Lithos最新文献

{"title":"Polymetamorphism and metastability in Paleozoic schists of the central Appalachian Baltimore Terrane, USA","authors":"","doi":"10.1016/j.lithos.2024.107824","DOIUrl":"10.1016/j.lithos.2024.107824","url":null,"abstract":"<div><div>Metapelitic assemblages are often considered highly reactive during prograde metamorphism, such that they effectively record a history of tectono-metamorphic processes. Across eastern North America, metamorphosed rift-to-drift stratigraphy has been central to disentangling the terminal history of Appalachian convergence. We report results from a single metapelitic outcrop in the Loch Raven Schist of Maryland's Baltimore Terrane, where regional metamorphism is historically interpreted to have derived only from the Ordovician Taconic orogeny. An aluminum-rich litho-horizon alludes to two phases of metamorphism: an early, low/medium-pressure (<em>P</em>) sillimanite-stabilizing phase largely overprinted by a subsequent medium/high-<em>P</em> kyanite-stabilizing event, terminating at c. 391–383 Ma. This provides evidence of substantial crustal disturbances in the central Appalachians during Avalonian collision of comparable timing to equivalent events in the north. In a subordinate and aluminum-poor litho-horizon, large (2–3.5 cm) garnet provides geochronological evidence only for a protracted phase of metamorphism at 440–424 Ma. We interpret this age as recording the early, low/medium-<em>P</em> phase of metamorphism that either: (a) extends the duration of the Taconic event; or (b) provides new evidence for metamorphism associated with Silurian tectonism and/or extension in the Central Appalachians. However, this assemblage appears to have been metamorphically unresponsive during Devonian overprinting, despite peak metamorphic conditions of ∼670 °C and ∼8 kbar. We suggest that a potential combination of the paucity of fluid, limited strain accumulation, and coarse refractive assemblages stabilized a kinetically sluggish and metastable composition.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142427783","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":"Age and emplacement depth of intrusions in the southeastern Canadian Cordillera: Implications for Jurassic to Paleocene exhumation","authors":"","doi":"10.1016/j.lithos.2024.107818","DOIUrl":"10.1016/j.lithos.2024.107818","url":null,"abstract":"<div><div>Synorogenic exhumation is important for understanding the evolution of mountain belts but is often difficult to discern because traditional thermochronology methods mostly date the final stages of exhumation. Intrusions emplaced during orogenesis provide an alternate method to elucidate these exhumation patterns since they preserve the timing and depth of their emplacement. We apply this concept the southern Omineca belt of the Canadian Cordillera by combining new and existing zircon U<img>Pb and mica Ar/Ar ages from 43 intrusions as well as new and existing estimates of emplacement depth from 23 contact aureoles. Seventeen new zircon U<img>Pb laser ablation inductively coupled plasma mass spectrometry results are presented in the paper, spanning the existing range of previous ages for four episodes of Phanerozoic magmatism in this region: Middle Jurassic (174–154 Ma), mid-Cretaceous (118–95 Ma), Late Cretaceous (78–76 Ma), and Paleocene (66–60 Ma). This new work has resolved two new distinct periods of Cretaceous magmatism at ∼100 and ∼ 76 Ma compared to what was previously considered to be a single mid-Cretaceous event (Bayonne magmatic suite). Furthermore, the Fry Creek batholith, previously considered to be emblematic of the Bayonne suite, the adjacent Shoreline stock, the ∼60 Ma Nelson stock located 40 km to the southwest, and the 55–62 Ma Ladybird magmatic suite form part of a newly identified phase of 66–55 Ma Paleocene magmatism in the region. Compiled intrusion ages were then combined with estimates of emplacement depth determined from metamorphic mineral assemblages in contact aureoles developed in pelitic host rocks. Jurassic intrusions typically have higher pressure staurolite + andalusite-bearing contact aureoles (3.3–4.0 kbar) corresponding to depths of 12.5–15 km, whereas Cretaceous and Paleocene intrusions mainly have lower pressure andalusite + cordierite-bearing contact aureoles (2.3–2.9 kbar) corresponding to depths of 8.5–11 km. These data indicate regional exhumation of 2–6 km occurred between the Middle Jurassic (180–160 Ma) and mid-Cretaceous to Paleocene (120–60 Ma) periods of Cordilleran orogenesis. In contrast, pluton emplacement depths changed by &lt;2 km, suggesting minimal exhumation occurred in the southern Canadian Cordillera between the mid-Cretaceous and Paleocene. This extended lull in exhumation may be related to the partitioning of compressional deformation east into the foreland along a basal decollement beneath the study area during this time.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142536321","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":"PGE-Ni-Cu sulphide segregation by interaction of basaltic melt and peridotite xenoliths of the Catalan Volcanic Zone (Spain)","authors":"","doi":"10.1016/j.lithos.2024.107820","DOIUrl":"10.1016/j.lithos.2024.107820","url":null,"abstract":"<div><div>Spinel lherzolite xenoliths from the Sant Corneli volcano (Catalan Volcanic Zone, NE Spain) carry the geochemical imprint of melt/rock reaction events that have affected the subcontinental lithospheric mantle (SCLM) beneath the northeastern Iberian margin. Trace element signatures of clinopyroxene indicate that this volume of the SCLM initially experienced low degrees (<em>F</em> = 8 %) of partial melting, followed by extensive refertilization by alkaline silicate melts undergoing chromatographic fractionation while percolating through the mantle peridotites. Furthermore, the presence of interstitial sulphide-bearing silicate glass, as well as secondary coronitic rims around mantle minerals, records the melt/rock reaction product associated with the infiltration of the host alkaline basalts while erupting to the surface. Abundant irregular/blocky sulphides located within the interstitial glass patches are comprised of myrmekitic intergrowths of pentlandite ± bornite ± chalcopyrite, suggesting their derivation from immiscible droplets of Fe-Ni-Cu sulphide melt transported by the host alkaline basalts. The variable chondrite-normalized platinum-group element (PGE) systematics and chalcogenes (Se, Te, As, Bi and Sb) abundances of these sulphides track two distinct transport mechanisms for their parental sulphide melts: 1) by unmixing of Ni-Cu-rich sulphide liquid in alkaline basalts attaining sulphide-saturation while interacting with the peridotite xenoliths, and 2) by mechanical transport of immiscible droplets of Ni-Cu-rich sulphide liquid originally extracted by residual monosulphide solid solution undergoing incongruent melting in their mantle source. In addition, many sulphides have PGE abundances that cannot be explained solely by solid-melt chemical partition coefficients but that were likely influenced by the mechanical entrapment, or early-magmatic segregation, of pre-existing PGE-rich nanoparticles or nanomelts. The geochemical signal of these mineral nanoparticles may significantly influence sulphides PGE distribution, sometimes resulting in pronounced positive anomalies in Ir<img>Rh, Au, or Ru<img>Rh, along with negative anomalies in Pt.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142427794","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":"Unraveling the polymetamorphism of calc-silicate rocks from 639 to 561 Ma in the Western Gondwana (Passo Feio Complex, Dom Feliciano Belt, South Brazil) based on U-Pb dating in titanite, apatite and zircon","authors":"","doi":"10.1016/j.lithos.2024.107822","DOIUrl":"10.1016/j.lithos.2024.107822","url":null,"abstract":"<div><div>Titanite is a valuable tool for studying polymetamorphism and understanding the evolution of orogenic belts as it potentially records different stages of metamorphic evolution. The combination of geochronology and Zr-in-titanite geothermometry has been widely used in petrochronology studies. However, there is ongoing debate regarding the significance of ages and temperatures obtained from titanite. Here, we conducted the first integrated titanite, zircon, and apatite U<img>Pb study, along with Zr-in-titanite geothermometry, on calc-silicate rocks from a polymetamorphic complex of the central Dom Feliciano Belt (Western Gondwana). Our aim was to investigate the impact of various metamorphic events on titanite grains. We carried out a geochronological, geochemical, and petrographic analysis of a calc-silicate sequence of the Passo Feio Complex, which was intruded by the Caçapava do Sul Granitic Complex (CSGC). The metamorphic complex experienced regional, contact, and hydrothermal metamorphism during the Neoproterozoic, but the ages and conditions of these metamorphic events remain widely debated. U<img>Pb analyses on over one hundred titanite grains from a K-feldspar-diopside schist revealed three distinct titanite populations. The older group, dated at 639 ± 3/7 Ma (2s; <em>n</em> = 19), was associated with the regional metamorphism event (M₁), likely initiated by the primary collision of the Dom Feliciano Belt. The intermediate group exhibited an age of 596 ± 1/6 Ma (2s; <em>n</em> = 91). Given the presence of high-K magmatism and a carbonatite intrusion in the study area, producing zircon U<img>Pb ages around 600 Ma, this group was associated with contact metamorphism (M₂), belike influenced by these intrusive igneous activities. The youngest titanite population showed an age of 566 ± 3/6 Ma (2s; <em>n</em> = 6), which closely aligns, within analytical error, with the age of 561 ± 1/6 Ma (2s; <em>n</em> = 46) obtained from U<img>Pb dating on apatite sourced from a diopside-phlogopite schist. The younger ages observed in both titanite and apatite are attributed to alterations resulting from interactions with hydrothermal fluids (M₃) during the cooling phase of the CSGC. Chemical analyses conducted with an electron microprobe assessed the Zr concentrations in fifty titanite grains, examining both bright and dark zones observed in back-scattered electron images. The lowest temperature recorded among the 50 grains was 629 °C, which corresponds to dark BSE zones. In the light zones, the minimum temperature was 639 °C. While temperatures estimated using the Zr content in titanite may not correspond precisely with U<img>Pb ages, combining titanite ages with those from other accessory minerals like zircon and apatite, along with microstructural analysis, can provide a more comprehensive understanding of orogenic belt evolution.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428474","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":"Diverse magmatism along the northern margin of Tarim during the Ediacaran: Transition from Rodinian dispersing to Gondwana assemblage","authors":"","doi":"10.1016/j.lithos.2024.107823","DOIUrl":"10.1016/j.lithos.2024.107823","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The Ediacaran igneous rocks and sedimentary sequences play a key role for our understanding the transition from dispersing of the Rodinian continents to the assemblage of the Gondwana. On the other hand, some continental massifs at the marginal area of the Rodinia and Gondwana could preserve solid evidences for deciphering the geodynamic background from the break-up of Rodinia to the assemblage of Gondwana. In this contribution, we report field observations, petrography, ages and systematic geochemistry of the diverse Ediacaran igneous activities in the northern margin of the Tarim Block, which was favored as a marginal continental massif in the Rodinia configuration by most geologists. The Ediacaran igneous rocks along the northern margin of Tarim include the Baicheng and Yangxia granites, Tiemenguan syenite, Kurle mafic dykes and the basalt layers in the Zamoketi Formation (northeastern Tarim) and the Sugetbrak Formation (northwestern Tarim). Precise zircon U&lt;img&gt;Pb dating revealed that these distinct rocks were broadly coeval with crystallization/eruption ages of 630–600 Ma. Bulk-rock elemental and Sr&lt;img&gt;Nd isotope compositions as well as zircon Lu&lt;img&gt;Hf isotope compositions demonstrate that the Baicheng and Yangxia granites were derived from Neoarchean mafic lower crust and underwent intensive fractionation before their emplacements. The Tiemenguan syenites have potassic andesitic compositions, in combination with their pronounced enriched Nd&lt;img&gt;Hf isotopes and extremely high Zr saturation temperatures (∼900 °C), we argue that their possible shoshonitic primary magmas were derived from previously metasomatized subcontinental lithospheric mantle source (amphibole-bearing) and then, coupling with assimilation and fractional crystallization (AFC) effects in magma chamber and/or en route to the emplacement space. This can account for their intriguing geochemical features. The ca. 615 Ma Zamoketi and Sugetbrak basalts and the slightly younger porphyrite dykes (ca. 580 Ma) cutting the Zamoketi basalt layer, show typical OIB-like geochemical signatures, they were most likely derived from a depleted asthenospheric mantle source with variable fractionation of olivine and pyroxene and negligible crustal contamination before eruption. On the whole, the geochemistry of the diverse Ediacaran igneous rocks unambiguously demonstrates that they were genetically related to an extensional environment. In combination with the significant passive continental features of the Ediacaran-Cambrian sedimentary sequences, we consider that these Ediacaran igneous rocks were the latest phase of igneous activity related to the dispersing of the Tarim at the margin of the Rodinia supercontinent.&lt;/div&gt;&lt;div&gt;The dispersing of the Rodinian supra-continent was diachronic with the assemblage of the Gondwana. Late Tonian to Ediacaran dispersing of the Tarim from northern margin of Australia induced the opening of the Proto-Tethys Ocean. Then the initiation of the sou","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142446564","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":"Li enrichment in peridotites and chromitites tracks mantle-crust interaction","authors":"","doi":"10.1016/j.lithos.2024.107819","DOIUrl":"10.1016/j.lithos.2024.107819","url":null,"abstract":"<div><div>The ultramafic massifs of the Serranía de Ronda in southern Spain are the Earth's largest exposures of subcontinental lithospheric mantle (SCLM) peridotites (∼450 km²). These ultramafic massifs experienced asthenosphere melt percolation during their crustal emplacement. Mixing of these mafic melts with anatectic melts and fluids led to the formation of a world's unique Ni-arsenide-rich chromitite ores (hereafter Cr<img>Ni ores) associated with orthopyroxenite and/or cordieritite (i.e., &gt; 90 % volume of cordierite) hosted within the peridotites. This study uses laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to investigate the Li in rock-forming minerals of peridotite and Cr<img>Ni ores to evaluate the role of Li as crustal tracer. Clinopyroxene crystallized from asthenospheric melts exhibits high Li contents (up to 8.5 ppm), exceeding the average values of the upper mantle (∼ 0.7 ppm), whereas orthopyroxene, olivine, and Cr-spinel from peridotite are mostly Li-depleted. In contrast, all rock-forming minerals of Cr<img>Ni ores have abnormally high Li contents, displaying an overall Li enrichment trend toward the external parts of ultramafic massifs, on the way to the crustal rocks. This trend is evident in Cr-spinel from the Cr<img>Ni ores, which display 6.9–7.9 ppm Li in the deepest portions of the massif (Arroyo de la Cala Cr<img>Ni ore) up to 1.4–8.5 ppm in the shallowest part (La Gallega Cr<img>Ni ore), as well as in orthopyroxenes that have 31.3–44.7 ppm Li in Arroyo de la Cala, and 45.1–51.4 ppm Li in La Gallega. Cordierite is present only in the Cr<img>Ni ores situated in the external part of the ultramafic massifs, exhibiting 113.15–160.82 ppm Li in the Barranco de las Acedías Cr<img>Ni ore and 36.5–60.5 ppm Li in La Gallega Cr<img>Ni ore. Similarly to Li, LREE, fluid-mobile elements (K, Rb, Ba), and Sr in orthopyroxenes from the Cr<img>Ni ores display enrichment from the inner to the outer parts of the ultramafic massif. These geochemical variations suggest that Li enrichment in Cr<img>Ni ores and host peridotites was a twofold process: (1) asthenospheric melt percolation slightly increased Li abundances in the SCLM peridotites by modal and cryptic metasomatism involving clinopyroxene; (2) additional infiltration of Li-bearing crustally-derived fluids during the intracrustal emplacement of the mantle section boosted the Li contents of minerals in the Cr<img>Ni ores. Our results highlight that Li may effectively track the interaction of the SCLM with crustal components.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428309","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":"Late Paleozoic–Early Mesozoic subduction history of Mudanjiang Ocean: New insights from greenschist in the Heilongjiang Complex, NE China","authors":"","doi":"10.1016/j.lithos.2024.107808","DOIUrl":"10.1016/j.lithos.2024.107808","url":null,"abstract":"<div><div>This paper presents zircon U-Pb ages, whole-rock major and trace element data, and Sr-Nd-Hf isotopic compositions for the greenschists from the Heilongjiang Complex in NE China. Based on the geochronological and geochemical characteristics, the greenschists from the Heilongjiang Complex can be categorized into three series: Early Permian tholeiitic series (275 ± 1 Ma and 273 ± 1 Ma), Middle Permian alkaline series (261 ± 1 Ma), and Early Jurassic alkaline series (179 ± 1 Ma). The Early Permian tholeiitic greenschist samples are characterized by remarkable negative Nb and Ta anomalies, and they exhibit relatively low whole-rock (⁸⁷Sr/⁸⁶Sr)_i values (0.703896–0.704252), along with positive ε_Nd(t) values (+7.66 to +8.65) and positive ε_Hf(t) values (+0.92 to +11.51), implying that their protoliths originated from the partial melting of a depleted mantle wedge that has been metasomatized by subducted slab fluids. The Middle Permian alkaline greenschist samples have high Nb (17.3–19.0 ppm), TiO₂ (1.40–1.64 wt%), and P₂O₅ (0.60–0.68 wt%) concentrations, and they are enriched in large ion lithophile elements and light rare earth elements, and depleted in high field strength elements and heavy rare earth elements, with high whole-rock (⁸⁷Sr/⁸⁶Sr)_i values (0.709434–0.709949), negative ε_Nd(t) values (−4.73 to −4.72) and varied ε_Hf(t) values (−10.11 to +4.86), which compositionally align with those of Nb-enriched basalts. Based on the geochronological and geochemical characteristics, we propose that the protolith generation of Middle Permian alkaline greenschists was associated with the partial melting of a mantle wedge that had been metasomatized by subduction slab-derived melts. The Early Jurassic alkaline greenschist samples display OIB affinities, characterized by whole-rock (⁸⁷Sr/⁸⁶Sr)_i values ranging from 0.705161 to 0.705926, ε_Nd(t) values between +6.16 and +6.19, and ε_Hf(t) values from +3.44 to +9.32, indicating the formation of the protolith for the Early Jurassic alkaline greenschist was related to the upwelling of the asthenosphere resulting from slab break-off. By integrating regional geological data, we can trace the subduction evolution of the Mudanjiang Ocean back to the Early Permian, and the slab break-off during the Early Jurassic likely corresponded to the early stage of the closure of the Mudanjiang Ocean.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428470","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":"Serpentinization of the Ronda Massif (Spain): Structural controls and fluid origin","authors":"","doi":"10.1016/j.lithos.2024.107817","DOIUrl":"10.1016/j.lithos.2024.107817","url":null,"abstract":"<div><div>Serpentinization is a ubiquitous hydrothermal alteration of ultramafic rocks. In the Ronda Massif (Andalusia, Spain), which represents the largest body of subcontinental peridotite exposed at the Earth surface, most studies focused on high-temperature deformation and petrology of mantle rocks. Serpentinization remains poorly constrained. Petro-structural and O and H isotope investigations allow us to identify three successive stages of serpentinization. The first stage of serpentinization is characterized by a widespread lizardite mesh-texture. The extent of serpentinization indicates a regional gradient, with a low proportion of serpentine (around 15 %) in the core of the Sierra Bermeja Massif. The second stage corresponds to highly localized serpentinization, characterized by the presence of lizardite, bastite and high content of magnetite. The third stage was intimately associated with brittle deformation, consisting of fibrous veins and a coating network within cataclastic shear zones. Structural analysis of shear veins of the third serpentinization stage enables identification of a regional <em>syn</em>-serpentinization extensional deformation that corresponded to a multi-directional horizontal stretching and a vertical shortening direction (i.e., flattening). All stages of serpentinization display comparable isotopic compositions, with the mean of δ¹⁸O values at ∼ +5.0 ‰ and δD at ∼ −80.5 ‰, suggesting that the two last stages occurred under conditions of fluid-rock interactions that preserved the compositions acquired during stage 1. The fluid source for this stage 1 was likely deeply seated, with a possible contribution of meteoric-derived fluids. Stage 3 serpentinization occurred at 170 ± 50 °C based on magnetite-serpentine isotopic equilibrium. We propose a model of continuous serpentinization that occurred during the rapid exhumation of the Ronda Massif during the Early Miocene period. The <em>syn</em>-serpentinization extensional brittle deformation we document may be compatible either with orogenic thickening (i.e., syn-thrusting) or with early post-thickening collapse.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142427795","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":"Magma through-flow and embedding of magmatic crystals in metasedimentary country rocks adjacent to the Peninsula Granite, Cape Granite Suite (South Africa)","authors":"","doi":"10.1016/j.lithos.2024.107812","DOIUrl":"10.1016/j.lithos.2024.107812","url":null,"abstract":"<div><div>The Sea Point contact in Cape Town, South Africa showcases the interaction between the Malmesbury Group metasedimentary rocks and the intrusive S-type Peninsula Granite of the Cape Granite Suite. The Malmesbury Group, comprising weakly metamorphosed mudstones and siltstones, has been intruded by various granitic injections of varying composition and mineralogical make-up. These granitic injections, displaying diffuse contacts with the country rock and termed “hybrid” granites, indicate varying degrees of assimilation of the country rocks. The injections occurred parallel to the country rock's fabric and anisotropies, particularly along the well-developed S₁ foliation. The granites exhibit compositional variations and contain K-feldspar megacrysts in a variable grain-sized groundmass. Some of these megacrysts are found within the Malmesbury Group, with or without quartzofeldspathic material envelopes. Most researchers agree that large K-feldspar megacrysts in granites develop through near-solidus growth, resulting from prolonged exposure to renewed magma input. However, the origin of K-feldspar and other phenocrysts in the adjacent country rocks is debated, with proposed mechanisms including entrapment due to magma through-flow and in situ growth due to K-metasomatism from granitic magma-derived fluids. This study compares the textures and chemistry of K-feldspar megacrysts in various granite types at the Sea Point contact with those in the Malmesbury Group country rock to determine the origin of the latter. The megacrysts in all lithologies show notable textural and compositional similarities, exhibiting poorly defined compositional zoning and consistent variations in K₂O, Na₂O, and BaO, along with rare earth element concentrations. These attributes suggest that the megacrysts formed through renewed magma injection and prolonged growth involving multiple magma pulses. The study proposes that filter pressing, where melt fractions separate from a crystal mush during crystallisation, occurred during active deformation so that filter pressing was strain-induced. During magma intrusion in a <em>syn</em>- to post-tectonic compressive regime, the melt and associated crystals moved into openings, with the melt fraction more easily mobilised and driven out compared to the crystal fraction during transpression. This left K-feldspar megacrysts embedded or mantled by the country rock. These isolated crystals, with or without associated crystallised magmatic material, mark former magma flow pathways through the country rock, contributing to understanding magma emplacement mechanisms and the formation of the continental crust.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428471","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":"Spatial and temporal characteristics of volatiles in the Cenozoic mantle beneath eastern China","authors":"","doi":"10.1016/j.lithos.2024.107815","DOIUrl":"10.1016/j.lithos.2024.107815","url":null,"abstract":"<div><div>Subduction of the paleo-Pacific Plate has transported volatiles from the surface to the interior of the Earth and significantly altered the chemical and physical properties of the Cenozoic mantle beneath eastern China. However, the characteristics of volatiles other than H₂O in the Cenozoic mantle remain poorly constrained. To describe the spatiotemporal distribution of volatiles, including S, Cl, and H₂O, in the Cenozoic mantle beneath eastern China, we performed reheating experiments and determined the composition of olivine-hosted melt inclusions from a large area (5.9 × 10⁵ km²) of basalts. Calculations of the mantle-source compositions indicate that the Cenozoic mantle in North China is enriched in S but deficient in H₂O and Cl, relative to that in South China. The distinctive features of volatiles likely arise from the different types of recycled materials in the mantle sources (such as Cl-containing sediments, carbonates, or sulfides in the altered oceanic crust) and their different proportions (from &lt;1.7 % to 7 % of subducted sediments). Both the North China and South China mantles reached high volatile contents at 17.5–11.9 Ma, indicating that the activation of the South China mantle and the destruction of the North China Craton may have occurred simultaneously. These novel findings improve our understanding of mantle evolution beneath eastern China and will help in evaluating the contributions of slab subduction to the spatiotemporal heterogeneity of the lithospheric mantle during the Cenozoic.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142312922","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}