Journal of Metamorphic Geology最新文献

{"title":"Interplay Between Mechanical and Petrochemical Models on the Fluid Extraction From Subduction Zones","authors":"Thorsten Andreas Markmann,&nbsp;Pierre Lanari","doi":"10.1111/jmg.70015","DOIUrl":"https://doi.org/10.1111/jmg.70015","url":null,"abstract":"<p>The breakdown of hydrous minerals during subduction results in a densification of the rocks, producing volume changes that can trigger fluid pressure fluctuations and hydrofracturing. These volume changes are controlled by the Clapeyron slope of the reaction and are quantified here using a macroscopic framework that integrates a zero-dimensional mechanical model and a one-dimensional petrological model. A Mohr–Coulomb–based mechanical model is coupled with phase equilibrium calculations (Theriak-Domino), oxygen isotope fractionation and trace element partitioning, using the compressed compensated Redlich–Kwong (CORK) equation of state to describe fluid properties. This model can predict fluid pressure fluctuations and brittle-failure events from successive Gibbs free energy minimisations while accounting for tensile strength and differential stress in the mechanical model. The code is released as an open-source Python library ThorPT. For intermediate subduction geotherms, results indicate up to 5 vol.% fluid-filled porosity without brittle failure, consistent with findings from several geophysical studies. In basalts and serpentinites, the calculated time-averaged permeability values show intermittent episodes of permeability exceeding 10⁻¹⁹ m². In serpentinite, the permeability increase can be attributed to olivine formation. In mafic rocks, episodes of increased permeability are associated with the breakdown of chlorite, amphibole and lawsonite during the transition from blueschist to eclogite. In the case of warm subduction geotherms, the model results show a strong correlation between dehydration-driven brittle failure, fluid migration and seismicity, particularly in the mafic crust. The blueschist–eclogite transition is associated with intense brittle failure, matching geothermal and geophysical models linking this depth range to seismic double layers. Our results highlight the coupled mechanism of dehydration reaction and brittle failure as a driver of episodic fluid extraction, with broad implications for fluid–rock interaction and mass transfer in subduction zones.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"44 2","pages":"85-111"},"PeriodicalIF":3.4,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.70015","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146139844","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Microscale Variations in Eclogite-Facies Trace Element Redistribution Controlled by Mineral Banding","authors":"Andrea E. Goltz,&nbsp;Will F. Hoover,&nbsp;F. Zeb Page,&nbsp;Alicia Cruz-Uribe,&nbsp;Kouki Kitajima","doi":"10.1111/jmg.70012","DOIUrl":"https://doi.org/10.1111/jmg.70012","url":null,"abstract":"<div>\u0000 \u0000 <p>Microanalysis of trace elements in garnet can yield new and important insights into the kinetics of garnet growth, metamorphic reactions and fluid–rock interaction in subduction zones; however, differentiating the effects of these processes on a garnet-by-garnet basis can be challenging. In this study, we couple microanalyses of trace elements and stable oxygen isotopes in garnet to isolate the causes of trace element variation in mineralogically banded blueschists and eclogites from the Franciscan Complex. Trace element variations in garnet are not apparently driven by interaction with externally derived fluids as recorded by rimward decreases in δ¹⁸O and can be best explained by local mineral reactions. Intrasample heterogeneity in garnet trace element zoning patterns can be attributed to localized differences in mineral assemblages, which impact the availability of trace elements to growing garnets. These mineralogical heterogeneities also control the extent of reaction with externally derived fluid and resulting δ¹⁸O zoning patterns through differences in reaction-induced porosity. Our study highlights the importance of linking petrography to advanced microanalysis and has important implications for understanding the chemical composition and physical pathways of fluids in the eclogitized downgoing slab.</p>\u0000 </div>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"44 1","pages":"47-69"},"PeriodicalIF":3.4,"publicationDate":"2025-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145983946","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":"Ultrahigh-Temperature Metamorphism and Near-Isobaric Cooling of Garnet-Orthopyroxene Granulite Xenoliths in the Sancheong Anorthosite, Yeongnam Massif, Korea","authors":"Yuyoung Lee,&nbsp;Moonsup Cho,&nbsp;Jeongmin Kim,&nbsp;Youn-Joong Jeong","doi":"10.1111/jmg.70014","DOIUrl":"https://doi.org/10.1111/jmg.70014","url":null,"abstract":"<p>Elevated heat flow associated with mafic magmatism in accretionary orogens has often been proposed as a driving mechanism for (ultra)high-temperature (UHT) metamorphism and anatexis. The Sancheong–Hadong complex, located in the southern Yeongnam Massif, Korea, consists of a ca. 1.87–1.86 Ga anorthosite–mangerite–charnockite–granite (AMCG) suite hosted by granulite-facies gneisses. We present new evidence for UHT metamorphism and near-isobaric cooling in garnet-orthopyroxene granulite xenoliths entrained in the Sancheong anorthosite. These xenoliths record partial melting, typified by leucosomes containing peritectic garnet and orthopyroxene. The development of garnet coronas or garnet-quartz symplectites at the orthopyroxene-plagioclase interface in the granulite reflects near-isobaric cooling under a low f_H2O condition. <i>P–T</i> pseudosection modelling of a garnet-orthopyroxene granulite reveals peak metamorphic conditions of 900°C–930°C and ~8.0 kbar, followed by near-isobaric cooling and melt crystallization at 800°C–830°C and ~7.4 kbar. Such a UHT condition is further supported by zircon crystallization temperatures of ~900 ± 30°C, estimated from Ti-in-zircon thermometry. Zircons in the granulite and leucosome are distinctly zoned into three domains (cores, inner rims and outer rims) that reflect successive recrystallization under high-temperature conditions. U(–Th)–Pb dating of zircon and monazite from two garnet-orthopyroxene granulites and one leucosome yields weighted mean ages of 1861 ± 5 Ma (<i>n</i> = 9) and 1863 ± 12 Ma (<i>n</i> = 3), respectively, coeval with the emplacement of anorthosite at 1861 ± 2 Ma. This result suggests an almost complete resetting of the U–Pb systematics during the transient UHT event at ~1860 Ma. The δ¹⁸O values of zircon in the granulite are uniform at 8.15 ± 0.11‰ (<i>n</i> = 83). Together with the zircon ɛ_Hf(t) values ranging from −7.0 to −0.3, such an elevated δ¹⁸O value indicates a derivation from crustal sources. Zircon rims in the leucosome yield slightly lower δ¹⁸O values (7.67 ± 0.10‰; <i>n</i> = 17) which are consistent with 7.52 ± 0.14‰ (<i>n</i> = 20) estimated from monazites of the granulite. In contrast, monazite from the leucosome has an even lower δ¹⁸O value of 6.57 ± 0.43‰. These results suggest that δ¹⁸O values decrease during cooling and melt crystallization, most likely due to the influx of lower δ¹⁸O juvenile fluids and/or melts during AMCG emplacement. Taken together, the lower crustal xenoliths of the southern Yeongnam Massif underwent UHT metamorphism and anatexis at ~1860 Ma, accompanied by anorthosite emplacement, within the context of a prolonged melt-bearing system during the late stage of the Paleoproterozoic hot orogenesis in the North China Craton.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"44 1","pages":"20-46"},"PeriodicalIF":3.4,"publicationDate":"2025-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.70014","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145983971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Vanishing Evidence of Ultrahigh-Pressure Metamorphism: A Case Study of the Rhodope Metamorphic Complex, Greece","authors":"Emily M. Peterman,&nbsp;Michael L. Williams,&nbsp;Andrew R. C. Kylander-Clark","doi":"10.1111/jmg.70011","DOIUrl":"https://doi.org/10.1111/jmg.70011","url":null,"abstract":"<div>\u0000 \u0000 <p>Evidence of metamorphism at ultrahigh-pressure (UHP) conditions is documented by the presence of coesite, diamond and/or majoritic garnet. However, the growth of UHP-stable phases such as majoritic garnet is often volumetrically low, and overprinting during exhumation can obscure evidence of UHP growth, making it difficult to positively identify UHP rocks. In this study, we selected garnet-kyanite schists from three microdiamond-bearing localities within the Rhodope Metamorphic Complex, located in eastern Greece. Samples from Xanthi, Sidironero, and Kimi have similar bulk rock compositions, but the pressure–temperature (P–T) paths differ. Because the major phases record vanishingly little evidence of metamorphism at UHP conditions, we analyzed zircon grains with complex textures to evaluate if zircon preserves a record of UHP metamorphism. Zircon grains from all localities have cores and rims separated by a characteristic interface domain, as revealed by cathodoluminescence (CL) imaging. The detrital igneous cores range in age from c. 2.5 Ga to 220 Ma and exhibit a negative Eu* anomaly, a Yb/Gd of 10–100, and variable Th/U (0–1.2). Rims yield dates of 150–125 Ma with Yb/Gd of 0.1–10 and Th/U of 0–0.2. Interface domains yield dates 165–145 Ma with Yb/Gd ranging between 0–1000 and Th/U &lt; 0.2. We interpret the distinctive CL textures and Yb/Gd of the interface domains as evidence of zircon that reacted at UHP. The interface domain in zircon from all petrographic contexts yields variable Yb/Gd ratios that are significantly higher than both cores and rims. We therefore interpret that zircon recrystallized via interface-coupled dissolution–reprecipitation reaction; this process preferentially partitioned heavy rare earth elements within the interface domain, which explains the higher Yb/Gd ratios. The rim domains equilibrated with the matrix, producing a relatively homogeneous and low Yb/Gd ratio in these domains.</p>\u0000 <p>The spatial extent and degree of preservation of interface domains are interpreted as a function of the P–T path and minor variations in bulk composition. Interface domains are best preserved in rocks from Xanthi and Sidironero; in these samples, thin, homogeneous, garnet-stable rims only partially overprint and crosscut the interface domain. In contrast, rocks from Kimi followed a higher-temperature trajectory and the zircon grains grew large rim domains that overprinted much of the interface domain and the detrital core. Zircon grains from plagioclase-rich versus quartz-rich domains within samples from Sidironero show differences in texture, which indicates that local bulk composition can affect what evidence of UHP metamorphism is preserved. Collectively, these samples provide a new, durable marker of metamorphism in UHP rocks and yield new insight about which factors affect the preservation of UHP textures.</p>\u0000 </div>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"44 1","pages":"1-19"},"PeriodicalIF":3.4,"publicationDate":"2025-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969651","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 Piedmont Zone From the Western Alps (Italy): New Insights From High-Pressure Ophiolitic Metasediments in the Soana Valley","authors":"Alessia Modesti,&nbsp;Francesco Gosio,&nbsp;Paolo Nimis,&nbsp;Paola Tartarotti,&nbsp;Omar Bartoli,&nbsp;Silvana Martin","doi":"10.1111/jmg.70013","DOIUrl":"https://doi.org/10.1111/jmg.70013","url":null,"abstract":"<p>Metaophiolites and metasediments of the Piedmont Zone are exposed in the Soana Valley, a poorly studied area of the Western Alps, located between the Europe-related Gran Paradiso massif and the Adria-related Sesia–Lanzo zone. Previous investigations reported the occurrence of only greenschist-facies metamorphic assemblages in the metasediments. We present new petrographic analyses and phase equilibria modelling of garnet-chloritoid- and garnet-lawsonite-choritoid-bearing mica schists from the Soana Valley. These mica schists preserve relicts of Alpine high-pressure mineral assemblages, testifying both a prograde and a decompressional evolution. Four main metamorphic stages are recognized from compositional zoning of garnet in a garnet-lawsonite-chloritoid-bearing mica schist: a subduction-related prograde stage at 17.0–18.5 kbar and 420°C–440°C (high-pressure blueschist-facies), a pressure peak at 19.0–21.5 kbar and 440°C–460°C (blueschist–eclogite-facies transition) and two decompressional stages at 17.5–18.5 kbar and 470°C–490°C (high-pressure blueschist-facies) and 14–15 kbar and 490°C–510°C (peak temperature). The peak pressure conditions of the Soana Valley metasediments are comparable (∆<i>P</i> ≤ 2–3 kbar) to those reported for some units of the external Western Alps located at structurally lower levels. Our results lead us to interpret the Piedmont Zone as a stack of tectonic slices, each one with its own metamorphic history, accreted together during subduction, rather than an assemblage of two juxtaposed belts characterized by distinct metamorphic histories, as traditionally reported.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"43 9","pages":"909-937"},"PeriodicalIF":3.4,"publicationDate":"2025-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.70013","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145479994","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Can Multiphase Inclusions in Garnet From Eclogite Facies Rocks Be a Product of Melt or Supercritical Fluid Entrapment During Subduction?","authors":"Shah Wali Faryad","doi":"10.1111/jmg.70009","DOIUrl":"https://doi.org/10.1111/jmg.70009","url":null,"abstract":"<p>Dehydration of rocks and minerals during high-pressure metamorphism is controlled by the thermal structure of the subduction zone and can be traced by the stability fields of hydrous phases. Consistent with the results of experimental works, the content of silicate components in fluids is assumed to increase from the fields of subcritical to supercritical fluid at higher pressure and to hydrous melt at higher temperature. As there is no direct information about the composition of these fluids along the subduction zone, the multiphase (polyphase) inclusions in anhydrous minerals in eclogite facies rocks are frequently interpreted as products of such fluids or melt, which became entrapped and subsequently crystallised. Although some of these multiphase inclusions are formed by quartz and feldspars and have a composition of granitic melt, most of them contain phases that do not support their formation from granitic or other types of melt. The assumption of their formation from supercritical fluids or melt has stimulated laboratory research to reproduce the original fluids or melts from which these multiphase inclusions could have originated. Therefore, petrological data useful to verify or falsify this assumption is essential for further direction in multidisciplinary research on fluid and melt generation in the subduction zone. This paper presents textural and compositional relations among multiphase inclusions in garnet from various lithologies subjected to high- to ultrahigh-pressure metamorphism. The aim is to substantiate the in situ formation of multiphase inclusions through recrystallisation of pre-existing (hydrous) solid phases enclosed within host minerals. In addition to the presence of original hydrous solid phases, evidence is provided for their transformation into high-pressure phases during prograde metamorphism as well as their subsequent modification and decomposition during retrogression or heating associated with decompression. Furthermore, it is discussed whether the crystallisation of garnet with inclusions is in agreement with bulk-rock fractionation and thermodynamic modelling and whether the compositions of multiphase inclusions correspond to the pressure–temperature fields of hydrous melts or supercritical fluids from experimental data. The results of the study on the textural and compositional relationships of the multiphase inclusions, along with the pressure stability fields of the host minerals, support the interpretation that these inclusions formed by recrystallisation of originally enclosed aqueous and anhydrous phases, rather than by entrapment from a melt.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"43 9","pages":"891-908"},"PeriodicalIF":3.4,"publicationDate":"2025-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.70009","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145479936","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Featured Cover","authors":"Zhen M. G. Li,&nbsp;Fred Gaidies,&nbsp;Yi-Chao Chen,&nbsp;Jia-Shun Hu,&nbsp;Chun-Ming Wu","doi":"10.1111/jmg.70010","DOIUrl":"https://doi.org/10.1111/jmg.70010","url":null,"abstract":"<p>The cover image is based on the Original Article <i>Thermodynamic and Kinetic Controls on the Growth of Metapelitic Garnet in the Danba Dome (SW China): Insights From Microstructure, Element Mapping and Thermodynamic Modelling</i> by Zhen M. G. Li et al., https://doi.org/10.1111/jmg.70005.\u0000 \u0000 <figure>\u0000 <div><picture>\u0000 <source></source></picture><p></p>\u0000 </div>\u0000 </figure></p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"43 8","pages":""},"PeriodicalIF":3.4,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.70010","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145021953","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Confronting Episodic vs. Continuous Heat Sources in Long-Lived Hot Orogens: Insights From Petrochronological Studies in the Nova Venecia Complex, Araçuaí Orogen (SE Brazil)","authors":"Lucas R. Schiavetti,&nbsp;Vinicius T. Meira,&nbsp;Sean Mulcahy,&nbsp;Jeffrey D. Vervoort,&nbsp;Peter L. Baker,&nbsp;George L. Luvizotto,&nbsp;Ricardo I. F. Trindade","doi":"10.1111/jmg.70007","DOIUrl":"https://doi.org/10.1111/jmg.70007","url":null,"abstract":"<p>Orogenic belts that sustain elevated temperatures at intermediate crustal depths for tens of millions of years are known as hot orogens. The evolution of these hot orogens is largely influenced by thermal maturation, primarily driven by the distribution of heat-producing elements (HPEs), such as K, Th and U in the overthickened crust. This process involves widespread anatexis, granulite facies metamorphism, extensive transfer of fluids and magma and large-scale crustal flow. Although most of the thermal evolution of hot orogens is controlled by HPEs, episodic heat transfer may also contribute to their geodynamic development. The Araçuaí orogen, located in southeastern Brazil, represents a Neoproterozoic hot orogen that exposes in its internal domain deeper levels of an overthickened crust, resembling the Tibetan plateau. Its evolution involves more than 120 million years of magmatism and metamorphism, including ultra-high-temperature metamorphism. Different geodynamic models have been suggested to explain the thermal evolution of this orogen, ranging from episodic heat sources within subduction-collisional orogeny to continuous long-lived heat sources in collisional or intracontinental settings. In this paper, we integrate detailed thermodynamic modelling, Lu–Hf and Sm–Nd garnet dating, and U–Pb and REE zircon data from an outcrop that includes granulite facies metasedimentary rocks (Nova Venecia complex) and an intrusive gabbroic stock (São Gabriel pluton). This key outcrop allows us to investigate the history of high-grade regional metamorphism within the internal domain of the Araçuaí orogen, as well as the thermal impact of the late-stage high-temperature magmatism on the later evolution of this hot orogen. Our data indicate that the studied rocks reached near-peak conditions (6.5–10 kbar and ~800°C) at 535–530 Ma and followed a near-isothermal decompression path to 5–6 kbar at ~530–520 Ma. Only local effects of contact metamorphism (~5 kbar and 900°C–1000°C) were observed along the contact between the gabbroic stock and its host rock. Based on this newly integrated dataset and the compilation of existing information, we argue that the Araçuaí orogen evolved from a single, continuous, long-lived heat source controlled by radiogenic decay from HPEs, rather than episodic advective heating from subduction/collision-related processes.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"43 9","pages":"863-890"},"PeriodicalIF":3.4,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.70007","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145480134","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tectonothermal Evolution of the NW Wyoming Province: Insights From Coupled Garnet Lu-Hf and Sm-Nd Geochronology","authors":"Tsai-Wei Chen,&nbsp;Jeff Vervoort,&nbsp;Julia Baldwin,&nbsp;Peter Baker","doi":"10.1111/jmg.70006","DOIUrl":"https://doi.org/10.1111/jmg.70006","url":null,"abstract":"<p>Understanding how Paleoproterozoic orogenic processes shaped the assembly of Laurentia remains a critical puzzle in deciphering Earth's ancient tectonic history. To address this challenge, the Montana metasedimentary terrane in the northwest Wyoming Province, which preserves a complex record of multiple metamorphic episodes, provides a unique opportunity. In this study, we integrate garnet composition with coupled Lu-Hf and Sm-Nd geochronology to unravel the polymetamorphic history of this terrane and constrain the timing and mechanisms of orogenic processes. Our new garnet Lu-Hf and Sm-Nd ages reveal three distinct age groups: 2.42, 2.19–2.06 and 1.83–1.70 Ga. Most analysed garnet samples demonstrate typical prograde zoning patterns with enriched Mn and Lu contents in their core, suggesting that the Lu-Hf ages from these samples reflect the timing of prograde metamorphism. The ~30 Myr younger Sm-Nd ages for most samples document the cooling process that followed peak metamorphic conditions during the orogenic cycle. One amphibolite sample shows reverse Lu zoning that likely resulted from mineral breakdown reactions, suggesting complex trace-element incorporation during high-grade metamorphic processes. By integrating our age data with the estimated peak metamorphic conditions reported by previous studies, we identify a spatial and temporal trend of decreasing metamorphic grade that progressed southeastward from the northwestern boundary of the terrane between 1.8 and 1.7 Ga. This pattern reveals a propagation of orogenic activity during the Big Sky orogeny, providing insights into the thermal evolution and incorporation of terranes during Laurentia assembly.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"43 8","pages":"839-862"},"PeriodicalIF":3.4,"publicationDate":"2025-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.70006","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145022167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fluid or Melt? Distinguishing Syn-Deformational Interaction Pathways","authors":"Hindol Ghatak,&nbsp;Nathan R. Daczko,&nbsp;Sandra Piazolo,&nbsp;Tom Raimondo","doi":"10.1111/jmg.70008","DOIUrl":"https://doi.org/10.1111/jmg.70008","url":null,"abstract":"<p>Understanding whether deformation occurred in the presence of aqueous fluid or silicate melt is crucial for interpreting ductile shear zones, impacting their thermal and geochemical evolution, and having rheological consequences. To identify the syn-deformational fluid type, we investigate contrasting shear zones active during the Alice Springs Orogeny in central Australia, focusing on their effects on dry granulite facies gneisses transformed into greenschist–amphibolite facies schists. Shear zones in the north-western part of the orogen (Reynolds–Anmatjira Ranges) exhibit greenschist–lower amphibolite facies muscovite–chlorite assemblages, quartz veins and microstructures indicative of solid-state deformation. These features collectively suggest deformation in the presence of aqueous fluid. In contrast, shear zones in the south-eastern part (Strangways Range) display upper amphibolite facies garnet–biotite–sillimanite assemblages, along with granitic dykes and lenses retaining igneous textures. Microstructures, such as ‘string of bead’ textures and felsic minerals forming films along grain boundaries or exhibiting low apparent dihedral angles, indicate the former presence of melt in high strain rocks. This suggests that hydration in the south-eastern shear zones was driven by externally sourced silicate melt and melt–rock reactions. Differentiating between the two types of shear zones using whole rock major and trace element data is challenging. However, rare earth element (REE) analyses show potential. Limited REE metasomatism is observed where aqueous fluids are inferred, with three samples in a transect displaying consistent patterns. In contrast, where silicate melt is interpreted as the metasomatic agent, REE metasomatism is more variable, exhibiting atypical REE patterns relative to common rock types and considerable variability between samples in a transect. This contrast is attributed to greater mobility of REEs in silicate melt compared to aqueous fluid.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"43 8","pages":"810-838"},"PeriodicalIF":3.4,"publicationDate":"2025-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.70008","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145022113","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}