Pub Date : 2024-03-28DOI: 10.1093/petrology/egae035
Cliff S J Shaw
Clinopyroxenite xenoliths comprised of cumulus clinopyroxene ± amphibole together with intercumulus phlogopite ± olivine ± apatite ± titanite form a large part of the xenolith load in the oldest deposits of the Rockeskyllerkopf Volcanic Complex (RVC) in the West Eifel volcanic field. The xenoliths also contain xenocrysts of olivine and clinopyroxene derived from mantle peridotite and clinopyroxene from lower crustal granulite. The clinopyroxenite xenoliths are divided into five groups on the basis of their modal mineralogy and mineral compositions. Groups 1 to 4 define a continuous compositional trend indicative of fractionation of a mafic alkaline magma. Group 5 xenoliths are compositionally distinct and have been tentatively linked to high pressure crystallization of phonolitic magma within the RVC system. Thermobarometry of the group 1 – 4 xenoliths indicates that they crystallised between 1 and 4 kilobars, equivalent to a depth of 4-14 km. Group 1 -3 xenoliths all crystallised at between 1050 and 1150 °C whereas the amphibole-rich group 4 xenoliths give temperature estimates of ~ 900 °C. The clinopyroxenites share a common parent magma with clinopyroxene – phlogopite veins found in subcontinental lithospheric mantle xenoliths. However, the vein forming mama was richer in incompatible elements, in particular Zr and Hf and is interpreted to be an early formed batch of magma with the clinopyroxenites crystallising from magma derived from the same mantle, which had been depleted by the earlier phase of melting. Intrusion of magma began around 155 ky prior to the eruption of the RVC. Fe-Mg interdiffusion profiles in zoned clinopyroxene show that the magma that formed the xenoliths was present in the crust for up to 28 ky prior to the eruption. However, most samples give interdiffusion times between 1.5 and 9.9 ky. Based on xenocryst residence times and the calculated P-T conditions for clinopyroxene, there were at least seven separate batches of magma emplaced below Rockeskyllerkopf, probably as sills.
{"title":"Clinopyroxenite xenoliths record magma transport and crystallisation in the middle and upper crust: A case study from the Rockeskyllerkopf Volcanic Complex, West Eifel, Germany","authors":"Cliff S J Shaw","doi":"10.1093/petrology/egae035","DOIUrl":"https://doi.org/10.1093/petrology/egae035","url":null,"abstract":"Clinopyroxenite xenoliths comprised of cumulus clinopyroxene ± amphibole together with intercumulus phlogopite ± olivine ± apatite ± titanite form a large part of the xenolith load in the oldest deposits of the Rockeskyllerkopf Volcanic Complex (RVC) in the West Eifel volcanic field. The xenoliths also contain xenocrysts of olivine and clinopyroxene derived from mantle peridotite and clinopyroxene from lower crustal granulite. The clinopyroxenite xenoliths are divided into five groups on the basis of their modal mineralogy and mineral compositions. Groups 1 to 4 define a continuous compositional trend indicative of fractionation of a mafic alkaline magma. Group 5 xenoliths are compositionally distinct and have been tentatively linked to high pressure crystallization of phonolitic magma within the RVC system. Thermobarometry of the group 1 – 4 xenoliths indicates that they crystallised between 1 and 4 kilobars, equivalent to a depth of 4-14 km. Group 1 -3 xenoliths all crystallised at between 1050 and 1150 °C whereas the amphibole-rich group 4 xenoliths give temperature estimates of ~ 900 °C. The clinopyroxenites share a common parent magma with clinopyroxene – phlogopite veins found in subcontinental lithospheric mantle xenoliths. However, the vein forming mama was richer in incompatible elements, in particular Zr and Hf and is interpreted to be an early formed batch of magma with the clinopyroxenites crystallising from magma derived from the same mantle, which had been depleted by the earlier phase of melting. Intrusion of magma began around 155 ky prior to the eruption of the RVC. Fe-Mg interdiffusion profiles in zoned clinopyroxene show that the magma that formed the xenoliths was present in the crust for up to 28 ky prior to the eruption. However, most samples give interdiffusion times between 1.5 and 9.9 ky. Based on xenocryst residence times and the calculated P-T conditions for clinopyroxene, there were at least seven separate batches of magma emplaced below Rockeskyllerkopf, probably as sills.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140322291","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-25DOI: 10.1093/petrology/egae031
Jackie M Kleinsasser, Adam C Simon, Dean Peterson, Amartya Kattemalavadi, Ian R Goan, Tobias Keller, George J Hudak, Kaitlin Koshurba
The Duluth Complex is a large mafic intrusive system located in northeastern Minnesota emplaced as part of the 1.1 Ga Midcontinent Rift. Several Fe-Ti oxide-bearing ultramafic intrusions are hosted along the Western Margin of the Duluth Complex, and are discordant bodies present in a variety of geometries, hosted in multiple rock types, and dominated by peridotite, pyroxenite, and semi-massive to massive Fe-Ti oxide rock types. Their origin has been debated, and here we present geochemical evidence and modeling that supports a purely magmatic origin for the Titac and Longnose Fe-Ti oxide-bearing ultramafic intrusions. Ilmenite and titanomagnetite textures indicate a protracted cooling process, and δ34S values of sulfides reveal little assimilation of the footwall Virginia Formation, a fine-grained pelitic unit that contains sulfide-rich bands. We model the crystallization of a hypothetical parental magma composition to the host intrusion of Longnose using Rhyolite-MELTS and demonstrate that the accumulation of Fe-Ti oxides in the discordant intrusions cannot be explained by density-driven segregation of crystallized Fe-Ti oxides. Instead, we show that the development of silicate liquid immiscibility, occurring by the unmixing of the silicate melt into conjugate Si- and Fe-rich melts, can result in the effective segregation and transportation of the Fe-rich melt. The Fe-rich melt is ~2 orders of magnitude less viscous than the Si-rich melt, allowing the Fe-rich melt to be more effectively segregated and transported in the mush regime (crystallinities > 50%). This suggests that viscosity, in addition to density, plays a significant role in forming the discordant Fe-Ti oxide-bearing ultramafic intrusions. We propose a genetic model that could also be responsible for the Fe-Ti oxide-rich layers or bands that are hosted within the igneous stratigraphy of mafic intrusions of the Duluth Complex.
德卢斯复合体是位于明尼苏达州东北部的大型岩浆侵入系统，是 1.1 Ga 中大陆裂谷的一部分。沿德卢斯复合体西缘有几处含铁钛氧化物的超基性侵入体，这些侵入体呈不和谐体，几何形态各异，赋存于多种岩石类型中，以橄榄岩、辉绿岩和半块状至块状铁钛氧化物岩石类型为主。它们的成因一直存在争议，在此，我们提出地球化学证据和模型，支持Titac和Longnose含铁钛氧化物超基性侵入体的纯岩浆成因。钛铁矿和榍石的纹理显示了一个漫长的冷却过程，而硫化物的δ34S值则显示了脚墙弗吉尼亚地层（包含富硫化物带的细粒辉长岩单元）的同化程度很低。我们使用 Rhyolite-MELTS 模拟了 Longnose 主侵入体的假定母岩浆成分的结晶过程，并证明不和谐侵入体中铁钛氧化物的累积不能用结晶铁钛氧化物的密度驱动偏析来解释。相反，我们证明了硅酸盐熔体不混合成共轭的富硅和富铁熔体所导致的硅酸盐液不溶解性的发展，可导致富铁熔体的有效偏析和运移。富Fe熔体的粘度比富Si熔体低约2个数量级，这使得富Fe熔体能够在蘑菇云状态（结晶度> 50%）下更有效地分离和运输。这表明，在形成不和谐的含铁钛氧化物超基性侵入体的过程中，除了密度之外，粘度也起着重要作用。我们提出了一个遗传模型，该模型也可能是德卢斯岩群黑云母侵入体火成岩地层中富含铁-钛氧化物层或带的成因。
{"title":"Genesis of Fe-Ti oxide-bearing ultramafic intrusions in the Duluth Complex, Minnesota, USA","authors":"Jackie M Kleinsasser, Adam C Simon, Dean Peterson, Amartya Kattemalavadi, Ian R Goan, Tobias Keller, George J Hudak, Kaitlin Koshurba","doi":"10.1093/petrology/egae031","DOIUrl":"https://doi.org/10.1093/petrology/egae031","url":null,"abstract":"The Duluth Complex is a large mafic intrusive system located in northeastern Minnesota emplaced as part of the 1.1 Ga Midcontinent Rift. Several Fe-Ti oxide-bearing ultramafic intrusions are hosted along the Western Margin of the Duluth Complex, and are discordant bodies present in a variety of geometries, hosted in multiple rock types, and dominated by peridotite, pyroxenite, and semi-massive to massive Fe-Ti oxide rock types. Their origin has been debated, and here we present geochemical evidence and modeling that supports a purely magmatic origin for the Titac and Longnose Fe-Ti oxide-bearing ultramafic intrusions. Ilmenite and titanomagnetite textures indicate a protracted cooling process, and δ34S values of sulfides reveal little assimilation of the footwall Virginia Formation, a fine-grained pelitic unit that contains sulfide-rich bands. We model the crystallization of a hypothetical parental magma composition to the host intrusion of Longnose using Rhyolite-MELTS and demonstrate that the accumulation of Fe-Ti oxides in the discordant intrusions cannot be explained by density-driven segregation of crystallized Fe-Ti oxides. Instead, we show that the development of silicate liquid immiscibility, occurring by the unmixing of the silicate melt into conjugate Si- and Fe-rich melts, can result in the effective segregation and transportation of the Fe-rich melt. The Fe-rich melt is ~2 orders of magnitude less viscous than the Si-rich melt, allowing the Fe-rich melt to be more effectively segregated and transported in the mush regime (crystallinities > 50%). This suggests that viscosity, in addition to density, plays a significant role in forming the discordant Fe-Ti oxide-bearing ultramafic intrusions. We propose a genetic model that could also be responsible for the Fe-Ti oxide-rich layers or bands that are hosted within the igneous stratigraphy of mafic intrusions of the Duluth Complex.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140297599","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-12DOI: 10.1093/petrology/egae023
Simon J E Large, Chetan L Nathwani, Jamie J Wilkinson, Thomas R Knott, Simon R Tapster, Yannick Buret
Subduction zone magmatism is a major control of volcanism, the generation of modern continental crust and the formation of economically important porphyry Cu-(Mo-Au) deposits. Reading the magmatic record of individual arc segments, and constraining the rates of magmatic changes, are critical in order to fully understand and quantify the processes that drive magma evolution in subduction settings during arc growth. This study focuses on the San Francisco Batholith and the Rio Blanco-Los Bronces porphyry deposit cluster in central Chile, which provides an igneous rock record over ~13.5 Myr of arc evolution. We use whole-rock geochemistry, zircon geochronology and Hf-isotope geochemistry to track changes in the crustal magmatic system of this arc segment during crustal thickening and porphyry Cu deposit formation. By combining the analytical dataset with Monte Carlo fractional crystallisation and assimilation fractional crystallisation modelling, we test a model for significant crustal involvement during magma evolution. Systematic and continuous increases in Dy/Yb, La/Yb, V/Sc and Sr/Y in the magmas over time indicate a transition in the main fractionation assemblage from plagioclase-dominated to amphibole-dominated that reflects deeper crystallisation and/or a higher melt water content. Concomitant decreases in εHf and Th/La as well as increasing Ba/Th are best explained by assimilation of progressively deeper crustal lithologies from low (Chilenia) to high Ba/Th (Cuyania) basement terranes. Our study highlights that an increasingly hydrous magma and a deepening locus of crustal magma differentiation and assimilation, driven by crustal thickening contemporaneous with increased tectonic convergence and ingression of the aseismic Juan Fernandez ridge, can account for all investigated aspects of the multi-Myr magmatic evolution leading up to the formation of the Rio Blanco-Los Bronces porphyry Cu deposits. Our findings corroborate the importance of high-pressure differentiation of hydrous magma for the formation of Andean-style porphyry deposits. Once magmas favourable for porphyry Cu mineralisation were generated in the lower crust, multiple episodes of efficient magma migration into the upper crust fed several, discrete, shallow magmatic-hydrothermal systems over ~3.5 Myr to form the world’s largest known Cu resource at Rio Blanco-Los Bronces.
俯冲带岩浆活动是火山活动、现代大陆地壳的生成以及具有重要经济价值的斑岩型铜（钼-金）矿床形成的主要控制因素。解读单个弧段的岩浆记录，并制约岩浆变化的速率，对于充分理解和量化弧长期间俯冲环境中岩浆演化的驱动过程至关重要。这项研究的重点是智利中部的旧金山岩浆岩和里奥布兰科-洛斯布朗塞斑岩矿床群，它们提供了约 13.5 Myr 的弧演化火成岩记录。我们利用全岩地球化学、锆石地质年代学和Hf-同位素地球化学来追踪该弧段在地壳增厚和斑岩铜矿床形成过程中地壳岩浆系统的变化。通过将分析数据集与蒙特卡洛分型结晶和同化分型结晶模型相结合，我们对岩浆演化过程中地壳的重要参与模型进行了测试。随着时间的推移，岩浆中的Dy/Yb、La/Yb、V/Sc和Sr/Y持续系统地增加，表明主要分馏组合从斜长石为主过渡到闪石为主，这反映了更深的结晶和/或更高的熔融水含量。εHf和Th/La的相应减少以及Ba/Th的相应增加最能解释从低Ba/Th（Chilenia）到高Ba/Th（Cuyania）基底地层岩性的逐渐深入同化。我们的研究强调，在地壳增厚的驱动下，岩浆含水量不断增加，地壳岩浆分化和同化的位置不断加深，与此同时，构造辐合加剧，无地震的胡安-费尔南德斯海脊侵入，这些因素可以解释导致 Rio Blanco-Los Bronces 斑岩铜矿床形成的多年岩浆演化的所有调查方面。我们的研究结果证实了含水岩浆高压分异对安第斯型斑岩矿床形成的重要性。一旦有利于斑岩型铜矿化的岩浆在下地壳产生，多次有效的岩浆迁移到上地壳，在大约3.5百万年的时间里，为几个离散的浅层岩浆-热液系统提供了能量，从而在Rio Blanco-Los Bronces形成了世界上已知的最大铜资源。
{"title":"Tectonic and crustal processes drive multi-million year arc magma evolution leading up to porphyry copper deposit formation in central Chile","authors":"Simon J E Large, Chetan L Nathwani, Jamie J Wilkinson, Thomas R Knott, Simon R Tapster, Yannick Buret","doi":"10.1093/petrology/egae023","DOIUrl":"https://doi.org/10.1093/petrology/egae023","url":null,"abstract":"Subduction zone magmatism is a major control of volcanism, the generation of modern continental crust and the formation of economically important porphyry Cu-(Mo-Au) deposits. Reading the magmatic record of individual arc segments, and constraining the rates of magmatic changes, are critical in order to fully understand and quantify the processes that drive magma evolution in subduction settings during arc growth. This study focuses on the San Francisco Batholith and the Rio Blanco-Los Bronces porphyry deposit cluster in central Chile, which provides an igneous rock record over ~13.5 Myr of arc evolution. We use whole-rock geochemistry, zircon geochronology and Hf-isotope geochemistry to track changes in the crustal magmatic system of this arc segment during crustal thickening and porphyry Cu deposit formation. By combining the analytical dataset with Monte Carlo fractional crystallisation and assimilation fractional crystallisation modelling, we test a model for significant crustal involvement during magma evolution. Systematic and continuous increases in Dy/Yb, La/Yb, V/Sc and Sr/Y in the magmas over time indicate a transition in the main fractionation assemblage from plagioclase-dominated to amphibole-dominated that reflects deeper crystallisation and/or a higher melt water content. Concomitant decreases in εHf and Th/La as well as increasing Ba/Th are best explained by assimilation of progressively deeper crustal lithologies from low (Chilenia) to high Ba/Th (Cuyania) basement terranes. Our study highlights that an increasingly hydrous magma and a deepening locus of crustal magma differentiation and assimilation, driven by crustal thickening contemporaneous with increased tectonic convergence and ingression of the aseismic Juan Fernandez ridge, can account for all investigated aspects of the multi-Myr magmatic evolution leading up to the formation of the Rio Blanco-Los Bronces porphyry Cu deposits. Our findings corroborate the importance of high-pressure differentiation of hydrous magma for the formation of Andean-style porphyry deposits. Once magmas favourable for porphyry Cu mineralisation were generated in the lower crust, multiple episodes of efficient magma migration into the upper crust fed several, discrete, shallow magmatic-hydrothermal systems over ~3.5 Myr to form the world’s largest known Cu resource at Rio Blanco-Los Bronces.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140115808","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-04DOI: 10.1093/petrology/egae028
Marie K Takach, Wendy A Bohrson, Frank J Spera, Marco Viccaro
The nearly continuous volcanic eruption record at Mt. Etna dating back ~700 years provides an excellent opportunity to investigate the geochemical evolution of a highly active volcano. Of particular interest is elucidating the cause of selective enrichment in alkali elements (K and Rb) and 87Sr/86Sr observed in various episodes of past activity. More recently, this alkali enrichment trend started to manifest in the 17th century and accelerated after 1971, and was accompanied by an increase in the volume, frequency, and explosivity of eruptions. Explanations for this signature include recharge of alkali-enriched magmas and/or crustal contamination from the subvolcanic basement. This study quantitatively examines the role of crustal contamination in post-1971 Etnean magma compositions via hundreds of open-system phase equilibria and trace element calculations based upon whole-rock major oxides, trace elements, 87Sr/86Sr ratios, and mineral compositional data. Available pre-1971 petrochemical data are satisfactorily reproduced by fractional crystallization of a high whole-rock MgO (12–17 wt.%), Ni (135–285 ppm), and Cr (920–1330 ppm) parental magma composition that is documented in Etna’s ~4-ka fall-stratified deposit. Observed post-1971 whole-rock and glass trends and phase equilibria are reproduced via modeled assimilation of a skarn and flysch mixture, lithologies that represent the uppermost 10–15 km of sedimentary rocks beneath Etna. Notably, models show that K2O (wt.%) and Rb (ppm) behave incompatibly during partial melting of skarn/flysch. Additionally, the observed elevation of 87Sr/86Sr in post-1971 samples is consistent with the addition of radiogenic Sr from wallrock partial melts. In best-fit models, which yield observed post-1971 K2O, Rb, and 87Sr/86Sr trends, ~17% anatectic melt is assimilated and there may be a subordinate stoped wallrock component of ≤2% (percentage is relative to the starting mass of pristine magma). Previous work has shown that metasomatized spinel lherzolite and garnet pyroxenite can be melted in different proportions to reproduce long- and short-term changes observed in Etna’s geochemical products. We propose that the alkali enrichment signature observed after 1971 can be fully explained through the combination of mantle heterogeneity and crustal contamination. In particular, up to ~20% crustal input coupled with mantle heterogeneity of primitive melts explains the geochemical signals quite well. The influence of crustal contamination on post-1971 lavas is, in part, the result of frequent recharge of magmas that thermally primed the middle to upper crust and enhanced its partial melting.
{"title":"The Role of Crustal Contamination Throughout the 1329–2005 CE Eruptive Record of Mt. Etna Volcano, Italy","authors":"Marie K Takach, Wendy A Bohrson, Frank J Spera, Marco Viccaro","doi":"10.1093/petrology/egae028","DOIUrl":"https://doi.org/10.1093/petrology/egae028","url":null,"abstract":"The nearly continuous volcanic eruption record at Mt. Etna dating back ~700 years provides an excellent opportunity to investigate the geochemical evolution of a highly active volcano. Of particular interest is elucidating the cause of selective enrichment in alkali elements (K and Rb) and 87Sr/86Sr observed in various episodes of past activity. More recently, this alkali enrichment trend started to manifest in the 17th century and accelerated after 1971, and was accompanied by an increase in the volume, frequency, and explosivity of eruptions. Explanations for this signature include recharge of alkali-enriched magmas and/or crustal contamination from the subvolcanic basement. This study quantitatively examines the role of crustal contamination in post-1971 Etnean magma compositions via hundreds of open-system phase equilibria and trace element calculations based upon whole-rock major oxides, trace elements, 87Sr/86Sr ratios, and mineral compositional data. Available pre-1971 petrochemical data are satisfactorily reproduced by fractional crystallization of a high whole-rock MgO (12–17 wt.%), Ni (135–285 ppm), and Cr (920–1330 ppm) parental magma composition that is documented in Etna’s ~4-ka fall-stratified deposit. Observed post-1971 whole-rock and glass trends and phase equilibria are reproduced via modeled assimilation of a skarn and flysch mixture, lithologies that represent the uppermost 10–15 km of sedimentary rocks beneath Etna. Notably, models show that K2O (wt.%) and Rb (ppm) behave incompatibly during partial melting of skarn/flysch. Additionally, the observed elevation of 87Sr/86Sr in post-1971 samples is consistent with the addition of radiogenic Sr from wallrock partial melts. In best-fit models, which yield observed post-1971 K2O, Rb, and 87Sr/86Sr trends, ~17% anatectic melt is assimilated and there may be a subordinate stoped wallrock component of ≤2% (percentage is relative to the starting mass of pristine magma). Previous work has shown that metasomatized spinel lherzolite and garnet pyroxenite can be melted in different proportions to reproduce long- and short-term changes observed in Etna’s geochemical products. We propose that the alkali enrichment signature observed after 1971 can be fully explained through the combination of mantle heterogeneity and crustal contamination. In particular, up to ~20% crustal input coupled with mantle heterogeneity of primitive melts explains the geochemical signals quite well. The influence of crustal contamination on post-1971 lavas is, in part, the result of frequent recharge of magmas that thermally primed the middle to upper crust and enhanced its partial melting.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140074593","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-02DOI: 10.1093/petrology/egae020
Gregor Weber, Jon Blundy
Experimentally calibrated models to recover pressures and temperatures of magmas, are widely used in igneous petrology. However, large errors, especially in barometry, limit the capacity of these models to resolve the architecture of crustal igneous systems. Here we apply machine learning to a large experimental database to calibrate new regression models that recover P-T of magmas based on melt composition plus associated phase assemblage. The method is applicable to compositions from basalt to rhyolite, pressures from 0.2 to 15 kbar, and temperatures of 675-1400°C. Testing and optimisation of the model with a filter that removes estimates with standard deviation above the 50th percentile show that pressures can be recovered with root-mean-square-error (RMSE) of 1.1-1.3 kbar and errors on temperature estimates of 21°C. Our findings demonstrate that, given constraints on the coexisting mineral assemblage melt chemistry, is a reliable recorder of magmatic variables. This is a consequence of the relatively low thermodynamic variance of natural magma compositions despite their relatively large number of constituent oxide components. We apply our model to two contrasting cases with well-constrained geophysical information: Mount St. Helens volcano (USA), and Askja caldera in Iceland. Dacite whole-rocks from Mount St Helens erupted 1980-1986, inferred to represent liquids extracted from cpx-hbl-opx-plag-mt-ilm mush, yield melt extraction source pressures of 5.1-6.7 kbar in excellent agreement with geophysical constraints. Melt inclusions and matrix glasses record lower pressures (0.7-3.8 kbar), consistent with magma crystallisation within the upper reaches of the imaged geophysical anomaly and during ascent. Magma reservoir depth estimates for historical eruptions from Askja match the location of seismic wave speed anomalies. Vp/Vs anomalies at 5-10 km depth correspond to hot (~990°C) rhyolite source regions, while basaltic magmas (~1120°C) were stored at 7-17 km depth under the caldera. These examples illustrate how our model can link petrology and geophysics to better constrain the architecture of volcanic feeding systems. Our model (MagMaTaB) is accessible through a user-friendly web application (https://igdrasil.shinyapps.io/MagmaTaBv4/).
{"title":"A machine learning-based thermobarometer for magmatic liquids","authors":"Gregor Weber, Jon Blundy","doi":"10.1093/petrology/egae020","DOIUrl":"https://doi.org/10.1093/petrology/egae020","url":null,"abstract":"Experimentally calibrated models to recover pressures and temperatures of magmas, are widely used in igneous petrology. However, large errors, especially in barometry, limit the capacity of these models to resolve the architecture of crustal igneous systems. Here we apply machine learning to a large experimental database to calibrate new regression models that recover P-T of magmas based on melt composition plus associated phase assemblage. The method is applicable to compositions from basalt to rhyolite, pressures from 0.2 to 15 kbar, and temperatures of 675-1400°C. Testing and optimisation of the model with a filter that removes estimates with standard deviation above the 50th percentile show that pressures can be recovered with root-mean-square-error (RMSE) of 1.1-1.3 kbar and errors on temperature estimates of 21°C. Our findings demonstrate that, given constraints on the coexisting mineral assemblage melt chemistry, is a reliable recorder of magmatic variables. This is a consequence of the relatively low thermodynamic variance of natural magma compositions despite their relatively large number of constituent oxide components. We apply our model to two contrasting cases with well-constrained geophysical information: Mount St. Helens volcano (USA), and Askja caldera in Iceland. Dacite whole-rocks from Mount St Helens erupted 1980-1986, inferred to represent liquids extracted from cpx-hbl-opx-plag-mt-ilm mush, yield melt extraction source pressures of 5.1-6.7 kbar in excellent agreement with geophysical constraints. Melt inclusions and matrix glasses record lower pressures (0.7-3.8 kbar), consistent with magma crystallisation within the upper reaches of the imaged geophysical anomaly and during ascent. Magma reservoir depth estimates for historical eruptions from Askja match the location of seismic wave speed anomalies. Vp/Vs anomalies at 5-10 km depth correspond to hot (~990°C) rhyolite source regions, while basaltic magmas (~1120°C) were stored at 7-17 km depth under the caldera. These examples illustrate how our model can link petrology and geophysics to better constrain the architecture of volcanic feeding systems. Our model (MagMaTaB) is accessible through a user-friendly web application (https://igdrasil.shinyapps.io/MagmaTaBv4/).","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140018042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Pleiades Volcanic Field (PVF) of northern Victoria Land (Antarctica) is made up of a dozen scoria cones whose erupted products present an unusually complete evolutionary trend from alkali-basalt to trachyte. With the aim of reconstructing the evolution of the PVF plumbing system, we have investigated the petrography and chemistry of main mineral phases using SEM-EDS coupled with major (EPMA-WDS) element analyses. We further focussed on clinopyroxene phenocrysts obtaining a more detailed characterisation by means of trace (LA-ICP-MS) element analyses coupled with machine learning thermobarometry. The results indicate that fractional crystallisation and magma mixing are the major processes determining the development of the complete evolution trend. While fractional crystallisation is a persistently active process in all parts of the plumbing system, mixing among differently evolved magma batches pertaining to the same association is responsible for the formation of intermediate compositions in the differentiation lineage at a specific pressure range (0.4-0.5 GPa). These processes are compatible with significant residence time of magmas at depth, resulting in multiple episodes of magma mixing, as testified by resorption and overgrowth textures in phenocryst assemblage occurring under isobaric conditions. The prolonged residence time likely increased the efficiency of the mixing process, leading to the formation of magmas with intermediate composition. In turn, the build-up of volatiles during the magma differentiation at depth could have favoured the eruption of these (variably differentiated) magmas. Considering that the PVF is situated in a glacial region, a process forcing long magma residence time can be envisaged associated with increased ice loading during glacial stages. This study specifically considers the ice fluctuations in the last 100 ka, theorising the possibility of a climate-controlled volcano plumbing system.
南极洲维多利亚陆地北部的昴宿星团火山场（PVF）由十几个火山灰锥组成，其喷发产物呈现出从碱性玄武岩到斜长岩的异常完整的演化趋势。为了重建 PVF 管道系统的演化过程，我们利用扫描电镜-电子显微镜和主要（EPMA-WDS）元素分析，对主要矿物相的岩相学和化学性质进行了研究。我们还通过痕量（LA-ICP-MS）元素分析和机器学习热压测量法，对陨石表晶进行了更详细的表征。结果表明，碎裂结晶和岩浆混合是决定完整演化趋势发展的主要过程。在管道系统的所有部分，碎裂结晶都是一个持续活跃的过程，而在特定的压力范围（0.4-0.5 GPa）内，属于同一联合体的不同演化岩浆批次之间的混合则是形成分异系中间成分的原因。这些过程与岩浆在深部的大量停留时间相适应，从而导致岩浆的多次混合，在等压条件下发生的表晶集合体的吸收和过度生长纹理就证明了这一点。停留时间的延长可能会提高混合过程的效率，从而形成具有中间成分的岩浆。反过来，岩浆在深部分化过程中挥发物的积累可能有利于这些（不同分化的）岩浆的喷发。考虑到滨海火山带位于冰川地区，可以设想在冰川期冰负荷增加的情况下，岩浆停留时间较长。本研究特别考虑了过去 100 ka 年的冰层波动，推测了气候控制火山管道系统的可能性。
{"title":"Textures and chemistry of crystal cargo of The Pleiades Volcanic Field, Antarctica: potential influence of ice load in modulating the plumbing system","authors":"Rocchi Irene, Tomassini Alice, Masotta Matteo, Petrelli Maurizio, Ágreda López Mónica, Rocchi Sergio","doi":"10.1093/petrology/egae027","DOIUrl":"https://doi.org/10.1093/petrology/egae027","url":null,"abstract":"The Pleiades Volcanic Field (PVF) of northern Victoria Land (Antarctica) is made up of a dozen scoria cones whose erupted products present an unusually complete evolutionary trend from alkali-basalt to trachyte. With the aim of reconstructing the evolution of the PVF plumbing system, we have investigated the petrography and chemistry of main mineral phases using SEM-EDS coupled with major (EPMA-WDS) element analyses. We further focussed on clinopyroxene phenocrysts obtaining a more detailed characterisation by means of trace (LA-ICP-MS) element analyses coupled with machine learning thermobarometry. The results indicate that fractional crystallisation and magma mixing are the major processes determining the development of the complete evolution trend. While fractional crystallisation is a persistently active process in all parts of the plumbing system, mixing among differently evolved magma batches pertaining to the same association is responsible for the formation of intermediate compositions in the differentiation lineage at a specific pressure range (0.4-0.5 GPa). These processes are compatible with significant residence time of magmas at depth, resulting in multiple episodes of magma mixing, as testified by resorption and overgrowth textures in phenocryst assemblage occurring under isobaric conditions. The prolonged residence time likely increased the efficiency of the mixing process, leading to the formation of magmas with intermediate composition. In turn, the build-up of volatiles during the magma differentiation at depth could have favoured the eruption of these (variably differentiated) magmas. Considering that the PVF is situated in a glacial region, a process forcing long magma residence time can be envisaged associated with increased ice loading during glacial stages. This study specifically considers the ice fluctuations in the last 100 ka, theorising the possibility of a climate-controlled volcano plumbing system.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140044320","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}
Pub Date : 2024-03-01DOI: 10.1093/petrology/egae029
{"title":"Correction to: The Effects of Partial Melting and Metasomatism on Peridotite Water Contents: Insights from Shuangliao Volcano Group, Northeast China","authors":"","doi":"10.1093/petrology/egae029","DOIUrl":"https://doi.org/10.1093/petrology/egae029","url":null,"abstract":"","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140275727","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}
Pub Date : 2024-03-01DOI: 10.1093/petrology/egae024
Gong-Jian Tang, Derek A Wyman, Wei Dan, Qiang Wang, Xi-Jun Liu, Ya-Nan Yang, Mustafo Gadoev, Ilhomjon Oimahmadov
Determining crustal melting in parallel with geodynamic evolution provides critical information on plateau crustal thickening and uplift. Here we investigate the timing and duration of crustal melting through in-situ analysis of zircon U-Pb ages, trace elements and Hf-O isotopes, and whole-rock elements and Sr-Nd-Hf isotopes for the granites and high-grade metamorphic rocks from the Pamir Plateau. Zircon dates record protracted crustal melting for both Central Pamir (43–33 Ma and 22–12 Ma) and South Pamir (28–10 Ma). The Pamir Cenozoic granites are characterized by significant elemental and isotopic heterogeneity. The elemental variability within the Pamir Cenozoic granites is attributed to fractional crystallization of dominantly K-feldspar and plagioclase with subordinate biotite from a variably fractionated melt, and the accumulation of early crystallized feldspar during magma ascent. Peritectic mineral entrainment and accessory mineral crystallization had some influence on the geochemical characteristics of the garnet-bearing leucogranite dikes. Zircon Hf isotopes and whole-rock Sr-Nd-Hf isotopes show secular variations for both Central and South Pamir granites. The Central Pamir granites show a mild decrease in whole-rock ƐNd(t) values from Eocene (-4.3 to -4.9) to Miocene (-6.2 to -7.7), and the zircon ƐHf(t) values decrease from c. 40 Ma (+2 to -5) to c. 10 Ma (-4 to -8). In contrast, the South Pamir granites have highly variable whole-rock Sr-Nd-Hf (87Sr/86Sr(i) = 0.70530 to 0.78302; ƐNd(t) = -31.5 to +0.2; ƐHf(t) = -40.0 to +8.2) and zircon Hf isotopes (ƐHf(t) = +7.5 to -31.7) and displays a strong decrease in ƐNd(t) and ƐHf(t) values from c. 25 Ma to c. 13 Ma. Geochemical and isotopic data indicate that both the Central and South Pamir experienced crustal melting from juvenile lower crust to ancient lower-middle crustal materials, and Indian crustal materials were incorporated into the melt region of the South Pamir leucogranites from c. 20 Ma. Our study highlights a causal link between a chain of events that includes magma underplating induced by lithosphere thinning and slab breakoff, lithosphere delamination and underthrusting of Indian lithosphere, and formation of the Cenozoic granites in Pamir. This series of processes are incorporated here into a comprehensive model for the geodynamic evolution of the Pamir during the India-Asia collision.
{"title":"Protracted and progressive crustal melting during continental collision in the Pamir and plateau growth","authors":"Gong-Jian Tang, Derek A Wyman, Wei Dan, Qiang Wang, Xi-Jun Liu, Ya-Nan Yang, Mustafo Gadoev, Ilhomjon Oimahmadov","doi":"10.1093/petrology/egae024","DOIUrl":"https://doi.org/10.1093/petrology/egae024","url":null,"abstract":"Determining crustal melting in parallel with geodynamic evolution provides critical information on plateau crustal thickening and uplift. Here we investigate the timing and duration of crustal melting through in-situ analysis of zircon U-Pb ages, trace elements and Hf-O isotopes, and whole-rock elements and Sr-Nd-Hf isotopes for the granites and high-grade metamorphic rocks from the Pamir Plateau. Zircon dates record protracted crustal melting for both Central Pamir (43–33 Ma and 22–12 Ma) and South Pamir (28–10 Ma). The Pamir Cenozoic granites are characterized by significant elemental and isotopic heterogeneity. The elemental variability within the Pamir Cenozoic granites is attributed to fractional crystallization of dominantly K-feldspar and plagioclase with subordinate biotite from a variably fractionated melt, and the accumulation of early crystallized feldspar during magma ascent. Peritectic mineral entrainment and accessory mineral crystallization had some influence on the geochemical characteristics of the garnet-bearing leucogranite dikes. Zircon Hf isotopes and whole-rock Sr-Nd-Hf isotopes show secular variations for both Central and South Pamir granites. The Central Pamir granites show a mild decrease in whole-rock ƐNd(t) values from Eocene (-4.3 to -4.9) to Miocene (-6.2 to -7.7), and the zircon ƐHf(t) values decrease from c. 40 Ma (+2 to -5) to c. 10 Ma (-4 to -8). In contrast, the South Pamir granites have highly variable whole-rock Sr-Nd-Hf (87Sr/86Sr(i) = 0.70530 to 0.78302; ƐNd(t) = -31.5 to +0.2; ƐHf(t) = -40.0 to +8.2) and zircon Hf isotopes (ƐHf(t) = +7.5 to -31.7) and displays a strong decrease in ƐNd(t) and ƐHf(t) values from c. 25 Ma to c. 13 Ma. Geochemical and isotopic data indicate that both the Central and South Pamir experienced crustal melting from juvenile lower crust to ancient lower-middle crustal materials, and Indian crustal materials were incorporated into the melt region of the South Pamir leucogranites from c. 20 Ma. Our study highlights a causal link between a chain of events that includes magma underplating induced by lithosphere thinning and slab breakoff, lithosphere delamination and underthrusting of Indian lithosphere, and formation of the Cenozoic granites in Pamir. This series of processes are incorporated here into a comprehensive model for the geodynamic evolution of the Pamir during the India-Asia collision.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140018338","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}
Pub Date : 2024-02-29DOI: 10.1093/petrology/egae019
Stephen J Barnes, Morgan Williams
According to the “trapped liquid” paradigm, whole-rock chemical compositions of cumulate rocks in layered intrusions can be represented as closed-system multicomponent mixtures of the cumulus phases and the liquids from which they crystallised. Alternative open-system models for cumulate solidification assert that intercumulus liquid is continuously mobile as a result of compaction of crystal mushes. In the closed-system models, all excluded elements, i.e. those incompatible in the cumulus phases, should be correlated with one another, whereas in open systems the more incompatible elements should be decoupled from the more compatible ones and correlations should be poor. These alternative hypotheses are tested using a database of more than 63,000 whole-rock analyses of mostly ultramafic cumulates from a single package of layers across the entire width of the Mirabela layered intrusion, a 2.5 km wide by >2 km thick intrusion with Great Dyke-like stratigraphy. Variably compatible elements Al, Na, Ti and P are found to show strong correlations with one other in olivine-pyroxene cumulates across the spectrum from mesocumulate to orthocumulate rocks, where drill-core sample intervals are composited over 3m; weaker correlations are found over 1m sample intervals. The closed-system trapped liquid model is robust for this suite of rocks at the scale of 3m lengths of drill core (approx. 1 kg of sample). Furthermore, a very smooth and symmetrical variation is observed from dominantly ad- to mesocumulate rocks in the geometrical centre of the intrusion towards orthocumulates at both margins, attributable to increase in cooling rate towards the margins. The most adcumulate rocks are gabbronorites at the base of the mafic sequence in the centre of the intrusion. There is no corresponding decrease in layer thickness towards the centre that would be predicted by a compaction model. The only incompatible element showing partial decoupling is K, which appears to have been mobile at a very late stage, probably in an aqueous fluid phase. There is no evidence for mobilisation of PGEs or other chalcophile elements by this fluid despite the presence of disseminated sulfide throughout the sampled interval.
{"title":"Postcumulus processes recorded in whole-rock geochemistry: a case study from the Mirabela layered intrusion, Brazil","authors":"Stephen J Barnes, Morgan Williams","doi":"10.1093/petrology/egae019","DOIUrl":"https://doi.org/10.1093/petrology/egae019","url":null,"abstract":"According to the “trapped liquid” paradigm, whole-rock chemical compositions of cumulate rocks in layered intrusions can be represented as closed-system multicomponent mixtures of the cumulus phases and the liquids from which they crystallised. Alternative open-system models for cumulate solidification assert that intercumulus liquid is continuously mobile as a result of compaction of crystal mushes. In the closed-system models, all excluded elements, i.e. those incompatible in the cumulus phases, should be correlated with one another, whereas in open systems the more incompatible elements should be decoupled from the more compatible ones and correlations should be poor. These alternative hypotheses are tested using a database of more than 63,000 whole-rock analyses of mostly ultramafic cumulates from a single package of layers across the entire width of the Mirabela layered intrusion, a 2.5 km wide by >2 km thick intrusion with Great Dyke-like stratigraphy. Variably compatible elements Al, Na, Ti and P are found to show strong correlations with one other in olivine-pyroxene cumulates across the spectrum from mesocumulate to orthocumulate rocks, where drill-core sample intervals are composited over 3m; weaker correlations are found over 1m sample intervals. The closed-system trapped liquid model is robust for this suite of rocks at the scale of 3m lengths of drill core (approx. 1 kg of sample). Furthermore, a very smooth and symmetrical variation is observed from dominantly ad- to mesocumulate rocks in the geometrical centre of the intrusion towards orthocumulates at both margins, attributable to increase in cooling rate towards the margins. The most adcumulate rocks are gabbronorites at the base of the mafic sequence in the centre of the intrusion. There is no corresponding decrease in layer thickness towards the centre that would be predicted by a compaction model. The only incompatible element showing partial decoupling is K, which appears to have been mobile at a very late stage, probably in an aqueous fluid phase. There is no evidence for mobilisation of PGEs or other chalcophile elements by this fluid despite the presence of disseminated sulfide throughout the sampled interval.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-02-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140008027","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}
The major- and trace-element compositions of amphiboles in andesite from Quaternary Yufu Volcano, northeastern Kyushu, Japan were analysed to investigate the generation processes of andesitic magma from Yufu Volcano. The amphiboles in andesite from Yufu volcano can be divided into two groups based on major-element composition: pargasite and magnesio-hornblende. To estimate temperature, pressure, and major- and trace-element compositions of melts in equilibrium with amphiboles, we used the recently proposed methods that can calculate temperature, pressure, major element compositions, and partition coefficients of trace-element between amphibole and melt using only the major-element compositions of amphibole. The estimated temperature, pressure, and major-element composition of melt in equilibrium with the amphibole phenocrysts indicate that each group crystallised under different conditions. These differences suggest that two magma chambers at different depths existed beneath Yufu Volcano and that the andesitic magma of Yufu Volcano was formed by mixing of the two magmas. The trace-element compositions of melts in equilibrium with the pargasite and magnesio-hornblende, estimated by applying the partition coefficients calculated from major-element compositions of amphibole to trace-element compositions of amphiboles, indicate magma derived from slab melt and the partial melting of crustal material, respectively. Because magma is a mixture of minerals and melt, we estimate the chemical compositional ranges of the two end-member magmas on the Y versus SiO2 diagram from the mixing relationship between amphibole and estimated melt, as well as phenocrysts of plagioclase, clinopyroxene, and orthopyroxene. The overlap of the estimated compositional range with the whole-rock composition represents the chemical compositions of the end-members of magma mixing, yielding estimates of the mafic (SiO2 ≈ 45 wt%) and felsic (SiO2 ≈ 68 wt%) end-member magmas. Furthermore, we estimate the concentrations of other elements in the end-member magmas by substituting the estimated SiO2 concentrations of the magmas into linear regression equations between the whole-rock contents of other elements and SiO2. The trace-element compositions of the mafic and felsic end-member magmas, as estimated in this study, have similar features to those of gabbroids and Cretaceous granitic rocks, respectively, that are presumed to lie beneath Yufu Volcano. These similarities could be explained by the possibility that the compositions of the end-member magmas were influenced by basement rocks.
{"title":"Genesis of andesitic magma erupted at Yufu Volcano, Kyushu Island, Southwest Japan arc: Evidence from the chemical compositions of amphibole phenocrysts","authors":"Ikuo Okada, Tomoyuki Shibata, Masako Yoshikawa, Hidemi Ishibashi, Takeshi Sugimoto, Yasutaka Hayasaka","doi":"10.1093/petrology/egae018","DOIUrl":"https://doi.org/10.1093/petrology/egae018","url":null,"abstract":"The major- and trace-element compositions of amphiboles in andesite from Quaternary Yufu Volcano, northeastern Kyushu, Japan were analysed to investigate the generation processes of andesitic magma from Yufu Volcano. The amphiboles in andesite from Yufu volcano can be divided into two groups based on major-element composition: pargasite and magnesio-hornblende. To estimate temperature, pressure, and major- and trace-element compositions of melts in equilibrium with amphiboles, we used the recently proposed methods that can calculate temperature, pressure, major element compositions, and partition coefficients of trace-element between amphibole and melt using only the major-element compositions of amphibole. The estimated temperature, pressure, and major-element composition of melt in equilibrium with the amphibole phenocrysts indicate that each group crystallised under different conditions. These differences suggest that two magma chambers at different depths existed beneath Yufu Volcano and that the andesitic magma of Yufu Volcano was formed by mixing of the two magmas. The trace-element compositions of melts in equilibrium with the pargasite and magnesio-hornblende, estimated by applying the partition coefficients calculated from major-element compositions of amphibole to trace-element compositions of amphiboles, indicate magma derived from slab melt and the partial melting of crustal material, respectively. Because magma is a mixture of minerals and melt, we estimate the chemical compositional ranges of the two end-member magmas on the Y versus SiO2 diagram from the mixing relationship between amphibole and estimated melt, as well as phenocrysts of plagioclase, clinopyroxene, and orthopyroxene. The overlap of the estimated compositional range with the whole-rock composition represents the chemical compositions of the end-members of magma mixing, yielding estimates of the mafic (SiO2 ≈ 45 wt%) and felsic (SiO2 ≈ 68 wt%) end-member magmas. Furthermore, we estimate the concentrations of other elements in the end-member magmas by substituting the estimated SiO2 concentrations of the magmas into linear regression equations between the whole-rock contents of other elements and SiO2. The trace-element compositions of the mafic and felsic end-member magmas, as estimated in this study, have similar features to those of gabbroids and Cretaceous granitic rocks, respectively, that are presumed to lie beneath Yufu Volcano. These similarities could be explained by the possibility that the compositions of the end-member magmas were influenced by basement rocks.","PeriodicalId":16751,"journal":{"name":"Journal of Petrology","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-02-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140007894","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}
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