Journal of Petrology最新文献

{"title":"Testing the limits of Ti-in-Quartz thermometry and diffusion modelling to determine the thermal history of the Fish Canyon Tuff","authors":"Karoline Brückel, Craig Campbell Lundstrom, Michael Ackerson, Christopher Campe","doi":"10.1093/petrology/egad082","DOIUrl":"https://doi.org/10.1093/petrology/egad082","url":null,"abstract":"How silicic magmas are stored in the upper crust before they erupt to form 100-1000s km3 ash-sheets remains a fundamental, but unanswered question in volcanology. While some studies posit storage in an eruptible state at low viscosity (<50% crystals) and high temperatures (>760-740°C) (warm storage), others suggest storage in a rigid state (>50% crystals) at lower, near-solidus temperatures (cold storage). Storage temperature and time spent near the solidus are typically constrained by mineral thermometry and diffusional relaxation modelling (at a given temperature), respectively. Since quartz is abundant over a range of temperatures and compositions and can incorporate titanium (Ti) at magmatic temperatures, a Ti-in-Quartz thermometer has been calibrated and Ti diffusion coefficients (DTi) have been measured. However, simply applying this thermometer or diffusion coefficient to volcanic quartz is burdened by an ongoing debate regarding their experimental calibration. This debate centers around three recent Ti-in-Quartz thermometers by Huang & Audétat (2012), Zhang et al. (2020), Osborne et al. (2022) and three DTi by Cherniak et al. (2007), Jollands et al. (2020), Audétat et al. (2021), each of which when applied to igneous systems favors either warm or cold storage. To determine their applicability for estimating the pre-eruptive thermal history of silicic magmatic systems, we apply the different Ti-in-Quartz thermometers and DTi to quartz from the Fish Canyon Tuff (USA). This tuff is an optimal location for such a study because it is a prime example of cold storage with multiple previous studies providing constraints on its storage conditions. We find that a temperature of 737 ± 16°C using the Zhang et al. (2020) thermometer is the most consistent with other temperature estimates for the Fish Canyon Tuff. Temperatures calculated using Huang & Audétat (2012) are acceptable, while those using Osborne et al. (2022) are unrealistic. Applying each of the DTi to quartz in the Fish Canyon Tuff and comparing these timescales to timescales from Ba-in-Sanidine diffusion and the total storage time of the mush (derived from the range in zircon U-Pb ages and the local eruption history), three different scenarios for pre-eruptive storage are possible. At a temperature of 737°C, timescales using DTi by Audétat et al. (2021) exceed the total storage time of the Fish Canyon system by ~2 Myr. These DTi are only consistent if storage temperatures were significantly higher, implying warm storage. Such a scenario is inconsistent with cold storage of the Fish Canyon system. Timescales derived from DTi by Jollands et al. (2020) and Cherniak et al. (2007) are consistent with cold storage of the Fish Canyon system. While DTi by Jollands et al. (2020) suggest long-term storage near 737°C and an extended period of pre-eruptive reheating, DTi by Cherniak et al. (2007) suggests storage below 737°C and rapid reheating.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2023-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138503738","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":"Middle-Late Miocene to Pleistocene post-collisional magmatism in the Arabia-Eurasia collision zone, an example from northwest Iran","authors":"Hadi Shafaii Moghadam, Kaj A Hoernle, Folkmar Hauff, Massimo Chiaradia, Dieter Garbe-Schönberg, Teresa Orozco-Esquivel, Ilya N Bindeman, Orhan Karsli, Ghasem Ghorbani, Naeim Mousavi, Federico Lucci","doi":"10.1093/petrology/egad081","DOIUrl":"https://doi.org/10.1093/petrology/egad081","url":null,"abstract":"Abstract Post-collisional volcanism contains important clues for understanding the processes that prevail in orogenic belts, including those in the mantle and the uplift and collapse of continents. Here we report new geochronological and geochemical data for a suite of post-collisional Miocene to Pleistocene volcanic rocks from northwest Iran. Four groups of volcanic rocks can be distinguished according to their geochemical and isotopic signatures, including: (1) Miocene depleted lavas with high Nd and Hf but low Pb and Sr isotopic ratios, (2) less depleted lavas with quite variable Pb isotopic composition, (3) lavas with non-radiogenic Nd and Hf isotopic values, but highly radiogenic Sr and Pb isotopic composition, and (4) Pleistocene adakitic rocks with depleted isotopic signatures. The isotopic data reveal that the Miocene rocks are derived from asthenospheric and highly heterogeneous sub-continental lithospheric mantle sources. Evidence suggests that the lithospheric mantle contains recycled upper continental material and is isotopically similar to the enriched mantle two (EMII) endmember. Analysis of Sr-Nd-Pb-Hf-O isotopes in both mineral and rock groundmass, in conjunction with energy-constrained assimilation and fractional crystallization (EC-AFC) numerical modeling, demonstrates that the incorporation of continental crust during magma fractionation via AFC had an insignificant impact on the isotopic composition of the Miocene lavas. Moreover, adakites are the youngest rocks and show a geochemical signature consistent with the partial melting of a young and mafic continental lower crust. Both seismological data and geochemical signatures on these Miocene to Pleistocene volcanic rocks indicate the initiation of asthenospheric upwelling and orogen uplift in the Arabia-Eurasia collision zone, which occurred after slab break-off, following the Neotethyan closure.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135545743","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":"Oceanic and continental lithospheric mantle in the 1.95 Ga Jormua Ophiolite Complex, Finland: implications for mantle and crustal evolution","authors":"Valerie A Finlayson, Mitchell Haller, James M D Day, Stephen Ginley, Brian O’Driscoll, Asko Kontinen, Eero Hanski, Richard J Walker","doi":"10.1093/petrology/egad080","DOIUrl":"https://doi.org/10.1093/petrology/egad080","url":null,"abstract":"Abstract The ca. 1.95 Ga Jormua Ophiolite Complex (JOC), Finland, is a rare Paleoproterozoic ophiolite that preserves a record of diverse upper mantle materials and melting processes. Meter-scale grid sampling of four JOC outcrops, as well as non-grid samples, permits evaluation of meter- to kilometer-scale mantle heterogeneity within the JOC. Significant heterogeneity is observed between the four grids, and also among a number of the non-grid samples examined. Variations in the concentrations of fluid-mobile elements are particularly large among different samples and locations. New whole-rock major, lithophile trace, and highly siderophile element data (HSE: Os, Ir, Ru, Pt, Pd, Re), including 187Re-187Os isotopic data, for serpentinized harzburgites indicate the presence of two distinct compositional types and probable modes of origin within the JOC. This is consistent with prior findings. Type 1 is similar to modern refractory abyssal-type mantle. Type 2 is more highly refractory than Type 1, and most likely represents samples from sub-continental lithospheric mantle (SCLM). Type 1 mantle is moderately heterogeneous with respect to major and trace element and Os isotopic compositions at both the meter and kilometer scales. By contrast, Type 2 mantle is considerably more homogeneous than Type 1 grids at the meter scale, but is more heterogeneous at the kilometer scale. The median initial γOs value for Type 1 mantle, calculated for 1.95 Ga, is ~-2.0 (where γOs is the % deviation in 187Os/188Os relative to a chondritic reference calculated for a specified time). This isotopic composition is consistent with a moderate, long-term decrease in Re/Os relative to the estimate for Primitive Mantle, prior to JOC formation. The similarity in this γOs value to the value for the modern abyssal mantle, as well as the initial values for several Phanerozoic ophiolites suggests that the upper mantle achieved a Re/Os ratio similar to the chondritic reference by ~2 Ga, then evolved along a subparallel trajectory to the chondritic reference since then. For this to occur, only limited Re could have been permanently removed from the upper mantle since at least the time the JOC formed. A localized secondary metasomatic event at ~2 Ga, concurrent with the estimated obduction age for the JOC and subsequent Svecofennian Orogeny, affected the HSE systematics of some Type 1 samples. By contrast, late Archean Os TRD model ages for Type 2 rocks indicate a depletion event superimposed upon the long-term Re depletion of the abyssal mantle. This event was established no later than ~2.6 Ga and may have occurred during a period of significant, well-documented crustal production in the Karelia craton at ~2.7 Ga.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135976655","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":"Zircon Microstructures in Large, Deeply Eroded Impact Structures and Terrestrial Seismites","authors":"Adam Andreas Garde, Leif Johansson, Nynke Keulen, Anja Schreiber, Richard Wirth","doi":"10.1093/petrology/egad079","DOIUrl":"https://doi.org/10.1093/petrology/egad079","url":null,"abstract":"Abstract Extraterrestrial cratering was a critical component in the evolution of the early Earth, but discovery of very ancient and deeply exhumed impact structures remains elusive, as identification tools are in short supply. The recognition of such structures is hindered by post-cratering geological processes, whereby impact-induced features common in younger, upper-crustal craters may be lost. In this study we make a detailed analysis of planar microstructures in zircons from four large, confirmed impact structures (Manicouagan, Rochechouart, Sudbury, Vredefort) preserved at different crustal levels, from two previously described non-impact seismites in SW Norway and northern Italy, and from the 3.0 Ga Maniitsoq structure in West Greenland. A total of ~3400 zircon grains were studied using exterior and interior scanning and transmission electron microscopy. We show for the first time that shocked zircons contain two successive, principally different types of planar microstructures, only one of which is diagnostic of impact. Closely spaced, contiguous microplanes (CP) are formed first, presumably by the shock wave. In Manicouagan and Rochechouart zircons the exterior CPs have ultrathin interior counterparts of straight dislocation arrays, as identified in Manicouagan zircon using transmission electron microscopy. They have the same close spacing and orientations as the exterior CPs and are abundantly decorated with tiny pores down to less than 50 nm across. These interior CPs are identical to shock-induced decorated, partly annealed amorphous planar microstructures in quartz (planar deformation features, PDFs) and are interpreted as such. The second type is open planar fractures (PF). They are widely and irregularly spaced and texturally younger than the CPs. They re-use and displace the CP orientations, which they cut in stepwise fashion. We interpret these PFs as formed by impact-induced seismic shaking in the wake of the shock wave. We confirm two previous reports of isolated planar fractures in zircons from non-impact seismites, showing that PFs per se are not impact-diagnostic. There are no CPs in any of these zircons. Zircons from different parts of the Maniitsoq structure contain CPs in various states of preservation besides PFs, corroborating that this very large and very deeply exhumed structure resulted from an extraterrestrial impact.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135218959","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":"New experimental constraints for the evolution and thermobarometry of alkali ultrabasic to intermediate igneous rocks","authors":"Andrés Fabián Salazar-Naranjo, Silvio Roberto Farias Vlach","doi":"10.1093/petrology/egad078","DOIUrl":"https://doi.org/10.1093/petrology/egad078","url":null,"abstract":"Abstract We report new experimental data from ultrabasic basanite and ultrabasic tephrite as starting material compositions in the 1350°C to 1000°C temperature range. Crystallization experiments under low- to high-pressure (0.5–2.0 GPa) were carried out under reduced conditions (≈CCO buffer), while one-atmosphere, anhydrous, experiments were performed ranging from reduced to oxidized conditions (−2 ≤ ∆QFM ≤ +2). The results highlight the ƒO2 role on the silica saturation of the alkali liquids differentiated from these primary ultrabasic magmas, on the mineral assemblage, and its composition. The liquid lines of descent (LLDs) from basanite are sodic and strongly SiO2 undersaturated, whereas from tephrite, the LLDs are sodic-potassic/potassic for both weakly SiO2-undersaturated and SiO2-saturated compositions, being more silica saturated under oxidized conditions. At the lowest temperature experiments, the percentage of liquid remaining is significantly higher in the basanite-derived products (ca. 35 wt.%) than in tephrite, indicating that the equivalent magmas are more prone to produce larger quantities of evolved melts. The best obtained Fe–Mg olivine/melt and clinopyroxene/melt exchange coefficients for these alkali compositions considering the new and available data are ${K_D}_{Fe^{2+}- Mg}^{Ol- Alkali melt}=0.285pm 0.014$ and ${K_D}_{Fe^{2+}- Mg}^{Cpx- Alkali melt}=0.245pm 0.008$, slightly lower than those observed in tholeiitic melts. Clinopyroxene compositions are Ti–Al-rich and Si-poor as compared with common clinopyroxenes in subalkali systems. We suggest that Ti should be allocated in the tetrahedral sites substituting for Si and that its contents are inversely correlated with pressure. Our results allow a simple new barometer based on clinopyroxene-only compositions, as follows:$$ Pleft(pm 0.16 GPa,1sigma right)=16.028left(pm 1.042right) Na-6.715left(pm 0.727right)frac{Ti}{Ti+ Al(t)}+0.494left(pm 0.441right) Si+0.144left(pm 0.079right) $$where Na, Ti, Al(t), and Si are molar proportions relative to 6O. This formulation accounts for the jadeite (NaAlSi2O6) component, herein computed from the Na contents, corrected for the Ti-diopside (CaMgTi2O6) component in clinopyroxene and also considers the evolutionary trend from Mg-augite to ferroan diopside. It applies to alkali ultrabasic to intermediate compositions in the examined P–T–ƒO2 range, resulting in more accurate estimates than the available calibrations. The MgO-in-melt thermometer was optimized for the studied compositions at one-atmosphere pressure and anhydrous conditions, as follows:$$ T left(pm 5{}^{circ}C,1sigma right)=27.35left(pm 0.65right) big({MgO}^{liq}big)+984left(pm 4right) $$which provides much more reliable liquidus temperatures for these alkali systems. Given data restriction, this formulation may be expanded to include the pressure effects for relatively low-H2O (< 3 wt.%) systems as:$$ T left(pm 20{}^{circ}C,1sigma right)=27.35left(pm 0.65right)big({MgO}^{liq}","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136034738","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":"An extended calibration of the olivine–spinel aluminum exchange thermometer: Application to the melting conditions and mantle lithologies of large igneous provinces","authors":"Yishen Zhang, Olivier Namur, Weiran Li, Oliver Shorttle, Esteban Gazel, Eleanor Jennings, Peter Thy, Timothy L Grove, Bernard Charlier","doi":"10.1093/petrology/egad077","DOIUrl":"https://doi.org/10.1093/petrology/egad077","url":null,"abstract":"Abstract The application of the olivine–spinel aluminum exchange thermometer to natural samples is limited by the restricted experimental dataset on which it was calibrated. Here, we present a new dataset of 46 high-temperature crystallization experiments and 21 reanalyzed published experiments, which we used to extend the calibration to higher and lower temperatures. The final calibration dataset spans a range of conditions relevant to crustal and upper mantle processes: 1174–1606 °C, 0.1–1350 MPa, QFM−2.5 to QFM+7.2 (oxygen fugacity, fO2, reported in log units relative to the quartz–fayalite–magnetite buffer, QFM), and 0–7.4 wt.% H2Omelt. We propose three new models. The first is thermodynamically self-consistent, based on spinel Fe, Mg, Al, and Cr compositions and Al exchange between olivine and spinel. The second and third are empirical models that consider fewer elemental exchanges: the second uses only Al exchange and spinel compositions, whereas the third considers olivine–spinel Al and Cr exchange. All models include the modest effect of pressure on olivine-spinel equilibrium chemistry, whereas fO2 and water content have negligible effects. In general, as fewer elements are considered in the olivine–spinel exchange, the fit to experimental data worsens. Conversely, the associated decrease in model complexity improves their robustness against systematic errors when applied to natural crystal pairs: the thermodynamic model may underestimate crystallization temperatures in natural samples due to spinel subsolidus re-equilibration, whereas the empirical models (independent of Fe and Mg in spinel) are less sensitive to re-equilibration but yield temperatures with larger uncertainties. We applied a statistical test to select the most appropriate model for application to natural samples. When applied to lavas from mid-ocean ridges, Iceland, Skye, Emeishan, Etendeka, and Tortugal, our new temperature estimates are 30–100 °C lower than previously proposed. The lower temperature estimates cause a lower mantle melting temperature and significant impacts on the mantle lithology constraints.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136063359","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":"Himalayan-like crustal melting and differentiation in the southern North American Cordilleran anatectic belt during the Laramide orogeny: Coyote Mountains, Arizona","authors":"James B Chapman, Cody Pridmore, Kevin Chamberlain, Gordon Haxel, Mihai Ducea","doi":"10.1093/petrology/egad075","DOIUrl":"https://doi.org/10.1093/petrology/egad075","url":null,"abstract":"Abstract The southern U.S. and northern Mexican Cordillera experienced crustal melting during the Laramide orogeny (ca. 80-40 Ma). The metamorphic sources of melt are not exposed at the surface, however, anatectic granites are present throughout the region, providing an opportunity to investigate the metamorphic processes associated with this orogeny. A detailed geochemical and petrochronological analysis of the Pan Tak Granite from the Coyote Mountains core complex in southern Arizona suggests that prograde metamorphism, melting, and melt crystallization occurred here from 62-42 Ma. Ti-in-zircon temperatures (TTi-zr) correlate with changes in zircon REE concentrations and indicate prograde heating, mineral breakdown, and melt generation took place from 62-53 Ma. TTi-zr increases from ~650 to 850 °C during this interval. A prominent gap in zircon ages is observed from 53-51 Ma and is interpreted to reflect the timing of peak metamorphism and melting, which caused zircon dissolution. The age gap is an inflection point in several geochemical-temporal trends that suggest crystallization and cooling dominated afterward, from 51-42 Ma. Supporting this interpretation is an increase in zircon U/Th and Hf, a decrease in TTi-zr, increasing zircon (Dy/Yb)n, and textural evidence for coupled dissolution-reprecipitation processes that resulted in zircon (re)crystallization. In addition, whole rock REE, LILE, and major elements suggest that the Pan Tak Granite experienced advanced fractional crystallization during this time. High silica, muscovite ± garnet leucogranite dikes that crosscut two-mica granite represent more evolved, residual melt compositions. The Pan Tak Granite was formed by fluid-deficient melting and biotite dehydration melting of meta-igneous protoliths, including Jurassic arc rocks and the Proterozoic Oracle Granite. The most likely causes of melting are interpreted to be a combination of 1) radiogenic heating and relaxation of isotherms associated with crustal thickening under a plateau environment, 2) heat and fluid transfer related to the Laramide continental arc, and 3) shear and viscous heating related to the deformation of the deep lithosphere. The characteristics and petrologic processes that created the Pan Tak Granite are strikingly similar to intrusive suites in the Himalayan leucogranite belt and further support the association between the North American Cordilleran anatectic belt and a major orogenic and thermal event during the Laramide orogeny.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135141736","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 Influence of Undercooling and Sector Zoning on Clinopyroxene–Melt Equilibrium and Thermobarometry","authors":"Alice MacDonald, Teresa Ubide, Silvio Mollo, Alessio Pontesilli, Matteo Masotta","doi":"10.1093/petrology/egad074","DOIUrl":"https://doi.org/10.1093/petrology/egad074","url":null,"abstract":"Abstract Thermobarometry provides a critical means of assessing locations of magma storage and dynamics in the lead up to volcanic eruptions and crustal growth. A common approach is to utilise minerals which have compositions sensitive to changes in pressure and/or temperature, such as clinopyroxene which is ubiquitous in mafic to intermediate magmas. However, clinopyroxene thermobarometry may carry significant uncertainty and require an appropriate equilibrium melt composition. In addition, the degree of magma undercooling (ΔT) affects clinopyroxene composition and zoning, with common sector zoning potentially obfuscating thermobarometry results. Here, we use a set of crystallisation experiments on a primitive trachybasalt from Mt. Etna (Italy) at ΔT = 25 – 233 °C, P = 400 – 800 MPa, H2O = 0 – 4 wt.% and fO2 = NNO+2, with clinopyroxene crystals defined by Al-rich zones (prisms and skeletons) and Al-poor zones (hourglass and overgrowths) to assess common equilibrium models and thermobarometric approaches. Under the studied conditions, our data suggest that the commonly applied Fe-Mg exchange (cpx-meltKdFe–Mg) is insensitive to increasing ΔT and may not be a reliable indicator of equilibrium. The combined use of DiHd (i.e., CaMgSi2O6 + CaFeSi2O6) and EnFs (Mg2Si2O6 + Fe2Si2O6) models indicate the attainment of equilibrium in both Al-rich and Al-poor zones for almost all investigated ΔT. In contrast, CaTs and CaTi models reveal substantial deviations from equilibrium with increasing ΔT, particularly in Al-rich zones. We postulate this reflects slower diffusion of Al and Ti in the melt compared to Ca and Mg and recommend the concurrent application of these four models to evaluate equilibrium between clinopyroxene and melt, particularly for sector-zoned crystals. Thermobarometers calibrated with only isothermal–isobaric experiments closely reproduce experimental P–T at low ΔT, equivalent to natural phenocrysts cores and sector-zoned mantles. Models which also consider decompression experiments are most accurate at high ΔT and are therefore suitable for phenocryst rims and groundmass microlites. Recent machine learning approaches reproduce P–T conditions across all ΔT conditions but carry larger uncertainties. Applying our experimental constraints to sector-zoned microphenocrysts and groundmass microlites erupted during the 1974 eccentric eruption at Mt. Etna, we highlight that both hourglass and prism sectors are suitable for thermobarometry, given that equilibrium is sufficiently tested for. The combination of DiHd, EnFs, CaTs and CaTi models identifies compositions closest to equilibrium with the bulk melt composition, and results in smaller differences in P-T calculated for hourglass and prism sectors compared to applying only DiHd and EnFs equilibrium models. This provides a framework to tackle crystallisation conditions in sector-zoned clinopyroxene crystals in mafic alkaline settings.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135739578","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":"Petrology and geochemistry of Adak Island plutonic xenoliths: implications for primitive magma generation and crustal differentiation in the Aleutian Island arc","authors":"Emma S Sosa, Claire E Bucholz, Mattison H Barickman, Jill A VanTongeren, Jacob B Setera, Suzanne Mahlburg Kay, Robert W Kay","doi":"10.1093/petrology/egad073","DOIUrl":"https://doi.org/10.1093/petrology/egad073","url":null,"abstract":"Abstract Deep crustal cumulates in arcs offer a window into the chemistry and crystallization conditions (P-T-H2O-fO2) of primitive basalts in the upper mantle and lower crust and can be studied in ancient exhumed terranes or in xenoliths erupted in young arc lavas. Here, we expand on previous studies and thoroughly characterize the extensive xenolith suites erupted from the Mt. Moffett and Mt. Adagdak volcanic centers (Adak Island, Central Aleutians), which range from primitive ultramafic cumulates to more evolved amphibole gabbros and hornblendites. We present detailed petrography as well as in situ trace and major element mineral chemistry. We use these data to calculate pressure, temperature, and fO2 estimates for the xenoliths, and compare these findings to experimental results to understand the crystallization sequence and P-T-H2O-fO2 under which the cumulates formed. The Moffett crystallization sequence is defined by early amphibole fractionation and an abrupt shift in oxide compositions from chromite to magnetite, while the Adagdak suite is characterized by simultaneous saturation of amphibole+plagioclase and oxide compositions that become increasingly aluminous before magnetite saturation. Olivine–spinel oxybarometry of the Adagdak xenoliths indicates that they are oxidized relative to MORB (FMQ +0.1 to +2.1). Highly fractionated REE and elevated Sr/Y ratios are observed in clinopyroxene from the most primitive cumulates, consistent with a contribution from a basaltic eclogite melt. This basaltic eclogite melt is hypothesized to come from partial melting of the slab or through melting of basalt introduced into the subarc mantle through forearc subduction erosion. These signatures are greatly diminished in the more evolved lithologies, which can be explained through fractionation of plagioclase and amphibole. Our findings support the presence of a complex magmatic plumbing system beneath Adak, with Mt. Moffett and Mt. Adagdak volcanic centers tapping compositionally distinct sources. More broadly, our results are consistent with studies suggesting that low-degree basaltic eclogite melts through slab melting or forearc subduction erosion contribute to arc magmas in the Aleutians, though the associated geochemical signatures are easily obscured by differentiation in the crust.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135695591","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":"Sheared Peridotites from northern Lesotho: Metasomatism-induced Deformation and Craton Destabilization","authors":"Catharina Heckel, Alan B Woodland, Jolien Linckens, Sally A Gibson, Hans-Michael Seitz","doi":"10.1093/petrology/egad076","DOIUrl":"https://doi.org/10.1093/petrology/egad076","url":null,"abstract":"Sheared peridotite xenoliths are snapshots of deformation processes that occur in the cratonic mantle shortly before their entrainment by kimberlites. The process of deformation that caused the shearing has, however, been highly debated since the 1970s and remains uncertain. To investigate the processes involved in the deformation, we have studied twelve sheared peridotites from Late Cretaceous (90 Ma) kimberlites in northern Lesotho, on the southeast margin of the Kaapvaal craton. Various deformation textures are represented, ranging from porphyroclastic to fluidal mosaic. Our sample suite consists of eleven garnet peridotites, with various amounts of clinopyroxene, and one garnet-free spinel peridotite with a small amount of clinopyroxene. All of the peridotites are depleted in Fe, and the Mg# of olivine and orthopyroxene range from 91 – 94. Three groups of sheared peridotites are present and have been identified primarily on the basis of Ca contents of olivine and orthopyroxene. The porphyroclasts preserve pre-deformation P-T conditions of 3.5 – 4.5 GPa and 900 – 1100°C (Group I), 5 – 5.5 GPa and 1200 – 1250°C (Group II) and 6±0.5 GPa and 1400±50°C (Group III). Group III samples lie above the 40mW/m² conductive geothermal gradient, indicating thermal perturbation prior to deformation.\u0000 The sheared peridotites from Lesotho were affected by various metasomatic events. Pre-deformation metasomatism, involving melts and fluids, is recorded in the porphyroclasts. In Group II and III samples the clinopyroxene porphyroclasts have similar compositions to Cr-rich and Cr-poor clinopyroxene megacrysts, respectively, that have previously described from southern African kimberlites. This suggests a relationship between them. Younger pre-deformation metasomatism is preserved in a zoned garnet from Group II (enrichment in Ti, Zr, Y+HREE) and orthopyroxene in a Group I sample. The latter exhibits a complex zonation, with a highly-enriched (Fe, Ti) inner rim and a less-enriched outer rim. These enrichments must have occurred shortly before deformation. Metasomatism during deformation is revealed by the complex chemical changes recorded in olivine neoblasts with, depending on the sample, increasing or decreasing contents of Ti, Ca, Al, Cr, Mn and Na. Crystallographic preferred orientations of olivine neoblasts are consistent with bimodal, B, C, E, AG-type fabrics and indicate the presence of a hydrous metasomatic agent.\u0000 We suggest that, akin to the shallower sheared peridotites (Group I), Group II and III were influenced by early (proto-)kimberlite melt pulses and propose the following model: (Proto-)kimberlitic melts invaded the lower lithosphere. These melts followed narrow shear zone networks, produced by deformation at the lithosphere-asthenosphere-boundary, heated and metasomatized the surrounding peridotites and were responsible for megacryst crystallization. Sheared peridotites from close to the melt conduits (Group III) have compositions comparable to C","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135662299","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}