Lithos最新文献

{"title":"Petrogenesis of magmatic charnockite-biotite granite suite from parts of the Chotanagpur Granite Gneissic Complex (CGGC), eastern Indian shield: Implication for the break down of the Columbia Supercontinent","authors":"Somdipta Chatterjee ,&nbsp;Subham Mukherjee ,&nbsp;Sanjoy Sanyal ,&nbsp;Pulak Sengupta","doi":"10.1016/j.lithos.2024.107802","DOIUrl":"10.1016/j.lithos.2024.107802","url":null,"abstract":"<div><p>A rare porphyritic charnockite that is girdled by and mineralogically grades to biotite granite occurs as a part of the Chotanagpur Granite Gneissic Complex (CGGC) in and around Massanjore, Jharkhand, India. Preservation of certain textural features, including (a) euhedral to subhedral grains of orthopyroxene, (b) low dihedral angle subtended by orthopyroxene and plagioclase grains, and (c) relict intergranular and porphyritic textures, are consistent with the view that orthopyroxene in the studied rocks has a magmatic origin. Preserved magmatic features and other petrological attributes of these rocks do not support any significant mass change beyond a few tens of microns during the overprinting high-grade metamorphism. The geochemical variation of the felsic rock suite (porphyritic charnockite and biotite granite) indicates that they are cogenetic and are derived from a ferroan A-type granitoid magma by crystal fractionation. The observed geochemical trend of the studied felsic rock suites has been simulated by phase equilibria modelling in the open system using the system components Na₂O-CaO-K₂O-FeO-MgO-Al₂O₃-SiO₂-H₂O-TiO₂-O₂. The observed mineralogical and geochemical attributes and the results of the modelling study are consistent with a petrogenetic process in which high magma temperature (&gt; 900 °C), low pressure, and low water activity in the parental melt favoured the separation of an orthopyroxene bearing cumulate assemblage (orthopyroxene + plagioclase + quartz + K-feldspar + ilmenite + magnetite) in the initial part of the magmatic differentiation. Removal of this anhydrous cumulitic assemblage raised the bulk H₂O content in the residual melt. Orthopyroxene became unstable with respect to biotite in the evolved melt that eventually crystallised minerals that formed the biotite granite. An increase in magma <em>f</em>O₂ also restricts the orthopyroxene stability in felsic magma. Taken together all the petrological and geochemical attributes, we demonstrate that fractionation of an orthopyroxene-bearing crystal cumulate from the melt is essential to form the charnockites, and that the biotite granite forms from the evolved melt after the fractionation. The charnockite-biotite granite association of the studied area was formed in an extensional tectonic setting, presumably during the breakdown of the Columbia Supercontinent.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107802"},"PeriodicalIF":2.9,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142274193","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":"Rheology modification in a subduction channel due to eclogite facies metasomatism (Rocky Beach Metamorphic Mélange, Port Macquarie, Australia)","authors":"M.A. Finch ,&nbsp;A. Olesch-Byrne ,&nbsp;T. Chapman ,&nbsp;M. Beilharz ,&nbsp;A.G. Tomkins","doi":"10.1016/j.lithos.2024.107797","DOIUrl":"10.1016/j.lithos.2024.107797","url":null,"abstract":"<div><p>The rheological properties of the interface between the down-going and overriding plates in subduction zones provides insight into how plate convergence is accommodated and the controls on seismic and aseismic slip. This interface is known as the subduction channel and exhumed examples provide the only direct information on deformation mechanisms and the impact of metamorphism on rheology. The Rocky Beach Metamorphic Mélange in eastern Australia is one such exhumed subduction channel, composed of eclogite, blueschist and greenschist facies blocks within a mélange matrix. Previous phase equilibria modelling indicates that high pressure blocks were subducted to ca. 100 km depth and then retrogressed during return flow and exhumation. We found that the rheology of blocks is modified by metasomatism, consistent with studies on other subduction channels. However, through comparison of blocks from different metamorphic grades we found that the effect of metasomatism on rheology varied depending on the pressure and temperature conditions of metasomatism. While unmetasomatised eclogites behaved as rigid objects in the mélange matrix, rocks with mineral assemblages that equilibrated during eclogite facies metasomatism accumulated significant strain, forming isoclinal folds and refolded folds. Deformation of these blocks began at eclogite facies and continued during return flow and retrogression to blueschist facies. At blueschist facies, metasomatised blocks developed mm-scale isoclinal folds with shearing parallel to fold limbs forming rootless isoclinal folds. At the transition between blueschist and greenschist facies, pressure solution became important, preferentially focusing along layers of lawsonite, dissolving it from the rock. At greenschist facies, dissolution-precipitation processes caused significant mass loss, producing mm-spacing between pressure solution seams and cuspate folds, analogous to dewatering structures in sediments. In the Rocky Beach Metamorphic Mélange eclogite facies metasomatism reduces the competence of rigid blocks, reducing overall subduction channel heterogeneity during return flow. We suggest that subduction channels that experience widespread eclogite facies metasomatism may be less likely to generate seismic slip during return flow, since the proportion of rigid blocks and block strength are both reduced.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107797"},"PeriodicalIF":2.9,"publicationDate":"2024-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024493724003104/pdfft?md5=97015ce7320717b4af856158332aa814&pid=1-s2.0-S0024493724003104-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142232133","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":"Tectonic and magmatic evolution of the southernmost Mariana convergent margin: Constraints from geochronology and geochemistry of the Challenger Deep sediments","authors":"Ming Yang ,&nbsp;Tao Wu ,&nbsp;Wen Zhang ,&nbsp;Liyan Tian ,&nbsp;Jianggu Lu ,&nbsp;Taoran Song ,&nbsp;Hengrui Zhu ,&nbsp;Yidi Hong ,&nbsp;Jiawang Chen","doi":"10.1016/j.lithos.2024.107796","DOIUrl":"10.1016/j.lithos.2024.107796","url":null,"abstract":"<div><p>The southernmost Mariana convergent margin (SMCM) is a distinct segment of the Izu-Bonin-Mariana (IBM) subduction system with unique east-west orientation, however, its nature and tectonic history remains enigmatic. Here, for the first time, we present the detailed geochemical data of detrital minerals and U<img>Pb ages of accessory minerals from two sediment samples recovered at the deepest part of Southern Marianna Trench including the Challenger Deep. Detrital magmatic zircon U<img>Pb ages can be divided into three groups. Group 1 zircons show a weighted mean age of 50.3 ± 1.2 Ma, contemporary to the published boninites from northern IBM. The ε_Hf(t) of these zircons (11.1–16.4) are also similar to the boninites (12.6–16.8) and volcanic arc rocks (4.2–14.2), but lower than forearc basalts (17.8–22.1), suggesting that these zircons are from boninitic or arc magmatism. The apatite U<img>Pb dating obtained a similar age of 55.0 ± 5.5 Ma. Therefore, if they are all from boninites, then subduction initiation magmatism ended at SMCM was likely coeval with northern IBM. Group 2 and Group 3 zircons have ε_Hf(t) values similar to Group 1 zircons, but recorded younger ²⁰⁶Pb/²³⁸U ages of 16.8 ± 1.8 Ma and 11.0 ± 0.2 Ma, respectively, which are most likely related to the arc volcanism at West Mariana Ridge (WMR). Additionally, a rutile age of 19.0 ± 0.6 Ma is identified, which is also likely related to WMR. The chemical composition and calculated P-T conditions of clinopyroxenes indicate that they are mainly from the Mariana forearc basalts and arc volcanic rocks. <em>In situ</em> Sr isotopic compositions of plagioclases also show strong affinity to the Mariana forearc basalts and arc volcanic rocks. Therefore, our study indicates that sediments at the deep trench can record the long-term tectonic and magmatic evolution of the convergent margin.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107796"},"PeriodicalIF":2.9,"publicationDate":"2024-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142172522","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 insights from plumbing system below composite mafic volcanoes: Post-glacial volatile contents and magmatic fluids from Villarrica magmas","authors":"Philippe Robidoux ,&nbsp;Yves Moussallam ,&nbsp;Estelle F. Rose-Koga ,&nbsp;Andrea Luca Rizzo ,&nbsp;Guillaume Georgeais ,&nbsp;Joao Lages ,&nbsp;Gilles Lévresse ,&nbsp;Simona Ferrando ,&nbsp;Alessandro Aiuppa","doi":"10.1016/j.lithos.2024.107786","DOIUrl":"10.1016/j.lithos.2024.107786","url":null,"abstract":"<div><div>Villarrica volcano, in the southern Andes, is a composite mafic volcano whose persistent open-vent activity is punctuated by frequent Strombolian/Hawaiian eruptions and, more rarely, by more energetic (sub-Plinian) events. Here, we investigate the volatile composition of the parental melts that sustain this activity, and the conditions of pre-eruptive magma storage, by characterizing the composition of olivine-hosted melt and fluid inclusions. We concentrate on inclusions entrapped in minerals from pyroclastic materials erupted from both Villarrica summit and from its flank Minor Eruptive Centers (MECs) post the 14.5–13.5 kyr caldera collapse event that formed the Licán ignimbrite. Our micro-FTIR and SIMS measurements indicate that the Pucón eruption records the highest volatile contents, with 6.0 wt% H₂O, &gt;1500 ppm CO₂, 1330 ppm S, 1556 ppm Cl, and 2055 ppm F. These volatile contents imply a volatile-saturated magma originating from a depth of 14.4 to 17 km below Villarrica. Results for other flank eruptions highlight a similarly deep (17–21 km depth) source for basaltic CO₂-rich mafic magmas erupted at regional MECs (Los Nevados, Caburgua). Melt inclusion results also reveal that deep rising mafic magma batches, when temporarily stored at 1–5 km depth, produce the more differentiated and degassed magma batches that sustain the decadal-old persistent effusive-explosive eruptive activity at Villarrica. Helium isotope ratios (³He/⁴He; Rc/Ra when corrected for atmosphere) measured in bulk noble gases from olivines (Fo₇₅–₈₈) indicate that the parental magmatic fluid signature (Rc/Ra = 6.7–7.6; CO₂/³He = 4.7–7.5E⁺⁰⁸) is only recorded during central paroxysmal sub-Plinian eruption, and that this primitive gas signal is diluted in lateral MECs (Rc/Ra &lt; 6.5; CO₂/³He = 1.4 × 10⁺⁹–3.1E⁺¹⁰).</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107786"},"PeriodicalIF":2.9,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142446360","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":"Geographic bias effects on interpretations of secular trends of Hf isotope times series in zircons","authors":"Kent C. Condie ,&nbsp;Stephen J. Puetz ,&nbsp;Kurt E. Sundell ,&nbsp;Sergei A. Pisarevsky ,&nbsp;Christopher J. Spencer ,&nbsp;Nick M.W. Roberts","doi":"10.1016/j.lithos.2024.107787","DOIUrl":"10.1016/j.lithos.2024.107787","url":null,"abstract":"<div><p>The analysis of εHf(t) time series data from zircon reveals notable discrepancies based on sample type (igneous versus detrital), statistical weighting methodology, and geographic sampling bias. These differences warrant caution when interpreting data in the context of tectonic settings and the history of supercontinents. In terms of tectonic setting, accretionary orogens dominate in both sedimentary basins that host detrital zircons and in igneous zircon sources. Because of differences between the various time series, emphasis in this study is on peaks, valleys and secular trends and not on absolute εHf(t) values. Specifically, the igneous time series for εHf(t) in zircons shows more peaks and valleys than corresponding detrital time series for both weighted and unweighted data (weighting corrects for disproportionate geographic sampling). Also, sample-based (each sample considered separately) and site-based (samples grouped by geographic location and age) results align closely to the igneous time series, whereas the site-based detrital series displays more negative εHf(t) values. Regardless of the type of time series, the failure to compensate for disproportionate geographic sampling increases the prospects of producing an unrepresentative time-series. Nine zircon age peaks (both detrital and igneous) have corresponding εHf(t) peaks (3200, 2700, 2500, 2150, 1500, 1100, 750 Ma) and two have corresponding age valleys (1800–2000, 550 Ma). With exception of a geographically widespread 1500 Ma peak, most of the εHf(t) peaks and valleys are controlled by specific geographic regions and are likely not be global in extent.</p><p>Two distinct periods (200–0 and 1800–1600 Ma) display εHf(t) signatures that rise steadily for 100–200 Myr, coinciding with the final stages of supercontinent assembly and the transition to the retreat of exterior orogens. An εHf(t) peak at 750 Ma and a high at 1400–1100 Ma partly overlap with supercontinent breakup and valleys at 550 Ma and 900 Ma with supercontinent assembly. A large εHf(t) valley at 2000–1800 Ma corresponds with the onset of craton collisions that led to the final assembly of Columbia at 1800–1600 Ma. The steep rise in εHf(t) in the last 200 Myr in both igneous and detrital zircons is controlled by sites in Circum-Pacific orogens in North and South America and Southwest Asia, and it parallels the breakup of Pangea. The general increase in zircon εHf(t) in the last 500 Myr in both detrital and igneous data reflects an increase in the proportion of isotopically juvenile components in accretionary orogens.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107787"},"PeriodicalIF":2.9,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150141","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":"Rapid emplacement of a Palaeogene silicic volcanic centre, Arran, western Scotland","authors":"Robert J. Gooday ,&nbsp;Daniel J. Condon ,&nbsp;David J. Brown ,&nbsp;Andrew C. Kerr ,&nbsp;Kathryn M. Goodenough","doi":"10.1016/j.lithos.2024.107789","DOIUrl":"10.1016/j.lithos.2024.107789","url":null,"abstract":"<div><p>The timing and duration of silicic magmatism at relatively small volcanic centres in the geological record remain poorly constrained but are vital for understanding the temporal evolution of magmatic provinces. The Palaeogene Central Arran Igneous Complex (CAIC), and the nearby North Arran Granite, show spatial and temporal relationships between silicic intrusions and intra-caldera volcanic deposits. High-precision U<img>Pb zircon geochronology, integrated with detailed field observations, allows a timeline of silicic magmatic activity on Arran to be constrained. Silicic magmatism in north and central Arran occurred as a very short-lived (∼0.5 Ma) ‘pulse’ during the protracted (&gt;8 Ma) evolution of the British Palaeogene Igneous Province (BPIP). Evolution of the CAIC volcano from caldera collapse to eruption of the youngest preserved unit (including several phases of eruption punctuated by quiescent periods of land surface erosion and deposition of sediments) took no more than 185 ka. Silicic magmatism at the complex (volcanism followed by intrusion of granites) lasted no more than 330 ka, with the North Arran Granite was emplaced shortly prior to the CAIC. This evidence of a short magmatic pulse accompanied by drastic land-surface changes has major implications for our understanding of localised silicic magmatism in other igneous provinces, both in the geological record and the present day.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107789"},"PeriodicalIF":2.9,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150138","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":"Early–Middle Jurassic magmatism, stratigraphy, and deformation in North and Northeast China: A prelude to the thinning of the North China Craton and subducted Izanagi Plate, and a Coda to the Mongol-Okhotsk Ocean","authors":"Zongyuan Tang ,&nbsp;Chenchang Chen ,&nbsp;Guochun Zhao ,&nbsp;Deyou Sun ,&nbsp;Jie Li ,&nbsp;Changzhou Deng ,&nbsp;Han Zheng","doi":"10.1016/j.lithos.2024.107784","DOIUrl":"10.1016/j.lithos.2024.107784","url":null,"abstract":"<div><p>The Early–Middle Jurassic period represented a crucial juncture for the Northeast Asian continent, marked by significant geological transformations. These included the initial thinning of the North China Craton (NCC), the closure of the Mongol-Okhotsk Ocean (MOO), and the subduction of the Izanagi Plate. Despite the acknowledged significance of these events, the specific temporal and spatial extents of the two tectonic regimes influencing the Northeast Asian continent remain uncertain. This study aims to elucidate these ambiguities, focusing on the spatiotemporal extents of magmatic activity and deformation driven by these distinct tectonic regimes. To achieve this, our research integrates comprehensive analyses of magmatism, stratigraphy, and deformation across the Northeast Asian continent. Our findings highlight the spatially non-uniform intensity of magmatism in Northeast China and the NCC during the Early–Middle Jurassic, pointing to a heterogeneous influence of the tectonic regimes over time and space. This early stage of the orogeny was also signed by local extensional tectonics within the NCC's eastern parts, as opposed to the compressional deformation in the western part, within the Songliao basin. However, the overall extension intensity over the entire region may not have been very pronounced. During the middle to late Middle Jurassic, there was a shift in the scenario, with compression-dominated deformation expanding across the Northeast Asian continent, indicating a significant change in tectonic dynamics. Further analysis reveals the distinct impacts of the Izanagi Plate's subduction beneath the Jiamusi–Khanka Block and the Yanshan fold-and-thrust belt, as well as the MOO tectonic regime's influence on the western Songliao basin, extending to the northern Ordos basin. Interestingly, a substantial portion of the craton remained relatively unaffected during the initial stages of Izanagi Plate's subduction and MOO's closure. However, these events laid the groundwork for the extensive destruction of the craton witnessed during the Late Jurassic–Early Cretaceous period. This study significantly contributes to our understanding of the geological processes in the Northeast Asian continent during the Mesozoic, offering valuable insights into the dynamic interplay of tectonic regimes that shaped this region. By delineating the spatial and temporal extents of magmatic activity and deformation, we provide a clearer picture of the geological evolution of the Northeast Asian continent, highlighting the complexity and variability of tectonic influences during the Early–Middle Jurassic.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107784"},"PeriodicalIF":2.9,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150139","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":"Ultrapotassic rocks in the Saray Peninsula, Northwest Iran: An example of carbonate peridotite melts in a post-collision system in the late Miocene","authors":"Hossein Azizi ,&nbsp;Fatemeh Nouri ,&nbsp;Yoshihiro Asahara ,&nbsp;Masayo Minami ,&nbsp;Motohiro Tsuboi ,&nbsp;Hiroshi A. Takahashi ,&nbsp;Scott A. Whattam","doi":"10.1016/j.lithos.2024.107788","DOIUrl":"10.1016/j.lithos.2024.107788","url":null,"abstract":"<div><p>Late Miocene ultrapotassic rocks are widely exposed in the Saray Peninsula of northwestern Iran. These rocks are mainly classified as tephrite-tephritic phonolite with some trachyte and lamprophyre dikes with porphyritic textures. Ca-rich pyroxene and leucite are the main phenocrysts. Olivine and phlogopite with some sodic amphiboles occur locally as phenocrysts. Chemically, the rocks are characterized by low contents of SiO₂ (45.4–47.3 wt%), with high contents of K₂O (3.4–6.6 wt%), K₂O/Na₂O (1.2–5.7), MgO (5.6–9.1 wt%), CaO (10.3–12.7 wt%) and Sr (826–2020 ppm) with low P₂O₅/Al₂O₃ (0.08–0.14). Chondrite normalized REE and primitive mantle-normalized patterns indicate the involvement of a LREE (La, Ce) and LILE (Cs, Ba, Pb) enriched mantle, and weak negative Ti-Nb-Ta anomalies are observed. Isotopically, the rocks show high ⁸⁷Sr/⁸⁶Sr ratios (0.7071–0.7084) and low εNd(t) values (–3.8 to –1.8). Their δ¹³C values show a variation from –13.4 ‰ to –6.5 ‰, confirming some organic carbon recycling in the subduction zone, and the absence of Ce/Ce* and Eu/Eu* negative anomalies confirm the redox system melting. The Sr<img>Nd isotopic values, higher contents of incompatible elements, and lower δ¹³C values suggest a continental crustal material involvement for the sources of these rocks. The presence of calcite in the matrix, the inclusion of melt droplets with some calcite, and the carbonation of leucite and pyroxene grains confirm the high CO₂ content during magmatic evolution and/or the late stages of reaction of CO₂-fluid rocks with earlier minerals. Due to the situation of the Saray ultrapotassic rocks near the junction of the Van microplate and the NW Iran block, dragging of the Van microplate beneath NW Iran is likely to have transported some carbonate rocks and biogenetic organic carbon into the mantle and converted the primitive mantle to carbonate peridotite. A very low rate of partial melting at a pressure of less than 3 GPa around the garnet-spinel stable zone produced ultrapotassic melts. The correlation with some neighboring ultrapotassic rocks shows that this process is a dominant factor to generate the kamafugite and/or interval of kamafugite-Roman type ultrapotassic series in a collision system, without considering the role of mantle phlogopite present in the deep metasomatized mantle. This work shows why most of the ultrapotassic rocks in Iran have developed near the suture zone after the closure of Neotethys.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107788"},"PeriodicalIF":2.9,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150142","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":"Diffusion-induced stress in crystals: Implications for timescales of mountain building","authors":"Benjamin L. Hess ,&nbsp;Jay J. Ague","doi":"10.1016/j.lithos.2024.107783","DOIUrl":"10.1016/j.lithos.2024.107783","url":null,"abstract":"<div><p>Intracrystalline chemical diffusion offers valuable insights into the durations of metamorphic and igneous processes. However, it can yield timescale estimates for orogenic and subduction zone events that are considerably shorter than those obtained via isotopic geochronology. One potential explanation that has been offered for the discrepancy is that the interdiffusion of species with different atomic or ionic radii may generate intracrystalline, compositional stresses that alter or limit diffusional relaxation. In this study we test this idea by developing and applying the compositional stress theory of materials scientists F. Larché and J. Cahn to garnet from the Barrovian sillimanite zone, Scotland. Relaxed contacts from the garnet, independent diffusion chronometers, and thermal modeling all indicate a &gt;100 kyr duration for peak temperature metamorphism. Nonetheless, the garnet records sharp, μm-scale variations in calcium and iron contents that standard diffusion treatments predict should relax in 1–10 kyr at peak temperature conditions. Our results show that the development of compositional stress during diffusional relaxation can explain the preservation of the observed short wavelength compositional oscillations at a &gt;100 kyr timescale. Thus, it may be necessary to account for compositional stress when modeling diffusion in solid solutions with appreciable differences in their endmember molar volumes. This will be particularly relevant when considering sharp, μm-scale chemical gradients involving grossular, the garnet endmember with the largest molar volume relative to pyrope, almandine, and spessartine. Neglecting compositional stress in such cases could result in the underestimation of the timescales of lithospheric processes by potentially orders of magnitude. The effects of compositional stress in garnet are predicted to be the most pronounced under amphibolite and blueschist–eclogite facies conditions. At lower temperatures diffusion is limited, and at higher temperatures both plastic deformation and more ideal solid solution behavior will act to diminish the impact of stress.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107783"},"PeriodicalIF":2.9,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150140","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":"Textural and chemical variations in peridotite induced by hydrous melt migration in mantle under the back-arc spreading","authors":"Ayu Harano ,&nbsp;Katsuyoshi Michibayashi","doi":"10.1016/j.lithos.2024.107776","DOIUrl":"10.1016/j.lithos.2024.107776","url":null,"abstract":"<div><p>This study presents the structural and petrological characteristics of mantle peridotites in relation to the rock-hydrous melt reaction found in the Hayachine ultramafic complex, NE Japan. We conducted sampling, microstructural observations, crystal-orientation analyses, and major element composition analyses of the major constituent minerals in the peridotites. We used 17 serpentinized peridotites that preserved better mantle textures. The peridotites are composed of lherzolite to harzburgite, consisting of olivine, orthopyroxene, clinopyroxene, amphibole, and spinel. The peridotites were classified into two textures according to olivine grain size: coarse-grained (ca. 2–3 mm) and fine-grained (ca. 0.3–0.5 mm). Fine-grained peridotites were newly found in this study and were characterized by aggregates of orthopyroxene and amphibole with a large number of spinel inclusions. Based on olivine crystal-preferred orientation (CPO), we found that the coarse-grained peridotites were further classified into Group 1 (A type CPO) and 2 (AG type CPO) and the fine-grained peridotites were accordingly classified into Group 3 (weak CPO). The systematic continuity in the chemical compositions of the minerals suggests that Group 1 peridotites partially melted to form Group 2 peridotites, followed by Group 3 peridotites, due to further reaction of Group 2 peridotites with hydrous melts. These textural and chemical variations in the peridotites could have resulted from rock-hydrous melt reactions under back-arc spreading and subsequent processes.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107776"},"PeriodicalIF":2.9,"publicationDate":"2024-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024493724002895/pdfft?md5=5feeeb52acefee7ee076cf20beaf6e5f&pid=1-s2.0-S0024493724002895-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142162011","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}