Magmatic Research Articles

Rock thermal conductivity and thermal inertia measurements under martian atmospheric pressures

The physical properties of rocks on planetary surfaces influence their bulk thermal conductivity (k) and thermal inertia (TI); however, there has been little work done to date to explore quantitative relationships between physical properties (bulk density, porosity, mechanical strength) and thermal properties (k and TI) at Mars-relevant pressures. We present the first k and TI measurements of a comprehensive suite of Mars-relevant igneous and sedimentary rocks under Mars atmospheric pressures. We used modified transient plane source (MTPS) and transient plane source (TPS) methods to measure k and TI values of 40 samples (3 monomineralic, 13 igneous, 24 sedimentary) at pressures between 1 and 10 mbar and at 1 bar, at ∼25 °C. The rock samples were characterized by bulk density, grain density, porosity, uniaxial compressive strength, mineralogy, and major and trace element abundances. We find that bulk density and porosity roughly correlate to k and TI values at Mars pressures by power law relationships. The relationships of the thermal properties with mechanical strength and chemical properties, however, are not straightforward. Many physical and chemical factors play a role in determining k and TI values; thus, it is not possible to relate a single physical or chemical property to k and TI directly based on these measurements. Rock TI values derived from rover surface temperature measurements on Mars agree with our results for similar rock types.

Synchronous felsic volcanism and carbonate sedimentation as a setting for VMS deposits localization at the Salair terrane, NE Central Asian Orogenic Belt

The Salair terrane located in the northern part of the Central Asian Orogenic Belt (CAOB) contains many epithermal deposits including volcanogenic massive sulphide (VMS) deposits. The host rocks mainly consist of felsic volcanic rocks such as lavas, volcanic breccias and tuffs that associated with thick strata of carbonates. In this study, we present zircon U–Pb ages, whole rock geochemistry, and Nd isotope data from the volcanic rocks, and results of geochemical and isotope (Sr, C, O) studies of carbonates to constrain their age and petrogenesis, and to characterize the tectonic setting. Zircon U–Pb dating reveals that the ore-bearing felsic lavas have age of 519.3 ± 1.9 Ma, while the felsic tuffs have age of 516.0 ± 0.9 Ma. These volcanic rocks are characterized by high SiO2 and Na2O contents, enrichment in light rare-earth elements, remarkable negative Eu anomalies, and pronounced depletion in Nb, Ta, P, and Ti. They have depleted ɛNd(t) values ranging from +4.9 to +6.3, and young two-stage Nd model ages (from 0.82 to 0.64 Ga). The felsic volcanic rocks from the Salair terrane are interpreted as highly evolved I-type magmatic rocks that might be produced by high degree partial melting of juvenile lower crust without a significant contribution of ancient crust and without crustal reworking.Felsic volcanism was accompanied by the formation of thick strata of carbonates. These carbonates are marine limestones with Mg/Ca ratios less than 0.007, δ18O(SMOW) values from 17.1 to 23.8 ‰ and δ13C(PDB) values between –0.9 and +0.9. Their Sr isotope composition varies in a narrow range within 0.70844–0.70859 that interpreted as representing proxy for coeval seawater. These values are consistent with depositional ages of 520–510 Ma and confirms the synchronicity of the formation of carbonates and felsic volcanism. Based on the regional geology and geochemistry, the ore-host rocks of the Salair terrane were formed in the back-arc setting where the marine transgression occurred as a result of graben subsidence. It is important for better understanding epithermal deposits in the northern CAOB and might provide new insights about prospecting the VMS deposits in similar tectonic settings.

Magma fizz: Tremor during the Kīlauea summit reservoir decompression

Typical eruptions at Kīlauea volcano involve the evacuation of magma from the summit and/or south caldera reservoirs towards the East or Southwest rift zones. The reservoir drainage provokes the summit deflation, and on extreme occasions, such as in 2018, the summit caldera collapse. Systematically, seismic tremor, often with a particular multichromatic spectral signature characterized by frequency gliding, accompanies summit deflation episodes. In 2018, this type of continuous tremor accompanied the steady subsidence stage, whereas discrete earthquakes dominated the collapse stage. In this work, we aim to understand the source mechanism of the syn-deflation tremor of 2018. To locate the seismic source, we develop a novel machine-learning-based algorithm as an alternative to the amplitude source location technique. We use a large high-resolution catalog to resolve a composite amplitude decay function. Under these conditions, our method outperforms the traditional technique. We locate the tremor source 1 km below the eastern perimeter of the Halema‘uma‘u crater, which coincides with the position of the summit magma reservoir, as determined in many other studies. Furthermore, we model the seismic source as pressure oscillations driven by gas porous flow at the roof of the reservoir. In this model, gas accumulates temporarily in many gas pockets between the magma and the roof. Our modeling shows that the gas flux is responsible for the tremor amplitude modulations, whereas the gas pocket thickness controls the frequency variations. Beyond a critical point of depressurization, the magma cannot contribute further to the tremor oscillations via decompression-driven degassing, nor support the roof above it, resulting in rock failure. This work advances our understanding of magma-degassing dynamics and tremor generation at Kilauea volcano, and provides novel seismological techniques for volcano seismology monitoring and research.

Fluid-rock interaction related to alpine subduction of Allalingabbro deduced from large-size μXRF element maps

Alpine subduction of a block of olivine gabbro produced a plethora of different assemblages and local structures typical of high-pressure and low-temperature metamorphism. However, gabbro with the locally well-preserved igneous assemblage olivine - augite - plagioclase occurs in some domains of a 2 km long outcrop (Allalinhorn, western Alps).A large variety of hydrate minerals including zoisite, glaucophane, talc, Mg-chloritoid, chlorite, paragonite and muscovite formed during Alpine subduction of the metagabbro. The three primary igneous minerals have been replaced by hydration reactions during Eocene subduction. Talc, omphacite, and zoisite + jadeite and are the main minerals in the local domains after olivine, augite and plagioclase respectively. The rocks preserved the coarse grained igneous texture.An excellent overview of the complex coarse textures of the eclogite facies rocks has been provided by element distribution maps produced from up to 25 cm large polished slabs of typical samples of Allalingabbro using a μXRF instrument. The RGB images suggest that the minerals formed at the high-pressure in the presence of an aqueous fluid. The pseudomorphing reactions progressed close to volume conservation. The hydration reactions required an H2O fluid containing dissolved solids. The mapped distribution of elements including trace elements provides important clues on the origin and mobility of these elements in the hydration fluid. The homogeneously distributed immobile Cr in omphacite portrays primary augite. The irregular patchy Sr distribution resulted from small-scale migration of components replacing plagioclase by Sr-bearing zoisite and jadeite. Coherent Ni signals are related to the presence of talc. The talc occurs as a late infill of structures produced by dissolving olivine. Mg-chloritoid, kyanite and mica coat the former grain-boundary of olivine and plagioclase suggesting that olivine dissolved at eclogite facies conditions. Talc formed at distinctly lower pressures, however, as implied by computed model reactions. The olivine replacement structures are often larger than the size thin section and can be excellently studied by the large size μXRF patterns used in this study.The fractured surroundings of the locations of olivine provided the necessary hydraulic conductivity for hydration reactions to progress. The fractures and small veinlets contain late Ni-bearing talc. Cl is only present in very late vein amphibole suggesting that hydration fluids in the subduction zone transported dissolved components as hydrous complexes (and their dissociated ions). There is no evidence for the presence of a Cl-brine during subduction. In addition to primary olivine as a local Ni source, the element may also have partly been imported with the hydration fluid and originate from dehydration of ophiolitic serpentinites in the slab.

Experimental Investigation of Knapping Characteristics of Dolerite and Implications for the Interpretation of Middle Stone Age Technologies

ABSTRACT This study examines knapping techniques in the production of stone tools made on dolerite to understand the knapping characteristics of this igneous tool stone. Extensive experimental research exists on the knapping of silica-rich materials like flint, yet studies on materials low in silica remain scarce. Dolerite, an igneous rock composed mainly of plagioclase, feldspar, and pyroxene, has been used during the Palaeolithic globally and the Middle Stone Age (MSA) of Africa specifically. We address two questions: (i.) Does the application of different knapping techniques to dolerite produce artifacts with distinguishable attributes? (ii.) Are these attributes similar to or different from those of flint? Using three direct percussion techniques, we created an experimental reference assemblage on dolerite and conducted a quantitative attribute analysis. Our findings indicate that knapping techniques can be distinguished at the assemblage level, with attributes significantly different from flint, highlighting the need for further studies on diverse lithic materials.

Geochemical and isotopic features of the Early Cretaceous volcanism of the Torey Volcanic Field (Eastern Transbaikalia, Russia) as a record of the transition from pyroxenite to eclogite mantle source

The Mesozoic magmatic activation in Central and Northeast Asia resulted in the formation of a large volume of volcanic rocks with diverse compositions. The most dramatic compositional change occurred at the end of the Early Cretaceous, when mainly alkaline basaltic lavas began to erupt after subalkaline differentiated lavas. The nature of crustal and mantle processes that led to this change in volcanism remains unclear. The Torey Volcanic Field (TVF) of Eastern Transbaikalia (Russia) demonstrates a similar compositional change. Therefore, the TVF is crucial to studying the cause of the difference in geochemical and isotopic signatures of the Mesozoic volcanism in Central and Northeast Asia.TVF belongs to the northeastern end of the Eastern Mongolia Volcanic Area (EMVA). Like other volcanic fields of the EMVA, TVF formed in two stages: early (∼121–129 Ma) and late (∼101–119 Ma). The TVF is composed of subalkaline and alkaline basaltic trachyandesites – trachyandesites. All TVF rocks are characterized by negative Ti and Sr anomalies and positive Ba and Pb anomalies. Compared to the late TVF rocks, the early TVF rocks have distinct negative Ta and Nb anomalies and are highly enriched in light rare earth elements relative to heavy rare earth elements. TVF rocks have the following isotopic characteristics: 87Sr/86Sr(t) = 0.70477–0.70540, εNd(t) = − 0.9 – +2.4, 206Pb/204Pb(t) = 17.9–18.4, and 207Pb/204Pb(t) = 15.5–15.6. However, older rocks mainly have higher εNd(t) values and 206Pb/204Pb(t) and 207Pb/204Pb(t) ratios.Geochemical and isotopic data of samples suggest that the TVF formed by melting in the continental metasomatized lithospheric mantle (CMLM). Phlogopite-amphibole-rutile-bearing pyroxenite veins played a major role in the formation of older rocks. Eclogite, represented by the recycled oceanic crust or the buried lower continental crust, was dominant in the source of younger rocks. The common source for both groups of the TVF rocks was metasomatized hydrous peridotite.Lithospheric extension and subsequent asthenospheric upwelling led to melting in the CMLM and the formation of the TVF. At the early stage of the volcanism, melting occurred at relatively low temperatures where amphibole, phlogopite, and rutile were stable. Due to ongoing lithosphere extension, the melting of eclogite occurred at a higher temperature and/or lower pressure at the late stage of the volcanism.

1.38 Ga magmatism and the extension tectonics in East Kunlun, northern Tibetan Plateau

Numerous Paleo- to Mesoproterozoic magmatic rocks were emplaced during the assembly, accretion and break-up of the Columbia supercontinent, and are keys to illustrating the supercontinent circle. The geological, petrological, geochronological and geochemical data of the newly discovered meta-felsic and meta-mafic magmatic rocks from the Wulonggou area are presented in this study to shed light on the Mesoproterozoic geodynamic setting of the Central Kunlun Belt and the Qaidam Block. Zircon U-Pb geochronological results indicate that the crystallization ages of the meta-felsic samples are 1385–1376 Ma, and the meta-mafic is 1379 ± 25 Ma (MSWD=0.17). Samples from the meta-felsic unit have SiO2 contents of 68.37–73.03 wt% and belong to the high-K calc-alkaline series. They exhibit similar REE distribution patterns and display enrichment in light rare earth elements (LREES) and negative Eu anomalies. Enrichments in Rb, Ba, Th, U and K, depletion in Nb, Ta, Sr, P and Ti are seen in the primitive mantle-normalized trace element pattern diagram. Magmatic zircons from different meta-felsic samples yield variable εHf(t) values of −8.14 to + 9.37 corresponding to ca. 1.7–2.0 Ga two-stage Hf model ages. Samples from the meta-mafic unit have low SiO2 concentrations of 49.87–50.43 wt%, high contents of Fe2O3T, MgO, CaO and TiO2, and Mg# values of 52–58. They show low total REE concentrations of 19.8–30.4 µg/g, and depletion in LREES, flat HREES distribution patterns with (La/Yb)N of 0.27–0.53 and insignificant Eu anomalies. Flat distribution pattern of high field strength elements (HFSEs) is observed in the primitive mantle-normalized trace element pattern diagram. They display similar immobile elements’ concentrations and distribution patterns, low Ti/Y, Nb/Y, La/Yb, and high Nb/La ratios, comparable with the present-day normal middle ocean ridge basalt. Zircons from the meta-mafic sample have mostly positive εHf(t) values ranging from −0.10 to + 4.10 with a single stage Hf model ages of ca. 1.7–2.0 Ga. The geochemical result implies that the meta-felsic unit was generated by partial melting of the Paleoproterozoic juvenile mafic lower-crustal material with mantle attributions, and the meta-mafic unit was probably from partial melting of the lithospheric mantle. Synthesizing the above evidences, Wulonggou Mesoproterozoic meta-magmatic rocks are a bimodal suite formed in a continental extensional tectonic setting which is probably related to the break-up of the Columbia supercontinent.

Is plate tectonics a post-Archean phenomenon? A petrological perspective

The petrogenesis of contemporary igneous and metamorphic rocks is commonly explained by plate tectonics, but how far back in time does this relationship hold? Here we investigate whether the distinctive petrological features of recent ocean crust, subduction-related magmatism and regional metamorphism can be unambiguously identified in the Archean geological record. From an igneous perspective based on geological relationships and Th–Nb systematics, it is difficult to claim that any Archean ‘ophiolite’ was part of a global plate system rather than deriving from a plume ascending through attenuating lithosphere. Furthermore, the rarity of subduction-related rocks, particularly their plutonic equivalents, which have good preservation potential, is consistent with the concept of local convergence and short-lived subduction. From a metamorphic perspective, the appearance of orogenic eclogites in the Paleoproterozoic, the widespread occurrence of blueschists and ultrahigh-pressure metamorphic rocks since the late Neoproterozoic, and a change from a unimodal to a bimodal distribution of metamorphic T / P during the Proterozoic, are responses to secular cooling and the evolution of global tectonics since the Archean. Our petrological perspective is that plate tectonics analogous to that on Earth today is probably a post-Archean phenomenon.

Mineralogical Characterization and Geochemical Signatures of Supergene Kaolinitic Clay Deposits: Insight of Ropp Complex Kaolins, Northcentral Nigeria

This study presents the chemical and mineralogical composition of clay deposits and associated rock types within the Ropp Complex in order to assess the influence of parent lithology on the kaolinization, genesis, and utility of the deposit. Representative kaolin samples from E horizons of the weathering profiles and their bedrocks were collected from six sites in the Ropp Complex. Clay mineralogy was determined via the XRD technique, while a geochemical analysis was conducted using XRF, SEM coupled with EDS, and ICP-MS. The results showed that all kaolins dominantly contain kaolinite with a content of 77%–98% except for the AS1 kaolin with only minor kaolinite (20%) but mainly illite (65%). The notably lower crystallinity of kaolinite (HI value of 0.53–1.1) as well as its markedly small grain size is consistent with the formation of kaolinite from intensive chemical weathering of igneous rocks. The AS1 kaolin was probably formed from hydrothermal alteration in the burial stage due to the heating of groundwater by the late volcanism. Mobile trace elements (Sr, Ba, and Eu) exhibited a depletion trend, while immobile elements (Hf, Ta, Th) showed enrichment. The relatively more zirconium in kaolins implies the formation of low-temperature kaolinization. The notably high kaolinite content, accompanied by reasonable levels of Fe2O3 and TiO2, signifies a medium-grade quality. Furthermore, chondrite-normalized rare earth element (REE) patterns exhibit congruent trends in rocks and kaolin samples, indicating a relative enrichment in light rare earth elements (LREEs) alongside a discernible negative Eu anomaly. The abundant kaolinite and silicon–aluminum composition make the kaolins suitable for refractories, pharmaceutics, cosmetics, and supplementary cementitious material (SCM).

Petrogenesis and Geodynamic Mechanisms of Porphyry Copper Deposits in a Collisional Setting: A Case from an Oligocene Porphyry Cu (Au) Deposit in Western Yangtze Craton, SW China

The Xifanping deposit is a distinct Cenozoic porphyry Cu (Au) deposit located in the Sanjing porphyry metallogenic belt 100–150 km east of the JinshajFiang fault in the western Yangtze craton. We present new zircon U–Pb–Lu–Hf isotopic studies and geochemical data of the ore-bearing quartz monzonite porphyry from the Xifanping deposit to determine their petrogenesis and geodynamic mechanisms. LA–ICP–MS zircon U–Pb dating yielded precise emplacement ages of 31.87 ± 0.41 Ma (MSWD = 0.86) and 32.24 ± 0.61 Ma (MSWD = 1.8) for quartz monzonite porphyry intrusions, and 254.9 ± 5.1 Ma (MSWD = 1.7) for inherited zircons of the monzonite porphyry. The ore-bearing monzonite porphyry is characterized by high-K calc–alkaline to shoshonite and peraluminous series, relatively enriched in light over heavy REEs, with no distinct Eu anomalies, as well as enrichment in LILEs and depletion of HFSEs, with adakitic affinities. The zircon Lu–Hf isotope data ranged from εHf(t) values of −2.94 to +3.68 (average −0.47) with crustal model (TDM2) ages ranging from 0.88 to 1.30 Ga, whereas the inherited zircons displayed positive εHf(t) values ranging from +1.83 to +7.98 (average +5.82), with crustal model (TDM2) ages ranging from 0.77 to 1.17 Ga. Results suggest that the Xifanping porphyry Cu (Au) deposit is related to two periods of magmatic activities. Early magmas were generated from the Paleo-Tethys oceanic subduction during the Late Permian. The subsequent porphyry magma was likely formed by the remelting of previously subduction-modified arc lithosphere, triggered by the continental collision between the Indian and Asian plates in the Cenozoic. The deep magmas and late hydrothermal fluids took advantage of the early magma transport channels along tectonically weak zones during the transition from an extrusive to an extensional–tensional tectonic environment. Early dikes from remelted and assimilated crust contributed to the two age ranges observed in the porphyry intrusions from the Xifanping deposit. The juvenile lower crust materials of the early magmatic arc were potential sources of the Cenozoic porphyry magmas, which has significant implications for mineral exploration and the geological understanding of porphyry Cu deposits in this region.

Overprinting Mineralization in the Huoluotai Porphyry Cu (Mo) Deposit, NE China: Evidence from K-Feldspar Ar-Ar Geochronology and S-Pb Isotopes

The Great Xing’an Range (GXR) is a significant belt of polymetallic deposits located in the eastern segment of the Central Asian Orogenic Belt. The recently found Huoluotai porphyry Cu (Mo) deposit is situated in the northern GXR region in northeastern (NE) China. The deposit has been studied extensively using field geology and geochronological methods, which have identified two distinct mineralization events. These events include an early occurrence of porphyry-type Cu (Mo) mineralization and a later occurrence of vein-type Cu mineralization. Prior geochronology investigations have determined an approximate age of 147 Ma for the early porphyry-type Cu (Mo) mineralization. 40Ar/39Ar dating of K-feldspar of the altered Cu-mineralized quartz diorite porphyry veins for the overprinting vein-type Cu mineralization provides plateau ages of 123.1 ± 1.5 Ma, 122.3 ± 2.8 Ma, and 122.2 ± 0.4 Ma. Sulfide S-Pb isotope compositions of the two mineralization events suggest that both have a magmatic source. The origin of ore-forming metals displays the features of a crust–mantle mixing origin. The regional extensional tectonic setting in NE China during the Early Cretaceous was caused by large-scale lithosphere delamination and upwelling of the asthenospheric mantle. These processes were triggered by the rollback of the Paleo-Pacific Plate. The tectonic event in question resulted in the lithospheric thinning, significant magmatic activity, and mineralization in NE China.

Origin of the coeval cordierite granite, metapelite and diorite in the Qinghai Nanshan (NW China): Evidences from petrology, geochemistry, geochronology and P-T conditions

The origin of coeval magmatic and metamorphic rock associations is of great significance in tectonic interpretations. In this study, spatially associated cordierite granite (S-type), metapelite and diorite from the Qinghai Nanshan (NW China) area were dated to be coeval at ∼247–244 Ma. The cordierite granite and metapelite have almost uniform peak pressure-temperature (P–T) conditions of c. 3.8–5.0 kbar / c. 740–790 °C, indicating a geothermal gradient of higher than ∼40 °C / km. The zircon crystallization temperature of the diorite pluton is estimated to be c. 760 °C by Ti-in-zircon thermometer, putting a lower limit of temperature for dioritic magma. Both cotectic (phenocrysts) and restitic cordierite crystals were identified in the cordierite granite. Similar whole rock compositions of the coarse-grained cordierite granite and the metapelite in the Qinghai Nanshan area as well as the average / median pelite worldwide, imply formation of the granite was from almost complete melting of autochthonous metapelite, followed by in-situ recrystallization with negligible / without melt extraction. These data indicate that the cordierite granite and metapelite are both products of the contact aureole surrounding the diorite pluton. This study presents an example for better understanding the transition from high-grade metapelite to S-type granite.

Mercury isotope evidence for the importance of recycled fluids in collisional ore systems.

The sources of fluids and metals in porphyry systems of continental-collision settings are poorly constrained. Mercury isotopes display unique mass-independent fractionation (expressed as Δ199Hg) and may provide important constraints on metal and volatile sources given that Hg is a highly volatile metal. Here, we report Hg isotope data on ore-forming porphyries, barren magmatic rocks, and mantle-derived mafic magmas from southern Tibet. The fertile porphyries and coeval mafic magmas display mainly positive Δ199Hg values (up to +0.25 per mil), while Δ199Hg values in barren magmatic rocks and mafic magmas are largely negative (-0.54 to 0.00 per mil). The positive Δ199Hg values observed here are consistent with seawater and marine sediments, suggesting that the ultimate source of fluids involved in the genesis of post-subduction porphyry copper deposits was the mantle lithosphere metasomatized by previous oceanic plate subduction. Our Hg isotope data provide an alternative view to current metallogenetic models on collisional porphyry systems that focus on melting of the lower continental crust.

Two-stage mineralization of the Jinkeng Sn-Cu deposit in Eastern Guangdong, Southeast China: Response to magmatic activities and tectonic transformation

The Jinkeng Sn-Cu polymetallic deposit in South China consists of two different types of orebodies: 1) NE-striking skarn- and vein-type Cu-Pb-Zn-Sn orebodies in volcanic rocks suffering subsequent ductile shear deformation, and 2) NW-striking quartz-cassiterite-sulfide veins filled in the faults at the porphyritic granodiorite outward from the fine-grained granite which does not exhibit deformation. The relationships among Sn-Cu polymetallic mineralization, regional magmatism, and deformation metamorphism are still controversial. To address it, the geochronological, whole-rock and mineral geochemical research along with the detailed field investigation were conducted in this study. Our zircon U-Pb dating results show that the volcanic rocks formed at 158–162 Ma, earlier than the porphyritic granodiorite which yields the emplacement age of 146–147 Ma. In-situ LA-ICP-MS U-Pb dating of cassiterite from the deformed skarn ores indicates the early-stage mineralization occurred at 146 ∼ 148 Ma, which is similar to the emplacement age of the porphyritic granodiorite, but earlier than the formation of quartz-cassiterite-sulfide veins and the fine-grained granite (141∼144 Ma). Further, the whole-rock and biotite geochemistry, and zircon Hf isotope compositions suggest that the porphyritic granodiorite exhibits a lower degree of magma differentiation, higher oxygen fugacity, higher Cl and lower F contents than the fine-grained granite. The porphyritic granodiorite might provide the most Cu-Pb-Zn budget accompanied by minor Sn for early-stage mineralization. Overall, our study suggests that the Jinkeng Sn-Cu polymetallic deposit formed in two scenarios where the early dominated Cu-Pb-Zn and minor Sn mineralization related to the emplacement of the porphyritic granodiorite is superimposed by the late vein-type Sn-dominated mineralization related to the emplacement of the fine-grained granite. The two isolated mineralizing events (∼147 Ma and ∼141 Ma, respectively) in Jinkeng were probably responded to the regional magmatic activities triggered by the tectonic transformation where two extensional tectonic events were separated by a short contractional event (147–144 Ma).

Resurgent dome and super-hot enhanced geothermal system: The Sahinkalesi Massif within the Hasandag Stratovolcanic Province, Central Anatolia, Turkey

The Sahinkalesi, a volcanic dome located NNE of Hasandağ, Türkiye exhibits anomalous heat flow value, geothermal gradient and the Curie point depth is located at very shallow depth in this region. Our investigation indicates presence of super-critical thermal regime (378°C) at about 4 km depth and the MT analysis indicate shallow magma chamber at about 5 km depth. The crust is relatively thin below this region with the low-velocity region located at depth of about 36 km. Thermo-Hydro-mechanical model investigation has been carried out using finite element discretization technique. For faulted zone reservoir models, 30 years of geothermal energy exploitation does not cause thermal breakthrough for mass flow rates up to 500 kg/s, however, the mean stress developed in the reservoir becomes much larger and may be unsustainable for the reservoir stability. To ensure the success of a fractured reservoir model, the use of multiple wellbores is recommended. In the case of a closed-loop geothermal system, the primary concern is the control of thermoelastic stress. This can be achieved either by increasing the wellbore depth while reducing the injection mass flow rate, or by extending the wellbore's horizontal component. The outlet temperature in both the cases maintained at 275°C. This is the first time a superhot EGS site has been identified in Türkiye.

Submarine cores record magma evolution toward a catastrophic eruption at Kikai Caldera

Magma evolution toward a caldera-forming eruption remains uncertain in many cases owing to the lack of successive volcanic records before catastrophic eruptions. Here we take an approach to this issue by analyzing a submarine core sampled near Kikai Caldera, southern Japan, which has recorded two caldera-forming eruptions at 95 and 7.3 ka and small eruptions between them. Discovery of mafic glass fragments in the submarine deposits of the 95-ka eruption, which had not been recognized in subaerial outcrops, implies the involvement of mafic magma in felsic magma-driven caldera-forming eruption. Inter-caldera volcanic activity resumed with binary mafic and felsic magma extrusions but then shifted to eruptions predominated by felsic magmas. In the final stage preceding the 7.3-ka caldera-forming eruption, the most felsic composition did not appear in glass fragments. We suggest that this period was the phase of felsic melt accumulation to grow a magma reservoir toward the next catastrophic eruption.

Successful subduction of oceanic plate after failed attempts in the Late Archean: Petrological and geochemical constraints

When and how plate tectonics started and evolved to the style as we know it today is a fundamental yet highly controversial question. Numerical geodynamic modelling predicts that the transition into plate tectonics in the Archean was episodic with possible alternation between success and failure of subduction. However, direct geological evidence for failed subduction is scarce. While this possibility has been suggested by numerical modelling, it is still lack of geological evidence. Here we present a combined study of zircon U-Pb ages and Hf-O isotopes, as well as whole-rock major and trace elements, for meta-igneous rocks from the Alxa Block in the westmost North China Craton (NCC). Two periods of Late Archean magmatism ca. 2.75 Ga and 2.5 Ga are identified to occur surrounding a pre-3.0 Ga continental nucleus. Geochemical analyses of the ca. 2.75 Ga meta-mafic and meta-felsic igneous rocks show two different modes of tectonic regime. The felsic rocks resemble typical Archean TTG (tonalite-trondhjemite-granodiorite) in composition, with variable εHf(t) values from -2.8 to 11.0 and δ18O values from 4.3 ‰ to 7.9 ‰. Petrogenetic modelling suggests that their magmatic source was the ca. 3.1–2.75 Ga oceanic crust that was hydrothermally altered at different temperatures and then mixed with the older continental crust and partially melted in lower crust in the garnet stability field. This requires tectonic accretion of the oceanic crust to the continental nucleus, signifying an attempted or failed subduction. On the contrary, the meta-mafic rocks exhibit arc-like trace element patterns and calc-alkaline evolution trend, indicating a metasomatic mantle source due to successful subduction of the oceanic slab to subarc depths. Taken together, the present results provide robust constraints on the behavior of oceanic slab at the Archean convergent margin, where successful oceanic subduction would be achieved after several failed attempts. Such failure-success processes of oceanic subduction may be applicable to the whole NCC and other cratons elsewhere in the world, reflecting the gradual maturation of plate tectonics in the Archean, consistent with predictions of numerical modelling.

Platinum-Group Elements and Nb-Ta geochemistry of the Deccan basalts from Kumbharli and other Ghat sections and the Koyna Seismic Zone, Maharashtra (India): Crustal contamination and implication for sulfide saturation of the magma

The Deccan basalts from Kumbharli, Nadlapur, Bijaynagar, Hazarmacchi, and Surli Ghat sections (surface samples) and the Koyna borehole-7 (KBH-7, sub-surface samples) from Maharashtra (western India) demonstrate a two-stage crystallization process. Olivine and chromite were crystallized earlier in a shallow crustal magma chamber while clinopyroxene and plagioclase phenocrysts were crystallized in the sub-volcanic conduits forming the crystal mush, and carried to the surface by the evolved Fe-Ti-rich ascending basaltic magma. The high modal abundance of plagioclase at the top and clinopyroxene at the bottom part of the Kumbharli Ghat section is responsible for an increase in Sr and a decrease in Sc content towards the upper flows. The surface and sub-surface basalt samples contain Pd = 5–31 ppb, Pt = 4–15 ppb, Ir = 1–4 ppb, Ru = 1–3 ppb, and Rh = 3–5 ppb. Negative relations of Pd/Ir, Pd/Ru, and Pd/Rh with MgO from both sets of samples indicate partitioning of Ir, Ru, and Rh to early fractionated cumulus chromite (or olivine). Magnetite is a late crystallizing phase from the evolved Fe-Ti-rich basaltic magma. With an increasing modal abundance of magnetite, there is an increase of FeO total , TiO 2 , and V with Pd indicating fractionation of Pd by magnetite. Geochemical characters show that the surface basalt samples are less contaminated compared to the sub-surface KBH-7 basalts. High Nb (6.8–13.6 ppm) and low Ta (0.2–0.37 ppm) content and elevated Nb/Ta ratios of the surface samples from the ghat sections indicate the possible interaction of the basaltic magma with the carbonate metasomatized subcontinental lithospheric mantle (SCLM). On the other hand, a high degree of partial melting with limited crustal contamination can also elevate the Nb/Ta ratios of the basalts from the ghat sections. Deccan basalts from the study areas do not bear the signature of sulfide supersaturation and subsequent immiscible sulfide segregation. This is evidenced by their high chalcophile element concentrations (Ni = 79–103 ppm, Cu = 121–259 ppm) and ratios like Cu/Zr (≥ 1), Ni/MgO (13.7–21.8) with low Cu/Pd (2140–29938) compared to other Ni-Cu (PGE) sulfide mineralized continental flood basalts. The lack of crustal sulfur in the various contaminants is perhaps the main reason for this sulfide-undersaturated character of the Deccan basalts of the current study.

Ground surface displacements and stress localization driven by dual magma chamber dynamics: analytical and numerical model estimates

Ground surface displacements and stress localization driven by dual magma chamber dynamics: analytical and numerical model estimates

Early terrestrial and lunar anorthosites: Comparative geochemistry and evolutionary processes

In a paper in 1970, Brian Windley first recognised that early terrestrial and lunar anorthosites both have calcic plagioclase, and low TiO2and high CaO and Al2O3contents. Despite these similarities, the geochemistry of early terrestrial and lunar anorthosites has not been rigorously compared and contrasted. To this end, we compiled 425 analyses from 212 early terrestrial anorthosite occurrences and 306 analyses from 16 lunar anorthosite occurrences. This was supplemented by a compilation of plagioclase anorthite (An) contents and pyroxene Mg# from early terrestrial and lunar anorthosites. Early terrestrial anorthosites have lower whole-rock An contents but similar Mg# to lunar anorthosites. The CaO contents of lunar anorthosites are higher than those of early terrestrial anorthosites for a given MgO and Al2O3content, early terrestrial anorthosites have higher SiO2contents than lunar anorthosites at a given MgO content, and lunar anorthosites have higher Eu/Eu* anomaly ratios yet broadly similar La/Yb and Nd/Sm ratios than early terrestrial anorthosites. Some early terrestrial anorthosites have less fractionated chondrite-normalised rare earth element (REE) patterns and less prominent positive Eu anomalies than lunar anorthosites. Lunar anorthosites have higher plagioclase An contents, yet a similar range of pyroxene Mg# compared to their early terrestrial counterparts. Some early terrestrial anorthositesare more fractionated than some lunar anorthosites. Our interpretations imply that most early terrestrial anorthosites crystallised from basaltic parental magmas that were generated by high-degree partial melting of sub-arc asthenosphere mantle wedge sources that were hydrated by slab-derived fluids, with the remainder being associated with mid-ocean ridge and mantle plume settings. Some of the arc-related early terrestrial anorthosites were influenced by crustal contamination. In addition, early terrestrial anorthosites originated from partial melting of the mantle at various depths with variable garnet residua, whereas lunar anorthosites formed without any significant garnet residua. Lower plagioclase CaO contents and pyroxene Mg# in early terrestrial anorthosites can be explained by higher proportions of clinopyroxene and olivine fractionation in terrestrial magma chambers than in the lunar magma ocean where orthopyroxene and olivine fractionation occurred. Low TiO2contents in both terrestrial and lunar anorthosites reflect rutile and/or ilmenite fractionation.