Journal of Petrology最新文献

{"title":"Bulk compositional influence on diverse metapelitic mineral assemblages in the Whetstone Lake area, Ontario","authors":"Jacob B Forshaw, David R M Pattison","doi":"10.1093/petrology/egad071","DOIUrl":"https://doi.org/10.1093/petrology/egad071","url":null,"abstract":"Abstract Understanding the interplay between bulk composition and metamorphic grade underpins our interpretations of metamorphism in orogenic belts. The focus of this study is the regional garnet-staurolite-kyanite-sillimanite metamorphic sequence of the Whetstone Lake area, southeastern Ontario. In the kyanite and lower sillimanite zones of this area, there is exceptional diversity in metapelitic mineral assemblages that cannot be accounted for by differences in metamorphic grade. We present a dataset of petrographic observations, phase proportions, whole-rock geochemical compositions, and mineral compositions, from thirty-two samples which encapsulate the range of assemblages found in these zones. Wide, as well as quite subtle, differences in bulk composition are the primary control on mineral assemblage development. Whole-rock XMg = molar MgO/(MgO+FeO) and ${mathrm{X}}_{mathrm{Fe}3+}=mathrm{molar} 2times {mathrm{Fe}}_2{mathrm{O}}_3/left(2times {mathrm{Fe}}_2{mathrm{O}}_3+mathrm{FeO}right)$ exert the greatest control on the observed mineral assemblages, whilst MnO, K2O, and Al2O3 have a secondary influence. We use a set of quality factors (Duesterhoeft and Lanari, 2020) to test the ability of thermodynamic models to reproduce the observed mineral assemblages, modal abundances, and mineral compositions in the diverse bulk compositions at Whetstone Lake. Eight samples were selected for phase equilibrium modelling, for which two bulk compositions were calculated for each sample: (1) a whole-rock bulk composition based on an X-ray fluorescence analysis and (2) a carefully considered local bulk composition based on combining mineral proportions with representative mineral compositions, as obtained from a single thin section. Our modelling uses thermodynamic dataset 6.2 (Holland and Powell, 2011) and the solution models of White et al. (2014a, 2014b) that incorporate several Fe3+ end members needed to model the natural data. Modelling in both types of bulk composition broadly predicted mineral assemblages matching those observed. In addition, predicted mineral assemblage fields overlap within uncertainty between 620-675°C and 6.5-7.5 kbar, consistent with the limited range of grade represented by the natural rocks. Predicted modal abundances better match those observed when phase diagrams are constructed using local bulk compositions compared to whole-rock bulk compositions. Despite the acceptable agreement between predicted and observed mineral assemblages, consistent discrepancies are found between predicted and observed mineral compositions. These include overestimation of XMg in garnet, staurolite, and cordierite, overestimation of Ti in staurolite and biotite, underestimation of Si in biotite, and overestimation of Al and underestimation of Fe3+, Fe2+, and Mg in muscovite. The Whetstone Lake suite of this study will be useful to test the predictive capability of future thermodynamic models.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136376027","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":"Experimental constraints on the ferric Fe content and oxygen fugacity in subducted serpentinites","authors":"Lisa Eberhard, Daniel J Frost, Catherine A McCammon, David Dolejš, James A D Connolly","doi":"10.1093/petrology/egad069","DOIUrl":"https://doi.org/10.1093/petrology/egad069","url":null,"abstract":"ABSTRACT Serpentinites play an important role in the delivery of water into subduction zones. In addition, serpentinites also contain ferric Fe and can transport significant redox potential. We present high-pressure and high-temperature experiments and Mössbauer spectroscopy measurements on natural lizardite and antigorite samples equilibrated at various oxygen fugacities in order to quantify the relationship between the oxygen fugacity f(O2) and the Fe3+/Fetot ratio in these two phases. In antigorite, Fe3+ partitions into the octahedral site and is charge balanced by tetrahedral Al. In lizardite, tetrahedral Fe3+ is observed only at low temperature as well as under high f(O2), whereas Fe3+ prefers the octahedral site at temperatures exceeding 500 °C and at 3 to 5 GPa. Although metastable, lizardite remains in redox equilibrium in our experiments at conditions above the lizardite to antigorite phase transformation at 300 °C and demonstrates a similar stability to antigorite. The Al concentration of lizardite is found to be temperature dependent, and it was possible to reequilibrate the Fe3+/Fetot ratio of lizardite from 0.1 to 0.9 by using redox buffers such as Fe metal, graphite, graphite–calcite, Re–ReO2 and Ru–RuO2. Our experiments on antigorite demonstrate that antigorite does not adjust its Al concentration on experimental time scales. Since Fe3+ is charge balanced by Al, it was also not possible to manipulate the Fe3+/Fetot ratio of antigorite. The coexisting phases, however, show chemical equilibration with this antigorite composition. We have retrieved the standard Gibbs energy for Fe3+- and Al-endmembers of antigorite and lizardite and calculated the metamorphic evolution of subducting serpentinites. The lizardite to antigorite transformation does not cause a decrease in the bulk Fe3+/Fetot ratio under f(O2) buffered conditions, in contrast to observations from some natural settings, but does result in the formation of additional magnetite due to antigorite having a lower Fe3+/Fetot ratio than lizardite at equilibrium. If the f(O2) of antigorite serpentinite is buffered during subduction, such as due to the presence of graphite and carbonate, the bulk Fe3+/Fetot ratio decreases progressively. On the other hand, in a closed system where the bulk serpentinite Fe3+/Fetot ratio remains constant, the f(O2) increases during subduction. In this scenario, the f(O2) of an antigorite serpentinite with a typical Fe3+/Fetot ratio of 0.4 increases from the fayalite–magnetite–quartz to the hematite–magnetite f(O2) buffer during dehydration. These f(O2) results confirm earlier inferences that fluids produced by antigorite dehydration may not contain sufficient oxidised sulphur species to oxidise the mantle wedge. Sufficiently high levels of f(O2) to mobilise oxidised sulphur species may be reached upon antigorite dehydration, however, if closed system behaviour maintains a high bulk redox potential across the lizardite to antigorite phase transformatio","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135394485","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":"Ten thousand years of magma storage preceding the last caldera-forming eruption of the Bandelier magmatic system, New Mexico, USA","authors":"Nicholas F Meszaros, James E Gardner, Matthew J Zimmerer, Kenneth S Befus","doi":"10.1093/petrology/egad067","DOIUrl":"https://doi.org/10.1093/petrology/egad067","url":null,"abstract":"Abstract In this study, we present new evidence for changes in magma storage conditions that preceded the 1232 ka caldera-forming eruption of the Bandelier magmatic system in the Jemez Mountains Volcanic Field. Using high precision 40Ar/39Ar sanidine dating we determine that at least eight rhyolites erupted within 8.6 ± 3.4 kyr of the ~400 km3 eruption that formed Valles caldera. Some of those rhyolites contain fayalite with or without biotite, others contain only biotite. An eruption of fayalite-bearing rhyolite at 1240.5 ± 2.1 ka ended an eruption hiatus of at least 100 kyr. Following that first post-hiatus episode of volcanism, at least four more eruptions of fayalite-bearing rhyolite and three eruptions of biotite-bearing rhyolite occurred prior to the caldera-forming eruption. We use phase equilibrium experiments and geothermobarometry to infer the storage conditions and processes that led to these differing crystal cargos and ultimately generated ~400 km3 of predominantly fayalite rhyolite ignimbrite (Tshirege Member of the Bandelier Tuff). We find that biotite-bearing rhyolites were stored at 695–750°C, 75–160 MPa, and at an oxygen fugacity more oxidizing than the quartz-fayalite-magnetite (QFM) buffer reaction. Fayalite-bearing rhyolites were similarly stored at 695–745°C and 70–190 MPa, but at more reducing conditions (${f}_{O_2}$≤ QFM). We suggest that the reduced, fayalite-bearing rhyolite was most likely produced via interaction of crystal-poor rhyolitic magma with a reducing, potentially Cl-bearing, and H2O-rich supercritical fluid phase. This fluid flux event was a key component of the substantial magmatic rejuvenation that enabled the mobilization of ~400 km3 of mostly fayalite-bearing rhyolite prior to not only the Tshirege event, but the older Otowi event as well.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135046626","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":"Correction to: Volatiles and Intraplate Magmatism: a Variable Role for Carbonated and Altered Oceanic Lithosphere in Ocean Island Basalt Formation","authors":"","doi":"10.1093/petrology/egad068","DOIUrl":"https://doi.org/10.1093/petrology/egad068","url":null,"abstract":"","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135349111","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":"Correction to: Mineralogy and Geochemistry of Nepheline Syenite From the Bang Phuc Massif of the Alkaline Cho Don Complex in North-Eastern Vietnam—Implications for Magma Evolution and Fluid–Rock Interactions","authors":"","doi":"10.1093/petrology/egad072","DOIUrl":"https://doi.org/10.1093/petrology/egad072","url":null,"abstract":"","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134995474","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":"Contrasting styles of lower crustal metamorphism from a granulite suite of rocks from Angul, Eastern Ghats Belt, India: Implications for the India-Antarctica correlation","authors":"Aparupa Banerjee, Proloy Ganguly, Kaushik Das, Nilanjana Sorcar, Sankar Bose","doi":"10.1093/petrology/egad065","DOIUrl":"https://doi.org/10.1093/petrology/egad065","url":null,"abstract":"Abstract The present work is focussed on a suite of high-grade rocks including mafic granulite, aluminous granulite, khondalite, charnockite, and augen gneiss along with medium-grade rocks like olivine-bearing metanorite, gabbro, and porphyritic granite of the Angul domain at the northern margin of the Proterozoic Eastern Ghats Province (EGP). Based on the petrological and geothermobarometric data, two distinct metamorphic events have been identified. The imprints of the earlier event (MA1) are preserved in the mafic granulite, aluminous granulite, khondalite, augen gneiss, and fine-grained charnockite, but those are best preserved in mafic granulite and aluminous granulite. In mafic granulite, orthopyroxene + clinopyroxene + plagioclase ± garnet+ ilmenite ± quartz assemblage was stabilised at the peak MA1 conditions, whereas the peak MA1 assemblage is represented by Fe3+-garnet + hematite + magnetite + cordierite + K-feldspar + plagioclase + sillimanite + quartz + melt in aluminous granulite. Phase equilibria modelling and thermobarometric data suggest the P–T conditions of >850°C, 7 to 8 kbar for this event. The retrograde metamorphism (MA1R) involved minor decompression (down to ~5 kbar) and subsequent cooling to form biotite- and hornblende-bearing mineral assemblages in aluminous granulite and mafic granulite, respectively. Texturally constrained monazite (U–Th–total Pb) and zircon (U–Pb) data from the former rock suggest ca. 1200 Ma age of the MA1 metamorphism, which was associated with granitic and charnockitic magmatism as constrained from oscillatory-zoned zircon domains in the augen gneiss and fine-grained charnockite. The rock ensemble was affected by a younger metamorphic event (MA2), which is texturally characterised by partial replacement of hornblende (developed during MA1R) to orthopyroxene ± clinopyroxene + plagioclase ± ilmenite + melt assemblage in mafic granulite. Moreover, biotite of aluminous granulite has undergone dehydration melting to produce garnet + cordierite-bearing assemblage. Garnet in the above assemblage did not form as porphyroblastic phase and overgrew the MA1 garnet. The MA2 event followed a counterclockwise P–T trajectory, causing heating (up to 800°C) with associated loading (from 4.0 to 5.8 kbar) along the prograde path. Monazite U–Th–total Pb data from aluminous granulite and khondalite suggest MA2 ages of 987 ± 12 and 975 ± 16 Ma, respectively. Fine-grained charnockite and augen gneiss also recorded the imprints of MA2 event by developing thin to thick sector-zoned overgrowth yielding group ages of 979 ± 12 and 982 ± 29 Ma, respectively. Zircon overgrowth in mafic granulite formed at 962 ± 13 Ma. The MA2 event coincides with the crystallisation of coarse-grained charnockite at 983 ± 22 Ma and porphyritic granite at 960 ± 10 Ma. Geochronological data, thus, indicate that the Angul domain underwent the MA2 metamorphism and associated magmatism at ca. 990 to 960 Ma. The apparent absence of MA1 event (","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135098950","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":"Correction to: Arc–Backarc Exchange Along the Tonga–Lau System: Constraints From Volatile Elements","authors":"","doi":"10.1093/petrology/egad070","DOIUrl":"https://doi.org/10.1093/petrology/egad070","url":null,"abstract":"","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135428964","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":"Large-scale Cretaceous adakitic magmatism induced by water-fluxed melting of continental crust during the North China Craton destruction","authors":"Shuo Xue, Wanzhu Zhang, Ming-Xing Ling, Weidong Sun, Xing Ding","doi":"10.1093/petrology/egad066","DOIUrl":"https://doi.org/10.1093/petrology/egad066","url":null,"abstract":"ABSTRACT The mechanism behind the destabilization of the North China Craton (NCC) remains a contentious topic among researchers. Large-scale Cretaceous adakitic magmatism in the NCC offers insights into the decratonization process. This study focuses on the Huashan and Laoniushan plutons located in the Lesser Qinling on the southern margin of the NCC and compiles published data for coeval adakitic rocks to investigate the role of water in adakitic rock petrogenesis during the peak destruction of NCC. Both the Huashan and Laoniushan plutons exhibit adakitic signatures, including high Sr (193–1080 ppm), low Yb (<14.8 ppm) and Y (<1.24 ppm) concentrations, as well as high Sr/Y (18–100) and La/Yb (24–58) ratios. The zircon Hf–O isotope compositions suggest that the primary source for the Huashan and Laoniushan plutons is the mafic lower crust of NCC. Nevertheless, there are significant differences in trace element characteristics between the two plutons. Specifically, the Huashan pluton displays higher Na2O/K2O ratios, lower levels of Rb, Rb/Sr, Nb, Ta content, and a weak Eu anomaly in comparison to the Laoniushan pluton. These variations in geochemical attributes cannot be accounted for by mechanisms like mantle-derived magma mixing, crustal contamination, or fractional crystallization processes. Instead, these disparities are attributed to distinct modes of crustal anatexis, involving both water-fluxed and dehydration melting. Subsequently, we conducted thermodynamic simulations of the melting process of mafic lower crust under different pressure (0.5–1.5 GPa) and water content conditions (1–3 wt.%). The simulation results suggest that the Huashan pluton is most likely formed through water-fluxed melting in a scenario with normal crustal thickness (1 GPa). On the other hand, the Laoniushan pluton might have originated from dehydration melting under normal crustal thickness and pressure conditions. Notably, high pressure (>1.5 GPa) is not necessary for the formation of intracontinental adakitic rocks. The release of water from metasomatized lithospheric mantle and subsequent hydration of the lower continental crust triggers extensive adakitic magmatism in the NCC. These findings emphasize the significance of deep water cycling in understanding large-scale magmatic events and illuminate the decratonization mechanism.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136284052","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":"Application of an Improved Olivine-Melt Thermometer/Hygrometer to the Colima Cone Basanites and Minettes of Western Mexico: Implications for the Mantle Source of Unusually High-MgO Melts","authors":"Xiaofei Pu, Rebecca A Lange, Gordon M Moore","doi":"10.1093/petrology/egad064","DOIUrl":"https://doi.org/10.1093/petrology/egad064","url":null,"abstract":"Abstract A collection of Quaternary, high-MgO (≤13.4 wt%) basanite and minette cinder and lava cones, with an enhanced arc geochemical signature, are located along the northern margin of the N-S Colima rift in western Mexico. The Colima rift overlies the lithospheric suture between the Jalisco block and Guerrero terrane, as well as the tear between the Rivera and Cocos subducting oceanic plates. From the literature, volatile analyses of olivine-hosted melt inclusions in the Colima cone samples document notably high concentrations of dissolved H2O in the melt (≤ 7.0 wt%) as well as degassing-induced phenocryst growth over a range of depths ≤ 25 km. In this study, it is shown that the high-MgO character of the Colima suite reflects liquid compositions, consistent with evidence for their rapid transit to the surface, without stalling in a crustal magma chamber. The most Mg-rich olivine analyzed in each sample matches the equilibrium composition at the liquidus based on olivine-melt Mn-Mg and Fe2+-Mg exchange coefficients. Application of both a Mg- and Ni-based olivine-melt thermometer, calibrated on the same experimental data set, to the Colima cone suite provides the temperature and dissolved H2O content at the liquidus. Because the Ni-thermometer is insensitive to dissolved H2O in the melt, it gives the actual temperature at the onset of olivine phenocryst growth. For the nine Colima samples that range from 13.4-9.2 wt% MgO, resulting temperatures range from 1221-1056 (± 6-11) °C. In contrast, the Mg-thermometer is sensitive to dissolved H2O in the melt, and its application (without a correction of H2O) gives the temperature of olivine crystallization under anhydrous conditions. When the Mg- and Ni-based temperatures are paired, the depression of the liquidus (∆T = TMg-TNi) due to dissolved H2O can be obtained. For the high-MgO (>9 wt%) Colima samples, ∆T values range from 188-109 °C. Corrections for the effect of pressure (i.e., evidence that phenocryst growth began at ~700 MPa), increase ∆T by ~21°C. An updated model calibration (on experiments from the literature) that relates ∆T with dissolved H2O in the melt shows that the best fit (R2= 0.95) is linear, wt% H2O = 0.047*∆T, with a standard error of ± 0.5 wt%. Although the experimental data set spans a wide range of melt composition (e.g., 47-58 wt% SiO2, 4.4-10.2 wt% MgO, 1.3-4.9 wt% Na2O, 0.1-5.0 wt% K2O, 0.3-5.3 wt% H2O), no dependence on anhydrous melt composition is resolved. Application of this updated model to the Colima suite gives H2O contents of 5.1-8.8 wt% H2O, consistent with those analyzed in olivine-hosted MIs from the literature. When the thermometry and hygrometry results for the Colima cone suite are compared to those for the adjacent calc-alkaline basalts from the Tancítaro Volcanic Field (TVF) in Michoacán, two distinct linear trends in a plot of wt% H2O vs. temperature are found, indicative of different mantle sources. It is proposed that the high-MgO (>11 wt%)","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136281098","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 high-δ18O mantle source for the 2.06 Ga Phalaborwa Igneous Complex, South Africa?","authors":"Joshua T. Munro, C. Harris","doi":"10.1093/petrology/egad063","DOIUrl":"https://doi.org/10.1093/petrology/egad063","url":null,"abstract":"\u0000 The 2060 ± 2 Ma Phalaborwa Complex is a pipe-like, ultramafic to carbonatite intrusion formed from multiple magma pulses. The complex is made up of a main pipe consisting of clinopyroxenites, ultramafic pegmatoids, carbonatites and foskorite (olivine-apatite-magnetite-calcite assemblage), surrounded by many smaller syenite plugs. The range in mineral δ18O values for all rock types and minerals analysed in the Phalaborwa Complex is 2.24 to 18.3‰. However, 24 analyses of the most abundant and robust mineral, diopside, all have δ18O values between 6.2 and 7.7‰. The δ18O values of baddeleyite, olivine, diopside, magnetite, apatite and aegirine are thought to be magmatic. Most mineral pairs have differences in δ18O value that are consistent with magmatic equilibrium at high temperatures down to closure temperature. Alkali feldspar and phlogopite have more variable δ18O values, and both minerals may have undergone subsolidus O-exchange. The δD values for petrographically fresh Phalaborwa Complex phlogopite range from -77 to -48‰ with a mean of -64 ± 9‰ (1σ, n=19). The phlogopite δD values are consistent with subduction-related magmatic water. Despite petrographic evidence for fluid-rock interaction in the carbonatite-foskorite rocks, the carbonatite δ13C and δ18O range (δ18O, 8.13 to 12.00‰; δ13C, -3.19 to -5.60‰) overlaps with the unaltered, primary igneous carbonatite field.\u0000 Magma δ18O values estimated from silicate and oxide minerals are mostly higher than normal mantle magmas (pyroxenites, ~7.6‰; foskorite, 7.2‰). The δ18O value of syenite magma estimated from aegirine is 7.8 ± 0.9‰ (1σ, n=8), in equilibrium with whole-rock syenite δ18O values (8.7 ± 0.4‰, 1σ, n=5). Local basement rocks have average bulk δ18O values of 8.6‰, and realistic proportions of assimilation by a mantle-derived magma (δ18O, 5.7‰) could not have produced the δ18O values in the pyroxenites or foskorites. Instead, it is proposed that the high-δ18O values of Phalaborwa Complex magmas reflect that of the mantle source. High δ18O values are also a feature of the Rustenburg Layered Suite of the Bushveld Complex (2060 to 2055 Ma), which may have had a similar high-δ18O mantle source. The higher δ18O values of the satellite syenites are consistent with an origin by partial melting of metasomatised country rock.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42917336","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}