Journal of Petrology最新文献

{"title":"Arc foundations and subduction initiation: Insights into the magmatic evolution of the lower crust/upper mantle of the Izu-Bonin forearc during subduction initiation","authors":"Matthew P Loocke, Jonathan E Snow","doi":"10.1093/petrology/egae038","DOIUrl":"https://doi.org/10.1093/petrology/egae038","url":null,"abstract":"Our understanding of the processes at work in the lower crust/upper mantle transition zone during subduction initiation and early arc development has suffered from a general lack of in situ samples. Here, we present the results of petrographic and geochemical analysis of 34 samples (9 harzburgites, 13 dunites, 2 orthopyroxenites, 3 olivine-gabbros, and 7 wehrlites) collected from the inner trench wall of the Bonin Ridge, Izu-Bonin forearc. The sample suite records three main melt-rock reaction events involving melts with forearc basalt (FAB)-like, boninitic, and transitional compositions. The wehrlitic and gabbroic rocks trend towards more transitional to FAB compositions and the rest towards more boninitic compositions. The crosscutting occurrence of all three events in a single sample (wehrlite D31-106) establishes a relative timing of the events like that reported for the volcanic edifice of the Bonin Ridge, which transitioned from forearc basalt volcanism at subduction initiation (c.a., 51-52 Ma) to boninitic volcanism (c.a., 50-51 Ma) as the subduction system matured. We therefore suggest that the lower crust/upper mantle transition of the Bonin Ridge preserves a record of the transition from FAB melts created by decompression melting at subduction initiation to arc-type flux melting and boninitic volcanism thereafter. Orthopyroxenites and two anomalously fresh harzburgites from the sample suite are suggested to represent the later boninitic melts and possibly the result of hybridization between such melts and residual peridotites, respectively. Diffuse melt-rock reaction between the later boninites and/or subduction-related fluids and the earlier-formed FAB-related crust is recorded by enrichments in fluid mobile elements and depletions in first row transition metals in clinopyroxenes from a metasomatic vein in wehrlite sample D31-106. The chemistry of the wehrlitic and gabbroic clinopyroxenes suggests that they crystallized from hydrous, highly-depleted melts which lack a slab fluid signature. We thus suggest that highly-depleted melt fractions might be created early on during subduction initiation by the introduction of seawater into the proto-mantle wedge. The overall FAB-like nature of the crustal wehrlites and gabbros would suggest that most of the lower arc crust was created by forearc extension during/following subduction initiation and that later, mature arc volcanism may have contributed little or no material to the lower crust/upper mantle record in the outer forearc.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":"53 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140585430","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Machine Learning in Petrology: State-of-the-Art and Future Perspectives","authors":"Maurizio Petrelli","doi":"10.1093/petrology/egae036","DOIUrl":"https://doi.org/10.1093/petrology/egae036","url":null,"abstract":"The present manuscript reports on the state-of-the-art and future perspectives of Machine Learning (ML) in petrology. To achieve this goal, it first introduces the basics of ML, including definitions, core concepts, and applications. Then, it starts reviewing the state-of-the-art of ML in petrology. Established applications mainly concern the so-called data-driven discovery and involve specific tasks like clustering, dimensionality reduction, classification, and regression. Among them, clustering and dimensionality reduction have been demonstrated to be valuable for decoding the chemical record stored in igneous and metamorphic phases and to enhance data visualization, respectively. Classification and regression tasks find applications, for example, in petrotectonic discrimination and geo-thermobarometry, respectively. The main core of the manuscript consists of depicting emerging trends and the future directions of ML in petrological investigations. I propose a future scenario where ML methods will progressively integrate and support established petrological methods in automating time-consuming and repetitive tasks, improving current models, and boosting discovery. In this framework, promising applications include (a) the acquisition of new multimodal petrologic data, (b) the development of data fusion techniques, physics-informed ML models, and ML-supported numerical simulations, and (c) the continuous exploration of the ML potential in petrology. To boost the contribution of ML in petrology, our main challenges are: (a) to improve the ability of ML models to capture the complexity of petrologic processes, (b) progressively link machine learning algorithms with the physical and thermodynamic nature of the investigated problems, (c) to start a collaborative effort among researchers coming from different disciplines, both in research and teaching.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":"117 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140322199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fluoritites produced by crystallization of carbonate-fluoride magma","authors":"Aleksandr S Stepanov, Jovid Aminov, Sharifjon Odinaev, Farukh Sh Iskandarov, Shao-Yong Jiang, Nikolai S Karmanov","doi":"10.1093/petrology/egae033","DOIUrl":"https://doi.org/10.1093/petrology/egae033","url":null,"abstract":"Fluorite-dominated rocks are occasionally found in association with carbonatites, but their geologic and petrologic relations are rarely reported. The Dunkeldyk area of the Pamir mountains in south-eastern Tajikistan contains dikes of distinctive rocks composed of calcite, fluorite, celestine-barite, sulfides, apatite, with minor quartz, biotite, and REE-fluorcarbonates. The dikes have sharp contacts with the host (meta-)sedimentary rocks and layering with ribbons, ranging from fluorite-bearing calcite carbonatites to fluoritites (rocks with >50% fluorite). The fluoritites are characterised by high Ca, F, Ba, Sr, REE and S coupled with anomalously low O. The geologic relations and textures suggest a magmatic origin of the dikes from melts close to calcite-fluorite eutectic that experienced nucleation-controlled differentiation during the crystallization of dikes and the formation of fluoritite cumulates in larger intrusions. The Dunkeldyk dikes demonstrate that sizable geological bodies of fluorite-dominated rocks could form from carbonate-fluoride melts originating by differentiation of alkaline silicate magmas.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":"87 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140325884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sub-arc mantle heterogeneity of the Northern Luzon Volcanic Arc: mineral and whole rock compositional variability in mantle xenoliths from Lutao Island","authors":"J Gregory Shellnutt, Meng-Wan Yeh, Tung-Yi Lee, Yoshiyuki Iizuka, Wei-Yu Chen, M P Manu Prasanth","doi":"10.1093/petrology/egae037","DOIUrl":"https://doi.org/10.1093/petrology/egae037","url":null,"abstract":"Mantle xenoliths hosted in volcanic rocks from the island of Lutao offer a glimpse into the nature of the mantle beneath the northern Luzon volcanic arc. The xenoliths are spinel-bearing and composed mostly of harzburgite with one lherzolite and one olivine orthopyroxenite. The olivine (Fo92.5-88.9), orthopyroxene (Mg# = 94.6-89.2), and clinopyroxene (Wo49.1-38.1En57.0-45.4Fs3.0-11.0) compositions are similar to those of abyssal peridotites. The spinel compositions are variable and can be principally divided into high-Al (Cr# < 45) and low-Al (Cr# > 45) groupings. The whole rock compositions are similar to abyssal peridotite (Al2O3 = 0.95-2.07 wt%; Mg# = 88.5-90.9) and have U-shaped chondrite normalized rare earth element patterns. The Sr-Nd isotopes of the xenoliths are broadly chondritic (87Sr/86Sri = 0.704400-0.707908; εNd(t) = 0.0-+1.5). The two-pyroxene equilibrium temperatures range from 900-1200°C with the majority of temperature estimates >1000°C. The olivine-orthopyroxene-spinel oxygen barometry estimates yielded ΔFMQ values from 0 to +2 and correspond to moderately oxidizing to oxidizing conditions. The xenoliths are likely derived from the Philippine Sea Plate lithospheric mantle that was modified by melt extraction and/or fluid enrichment processes. Trace element and isotopic mixing modeling indicate that 1% to 2% contamination by subducted South China Sea sediment can explain the Sr-Nd isotopic enrichment and Th and U elemental variability within the xenoliths assuming an initial composition similar to enriched depleted mid-ocean ridge mantle (E-DMM). The anomalously high two-pyroxene equilibrium temperatures of the Lutao xenoliths relative to other regions of the northern Luzon volcanic arc (Iraya < 1000°C) indicate that they were affected by a high temperature event that was likely a consequence of recent intra-arc rifting that occurred after collision (< 6 Ma) between the Luzon arc and the Eurasian margin.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":"108 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140322287","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Self-organisation in gabbroic cumulates: a new patterning mechanism driven by differential migration of immiscible liquids in a crystal mush?","authors":"Marian B Holness","doi":"10.1093/petrology/egae034","DOIUrl":"https://doi.org/10.1093/petrology/egae034","url":null,"abstract":"Self-organisation in plutonic igneous rocks has been suggested to form by a variety of mechanisms including oscillatory nucleation and growth, competitive particle growth (CPG), and preferential dissolution and re-precipitation during fluid infiltration enhanced by compaction, with driving forces including reduction of the interfacial energy budget by either Ostwald ripening or because the energy of boundaries between two grains of the same mineral is less than that between two grains of different minerals. An investigation of the Stillwater inch-scale layering shows that the CPG patterning mechanism leaves a characteristic microstructural signature preserving evidence for a highly interconnected melt in textural equilibrium, and slow super- and sub-solidus cooling: such a signature is also preserved in chromite-bearing fine-scale layers in the Bushveld intrusion. The cm-scale micro-rhythmic layering of the Skaergaard intrusion, superimposed on single modally-graded layers, does not have these microstructural features. Furthermore, the energy of all relevant inter-phase grain boundaries in the Skaergaard gabbros is less than that of grain boundaries involving only one mineral, viscous compaction was not a significant process in the Skaergaard intrusion, and patterning by oscillatory nucleation and growth is precluded by the fact that the micro-rhythmic layering is superimposed on modally graded layers formed by sedimentation. A new patterning mechanism is proposed, operational only in intrusions in which the interstitial liquid of the crystal mush intersects a binode and splits into two immiscible conjugates. Cm-scale separation of the immiscible conjugate liquids in a compositionally-graded mush, due to both gravity and capillary forces, leads to layering due to differences in their wetting properties. The positive feedback required for pattern formation is due to the two immiscible conjugates predominantly crystallising the minerals which they preferentially wet.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":"45 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140322193","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Clinopyroxenite xenoliths record magma transport and crystallisation in the middle and upper crust: A case study from the Rockeskyllerkopf Volcanic Complex, West Eifel, Germany","authors":"Cliff S J Shaw","doi":"10.1093/petrology/egae035","DOIUrl":"https://doi.org/10.1093/petrology/egae035","url":null,"abstract":"Clinopyroxenite xenoliths comprised of cumulus clinopyroxene ± amphibole together with intercumulus phlogopite ± olivine ± apatite ± titanite form a large part of the xenolith load in the oldest deposits of the Rockeskyllerkopf Volcanic Complex (RVC) in the West Eifel volcanic field. The xenoliths also contain xenocrysts of olivine and clinopyroxene derived from mantle peridotite and clinopyroxene from lower crustal granulite. The clinopyroxenite xenoliths are divided into five groups on the basis of their modal mineralogy and mineral compositions. Groups 1 to 4 define a continuous compositional trend indicative of fractionation of a mafic alkaline magma. Group 5 xenoliths are compositionally distinct and have been tentatively linked to high pressure crystallization of phonolitic magma within the RVC system. Thermobarometry of the group 1 – 4 xenoliths indicates that they crystallised between 1 and 4 kilobars, equivalent to a depth of 4-14 km. Group 1 -3 xenoliths all crystallised at between 1050 and 1150 °C whereas the amphibole-rich group 4 xenoliths give temperature estimates of ~ 900 °C. The clinopyroxenites share a common parent magma with clinopyroxene – phlogopite veins found in subcontinental lithospheric mantle xenoliths. However, the vein forming mama was richer in incompatible elements, in particular Zr and Hf and is interpreted to be an early formed batch of magma with the clinopyroxenites crystallising from magma derived from the same mantle, which had been depleted by the earlier phase of melting. Intrusion of magma began around 155 ky prior to the eruption of the RVC. Fe-Mg interdiffusion profiles in zoned clinopyroxene show that the magma that formed the xenoliths was present in the crust for up to 28 ky prior to the eruption. However, most samples give interdiffusion times between 1.5 and 9.9 ky. Based on xenocryst residence times and the calculated P-T conditions for clinopyroxene, there were at least seven separate batches of magma emplaced below Rockeskyllerkopf, probably as sills.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":"31 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140322291","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Genesis of Fe-Ti oxide-bearing ultramafic intrusions in the Duluth Complex, Minnesota, USA","authors":"Jackie M Kleinsasser, Adam C Simon, Dean Peterson, Amartya Kattemalavadi, Ian R Goan, Tobias Keller, George J Hudak, Kaitlin Koshurba","doi":"10.1093/petrology/egae031","DOIUrl":"https://doi.org/10.1093/petrology/egae031","url":null,"abstract":"The Duluth Complex is a large mafic intrusive system located in northeastern Minnesota emplaced as part of the 1.1 Ga Midcontinent Rift. Several Fe-Ti oxide-bearing ultramafic intrusions are hosted along the Western Margin of the Duluth Complex, and are discordant bodies present in a variety of geometries, hosted in multiple rock types, and dominated by peridotite, pyroxenite, and semi-massive to massive Fe-Ti oxide rock types. Their origin has been debated, and here we present geochemical evidence and modeling that supports a purely magmatic origin for the Titac and Longnose Fe-Ti oxide-bearing ultramafic intrusions. Ilmenite and titanomagnetite textures indicate a protracted cooling process, and δ34S values of sulfides reveal little assimilation of the footwall Virginia Formation, a fine-grained pelitic unit that contains sulfide-rich bands. We model the crystallization of a hypothetical parental magma composition to the host intrusion of Longnose using Rhyolite-MELTS and demonstrate that the accumulation of Fe-Ti oxides in the discordant intrusions cannot be explained by density-driven segregation of crystallized Fe-Ti oxides. Instead, we show that the development of silicate liquid immiscibility, occurring by the unmixing of the silicate melt into conjugate Si- and Fe-rich melts, can result in the effective segregation and transportation of the Fe-rich melt. The Fe-rich melt is ~2 orders of magnitude less viscous than the Si-rich melt, allowing the Fe-rich melt to be more effectively segregated and transported in the mush regime (crystallinities > 50%). This suggests that viscosity, in addition to density, plays a significant role in forming the discordant Fe-Ti oxide-bearing ultramafic intrusions. We propose a genetic model that could also be responsible for the Fe-Ti oxide-rich layers or bands that are hosted within the igneous stratigraphy of mafic intrusions of the Duluth Complex.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":"1 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140297599","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tectonic and crustal processes drive multi-million year arc magma evolution leading up to porphyry copper deposit formation in central Chile","authors":"Simon J E Large, Chetan L Nathwani, Jamie J Wilkinson, Thomas R Knott, Simon R Tapster, Yannick Buret","doi":"10.1093/petrology/egae023","DOIUrl":"https://doi.org/10.1093/petrology/egae023","url":null,"abstract":"Subduction zone magmatism is a major control of volcanism, the generation of modern continental crust and the formation of economically important porphyry Cu-(Mo-Au) deposits. Reading the magmatic record of individual arc segments, and constraining the rates of magmatic changes, are critical in order to fully understand and quantify the processes that drive magma evolution in subduction settings during arc growth. This study focuses on the San Francisco Batholith and the Rio Blanco-Los Bronces porphyry deposit cluster in central Chile, which provides an igneous rock record over ~13.5 Myr of arc evolution. We use whole-rock geochemistry, zircon geochronology and Hf-isotope geochemistry to track changes in the crustal magmatic system of this arc segment during crustal thickening and porphyry Cu deposit formation. By combining the analytical dataset with Monte Carlo fractional crystallisation and assimilation fractional crystallisation modelling, we test a model for significant crustal involvement during magma evolution. Systematic and continuous increases in Dy/Yb, La/Yb, V/Sc and Sr/Y in the magmas over time indicate a transition in the main fractionation assemblage from plagioclase-dominated to amphibole-dominated that reflects deeper crystallisation and/or a higher melt water content. Concomitant decreases in εHf and Th/La as well as increasing Ba/Th are best explained by assimilation of progressively deeper crustal lithologies from low (Chilenia) to high Ba/Th (Cuyania) basement terranes. Our study highlights that an increasingly hydrous magma and a deepening locus of crustal magma differentiation and assimilation, driven by crustal thickening contemporaneous with increased tectonic convergence and ingression of the aseismic Juan Fernandez ridge, can account for all investigated aspects of the multi-Myr magmatic evolution leading up to the formation of the Rio Blanco-Los Bronces porphyry Cu deposits. Our findings corroborate the importance of high-pressure differentiation of hydrous magma for the formation of Andean-style porphyry deposits. Once magmas favourable for porphyry Cu mineralisation were generated in the lower crust, multiple episodes of efficient magma migration into the upper crust fed several, discrete, shallow magmatic-hydrothermal systems over ~3.5 Myr to form the world’s largest known Cu resource at Rio Blanco-Los Bronces.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":"10 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140115808","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Role of Crustal Contamination Throughout the 1329–2005 CE Eruptive Record of Mt. Etna Volcano, Italy","authors":"Marie K Takach, Wendy A Bohrson, Frank J Spera, Marco Viccaro","doi":"10.1093/petrology/egae028","DOIUrl":"https://doi.org/10.1093/petrology/egae028","url":null,"abstract":"The nearly continuous volcanic eruption record at Mt. Etna dating back ~700 years provides an excellent opportunity to investigate the geochemical evolution of a highly active volcano. Of particular interest is elucidating the cause of selective enrichment in alkali elements (K and Rb) and 87Sr/86Sr observed in various episodes of past activity. More recently, this alkali enrichment trend started to manifest in the 17th century and accelerated after 1971, and was accompanied by an increase in the volume, frequency, and explosivity of eruptions. Explanations for this signature include recharge of alkali-enriched magmas and/or crustal contamination from the subvolcanic basement. This study quantitatively examines the role of crustal contamination in post-1971 Etnean magma compositions via hundreds of open-system phase equilibria and trace element calculations based upon whole-rock major oxides, trace elements, 87Sr/86Sr ratios, and mineral compositional data. Available pre-1971 petrochemical data are satisfactorily reproduced by fractional crystallization of a high whole-rock MgO (12–17 wt.%), Ni (135–285 ppm), and Cr (920–1330 ppm) parental magma composition that is documented in Etna’s ~4-ka fall-stratified deposit. Observed post-1971 whole-rock and glass trends and phase equilibria are reproduced via modeled assimilation of a skarn and flysch mixture, lithologies that represent the uppermost 10–15 km of sedimentary rocks beneath Etna. Notably, models show that K2O (wt.%) and Rb (ppm) behave incompatibly during partial melting of skarn/flysch. Additionally, the observed elevation of 87Sr/86Sr in post-1971 samples is consistent with the addition of radiogenic Sr from wallrock partial melts. In best-fit models, which yield observed post-1971 K2O, Rb, and 87Sr/86Sr trends, ~17% anatectic melt is assimilated and there may be a subordinate stoped wallrock component of ≤2% (percentage is relative to the starting mass of pristine magma). Previous work has shown that metasomatized spinel lherzolite and garnet pyroxenite can be melted in different proportions to reproduce long- and short-term changes observed in Etna’s geochemical products. We propose that the alkali enrichment signature observed after 1971 can be fully explained through the combination of mantle heterogeneity and crustal contamination. In particular, up to ~20% crustal input coupled with mantle heterogeneity of primitive melts explains the geochemical signals quite well. The influence of crustal contamination on post-1971 lavas is, in part, the result of frequent recharge of magmas that thermally primed the middle to upper crust and enhanced its partial melting.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":"63 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140074593","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A machine learning-based thermobarometer for magmatic liquids","authors":"Gregor Weber, Jon Blundy","doi":"10.1093/petrology/egae020","DOIUrl":"https://doi.org/10.1093/petrology/egae020","url":null,"abstract":"Experimentally calibrated models to recover pressures and temperatures of magmas, are widely used in igneous petrology. However, large errors, especially in barometry, limit the capacity of these models to resolve the architecture of crustal igneous systems. Here we apply machine learning to a large experimental database to calibrate new regression models that recover P-T of magmas based on melt composition plus associated phase assemblage. The method is applicable to compositions from basalt to rhyolite, pressures from 0.2 to 15 kbar, and temperatures of 675-1400°C. Testing and optimisation of the model with a filter that removes estimates with standard deviation above the 50th percentile show that pressures can be recovered with root-mean-square-error (RMSE) of 1.1-1.3 kbar and errors on temperature estimates of 21°C. Our findings demonstrate that, given constraints on the coexisting mineral assemblage melt chemistry, is a reliable recorder of magmatic variables. This is a consequence of the relatively low thermodynamic variance of natural magma compositions despite their relatively large number of constituent oxide components. We apply our model to two contrasting cases with well-constrained geophysical information: Mount St. Helens volcano (USA), and Askja caldera in Iceland. Dacite whole-rocks from Mount St Helens erupted 1980-1986, inferred to represent liquids extracted from cpx-hbl-opx-plag-mt-ilm mush, yield melt extraction source pressures of 5.1-6.7 kbar in excellent agreement with geophysical constraints. Melt inclusions and matrix glasses record lower pressures (0.7-3.8 kbar), consistent with magma crystallisation within the upper reaches of the imaged geophysical anomaly and during ascent. Magma reservoir depth estimates for historical eruptions from Askja match the location of seismic wave speed anomalies. Vp/Vs anomalies at 5-10 km depth correspond to hot (~990°C) rhyolite source regions, while basaltic magmas (~1120°C) were stored at 7-17 km depth under the caldera. These examples illustrate how our model can link petrology and geophysics to better constrain the architecture of volcanic feeding systems. Our model (MagMaTaB) is accessible through a user-friendly web application (https://igdrasil.shinyapps.io/MagmaTaBv4/).","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":"37 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140018042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}