentation than hitherto known today. Petrological studies indicate the presence of two types of carbonate units that overly the crystalline basement. A relatively coarse‐grained sparry carbonate rock immediately overlies the basement (Sample KIL‐7). The size of the carbonate crystals in the sparite vary from 100 to 500 μm. This unit is overlain by an extremely fine‐grained micrite resembling lime mud (Sample KIL‐6). Micrite is made of carbonate grains with an average size of 10 μm. X‐ray diffraction studies indicate that calcite is the dominant carbonate mineral, while dolomite and quartz occur in minor amounts. Geochemical analyses indicate that in these two samples of carbonate rock that overlie the basement, CaO (33.38 to 38.16 wt %) is higher than MgO (16.0–23.85 wt%). These infratrappeans sediments are also characterized by stable carbon (δ13C) and oxygen (δ18O) isotopic ratios ranging from −1.59 to −8.74‰ and −9.12 to −13.50‰ versus PDB, respectively, thereby conforming to non‐marine fresh water deposits. These findings provide first evidences of reactivation and rifting of Dharwar intracratonic regions during earliest Permian Gondwana Period, which led to severe lithospheric mantle destruction, and massive regional uplift and erosion of the granitic‐gneissic upper crust. Large scale inland‐rifting during the Gondwana sedimentation period was possibly a prelude to India‐Antarctic breakup during the early Cretaceous.

Dolomite porosity related to peritidal microbialites textures and facies succession in Mesoproterozoic Wumishan Formation, North China

There are three main types of microbial dolostones in Mesoproterozoic Wumishan Formation in Jixian, North China. They are stromatolite, thrombolite and granular microbialite. The microbialite lithofacies are intensely environmentally associated. Several kinds of stromatolite can be found in the peritidal environments. Mostly planar or wavy stromatolites show in intertidal and supratidal zones while domy and conic stromatolites occur in subtidal or lower intertidal zones. In more agitated subtidal zone or tidal channels, microbial grains deposited, such as thrombolite, oncolite, and sand- gravel sized microbial-coated grains. The intraclasts related laminite facies mostly deposited in shallow subtidal zone.Representative four outcrop sections of Wumishan Formation in Jixian are measured and documented. The petrophysical and petrological study from the outcrop and well core samples reveals that the reservoir rocks are closely related to lithofacies and their depositional environments. The more agitated the depositional environment is, the better the reservoir quality, even so that after the diagenesis (surface and burial). The dolostone porosity of planar stromatolite in supratidal and intertidal are much worse than the subtidal high-agitated microbialite rocks, whether samples from the outcrops or drilling cores.The effective reservoir interval is normally located in the lower part of a peritidal microbial facies succession, mainly consists of subtidal microbialite, such as thrombolite, thrombo-stromatolite, oncolite, columnar stromatolite and coated intraclastic grainstone and rudstone, commonly deposited in agitated environment. The thickness of reservoir rocks in microbialite para-sequences ranges commonly from 4 to 14 m, deeply related to depositional cycles or sequence stratigraphy in vertical lithofacies texture and their areal extent to the paleogeography.

Fe and Mg Isotope Compositions Indicate a Hybrid Mantle Source for Young Chang’E 5 Mare Basalts

The Chang’E 5 (CE-5) samples represent the youngest mare basalt ever known and provide an access into the late lunar evolution. Recent studies have revealed that CE-5 basalts are the most evolved lunar basalts, yet controversy remains over the nature of their mantle sources. Here we combine Fe and Mg isotope analyses with a comprehensive study of petrology and mineralogy on two CE-5 basalt clasts. These two clasts have a very low Mg# (∼29) and show similar Mg isotope compositions to Apollo low-Ti mare basalts as well as intermediate TiO2 and Fe isotope compositions between low-Ti and high-Ti mare basalts. Fractional crystallization or evaporation during impact cannot produce such geochemical signatures that otherwise indicate a hybrid mantle source that incorporates both early- and late-stage lunar magma ocean (LMO) cumulates. Such a hybrid mantle source would be also compatible with the KREEP-like Rare Earth Elements pattern of CE-5 basalts. Overall, our new Fe–Mg isotope data highlight the role of late LMO cumulate for the generation of young lunar volcanism.

Stone-working and the earliest steel in Iberia: Scientific analyses and experimental replications of final bronze age stelae and tools

The south-western Iberian stelae from the Final Bronze Age (FBA) and Early Iron Age (EIA) have long been the centre of archaeological interest. These monuments show representations of human and animal figures, objects such as weapons, ornaments and chariots. Moreover, they provide insights into prehistoric stone working and sculpting techniques. On the downside, petrological studies of the rocks and consequent reflections on suitable tools are still the exception. Due to the lack of analysis and technological studies, this research will put emphasis on a multidisciplinary approach involving petrographic and metallurgic analyses, complemented by experimental archaeology.Firstly, an accurate lithological determination of stelae from Capilla (Spain) has been established with petrographic methods. According to the results, two slabs for replications of stelae were obtained from the identified mono-mineral quartz-sandstone (“quartzite”) outcrop. The experiment involved the trial of chisels made from all expedient materials that were available in the FBA-EIA by a professional stonemason. Considering that such extremely hard rocks require robust tools for carving, a long ignored iron chisel from the FBA site of Rocha do Vigio (Portugal) was studied with metallography and exposed heterogeneous, however surprisingly high-carbon steel. The analysed rocks are amongst the hardest that can be used for sculpting, and in the course of the experiment, bronze and lithic tools could be discarded. The only tool that showed an effect was the replication of the steel chisel from Rocha do Vigio with a hardened edge. The distinct work traces were compared to the original monuments. We hypothesize that the production of carbon steel as well as its hardening were possibly already known at the FBA-EIA transition in Iberia. Hence, only the access to iron technology allowed for the making of stelae from the lithotypes that were frequently used in the Zújar basin around the municipality of Capilla.

Anthropic Influence and Heritage Value of the Quaternary Deposits of Rio de Janeiro, Brazil

This study discusses the cause of local lithification in sediments from quaternary beach ridges of Paraíba do Sul Deltaic Complex (Rio de Janeiro, Brazil) and its application to the concept of geological heritage. These beach ridges were excavated to construct the Campos - Macaé Canal, opened in the 19th century predominantly by slave labor. A detailed sedimentological, mineralogical and petrological study was performed. The consolidated material consists to fine-grained sandstone with incipient parallel lamination. Kaolinite associated with iron oxides/hydroxides is organized in thin coatings, sometimes forming meniscus and bridges. The heavy mineral assembly of the sandstone is similar to those found in the beach ridges friable samples. The sandstone granulometry increases from east to west along the canal margins and the same pattern is observed in the adjacent beach ridges. We suggest that pedogenic processes acted intensively on Canal margins after its opening, causing mechanical infiltration and translocation of clay minerals, promoting differentiated consolidation of sediments only in that part that was deepened during the excavation. The anthropic action altered the local physiography by exposing the sediments of beach ridges. Therefore, this sandstone should be considered a geological heritage due to its unique occurrence, touristic, historical, scientific and educational value.

Volcano–Plutonic Complex of the Tumrok Range (Eastern Kamchatka): An Example of the Ural-Alaskan Type Intrusion and Related Volcanic Series

Zoned plutons, composed of dunites, pyroxenites, and gabbroic rocks, have been referred to as the Ural-Alaskan type complexes (UA-complexes) and occur in numerous paleo-arc settings worldwide. Many of these complexes are source rocks for economic placers of platinum-group metals. Thus, it is important to understand how UA-complexes form and the origin and behavior of platinum-group elements (PGEs). It is widely assumed that the UA-complexes result from differentiation of supra-subduction high-Ca high-Mg sub-alkaline magmas. However, there is a lack of direct evidence for the existence and differentiation of such magmas, mainly because cases of UA-complexes being spatially and temporally linked to co-genetic volcanics are unknown. We studied an UA-complex from the Tumrok range (Eastern Kamchatka) where a dunite-clinopyroxenite-gabbro assemblage is spatially and temporary related to high-Ca volcanics (i.e., picrites and basalts). Based on the mineral and chemical composition of the rocks, mineral chemistry, and composition of melt inclusions hosted within rock-forming minerals, we conclude that the intrusive assemblage and the volcanics are co-genetic and share the same parental magma of ankaramitic composition. Furthermore, the compositions of the plutonic rocks are typical of UA-complexes worldwide. Finally, the rocks studied exhibit a full differentiation sequence from olivine-only liquidus in picrites and dunites to eutectic crystallization of diopside or hornblende, plagioclase, and K-Na feldspar in plagio-wehrlites and gabbroic rocks. All these results make the considered volcano–plutonic complex a promising case for petrological studies and modelling of UA-complex formation.

The effect of meteoric water on the very fine crystalline dolomite reservoir in the shallow burial zone: A case study of the Ma55 submember of Majiagou Formation in Ordos Basin

The meteoric water has obviously changed the physical properties of dolostone reservoirs in the vertical vadose zone and the horizontal phreatic zone, but its influence on the dolostone reservoirs in the shallow burial zone beneath the phreatic surface is still unclear. This study aims to reveal the effect of meteoric water on the dolostone reservoirs in the shallow burial zone through X-ray diffraction, cathodoluminescence, C, O, and Sr isotope using the sample from Majiagou Formation in the Daniudi gas field, Ordos Basin. The diagenesis and paragenesis of the Ma 55 submember were identified and interpreted through petrological study, combined with data from electron probe, X-ray diffraction analysis, and geochemical parameters of diagenetic minerals. The color of the very fine crystalline dolomite under the cathodeluminescence is dark red and red. The order degree of dolomite ranges from 0.54 to 0.91, showing the origin of early seepage-reflux dolomitization. There are a large number of different calcite cements as fills within the pores and fractures. The color of the calcite cement under the cathodoluminescence is orange-yellow, with a zonal structure. Hydrothermal fluid during late diagenesis could be identified by the authigenic fluorite filling in the fractures. According to the assembly of diagenetic minerals, the very fine crystalline dolostones have experienced the seepage-reflux dolomitization, meteoric water dissolution, shallow burial cementation and late cementation. The void spaces of the very fine crystalline dolostones are intercrystalline pores and microfractures. Although a large number of dissolved pores and caves developed in the period of meteoric water dissolution, these caves and dissolved pores has been mostly filled by multi-stages of cementation. Therefore, the effect of meteoric water on dolostone reservoirs in the shallow burial zone beneath the phreatic surface is not obvious. The main controlling factor for the quality of dolostone reservoir was dolomitization. This study provides a new understanding of the influence of meteoric water on reservoir quality in the shallow burial zone during the paleokarst period.

Sedimentological Studies of Marine Oil Fields in Order to Reduce Drilling Risk and Environmental Pollution: A Case Study of South of Iran

Detailed studies of sedimentology and petrology of oil fields, especially oil fields located in the seas, play a very important role in reducing the risk of danger, increasing harvest, and reducing the amount of environmental pollution. The South Pars gas field in the waters of the Persian Gulf on the joint border line of Iran and Qatar and on the south coast of Iran has been used as a comprehensive model for this type of study. In these studies, the sedimentary environment and sequential stratigraphy of the Scorpion and Sarvak Formations in the South Pars gas field in wells 1 and 3 have been investigated. Microscopic studies and analysis of gamma-ray and acoustic diagrams of these formations have led to the identification of 9 facies in three facies belts related to wetland, dam, and open sea. Dam facies have been identified only in Sarvak formation. This study shows that the facies belts of the abovementioned formations in a ramp platform are also sloping. Sequence stratigraphy of Kazhdomi and Sarvak Formations in the study wells shows that Kazhdomi Formation has one sedimentary sequence (third category cycle) and Sarvak Formation has two sedimentary sequences. The lower boundaries of sequences 1 and 2 and the upper boundary of sequence 3 have type 1 (SB1) discontinuities, and the boundary between sequences 2 and 3 has type 2 (SB2) discontinuities.

Large-scale replacement of ancient mantle lithosphere during supercontinent assembly: Evidence from the South China Craton

The modification and destruction of the sub-continental lithospheric mantle (SCLM) has been identified in numerous studies. However, what principally controls the susceptibility and extent of destruction of the SCLM and how this leads to the corresponding variation of the overlying crust remain long-standing issues. Here we provide an integrated study of petrology, mineralogy, and geochemistry, including highly siderophile element (HSE) abundances and whole-rock and/or mineral Os-Hf-Sr-Nd isotopic compositions of mantle peridotite xenoliths from Hainan Island, together with a compiled dataset from the eastern South China Craton (SCC) to investigate the mechanism and timing of replacement and destruction of the SCLM. The mantle xenoliths from the eastern SCC are overall more fertile than cratonic lithospheric mantle, and have generally experienced various extents of metasomatic enrichment, including carbonate and silicate melt metasomatism. In addition, the absence of Archean ages and compositional or temporal stratification of the SCLM beneath the eastern SCC indicates that the Archean lithospheric mantle may have been replaced/reworked and has essentially vanished, hence the present underlying lithospheric mantle is a relatively new and young lithospheric mantle. The formation time of the SCLM underneath Hainan Island constrained by both the ReOs and LuHf isotopic systems is late Mesoproterozoic (∼1.2 Ga), largely consistent with the Meso- to Neoproterozoic peak of whole-rock TRD ages (0.9–1.3 Ga) of the refractory mantle peridotites in the compiled dataset. This age distribution can be reconciled with the assembly time of the Rodinia supercontinent, indicating a close linkage between the replacement of large-scale lithospheric mantle via mantle convection erosion and regional continental amalgamation. Meanwhile, the relative location to the plate margins influences the preservation of the cratonic mantle. The SCLM located at the plate margin (e.g., eastern SCC compared to western SCC), where destructive processes frequently occur, is susceptible to destruction, whereas that within the plate interior is likely to remain relatively intact.

A Petrological Study of Columnar Joints with Geoheritage Value in the Cenozoic Sedimentary Basin, Korea

A comparative petrological study was conducted on the columnar joints of Guryongpo, Pohang, Yangnam, Gyeongju, and Gangdong-hwaam, Ulsan in the Cenozoic Miocene sedimentary basin. Horizontal columnar joints, in these columnar joints, are characteristically developed, and the cross-sectional shape of each columnar joint is predominantly quadrilateral and pentagonal in Guryongpo and Yangnam columnar joints, and pentagonal to hexagonal in Gangdong-hwaam columnar joint. As a result of XRF analysis, it was confirmed that Guryongpo columnar joint is andesite, Yangnam columnar joint is basalt, and Gangdong-hwaam columnar joint is basaltic andesite, all of which are sub-alkaline. They are easily distinguished because Guryongpo columnar joint contains small-sized plagioclase (1∼2 mm), while rather large plagioclase phenocrysts (several mm∼1 cm) are uniformly distributed both in Yangnam and Gangdong-hwaam columnar joints. The value of whole rock magnetic susceptibility (WRMS) are also well classified according to the rock composition. In addition, in the tectonic discriminant diagram, these columnar joints correspond to the orogeny zone and island-arc tholeiite regions of the orogeny, but the AFM diagram and WRMS analysis show that each columnar joint was formed from the different magmas.

Seismic tremor location of 10 large paroxysmal eruptions of Tungurahua volcano, Ecuador

SUMMARYThe most recent eruptive period of Tungurahua volcano lasted 17 yr (1999–2016), generating strong eruptive phases with the release of large amounts of seismic and acoustic energies. We have selected 10 large eruptions and located their seismic sources. The location method involves applying a new method for correcting for site effects in the seismic records and identifying, in the frequency domain, the signals from the ground-coupled airwaves and pyroclastic flows. The locations are computed by minimizing the differences of the source energy rates in the [0.4, 2.5] Hz range. The results suggest that the first three eruptions have locations mainly concentrated at the [−1, 2] km depth range (asl), and the locations of the fourth eruption are mainly coincident with depths of a possible reservoir estimated from petrological studies. This fact strongly suggests that this eruption was responsible of changes in the dynamics of Tungurahua, making the volcano prone to produce Vulcanian eruptions.