Melt Production Research Articles

Quantification of Impact‐Induced Melt Production in Numerical Modeling Revisited

AbstractMelting and vaporization of rocks in impact cratering is mostly attributed to be a consequence of shock compression. However, other mechanism such as plastic work and decompression by structural uplift also contribute to melt production. In this study we expand the commonly used method to determine shock‐induced melting in numerical models from the peak shock pressure by a new approach to account for additional heating due plastic work and internal friction. We compare our new approach with the straight‐forward method to simply quantify melting from the temperature relative to the solidus temperature at any arbitrary point in time in the course of crater formation. This much simpler method does account for plastic work but suffers from reduced accuracy due to numerical diffusion inherent to ongoing advection in impact crater formation models. We demonstrate that our new approach is more accurate than previous methods in particular for quantitative determination of impact melt distribution in final crater structures. In addition, we assess the contribution of plastic work to the overall melt volume and find, that melting is dominated by plastic work for impacts at velocities smaller than 7.5–12.5 km/s in rocks, depending on the material strength. At higher impact velocities shock compression is the dominating mechanism for melting. Here, the conventional peak shock pressure method provides similar results compared with our new model. Our method serves as a powerful tool to accurately determine impact‐induced heating in particular at relatively low‐velocity impacts.

Temporal variations in plume flux: characterizing pulsations from tilted plume conduits in a rheologically complex mantle

SUMMARY Along age-progressive hotspot volcano chains, the emplacement rate of igneous material varies through time. Time-series analysis of changing emplacement rates at a range of hotspots finds that these rates vary regularly at periods of a few to several tens of millions of years, indicative of changing melt production within underlying mantle plumes. Many hotspots exhibit at least one period between ∼2 and 10 Myr, consistent with several proposed mechanisms for changing near-surface plume flux, and thus melting rate, such as small-scale convection, solitary waves and instability formation in tilted plume conduits. Here, we focus on quantifying instability growth within plumes tilted by overlying plate motion. Previous studies using fluids with constant or temperature-dependent viscosity suggest that such instabilities should not form under mantle conditions. To test this assertion, we use a modified version of the finite element code ASPECT to simulate 400 Myr of evolution of a whole-depth mantle plume rising through the transition zone and spreading beneath a moving plate. In a 2-D spherical shell geometry, ASPECT solves the conservation equations for a compressible mantle with a thermodynamically consistent treatment of phase changes in the mantle transition zone and subject to either a temperature- and depth-dependent linear rheology or a temperature-, depth- and strain-rate dependent non-linear rheology. Additionally, we examine plume evolution in a mantle subject to a range of Clapeyron slopes for the 410 km (1–4 MPa K–1) phase transitions. Results suggest that plume conduits tilted by >67° become unstable and develop instabilities that lead to initial pulses in the transition zone followed by repeated plume pulsing in the uppermost mantle. In these cases, pulse size and frequency depend strongly on the viscosity ratio between the plume and ambient upper mantle. Based upon our results and comparison with other studies, we find that the range of statistically significant periods of plume pulsing in our models (∼2–7 Myr), the predicted increase in melt flux due to each pulse (3.8–26 × 10−5 km3 km−1 yr−1), and the time estimated for a plume to tilt beyond 67° in the upper mantle (10–50 Myr) are consistent with observations at numerous hotspot tracks across the globe. We suggest that pulsing due to destabilization of tilted plume conduits may be one of several mechanisms responsible for modulating the melting rate of mantle plumes as they spread beneath the moving lithosphere.

Building archean cratonic roots

Geophysical, geochemical, and geological investigations have attributed the stable behaviour of Earth’s continents to the presence of their Archean cratonic roots. These roots are likely composed of melt-depleted, low density residual peridotite with high magnesium number (Mg#), while devolatilisation from the upper mantle during magmatic events might have made these roots more viscous and intrinsically stronger than the convecting mantle. Several conceptual dynamic and petrological models of craton formation have been proposed. Dynamic models invoke far-field shortening or mantle melting events, e.g., by mantle plumes, to create melt-depleted and thick cratons. Compositional buoyancy and rheological modifications have also been invoked to create long-lived stable cratonic lithosphere. However, these conceptual models have not been tested in a dynamically self-consistent model. In this study, we present global thermochemical models of craton formation with coupled core-mantle-crust evolution driven entirely by gravitational forces. Our results with melting and crustal production (both oceanic and continental) show that formation of cratonic roots can occur through naturally occurring lateral compression and thickening of the lithosphere in a self-consistent manner, without the need to invoke far-field tectonic forces. Plume impingements, and gravitational sliding creates thrusting of lithosphere to form thick, stable, and strong lithosphere that has a strong resemblance to the Archean cratons that we can still observe today at the Earth’s surface. These models also suggest the recycling of denser eclogitic crust by delamination and dripping processes. Within our computed parameter space, a variety of tectonic regimes are observed which also transition with time. Based on these results, we propose that a ridge-only regime or a sluggish-lid regime might have been active on Earth during the Archean Eon as they offer favourable dynamics and conditions for craton formation.

Lithological structure of western Pacific lithosphere reconstructed from mantle xenoliths in a petit-spot volcano

The lithospheric mantle, formed at the mid-ocean ridge as a residue of crustal production, comprises theoretically depleted peridotite, but more fertile components (e.g., lherzolite and pyroxenite) have been reported, creating an enigmatic picture of the lithosphere. The oceanic lithosphere has also been found to be locally modified by intraplate magmatism as proposed from geochemistry of mantle xenolith. Petit-spot xenoliths are particularly notable as direct evidence of old lithospheric mantle and expected to retain essential information about oceanic lithosphere prior to its subduction. In this study, we report on the lithological structure of Pacific lithosphere aged at 160 Ma, just subducting into Mariana Trench, based on petrology and chemistry of ultramafic xenoliths from a petit-spot knoll, and then, we suggest the occurrence of petit-spot melt infiltration resulting in mantle metasomatism and formation of pyroxene-rich vein. Our petit-spot ultramafic xenoliths can be divided into three main types: a depleted peridotite as a residue of crust production, an enriched peridotite, and fertile pyroxenites as the product of melt–rock interactions prior to entrapment. Geothermobarometry also suggests that the depleted peridotite was derived from the uppermost lithospheric mantle, whereas the enriched peridotite and Al-augite pyroxenites were obtained from deeper layers of the lithosphere. Moreover, thermal gradient of the lithosphere estimated from these data is considerably hotter than pristine geotherm estimated on the basis of plate age. Hence, we could illustrate that the oldest portion of the Pacific lithosphere (160 Ma), which was not observed before, was locally fertilized and heated by prior multiple petit-spot magmatic events, and pyroxene-rich metasomatic veins penetrated from the base to the middle/upper lithosphere. Such local lithospheric fertilization is plausible at the plate-bending field, and the nature of Pacific Plate subducting into Mariana Trench may be partly different from what has been assumed so far.

Oligocene calc-alkaline lamprophyres and K-rich association in the eastern Iranian ranges: Products of low-degree melting of subduction-modified lithospheric mantle in post-orogenic setting

Late- to post-orogenic lamprophyric and K-rich associations in the eastern Iranian ranges may be able to reveal some obscure issues about the petrogenesis and the role of tectonics in the formation of this rare group of igneous rocks. In this paper, we investigate new zircon U–Pb ages and elemental and Sr–Nd isotope characteristics of coexisting various rock suites as the post-tectonic products of the Paleogene orogeny . Lamprophyres are found in three occurrence modes in the eastern Iranian ranges. The first group is composed of olivine minette/shonkinite bodies in the Lar Complex, which is expressed as a post-tectonic volcano with Calderon subsidence that occurs currently as a ring-dike association and related explosion breccia . The second group consists of lamprophyric lavas of mainly mafic phonolite composition in Hormak. The last group is appinite/porphyrite occurring as stock/sub-volcanic bodies in Malek Siah Kuh. These three magmatic suites including lamprophyre and associated magmatic rocks are genetically, spatially and temporally related to one common K-rich mantle-derived magma . Zircon U–Pb dating of representative monzonite/syenite samples of the Lar Complex yielded ages of 31.43 ± 0.3 and 31.60 ± 0.40 Ma, respectively. Whole-rock geochemical and Sr–Nd isotope investigations demonstrated similar rare earth element (REE) patterns, with distinct enrichment in large lithophile elements (LILEs) and depletion in Ta–Nb–Ti, and limited variations in εNd (t) (+0.50 − +4.80) and 87 Sr/ 86 Sr (0.7043–0.7066) values. These characteristics, together with modeling of batch melting suggest that they were comagmatic and derived from a metasomatized lithospheric mantle source modified by a precursory subduction episode, through a low degree of partial melting (2–5%) at high-pressure conditions at depths >70 km with garnet in the residue. The Harirud fault activity possibly controlled the path, station and rapidity of magma ascent to the crustal levels, and, consequently, the water pressure of crystallization of the K-rich magmas and diversity of magmatic products. • The lithospheric mantle in the eastern Iranian ranges is highly heterogeneous. • Lamprophyres and K-rich association were products of post-orogenic magmatism. • The Harirud fault has crucial role in generation, transport and evolution of K-rich magmas.

Status of benchmark exercises in the frame of the NUGENIA QUESA project

Severe accidents in nuclear power plants with loss of cooling or loss of coolant and core uncovery can lead to air ingress into fuel assemblies. If air or a steam–air-mixture comes into contact with cladding material, the exothermal character of zirconium oxidation and nitride formation leads to enhanced cladding oxidation, heat-up and degradation up to core melt and fission product release. Two experiments, QUENCH-18 and CODEX-AIT-3 were performed in the frame of EC projects ALISA and SAFEST to fill knowledge gaps on relevant phenomena. Both tests are accompanied by pre- and post-test benchmarks within the NUGENIA project QUESA. The pre-test benchmarks were completed, while the post-test benchmarks are currently running. Results of the pre-test benchmarks indicate that participating codes can qualitatively predict the experimental observations. Generally, the range of the predictions are wider for CODEX-AIT-3 while the trend is close except one for QUENCH-18. The specification of both test procedures was additionally supported by parameter studies. First post-test benchmark results for QUENCH-18 show that code predictions are in good agreement during the pre-oxidation and mixed steam/air phase. In the subsequent reflooding phase with intensive melt release, relocation and oxidation, notable differences between codes and simultaneously deviations from experimental results are observed. In the paper the main findings of the QUENCH-18 test are discussed, but the focus will be on the pre-test analyses of CODEX-AIT-3.

Zircon evolution from migmatite to crustally-derived granite: A case study of late Neoarchean migmatite in the Yishan area, western Shandong, North China Craton

Sequential changes in the texture, composition and U-Pb age of zircon from the late Neoarchean migmatites and related rocks in the Yishan area of western Shandong, eastern North China Craton, record the evolution of melt and magma from paleosome to crustally-derived granite. Zircon grains from the paleosome and metatexite have features of recrystallization, with narrow rims; those from leucosome have inherited cores and wide homogenous rims; those from diatexite preserve evidence of a complex evolution involving dissolution and growth, with the euhedral morphology of the rims, and the cross-cutting relationship between cores and rims, consistent with a magmatic origin. With the increase in melt content toward granite, the newly-grown zircon has clearer magmatic zoning and higher Th/U ratios. The low whole-rock Zr saturation temperatures (684–728 ℃) indicate that the diatexites, with abundant residual zircon, might be the product of low-temperature melting. The contemporaneous, crustally-derived granites, however, contain no or much less xenocrystic zircon and have high zircon saturation temperatures (740–868 ℃). Only at the higher temperature was sufficient partial melt produced to start the migration of magma out of the source region to form the granites. Anatectic (magmatic) zircons in diatexite commonly contain xenocrystic (residual) zircons, no matter how the magmatic system evolves further, the xenocrystic zircons in the anatectic (magmatic) zircons will still be retained. On the other hand, the crustlly-derived granites widely distributed in the area contain few residual zircons. Therefore, the crustally-derived granites widely distributed in western Shandong cannot form by further evolution of the diatexites, but require a higher degree of partial melting under higher temperature conditions. SHRIMP U-Pb zircon dating, combined with CL imaging, reveals that zircon crystals from the diatexites mostly are characterized by inherited cores with thick magmatic overgrowths, recording a regional anatectic event at ∼2.51 Ga. Residual source rock enclaves and xenocrystic zircons in the diatexites mostly have ages of ∼2.70 Ga and ∼2.53 Ga, suggesting that the diatexites were derived from Neoarchean continental crust.

Neoproterozoic–Early Cambrian igneous and sedimentary sequences in the Songliao Block, NE China: Records of Rodinia supercontinent evolution in eastern Central Asian orogenic Belt

As the core of NE China blocks (i.e., Songliao, Jiamusi-Khanka, Erguna, Xing’an), the Songliao Block plays an important role in understanding the Precambrian evolutionary history of the eastern Central Asian Orogenic Belt (CAOB), as well as the linkage with reconstructions of Rodinia supercontinent. In this work, we present sedimentological, whole-rock geochemical, and zircon U–Pb–Hf isotopic data for the Neoproterozoic-early Cambrian igneous and sedimentary rocks in eastern Songliao Block. The newly identified 954 ± 2 Ma gneissic syenogranite pluton，916 ± 5 Ma meta-basaltic andesite, and the reported 929–841 Ma intrusive rocks formed the Precambrian crystalline basement of the eastern Songliao Block, which was overlain by the late early Neoproterozoic to early Cambrian stable sedimentary cover. The early Neoproterozoic (954 Ma) gneissic syenogranite was likely the product of muscovite dehydration melting of sedimentary rocks in deep crust during the post-collisional setting, probably associated with the collision between the Songliao and Jiamusi-Khanka blocks. The late Neoproterozoic to early Cambrian Chenming Formation displays characteristics of passive margin deposition, which formed after the opening of Paleo-Mudanjiang Ocean at 777 Ma. Integration of the spatial and temporal distributions of Neoproterozoic magmatism and sedimentation in the Songliao, Erguna, Xing'an and Jiamusi-Khanka blocks, as well as the geochemical variations from 0.96 to 0.73 Ga, we suggest that the blocks in NE China have experienced a similar two-stage Neoproterozoic tectonic evolutionary history associated with the Rodinia assembly and breakup. An early advancing subduction along peripheral Rodinia led to the collision and collapse extension between the Songliao and Jiamusi-Khanka blocks before 954 Ma, and the generation of 929–880 Ma syenites and granitoids in compressional continental arc setting. Then the retreating subduction formed the 850–737 Ma mafic and felsic rocks in Songliao, Erguna and Jiamusi-Khanka blocks, and caused breakup of the joint continent and opening of the Paleo-Mudanjiang and Paleo-Xinlin oceans, two branches of Paleo-Asian Ocean, since 777 Ma. In response to the oceanic spreading, the passive continental margin sedimentation developed in these blocks during 750–520 Ma.

Petrogenesis of peridotites in the Dargai Complex ophiolite, Indus Suture Zone, Northern Pakistan: Implications for two stages of melting, depletion, and enrichment of the Neo-Tethyan mantle

The upper mantle section of the Dargai ophiolite along the Indus Suture Zone, also known as the Main Mantle Thrust of northern Pakistan, consists mainly of clinopyroxene-bearing (Cpx)-harzburgites, depleted harzburgites, and dunites. Here we document a two-stage origin for these ultramafic rocks using new mineral and whole-rock geochemistry, integrated with Re -Os isotopic data of these upper mantle peridotites. Chromian spinel in the Cpx-harzburgites have significantly lower Cr# values (15.2–20.7) than the depleted harzburgites (38.4–75.2) and dunites (75.0–81.9). The Cpx-harzburgites are characterized by high average Al 2 O 3 (2.04 wt%), CaO (2.26 wt%), ∑REE (24.3 ppb), and 187 Os/ 188 Os values ranging between 0.12495 and 0.12997. In contrast, the depleted harzburgites and dunites are characterized by lower average Al 2 O 3 (0.51 wt% and 0.14 wt%, respectively), CaO (0.68 wt% and 0.19 wt%, respectively), and ∑REE (3.41 ppb and 0.92 ppb, respectively). The 187 Os/ 188 Os of the depleted harzburgites range between 0.11699 and 0.12612, values that are less radiogenic than those of the Cpx-harzburgites. The mantle-normalized trace element patterns of the Cpx-harzburgites reflect low degrees of partial melting (~10–15%), whereas those of the depleted harzburgites and dunites record somewhat higher degrees of partial melting (~15–23% additional melting of the Cpx-harzburgites). The low degree of melting, coupled with low degrees of melt extraction, therefore point to a spreading center at amid-ocean ridge (MOR) or in a distal forearc basin. In contrast, the depleted harzburgites and dunites formed during the second stage of melting and related refertilization, and were clearly linked to a supra-subduction zone (SSZ) setting. The Re -Os isotopic compositions of the Dargai Complex peridotites provide model ages of ca. 250 and ca. 450 Ma recording protracted tectonic events in close association with the geodynamic evolution of the Neo-Tethyan, Rheic, and Proto-Tethyan oceans. The extremely heterogeneous Os isotopic compositions of this part of the Neo-Tethyan upper mantle reflect multiple melt production and melt extraction processes throughout its tectonic evolution. • Peridotites in the Dargai Complex are formed by episodic melt-rock reaction. • The Dargai Complex peridotites experienced two stage of depletion and enrichment. • Peridotites were formed in the Indus Suture Zone after low-high degrees partial melting. • Re-Os isotopic composition infer derivation from heterogeneously depleted mantle.

Rhyolitic melt production in the midst of a continental arc flare-up—The heterogeneous Caspana ignimbrite of the Altiplano-Puna volcanic complex of the Central Andes

Abstract The ~5 km3, 4.54–4.09 Ma Caspana ignimbrite of the Altiplano-Puna volcanic complex (APVC) of the Central Andes records the eruption of an andesite and two distinct rhyolitic magmas. It provides a unique opportunity to investigate the production of silicic magmas in a continental arc flare-up, where small volumes of magma rarely survive homogenization into the regional magmatic system that is dominated by supereruptions of monotonous dacitic ignimbrites. The fall deposit and thin flow unit that record the first stage of the eruption (Phase 1) tapped a crystal-poor peraluminous rhyolite. The petrological and geochemical characteristics of Phase 1 are best explained by partial melting of or reheating and melt extraction from a granodioritic intrusion. Phase 2 of the eruption records the emplacement of a more extensive flow unit with a crystal-poor, fayalite-bearing rhyolite and a porphyritic to glomeroporphyritic andesite containing abundant plagioclase-orthopyroxene-Fe-Ti oxide (norite) glomerocrysts. The isotopic composition of Phase 2 is significantly more “crustal” than Phase 1, indicating a separate petrogenetic path. The mineral assemblage of the noritic glomerocrysts and the observed trend between andesite and Phase 2 rhyolite are reproduced by rhyolite-MELTS–based models. Pressure-temperature-water (P-T-H2O) estimates indicate that the main (Phase 2) reservoir resided between 400 and 200 MPa, with the andesite recording the deeper pressures and a temperature range of 920–1060 °C. Rhyolite phase equilibria predict an estimated temperature of ~775 °C and ~5 wt% H2O. Pressures derived from phase equilibria indicate that the rhyolite was extracted directly from the noritic cumulate at ~340 MPa and stored at slightly shallower pressures (200–300 MPa) prior to eruption. The rhyolite-MELTS models reveal that latent-heat buffering during the extraction and storage process results in a shallow liquidus during the extensive crystallization that produced a noritic cumulate in equilibrium with a rhyodacitic residual liquid. Spikes in latent heat facilitated the segregation of the residual liquid, creating the pre-eruptive compositional gap of ~16 wt% SiO2 between the andesite and the Phase 2 rhyolite. Unlike typical Altiplano-Puna volcanic complex (APVC) magmas, low fO2 conditions in the andesite promoted co-crystallization of orthopyroxene and ilmenite in lieu of clinopyroxene and magnetite. This resulted in relatively high Fe concentrations in the rhyodacite and Phase 2 rhyolite. Combined with the co-crystallization of plagioclase, this low oxidation state forced high Fe2+/Mg and Fe/Ca in the Phase 2 rhyolite, which promoted fayalite stability. The dominance of low Fe3+/FeTot and Fe-Ti oxide equilibria indicates low fO2 (ΔFMQ 0 − ΔFMQ − 1) conditions in the rhyolite were inherited from the andesite. We propose that the serendipitous location on the periphery of the regional thermal anomaly of the Altiplano-Puna magma body (APMB) permitted the small-volume magma reservoir that fed the Caspana ignimbrite eruption to retain its heterogeneous character. This resulted in the record of rhyolitic liquids with disparate origins that evaded assimilation into the large dacite supereruption-feeding APMB. As such, the Caspana ignimbrite provides a unique window into the multi scale processes that build longlived continental silicic magma systems.

Hydration, melt production and rheological weakening within an intracontinental gneiss dome

The Entia Gneiss Complex (EGC) in central Australia represents a deeply exhumed Paleoproterozoic basement terrane that underwent fluid-catalysed transformation culminating in the formation of a migmatitic gneiss dome during the 450–300 Ma intracontinental Alice Springs Orogeny (ASO). Foremost amongst the changes the EGC experienced during this event was the regional-scale conversion of nominally anhydrous granulite and igneous crust to hydrous amphibolite facies migmatite, together with the emplacement of locally voluminous mica-bearing pegmatite swarms. LA–ICP–MS U–Pb dating of zircon, monazite and xenotime demonstrates that pegmatite emplacement dominantly occurred late in the Alice Springs Orogeny (c. 360–300 Ma). The oldest generation of pegmatites are transposed into the regional Palaeozoic gneissic fabric and formed at c. 1770 Ma, indicating they belong to protolith rocks of the EGC. Three subsequent generations of pegmatite have ages that range between 360 and 300 Ma. The oldest of these is parallel to the migmatitic gneissic fabric and dated at c. 360 Ma, whereas the younger two generations are largely undeformed, discordant and intruded throughout the period c. 350–300 Ma. The capability for a comparatively dry intracratonic orogenic core to repeatedly produce melt over an interval of c. 60 Myr requires explanation. We suggest crustal-scale duplex development during the latter stages of the ASO resulted in the juxtaposition of dry and mechanically strong Paleoproterozoic basement over deeply buried Neoproterozoic–Cambrian sedimentary sequences. Fluid derived from the metamorphic dehydration of these sequences led to hydration, partial melting and rheological weakening of the basement slab. Prior to its hydration at c. 360 Ma, the EGC was metamorphically unresponsive, accounting for its comparatively late timing of deformation and partial melting compared to the overall history of the Alice Springs Orogeny. The development of the crustal-scale duplex system, combined with hydrous melting of the low-density basement slab beneath high-density supracrustal rocks, resulted in a thermomechanically unstable architecture that facilitated the formation of an orogen-scale gneiss dome during the waning stages of intracontinental orogenesis.

Significance of selective crystal entrainment and differential crystal‐melt separation in petrogenesis of granites from the Tongbai orogen

AbstractPartial melting has been shown to be an important mechanism for intracrustal differentiation and granite petrogenesis. However, a series of compositional differences between granitic melt from experiments and natural granites indicate that the processes of crustal differentiation are complex. To shed light on factors that control the processes of crustal differentiation, and then the compositions of granitic magma, a combined study of petrology and geochemistry was carried out for granites (in the forms of granitic veins and parautochthonous granite) from a granulite terrane in the Tongbai orogen, China. These granites are characterized by high SiO2 (>72 wt%) and low FeO and MgO (<4 wt%) with low Na2O/K2O ratios (<0.7). Minerals in these granites show variable microstructures and compositions. Phase equilibrium modelling using P–T pseudosections shows that neither anatectic melts nor fractionated melts match the compositions of the target granites, challenging the conventional paradigm that granites are the crystallized product of pure granitic melts. Based on the microstructural features of minerals in the granites, and a comparison of their compositions with crystallized minerals from anatectic melts and minerals in granulites, the minerals in these granitoids are considered to have three origins. The first is entrained garnets, which show comparable compositions with those in host granulites. The second is early crystallized mineral from melts, which include large plagioclase and K‐feldspar (with high Ca contents) crystals as well as a part of biotite whose compositions can be reproduced by crystallization of the anatectic melts. The compositions of other minerals such as small grained plagioclase, K‐feldspar and anorthoclase in the granites with low Ca contents are not well reconstructed, so they are considered as the third origin of crystallized products of fractionated melts. The results of mass balance calculation show that the compositions of these granites can be produced by mixing between different proportions of crystallized minerals and fractionated melts with variable amounts of entrained minerals. However, the calculated modal proportions of different crystallized minerals (plagioclase, K‐feldspar, biotite and quartz) in the granites are significantly different from those predicted by melt crystallization modelling. Specifically, some rocks have lower modes of biotite and plagioclase, whereas others show lower K‐feldspar modes than those produced by melt crystallization. This indicates that the crystallized minerals would be differentially separated from the primary magmas to form the evolved magmas that produce these granites. Therefore, the crystal entrainment and differential melt‐crystal separation make important contributions to the composition of the target granites. Compared with leucogranites worldwide, the target granites show comparable compositions. As such, the leucogranites may form through the crystal fractionation of primary granitic magmas at different extents in addition to variable degrees of partial melting.

LSQP-DB: a species-specific quantitative PCR primer database for 307 Lactobacillaceae species

Quantitative real-time PCR is widely used to determine absolute abundance of microbes in food fermentation. However, it remains challenges in the application for quantification at the species level due to the difficulty in designing species-specific primer sets. This work, using Lactobacillaceae, a dominant family within the lactic acid bacteria that involved in diversity food fermentations, as a case, presents an extendable strategy to design species-specific primer sets for microbial quantitative analysis. 136,257 species-specific genes were obtained from all 307 species within Lactobacillaceae family through comparative genomics analysis. A total of 130,521 primer sets were designed using species-specific genes. Among them, 81,710 primer sets had 100% interspecific specificity and 100% intraspecific coverage, and were reserved to quantify all 307 individual Lactobacillaceae species. These primer sets had uniform melting temperature (57–63 ℃) and product size (100–300 bp), that allowed simultaneously quantify different Lactobacillaceae species with the same qPCR condition. We then established a Lactobacillaceae species quantitation primer database (LSQP-DB, http://lsqp-db.com ) containing all 81,710 species-specific primer sets. The database would facilitate a fast and easy absolute quantitation analysis of all individual Lactobacillaceae species. This work represented the first ever large-scale integration of species-specific primer sets for microorganism, it can be extended to other bacterial and fungal genera to advance development of microbial absolute quantification.

Permian arc magmatism in southern Tibet: Implications for the subduction and accretion of the Zhikong–Sumdo Paleo-Tethys Ocean

The tectonic evolution of the Zhikong–Sumdo Paleo-Tethys Ocean (Hereafter referred to as Zhikong–Sumdo Ocean) in southern Tibet is controversial due to the limited records of arc magmas. Here, the newly discovered Zhangda complex in the Zhikong area of Tibet is selected as the research object. Zircon U–Pb geochronology, zircon Hf isotopes, whole-rock geochemistry and Sr-Nd isotope analyses performed based on field geological surveys show that the Zhangda complex is composed of Early Permian hornblende gabbro (278.3 ± 1.1 Ma), cumulate gabbro (277.4 ± 1.7 Ma), tonalite dike (281.1 ± 1.9 Ma), Middle–Late Permian gabbro diorite (267.8 ± 2.9 Ma, 269.0 ± 3.1 Ma), and tonalite (258.0 ± 2.7 Ma). The Zhangda mafic rocks show weak fractionation of light and heavy rare earth elements, and they are enriched in large ion lithophile elements and depleted in high field strength elements. Meanwhile, the Zhangda tonalites show the characteristics of metaluminous calc-alkaline I-type granite. They are enriched in light rare earth and large ion lithophile elements and are depleted in heavy rare earth and high field strength elements. The ɛHf(t), ɛNd(t) and the initial 87Sr/86Sr values of the mafic rocks are + 9.3–+14.4, +4.2–+5.9 and 0.702803–0.704264, respectively, while the ɛHf(t), ɛNd(t) and initial 87Sr/86Sr values of the tonalites are + 9.8–+16.3, +5.5–+6.1 and 0.703105–0.704071, respectively. Combined with the regional geological survey results, the Permian Zhangda complex was found to be formed in a tectonic setting of subduction north of the Zhikong–Sumdo Ocean. The Zhangda mafic rocks were formed by partial melting of the depleted mantle modified by subducted metasomatic fluids, while the Zhangda tonalites were the products of partial melting of the juvenile crust. During the Zhikong–Sumdo Ocean subduction, mantle-derived magma underplating led to the growth of juvenile crust in southern Tibet.

Early Eocene A-type (ferroan) rhyolites in southwestern Tibet: A far-field tectonic effect of the India–Eurasia collision

ABSTRACT Eocene igneous rocks along the Gangdese belt in southern Tibetan Plateau are important for understanding the India–Eurasia collision and Tibetan Plateau uplift. These magmatic rocks are widely considered to be related to roll-back or break-off of the Neotethyan slab during northward subduction. However, Eocene rhyolites in the northwestern Gangdese belt (SW Qiangtang margin) do not fit either the rollback or breakoff models. This paper investigates these Early Eocene lavas and compares them with contemporaneous igneous rocks along the Gangdese belt via detailed field observations, petrology, zircon geochronology, zircon Lu–Hf isotopes and whole-rock geochemistry. These felsic lavas form large outcrops in western Tibet and have two zircon U–Pb ages of 54.71 ± 0.14 Ma and 54.74 ± 0.27 Ma. They have high SiO2 and alkali contents, FeO*/MgO, and Ga/Al ratios as well as strongly negative Eu anomalies and slightly positive zircon εHf(t) values (+2.5 to +4.4). Both Ti-in-zircon and Zr saturation thermometers confirm high magmatic temperatures (~900°C). They are ferroan, A-type rhyolites. Furthermore, the distinctive low εHf(t) values imply that these rhyolites are likely partial melting products of the southwestern Qiangtang Terrane. The lithosphere in this region undergone long-term shortening and thickening since 80–95 Ma. Pre-thickened lithosphere may be a prerequisite for the Early Eocene delamination, and the simultaneous inducement is a far-field tectonic effect from the India–Eurasia collision. We suggest that: (1) India collided with Eurasia before 55 Ma and triggered delamination to form the Shiquanhe A-type rhyolites on the southwestern Qiangtang margin thereafter; and (2) tectonic stresses related to India–Eurasia collision during the Eocene were transmitted efficiently over large distances.

Geochronology of scapolite pegmatites from the Nordøyane ultra-high-pressure domain, Western Gneiss Region, Norway: Protracted crystal-melt reaction during Scandian exhumation

Titanite and zircon from a suite of scapolite pegmatites in the Nordøyane ultra-high-pressure domain, Western Gneiss Region, Norway, were analysed by laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS). Titanite yielded U Pb ages ranging from 420 to 390 Ma, with dates from prismatic crystals overlapping at 400–390 Ma. Complex zoning and resorption of older titanite grains (>415 Ma), interpreted as inherited, suggests that protracted crystal-melt reaction led to variable REE enrichment. Zircon rim zones yielded U Pb ages of 392–385 Ma, with inherited cores yielding 207 Pb/ 206 Pb ages of 1774–1575 Ma. In combination, the zircon and titanite U Pb data suggest that the pegmatites crystallised at ca. 400–385 Ma, consistent with the results of earlier studies. Trace element data are compatible with crystallisation at amphibolite facies conditions from melts in which fluid activity may have increased with time. Based on the ages of inherited zircon cores and titanite εNd 400 values of −8 to −11, the melts that gave rise to the scapolite pegmatites are interpreted to have been derived from Proterozoic Baltican crust. Partial melting initiated during subduction of Baltican crust in response to an influx of mantle fluid, with melt production greatly enhanced during exhumation and decompression. Complex zoning and age signatures in both titanite and zircon point to crystal-melt-fluid interaction over a protracted interval of melt production, migration, and crystallisation. • Nordøyane scapolite pegmatites intruded during amphibolite-facies retrogression. • The pegmatites crystallised at 400–385 Ma from melts derived from Baltican crust. • Inherited titanite grains, ca. 420 Ma, survived interaction with melt at T ≥ 750 °C. • Textures and age ranges of dated grains suggest protracted crystal-melt reaction.

Optimized synthesis of mullite ceramics in thermal plasma

Mullite has low thermal expansion coefficient, thermal conductivity and excellentresistance to thermal shock, and plays therefore an important role in the synthesis of modern ceramic materials. The paper presents the experimental results of mullite ceramics synthesis using thermal plasma. The ceramic samples are obtained from natural raw materials such as boehmite and silica sand in the stoichiometric Al2O3/SiO2 ratio of 1.86, 3 and 5.67. It is shown that the optimal operation mode of the arc plasma torch in the synthesis of mullite-containing samples from an 8 g charge weighing includes 80 A current, 100 V voltage, and 60 s exposure time. With such technological parameters, the melting product is a hemisphere with diameter 23 mm and thickness 11 mm, which indicates to a complete transition of the initial components to the molten state. The synthesized ceramic samples are characterized by the crystalline phase of mullite 3Al2O3 ·2SiO2. At the same time, at the Al2O3/SiO2 ratio of 1.86, cryptocrystalline diffraction maxima are observed at 2θ = 53–54° and 69–76° due to the increased content of SiO 2 . According to morphological studies performed for the Al 2O3/SiO2 ratio of 3, which is the traditional stoichiometric ratio for the mullite phase synthesis, the matrix of the synthesized sample is represented by the amorphous phase penetrated by filamentary single crystals of mullite with the average length of 3.3 μm and 0.86 μm thickness. It is found that the transition layer between these phases has a glass-ceramic structure, which is consistent with the results of the X-ray phase analysis.

Raman study of quench products of alkaline carbonate melt at 3 and 6 GPa: Link to the pressure of origin

AbstractInclusions of former alkaline carbonate melts occur in igneous minerals, mantle xenoliths, and diamonds from kimberlites and lamproites. However, the identification of most daughter phases remains undetermined owing to the lack of their Raman spectra. Yet, the phase compositions of the alkali carbonate melt at different pressure are interesting to know because Na‐Ca, Na‐Mg, K‐Ca, and K‐Mg double carbonates have a number of pressure‐induced phase transitions. Here, we studied the quench products of K‐Ca, K‐Mg, and Na‐Ca carbonate melts obtained at 3 and 6 GPa. Scanning electron microscopy coupled with energy‐dispersive spectroscopy with silicon drift detector (EDS‐SDD) and Raman spectroscopy were employed for phase characterization. The following carbonates were detected among the quench products: γ‐Na2CO3, Na4Ca(CO3)3 (Ia3d), Na2Ca3(CO3)3 (P1n1), K2Ca(CO3)2 ( ) bütschliite, disordered K2Ca3(CO3)4 (Pnam), K2Mg(CO3)2 ( ), aragonite, magnesite at 6 GPa; and CaCO3‐bearing K2CO3, K2Ca(CO3)2 ( ) bütschliite, K2Ca2(CO3)3 (R3), and ordered K2Ca3(CO3)4 (P212121) at 3 GPa. The results indicate that the quench products of carbonate melt consist of carbonates thermodynamically stable at the pressure of quenching. Thus, the daughter phases in carbonatitic inclusions could be identified by obtained Raman spectra and reflect the pressure conditions of their entrapment.

Age, Genesis and Tectonic Setting of the Sayashk Tin Deposit in the East Junggar Region: Constraints from Lu–Hf Isotopes, Zircon U–Pb and Molybdenite Re–Os Dating

The Sayashk tin (Sn) deposit is located within the southern part of the Eastern Junggar orogenic belt in Xinjiang Province and forms part of the Kalamaili alkaline granite belt. There are many Sn polymetallic deposits in the area. To constrain the age, genesis, and tectonic setting of the Sayashk tin deposit in the East Junggar region, we conducted a bulk-rock geochemical analysis of the granite porphyry (SR1) and medium- to fine-grained granite (SR2) hosts of the deposit, LA-ICP-MS zircon U–Pb dating and Lu–Hf isotopic analysis, as well as molybdenite Re–OS dating and combined our results with the metallogenic conditions and other geological characteristics of the deposit. The results show that the Sayashk Sn deposit is indeed spatially, temporally, and genetically closely related to the granite porphyry and medium-fine-grained granite. Both zircon U–Pb ages are 308.2 ± 1.5 Ma and 310.9 ± 1.5 Ma, respectively. The isochron age of molybdenite is 301.4 ± 6.7 Ma, which represents the crystallization age of the granite porphyry and medium-fine-grained granite. Therefore, all of them formed in the late Carboniferous epoch. The medium-fine-grained granites and granite porphyry are characteristically rich in Si and alkali, poor in Ca and Mg, rich in high field-strength elements (HFSE, e.g., Zr, Hf) and Ce, and deficient in Ba, Sr, Eu, P, and Ti. They are typical A-type granites, showing the characteristics of a mixed crustal mantle source. The εHf(t) values of the zircon from the granite porphyry (SR1) range from 10.27 to 16.17 (average 13.71), εHf(t) values of the zircon from the medium-fine-grained granites (SR2) are between 5.72 and 9.21 (average 7.08), and the single model ages (TDM1) and two-stage model ages (TDM2) of the granite porphyry (SR1) fall within the ranges of 319~535 Ma and 339~644 Ma. The single model ages (TDM1) and two-stage model ages (TDM2) of the medium-fine-grained granites (SR2) fall within the ranges of 346~479 Ma and 309~557 Ma. There is little difference between their two-stage model ages and zircon U–Pb ages, indicating that the Sayashk granite may be the product of partial melting of juvenile crustal. Combined with previous research results, the Sayashk Sn deposit formed in a post-collision extensional tectonic setting after the late Carboniferous in the Kalamaili area.

A detailed record of early solar system melting in the carbonaceous achondrites Northwest Africa 7680 and 6962

AbstractDetailed textural and geochemical analyses of the carbonaceous achondrites Northwest Africa (NWA) 7680 and NWA 6962 support a rapid progression of thermal events, by similar processes, on the same parent body. The achondrites have olivine compositions of Fa44.8 and Fa47.4 for NWA 7680 and NWA 6962, respectively. Replicate oxygen isotope analyses of grains and bulk powders from NWA 7680 yielded average Δ17O values of −1.04 ± 0.03‰ and −1.00 ± 0.05‰, respectively, which is identical to that reported for NWA 6962. The whole rock ɛ54Cr compositions are also equivalent for NWA 7680 and NWA 6962 (1.36 ± 0.05 and 1.30 ± 0.05, respectively). Both meteorites are plagioclase‐rich, and NWA 7680 is also Fe‐metal‐rich, suggesting they both formed via differentiation processes that resulted in the pooling of partial melt products. Major element geochemical trends show that both rocks could be formed through the melting of chondritic material on a CR chondrite‐like parent body. This is consistent with oxygen isotope and chromium isotope compositions. Intrusion of a late‐stage melt is evident in both meteorites and the crystallization products include silica‐rich, alkali‐deficient nepheline. The late‐stage liquid has partially melted and mixed with primary plagioclase in NWA 6962. In contrast, the late‐stage liquid was often restricted to grain boundaries in NWA 7680, leaving some of the primary plagioclase crystals intact. In situ dating of NWA 7680 phosphate minerals (merrillite and fluorapatite) reveals that it has not experienced long duration thermal metamorphism, or impact‐related Pb loss and age resetting since 4578 ± 17 Ma (207Pb/206Pb age ± 2σ, within error of solar system age). Phosphates associated with the late‐stage melt in NWA 6962 yield a 207Pb/206Pb age of 4556.6 ± 8.0 Ma (2σ) within 2σ of the NWA 7680 age. These early dates indicate that the observed chromium isotope signatures in these meteorites were not introduced by a later high‐temperature event, such as late impact accretion processes. These data are consistent with a rapid separation of inner and outer solar system chemical reservoirs, planetesimal melting, differentiation, and cooling, all within several million years of calcium‐aluminum‐rich inclusion formation.