Journal of Petrology最新文献

{"title":"Links between calcite kimberlite, aillikite and carbonatite in West Greenland: Numeric modeling of compositional relationships","authors":"L. Pilbeam, T. F. D. Nielsen, T. Waight, S. Tappe","doi":"10.1093/petrology/egae059","DOIUrl":"https://doi.org/10.1093/petrology/egae059","url":null,"abstract":"\u0000 Textural, mineralogical and mineral compositional observations in a suite of Neoproterozoic aillikite and calcite kimberlite dykes from southern West Greenland point to consistent variations in melt major element compositions amongst these silica-undersaturated magma types. The aillikites have notably higher bulk SiO2/CO2, H2O/CO2 and K2O compared to calcite kimberlite. Bulk rock arrays, together with field and petrographic observations, emphasize that flow sorting of olivine and other crystalline phases during magma emplacement is important in controlling the compositions of individual samples from these ultramafic dykes. Flow sorting together with variable overall proportions of entrained lithospheric mantle material result in scatter on element–element plots, which makes the interpretation of regional scale major and trace element geochemical datasets difficult. We argue that a significant proportion of the regional Ni—MgO variation in the ultramafic dyke suite of SW Greenland is due to variation in the proportion of an entrained refractory lithospheric mantle component. Therefore, ratios of elements to MgO can be used as proxies for melt compositions. Ratios of SiO2, TiO2, Al2O3, FeO and K2O over MgO are systematically higher, and CO2/MgO lower, in aillikites compared to calcite kimberlites. The trace element patterns of the calcite kimberlite and aillikite dykes show strong similarities in incompatible element concentrations, resulting in overlapping ratios for the highly to moderately incompatible elements. However, differences in Zr-Hf concentrations between rock types imply differences in mantle source mineralogy. Guided by our observations, we present mixing models that demonstrate that partial flux-melting of phlogopite–ilmenite metasomes within the cratonic mantle lithosphere is capable to produce the geochemical characteristics of aillikites and mela-aillikites in West Greenland. Fusion of cratonic metasomes was initiated by infiltrating asthenosphere-derived carbonatitic melts previously identified as the parental liquids to calcite kimberlite.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141381627","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":"Critical differences between typical arc magmas and giant porphyry Cu ± Au systems: Implications for exploration","authors":"Hongda Hao, Ian H Campbell, Jung-Woo Park","doi":"10.1093/petrology/egae058","DOIUrl":"https://doi.org/10.1093/petrology/egae058","url":null,"abstract":"\u0000 Porphyry Cu, and porphyry Cu-Au deposits, are associated with arc magmatism and their ore-forming systems generally follow the magmatic evolution of typical arcs. However, most arc magmas are barren and giant economic porphyry Cu ± Au deposits are rare. In this study, we model variations in rare earth element concentrations in the evolving arc magmas and giant porphyry Cu ± Au systems to quantify the percentage of the fractionating minerals required to produce the observed changes. We find that, during the andesitic stage of fractionation, ore-forming systems in thick crusts fractionate ~35% more amphibole than an average of thick arc magma systems (the thick-crust reference suite) and that ore-forming systems in thin crusts fractionate twice as much amphibole as their equivalent thin-arc magma reference suite. Thick-crust ore-forming suites also fractionate ~50% less plagioclase, and thin-crust ore systems ~40% less plagioclase, than their associated reference suites during the same andesitic stage of fractionation. Taken together, these observations imply that ore-producing magmas are appreciably wetter than their associated barren reference suites. Our modelling also shows that 80% more amphibole is required to reproduce the andesite stage of fractionation in the thick-crust reference suite than in its thin-crust equivalent, suggesting that magmas produced under thick crusts are wetter than those produced under thin crusts. On the other hand, the chalcophile element contents of the thick- and thin-crust ore-forming systems are similar to and higher than those of the thick- and thin-crust reference suites, respectively. Therefore, we suggest that the high water content plays a critical role in the formation of giant porphyry Cu ore in thick crusts, whereas both high chalcophile contents and high water contents are required to form giant porphyry Cu-Au deposits in thin crusts.\u0000 The high fraction of amphibole fractionation in giant economic porphyry suites, compared with their relevant reference suites, results in lower Y in the ore-associated suites and this difference increases with fractionation. As a consequence, plots of Y against MgO can be used to identify porphyries that have economic potential and are preferred to Sr/Y plots because they are less affected by the intense alteration associated with giant porphyry Cu ± Au deposits.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141272956","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":"Reinterpretation of the post 26ka Taupō rhyolitic magmatic system (New Zealand) as deep and vertically extensive based on Isotope thermometry and measured and modeled zircon destinies","authors":"I N Bindeman","doi":"10.1093/petrology/egae055","DOIUrl":"https://doi.org/10.1093/petrology/egae055","url":null,"abstract":"Taupō volcanic zone, the site of the 26ka Oruanui supereruption, produced ~70km3 of new rhyolites since 11ka, culminating in 50 km3 Taupō eruption 1.8 ka. Major phenocrysts decrease from 4 to 1 vol%, and Oruanui and post-Oruanui ignimbrites all have identical high-d18Omelt values of 7.39±0.1‰ and lack low-d18O values despite overlapping calderas. The D’17O values are -0.07‰, lower than the mantle and indicate source contamination of high-d18O, low-D’17O metasediments, and limited interaction with high-D’17O hydrothermally altered crust. Previously published U-Th-Pb zircon ages demonstrate their diversity spanning 104-105 years for each unit. Zircon crystal size distribution shows a decrease in abundance and the mean size, and some units lack small (<~10 um) zircons suggesting that zircons were both growing and dissolving in the coexisting magma generation areas. Isotope thermometry indicates heating of the system from ~812±35°C to 874±36°C past zircon saturation in 1.8ka eruption. We advocate that a deep vertically continuous and laterally discontinuous silicic magma system at the base of the Taupō rift, rather than a shallow batholith or an evolving mush, drives volcanism at Taupō. To explain the post-Oruanui magma production, rift-base silicic magma origin and moderate (~2 km3/1000years) rhyodacitic magma flux from a growing and heating liquid magma body there creates a sufficient solution for the most recent magmatism.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141197195","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":"Ferric iron in eclogitic garnet and clinopyroxene from the V. Grib kimberlite pipe (NW Russia): evidence of a highly oxidized subducted slab","authors":"Marras Giulia, Mikhailenko Denis, A McCammon Catherine, Agasheva Elena, Stagno Vincenzo","doi":"10.1093/petrology/egae054","DOIUrl":"https://doi.org/10.1093/petrology/egae054","url":null,"abstract":"\u0000 Estimates of oxygen fugacity of eclogitic rocks are linked to the redox evolution of the oceanic protolith during subduction and its residence in the lithospheric mantle, and, based on knowledge of pressures and temperatures, allow modelling of the speciation of volatile elements and diamond (or graphite) versus carbonate stability. To date, the oxygen fugacity of mantle eclogites has been shown to vary between -6 (Kasai, Congo and Udachnaya, Siberia) and -0.1 (Udachnaya, Siberia) log units (relative to the fayalite-magnetite-quartz buffer, FMQ), linked to the low Fe3+ contents of garnets. In this study we investigated the Fe oxidation state of coexisting garnet and clinopyroxene hand-picked out of 17 diamond-free high-MgO and low-MgO mantle eclogites (dated at 2.84 Ga) from the V. Grib kimberlite pipe (East-European platform). Measured Fe3+/∑Fe values range between 0.03 and 0.19 for garnet and 0.18 to 0.38 for clinopyroxene, the former being higher than what was measured previously in garnets equilibrated at mantle conditions. The Fe3+/∑Fe of the reconstructed bulk rock ranges between 0.10 and 0.15 for high-MgO eclogites and 0.10 and 0.24 for low-MgO eclogites (with uncertainties of ± 0.02 and ± 0.03 in both cases). Thermobarometric calculations result in equilibration pressures and temperatures of 3.0 - 5.2 (± 0.4) GPa and 720 - 1050 (± 60) °C for both high-MgO and low-MgO eclogites, slightly lower than previous P-T estimates of mantle eclogites from the Udachnaya kimberlite pipe (Siberian craton). At these conditions, ∆logfo2 (FMQ) calculated using the available oxythermobarometric model varies from -1.7 to -0.6 log units for high-MgO eclogites and from -2.9 to 0.9 log units for low-MgO eclogites. Samples recording ∆logfo2 (FMQ) ≤ -1 log units overlap with North Slave, West Africa and Udachnaya eclogites, with no difference among eclogite types. The average values of -1.2 (± 0.4) log units for high-MgO and -0.6 (± 1.1) log units for low-MgO eclogites suggest different redox conditions of basaltic protoliths during subduction worldwide. Previous geochemical studies on the same rock samples reported evidence of cryptic metasomatism in both garnet and clinopyroxene that we demonstrate being not recorded by their major elements, while modal metasomatism evidenced by the presence of phlogopite as a product of interaction with a kimberlitic melt only affects the MgO of the bulk rock. Therefore, we suggest that high Fe3+/∑Fe ratios for garnet (> 0.10) and for reconstructed bulk rocks in the case of both low-MgO and high-MgO samples cannot be due to metasomatic interaction with an oxidized fluid, but rather are the consequence of Fe3+ redistribution in an unusually oxidized mafic protolith upon metamorphism. Our results highlight the redox variability of eclogites of Archaean age at conditions more oxidized than present-day MORBs and imply an oxidizing nature of the convective mantle source where magma was formed with consequent speciation of C in t","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141101176","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 trans-crustal evolution of Miocene magmatism parental to epithermal mineralization in the Sierra Madre del Sur, southern Mexico","authors":"Néstor Cano, B. Martiny, A. Camprubí, E. González-Partida, Peter Schaaf, C. Ortega-Obregón, G. Solís-Pichardo","doi":"10.1093/petrology/egae053","DOIUrl":"https://doi.org/10.1093/petrology/egae053","url":null,"abstract":"\u0000 Arc-related volcanism results from the interplay of magmatic processes occurring in trans-crustal systems that consolidate over time in a given location. Trans-crustal systems comprise extensive networks of magma reservoirs and conduits at different depths, wherein melts cyclically differentiate and segregate before reaching the surface. The study of these systems provides valuable insights into crustal-scale phenomena, such as the evolution of the continental crust and the formation of metallogenic regions. In this study, we address the trans-crustal magmatic evolution of lower Miocene magmatism parental to several intermediate-sulfidation epithermal deposits in the eastern Sierra Madre del Sur igneous province, southern Mexico. Using a multi-methodological approach, we document changes over ca. 1.1 M.yr. in the magmatic system that fed andesitic-to-felsic volcanism in this region. We employ whole-rock REE ratios and λ parameters—which are used to quantify the shape of a REE pattern—to track the involvement of pressure-sensitive minerals in the deep-crustal magmatic evolution. The andesitic rocks consist of lava flows, porphyries, and dikes that collectively show REE patterns suggestive of control by fractionated or residual (i.e., in crustal melting) amphibole and/or clinopyroxene. In contrast, the felsic rocks consist of rhyolitic–dacitic ignimbrites, domes, and dikes that show contrasting REE patterns suggestive of control by plagioclase, clinopyroxene, amphibole, and/or garnet. The distinct pressure-sensitive mineral assemblages in the andesitic and felsic rocks indicate that the locus of deep-crustal magma evolution varied within the middle–lower crust. These magmas were episodically injected into ephemeral shallow crustal reservoirs (shortly?) before being erupted, inducing a progressive thermomechanical maturation of the middle–upper crust. Meanwhile, low degrees of crustal assimilation occurred as recorded by Mesozoic inherited zircon ages and Sr–Nd–Pb radiogenic isotopes. An extensive middle–lower crustal magma evolution has been linked to the formation of porphyry Cu deposits (i.e., ‘fertile’ magmatism). Given that intermediate-sulfidation epithermal deposits may be genetically linked with porphyry Cu deposits, the documented processes could have contributed to the formation of epithermal deposits in the region. However, magmatic fertility proxies resemble those from infertile magmas worldwide. Since these proxies have been exclusively applied to porphyry-type deposits, our results highlight the importance of developing new geochemical exploration tools applicable to a wider range of ore deposits.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141119726","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":"Accretion of the lower oceanic crust at fast-spreading ridges: Insights from Hess Deep (East Pacific Rise, IODP Expedition 345)","authors":"Valentin Basch, Alessio Sanfilippo, Jonathan E Snow, Matthew Loocke, Alberto Zanetti","doi":"10.1093/petrology/egae048","DOIUrl":"https://doi.org/10.1093/petrology/egae048","url":null,"abstract":"At mid-ocean ridges, melts that formed during adiabatic melting of a heterogeneous mantle migrate upwards and ultimately crystallize the oceanic crust. The lower crustal gabbros represent the first crystallization products of these melts and the processes involved in the accretion of the lowermost crust drive the chemical evolution of the magmas forming two thirds of Earth’s surface. At fast-spreading ridges, elevated melt supply leads to the formation of a ⁓6 km-thick layered oceanic crust. Here, we provide a detailed petrochemical characterization of the lower portion of the fast-spread oceanic crust drilled during IODP Expedition 345 at the East Pacific Rise (IODP Holes U1415), together with the processes involved in crustal accretion. The recovered gabbroic rocks are primitive in composition and range from troctolites to olivine gabbros, olivine gabbronorites and gabbros. Although textural evidence of dissolution-precipitation processes is widespread within this gabbroic section, only the most interstitial phases record chemical compositions driven by melt-mush interaction processes during closure of the magmatic system. Comparing mineral compositions from this lower crustal section with its slow-spreading counterparts, we propose that the impact of reactive processes on the chemical evolution of the parental melts is dampened in the lower gabbros from magmatically productive spreading centres. Oceanic accretion thereby seems driven by fractional crystallization in the lower gabbroic layers, followed by upward reactive percolation of melts towards shallower sections. Using the composition of clinopyroxene from these primitive, nearly unmodified gabbros, we estimate the parental melt trace element compositions of Hess Deep, showing that the primary melts of the East Pacific Rise are more depleted in incompatible trace elements compared to those formed at slower spreading rates, as a result of higher melting degrees of the underlying mantle.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931849","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":"Fluid-melt-rock interaction during the transition from magmatism to HT-UHT-granulite- and amphibolite-facies metamorphism in the Ediacaran Adrar-Suttuf Metamafic Complex, NW Margin of the West African Craton (Southern Morocco)","authors":"José Francisco Molina, Fernando Bea, Pilar Montero, Faouziya Haissen, Leticia Barcos, Aitor Cambeses, Irene Morales, Maria Monika Repczynska, Othman Sadki, Antonio García-Casco","doi":"10.1093/petrology/egae049","DOIUrl":"https://doi.org/10.1093/petrology/egae049","url":null,"abstract":"Underplated mafic intrusions ponded at the base of the lower continental crust in extensional settings can experience ultra-high temperature (UHT) granulite-facies metamorphism during tens of My due to slow cooling rates, being also the source of heat and carbonic fluids for regional high-temperature (HT) granulite-facies metamorphism in the continental crust. This work analyses the fluid-melt-rock interaction processes that occurred during the magmatic to HT-UHT-granulite- and amphibolite-facies metamorphic evolution of high-grade mafic rocks from the Eastern Ediacaran Adrar-Suttuf Metamafic Complex (EASMC) of the Oulad Dlim Massif (West African Craton Margin, Southern Morocco). P-T conditions were determined using Ti-in-amphibole thermometry, two-pyroxene and amphibole-plagioclase thermobarometry, and phase diagrams calculations. The thermobarometric study reveals the presence of tectonically juxtaposed lower- and mid-crustal blocks in EASMC that experienced decompression-cooling paths from, respectively UHT and HT granulite-facies conditions at ca. 1.2 ±0.28 GPa and 975 ±50 °C, and ca. 0.82 ±0.15 GPa and 894 ±50 °C, to amphibole-facies conditions at ca. 0.28 ±0.28 GPa and 787 ±45 °C (precision reported for the calibrations at 1s level). An age for the magmatic to UHT granulite-facies metamorphic transition of 604 Ma was constrained from published SHRIMP Th-U-Pb zircon ages of the igneous protoliths. An amphibole 40Ar-39Ar cooling age of 499 ±8 Ma (precision at 2s level) was obtained for the lower-crustal blocks. Amphibole 40Ar-39Ar closure temperatures of 520-555 °C were obtained for an age range of 600-499 Ma and an average constant cooling rate of 4.2 °C/My, suggesting that the lower-crustal blocks cooled down to the greenschist-amphibolite facies transition in ca. 100 My. During the high-temperature stage, interstitial hydrous melts caused incongruent dissolution melting of olivine and pyroxenes, and, probably, the development of An-rich spikes at the grain rims of plagioclase, and assisted textural maturation of the rock matrix and local segregation of pargasite into veins. Subsequent local infiltration of reactive hydrous metamorphic fluids along mineral grain boundaries during cooling down to amphibolite-facies conditions promoted mineral replacements by coupled dissolution-precipitation mechanisms and metasomatism. Ubiquitous dolomite grains, with, in some cases, evidence for significant textural maturation, appear in the granoblastic aggregates of the high-grade mafic rocks. However, calculated phase relationships reveal that dolomite could not coexist with H2O-CO2 fluids at HT-UHT granulite- and low-medium P amphibolite-facies conditions. Therefore, it is proposed that it may have been generated from another CO2-bearing phase, such as an immiscible carbonatitic melt exsolved from the parental mafic magma, and preserved during cooling due to the prevalence of fluid-absent conditions in the granoblastic matrix containing dolomite. The l","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931980","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":"Magmatic-Hydrothermal Evolution at the Barren Wushan Pluton, Southeast China: Insight into Controls on Mineralization Potential","authors":"Zhe Chi, Jun-Yi Pan, Pei Ni","doi":"10.1093/petrology/egae047","DOIUrl":"https://doi.org/10.1093/petrology/egae047","url":null,"abstract":"A-type granites typically exhibit enrichment and mineralization of critical metals such as molybdenum and tin, essential for emerging technologies. However, the key factors influencing their mineralization potential remain elusive. The scarcity of studies on barren systems impedes the understanding of this question. Here, a detailed melt and fluid inclusion study was conducted on the barren Wushan pluton to reconstruct its magmatic evolution and magmatic-hydrothermal transition and to explore the factors controlling the metallogenic potential of Mo and Sn in A-type granites. The Wushan pluton displays apparent lithological zoning consisting of two major phases, i.e., medium-grained seriate to porphyritic alkali feldspar granite and fine-grained porphyritic granite. Miarolitic cavities are widely developed in each lithofacies. The silicate melt inclusions from two granitic phases are rhyolitic, with moderate F contents (0.06–0.53 wt %) and depleted H2O contents (2.0–3.5 wt %). Melt inclusions show a wide range of incompatible element contents, such as Cs (9–1977 μg/g) and Rb (268–2601 μg/g), suggesting that Wushan has undergone a high degree of magma evolution. Mo behaves incompatibly in the magmatic evolution, and its content is enriched with the increasing degree of fractional crystallization, but remains constant after the Cs content exceeds 50 μg/g. Rayleigh fractionation model suggests a large amount of Mo is extracted from fluid exsolution, which restrains Mo from further enrichment. In contrast, Sn behaves as a mildly incompatible element during the entire magmatic evolution history. The contents of Sn increase slowly compared to the trend of Mo, and the maximum contents reach ~30 μg/g in the highly evolved melts. The separation and crystallization of Sn-bearing minerals such as biotite, magnetite, and titanite inhibit the enrichment of Sn. Intermediate-density (ID-type) fluid inclusions hosted in the miarolitic quartz, representing the initial fluid exsolving from magma, display high Mo but low Sn concentrations. Constrained from two assemblages of coexisting ID-type fluid and melt inclusions, the fluid/melt partition coefficients of metals are obtained, with DMo, fluid/melt at 16–19, while DSn, fluid/melt is only about 1. The comparison between Mo-mineralized and barren intrusions worldwide shows that the metal contents in melts and fluids are not fundamentally different. The mineralized intrusions are characterized by the lower melt viscosity and the development of apophyses, both of which facilitate the extraction of metals and fluids from large magma chambers, followed by their concentration into a small rock volume. Consequently, it appears that physical and structural conditions rather than chemical compositions play a crucial role in the Mo mineralization process. Enrichment of Sn in melts is necessary but not decisive for Sn mineralization, whereas Sn enrichment in the initial exsolving fluid determines the Sn mineralization potent","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931853","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":"Identifying Ultrahigh-Temperature Metamorphism in Basic Granulites","authors":"Bin Wang, Chunjing Wei","doi":"10.1093/petrology/egae046","DOIUrl":"https://doi.org/10.1093/petrology/egae046","url":null,"abstract":"Identifying ultrahigh-temperature (UHT) metamorphism in basic granulites is challenged by the uncertainty of peak temperatures. Consequently, available temperature indicators are desiderated all along. In this study, we investigated low-pressure basic granulites from Daqingshan, North China Craton, and determined a UHT peak condition around 1000–1050 °C and 0.8–0.9 GPa. This peak condition was constrained by combining the AlT of 0.10–0.12 in clinopyroxene (Cpx) cores, maximum Ti of 0.36–0.38 in amphibole (Amp) cores and anorthite proportion (XAn) of 0.67–0.70 and 0.61–0.63 in plagioclase (Pl) cores/mantles analyzed in two selected samples. The P–T records obtained from several thermobarometers related to amphibole, plagioclase and/or clinopyroxene were also verified to be in agreement with the phase equilibria modelling results. Notably, AlT-in-Cpx is assessed to be a reliable temperature indicator in basic granulites with the Opx–Cpx–Pl–Amp assemblage, albeit could be influenced by bulk-rock compositions in some extent and has a temperature standard error of ~70 °C. Besides, the post-peak evolution was dominated by near isobaric cooling at 1.94–1.93 Ga, to a fluid-absent solidus as high as ~940 °C. During the cooling process, plagioclase and amphibole grew together at the expense of Al-rich clinopyroxene and unsegregated melts, accompanied by the (rimward) decrease of AlT-in-Cpx, Ti-in-Amp and XAn-in-Pl. A pre-peak process is inferred to be decompressional heating. The UHT metamorphism in Daqingshan is interpreted to result from asthenosphere upwelling and thermal advection from regional mantle-derived magmatism during post-orogenic extension, in a newly developed back-arc-related environment.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140883148","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 New Calibration of the OPAM Thermobarometer for Anhydrous and Hydrous Mafic Systems","authors":"Oliver Higgins, Michael J Stock","doi":"10.1093/petrology/egae043","DOIUrl":"https://doi.org/10.1093/petrology/egae043","url":null,"abstract":"Melt-based thermobarometers are essential tools to recover pre-eruptive magma storage conditions through their application to bulk rock and liquid chemistry. In active volcanic systems, thermobarometric results can be combined with independent geophysical data during or after an eruption to validate conceptual models. In this contribution, we revisit the thermobarometer for melts equilibrated with the mineral assemblage of olivine + plagioclase + augitic clinopyroxene (OPAM). We first demonstrate that the most widely applied OPAM thermobarometer suffers from both random and systematic uncertainty even for anhydrous melts, and that the uncertainty increases proportionally with melt H2O. To address this issue, we use a modern compilation of anhydrous and hydrous OPAM-saturated experiments to regress a new empirical melt-based OPAM thermometer and barometer. Our new equations recover a validation dataset with a standard error estimate (SEE) of ±1.14 kbar and ±36 °C for pressure and temperature respectively, as well as a low systematic uncertainty that does not depend on melt H2O. Additionally, we present a novel statistical approach to determine the probability that a given melt is OPAM-saturated, which can be used alongside rigorous petrographic and geochemical observations. Our thermobarometer and saturation test are presented as a user-friendly R script which reads from an input csv file to be populated with natural data. We benchmark the new calibrations on the products of the 2015 eruption of Wolf Volcano (Isabela Island, Galápagos archipelago) and the 2014-2015 Holuhraun eruption (Iceland), both of which have independent geophysical estimates of magma storage that agree well with our thermobarometric results.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140883098","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}