Lithos最新文献

{"title":"Spatio-temporal evolution of the Paleo-Tethys in western Yunnan: Insights from mafic rocks in the Lancang tectonic belt","authors":"Ya Cui ,&nbsp;Yuejun Wang ,&nbsp;Renjie Zhou ,&nbsp;Yang Wang ,&nbsp;Teresa Ubide ,&nbsp;Xin Qian ,&nbsp;Cheng Wang ,&nbsp;Xin Wang","doi":"10.1016/j.lithos.2024.107830","DOIUrl":"10.1016/j.lithos.2024.107830","url":null,"abstract":"<div><div>The Sanjiang orogenic belt in the southeastern Tibetan Plateau provides an excellent record of the Paleo-Tethys tectonic evolution. This study introduces new constraints on the spatio-temporal evolution of the Paleo-Tethys through zircon U<img>Pb ages, in-situ Lu<img>Hf isotope data, and analyses of whole-rock major oxides, trace elements, and Sr-Nd-Pb isotopic compositions from Late Paleozoic mafic rocks in the Lancang tectonic belt. The mafic rocks from the Xiaoheijiang, Banpo, and Yakou areas were dated to approximately 281–267 Ma, 295–292 Ma, and 293–291 Ma, respectively. The Xiaoheijiang mafic rocks exhibit geochemical signatures resembling those of fore-arc basalt, characterized by low (La/Sm)_N, relatively flat rare earth element (REE)-normalized patterns, positive ε_Nd(t) (+5.6 to +10.1), and zircon in-situ ε_Hf(t) values (+10.0 to +14.9). These features indicate an origin from a depleted mantle source with minor contributions from slab-derived components. The Banpo and Yakou mafic rocks display geochemical affinities to back-arc basin basalt, similar to the Okinawa Trough back-arc basin basalt. Their ε_Nd(t) values range from +5.6 to +9.9 and ε_Hf(t) values from +9.5 to +15.0, suggesting derivation from a mantle wedge source modified by slab-derived fluids or melts. In combination with available geochronological data concerning the Paleo-Tethys evolution along the Lancang tectonic belt, our findings support the hypothesis that the slow-speed, low-angle subduction of the Paleo-Tethys Ocean led to the formation of a forearc accretionary complex. The slab-derived fluids metasomatized the mantle wedge as subduction depth and angle increased, facilitating the development of the Lincang arc magmatism and the opening of the Banpo-Yakou back-arc basin. Continuous subduction promoted slab retreat under gravitational forces, inducing the upwelling of depleted mantle and the forming of forearc magmas.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107830"},"PeriodicalIF":2.9,"publicationDate":"2024-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142427784","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":"Supergene formation of sulfur-rich, tochilinite-bearing serpentinites in the Oman ophiolite","authors":"James Andrew Leong ,&nbsp;Juan Carlos de Obeso ,&nbsp;Thomas Sharp ,&nbsp;Everett Shock ,&nbsp;Peter Kelemen","doi":"10.1016/j.lithos.2024.107828","DOIUrl":"10.1016/j.lithos.2024.107828","url":null,"abstract":"<div><div>Mass transfer processes between fluids and ultramafic rocks produce subsurface environments encompassing a wide range of redox conditions. A notable locality where an extensive range of redox conditions is observed in one location is Hole BA1B, a ∼ 400 m borehole drilled by the Oman Drilling Project. A sulfur-enriched serpentinite zone, containing up to 0.6 wt% S, occurs between shallow oxidized serpentinites (&lt;30 m) and deep partially serpentinized harzburgite (&gt;150 m). All three alteration zones are predominantly composed of serpentine. However, microanalysis of samples from the sulfur-enriched zone shows that mesh textures after olivine are composed of serpentine, brucite, and tochilinite mixtures, yielding optically black thin-section samples that characterize this sulfidic zone. It is proposed that sulfur accumulates in this zone via a process similar to those found in supergene ore deposits. Reaction-path models show that at shallow conditions open to atmospheric input, sulfur is mobilized via oxidative weathering of serpentinized dunite and harzburgite. Sulfate-bearing fluids percolate deeper and react with host rocks in a system closed to atmospheric input. As fluids become more reduced, dissolved sulfate is precipitated as sulfide minerals yielding rocks with ∼0.4 wt% S, like those observed in Hole BA1B. Despite enrichment of S in the sulfidic zone in Hole BA1B, Ni and Co contents are uniform throughout all three layers in the borehole. This is consistent with model results which show that Ni (and, by analogy, Co) is less mobile than S, and can be hosted in serpentine and NiFe alloys in addition to sulfides. The sulfur enrichment process may occur abiotically. However, sulfide enrichment via microbial reduction of sulfate and other sulfur species can also facilitate the formation of the sulfidic zone. Bioenergetic calculations show that abundant energy is available for sulfur reducing microbes, consistent with previous work demonstrating the presence of active, sulfate-reducing microorganisms in Hole BA1B and other nearby boreholes. This suggests that the observed sulfur enrichment is an ongoing process. Overall, this work shows that variable redox conditions are attained as fluids percolate and react with serpentinized ultramafic rocks at variable extents of interaction between aquifer fluids, host ultramafic rocks, and the atmosphere.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107828"},"PeriodicalIF":2.9,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142427796","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":"Metamorphism and geochronology of the Foping gneiss dome: Insights into Early Triassic collision of the Qinling Orogen, Central China","authors":"Jiali You,&nbsp;Zhao Yang,&nbsp;Longlong Gou,&nbsp;Yunpeng Dong,&nbsp;Xiaohui Shi,&nbsp;Dengfeng He","doi":"10.1016/j.lithos.2024.107827","DOIUrl":"10.1016/j.lithos.2024.107827","url":null,"abstract":"<div><div>The Foping gneiss dome, which outcrops in the narrowest part of the Qinling Orogen, contains high-grade metamorphic rocks that record the collision between the North China Block (NCB) and South China Block (SCB). Herein, petrography, mineral chemistry, phase equilibria modeling and U<img>Pb geochronology are used to constrain the collision events responsible for the high-grade metamorphism and exhumation of the Foping gneiss dome. The pelitic and mafic granulites sampled from the dome reveal peak metamorphism at P/T conditions of 6.2–7.4 kbar/ 805–855 °C, and document clockwise <em>P-T-t</em> paths with retrograde metamorphism of amphibolite-facies at 3.4–4.7 kbar/ 605–715 °C. While the pelitic schist from the rim of this dome witnessed peak metamorphism at P/T conditions of 4.9–5.1 kbar/ 590–605 °C and retrograde metamorphism at 3.5–3.7 kbar/ 510–520 °C. U<img>Pb dating of zircon and monazite confirm ages of ∼247–240 Ma for peak metamorphism with granulite-facies, ages of ∼208–198 Ma for retrograde metamorphism. The two metamorphic stages may record the transition from crustal thickening to dome exhumation, and the age of peak metamorphism probably marks the timing of the collision between the NCB and SCB along the Qinling Orogen in the Early Triassic. The collision probably terminated in the Late Triassic. The new discovery of the Triassic metamorphic event in the Qinling, combined with previously reported collision event of the Dabie Orogen to the east, supports the idea that the continental collision between the NCB and SCB along the Qinling-Dabie Orogen was synchronous.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107827"},"PeriodicalIF":2.9,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428472","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":"The volcanic/plutonic ratio in space and time, on Earth and beyond; How efficiently do magmas reach the surface during planetary evolution?","authors":"Olivier Bachmann ,&nbsp;Christian Huber","doi":"10.1016/j.lithos.2024.107825","DOIUrl":"10.1016/j.lithos.2024.107825","url":null,"abstract":"<div><div>With the recognition of multiple crustal cross sections on our planet, the advent of high-precision geochronology, and the ever-increasing application of geophysical imaging beneath volcanoes, we now know that volcanic rocks are the tip of a magmatic “heat”berg, overlying a significant igneous plumbing system that leaves many types of plutonic rocks in the crust. The ratio of volcanic to plutonic rocks in a given magmatic province (the V/P ratio) varies in space and in time as a function of several parameters controlled by the tectonic setting, geological age of the magmatic province, duration of magmatic activity, rheology of the crust, physical properties of the magma and state of the magma reservoirs. This contribution intends to explore these different parameters, in order to better constrain how the V/P ratios evolve in space and time in the course of planetary crust evolution. In particular, we stress that the efficiency of phase separation (in particular crystal / melt separation) in crustal magma reservoirs, fundamental to igneous differentiation and crust formation, is a key factor in controlling the V/P ratios. This efficiency, in turns, depends on parameters such as magma fluxes (“mantle productivity”) and chemical compositions (including volatile content), as well as the mechanical properties of the multi-phase magma and of its the crustal container. The emergence of thermo-mechanical modeling tools coupling the magma reservoir with its surrounding wall-rocks is paving the way to a more quantitative understanding of the fundamental processes that control the fate of magmas traversing through planetary crusts.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107825"},"PeriodicalIF":2.9,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142434449","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":"New constraints on the tectonic history of the basement of the Western Cordillera and coastal forearc of Ecuador","authors":"Richard Spikings ,&nbsp;Sebastian Betancur ,&nbsp;Cristian Vallejo ,&nbsp;Massimo Chiaradia ,&nbsp;Alexey Ulianov ,&nbsp;Antoine de Haller ,&nbsp;Stephen Forti ,&nbsp;Wilfried Winkler ,&nbsp;Bernardo Beate","doi":"10.1016/j.lithos.2024.107821","DOIUrl":"10.1016/j.lithos.2024.107821","url":null,"abstract":"<div><div>The Western Cordillera and forearc of the Northern Andes (north of 5° S) are constructed from allochthonous terranes floored by oceanic crust. A paucity of accurate geochronological data from the ultramafic and mafic basement sequences of the Western Cordillera and Coastal region of Ecuador has lead to distinct differences in published tectonic models, with different allochthonous units and contrasting timelines of accretion and collision. We present new zircon U<img>Pb and groundmass ⁴⁰Ar/³⁹Ar dates of the basement units, which have been combined with new whole rock geochemical and isotopic data to constrain their tectonic histories prior to and during their accretion to South America. Ultramafic and mafic rocks with oceanic plateau affinities can be divided into two plateau sequences, where an inboard, younger plateau (85–92 Ma; Pallatanga Block) is sutured against South America, and was modified by a pre-accretionary intra-oceanic arc (Pilatón-Pujilí arc) that was terminated by the accretionary process. An older, outboard oceanic plateau sequence (∼120 Ma) forms the basement to a series of coastal blocks within the present forearc (Piñon, San Lorenzo, Pedernales and probably the Esmeraldas blocks). The outer plateau also hosts a pre-accretionary intra-oceanic arc (Pascuales – San Lorenzo arc), which remained active during and post-accretion (San Lorenzo – Rio Cala arc). Coeval changes in palaeomagnetic declination, the onset of rapid exhumation (&gt;1 km/My) of the Early Cretaecous continental margin and sedimentation within the newly formed retro-arc foreland basin and foreland region supports a model where both oceanic plateau sequences accreted to South America in a single accretion event at 75–70 Ma. Thus, it is likely that the accreted oceanic plateau was composite, and included both the younger and older plateau sequences prior to accretion. We test an alternative model where the inner (younger) and outer (older) oceanic plateaus accrete in sequence, although this fails to account for the timing of block rotations in the forearc.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107821"},"PeriodicalIF":2.9,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142427785","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":"Crustal-derived versus mantle-derived carbonatites","authors":"Ben-Xun Su ,&nbsp;Shi-Ying Wang ,&nbsp;Jing Wang ,&nbsp;Hong-Rui Fan","doi":"10.1016/j.lithos.2024.107826","DOIUrl":"10.1016/j.lithos.2024.107826","url":null,"abstract":"<div><div>Mantle-derived carbonatites are an important type of igneous carbonate rock found in diverse tectonic settings. They are commonly associated with alkaline rocks and can contain various mineralization. In contrast, crustal-derived carbonatites form from the direct melting of limestones or marbles at depths within the Earth's crust. These crustal-derived carbonatites are exclusively found in orogenic belts, alongside metamorphic silicate rocks and marbles, and generally do not develop mineralization. Both types of carbonatites exhibit distinct differences in their sources, as well as their elemental and isotopic geochemistry. They can be classified as ortho‑carbonatite (mantle-derived) and para‑carbonatite (crustal-derived). The radiogenic Sr<img>Nd isotope compositions of both types of carbonatites, along with additional stable C<img>O isotopes and radiogenic Hf isotopes in para‑carbonatites, show correlations with geological time. These temporal variations could provide valuable insights into the Earth's evolutionary history.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107826"},"PeriodicalIF":2.9,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428469","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":"Polymetamorphism and metastability in Paleozoic schists of the central Appalachian Baltimore Terrane, USA","authors":"Freya R. George ,&nbsp;Daniel R. Viete ,&nbsp;George L. Guice ,&nbsp;Kayleigh M. Harvey ,&nbsp;Stephanie Walker ,&nbsp;Ethan F. Baxter","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":"488 ","pages":"Article 107824"},"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":"Douglas R. MacLeod,&nbsp;David R.M. Pattison","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":"488 ","pages":"Article 107818"},"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":"Miguel Roquet ,&nbsp;Erwin Schettino ,&nbsp;Marc Campeny ,&nbsp;José María González-Jiménez ,&nbsp;Michel Grégoire ,&nbsp;Rubén Piña ,&nbsp;Mathieu Leisen ,&nbsp;Joaquín A. Proenza ,&nbsp;Oscar Laurent ,&nbsp;Llorenç Planagumà ,&nbsp;Xavier Llovet","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":"488 ","pages":"Article 107820"},"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":"Daniel da Rosa Madruga ,&nbsp;Marcus Vinicius Dorneles Remus ,&nbsp;Guilherme Sonntag Hoerlle ,&nbsp;Ariela Oliveira Mazoz ,&nbsp;Cristiano de Carvalho Lana ,&nbsp;Norberto Dani","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":"488 ","pages":"Article 107822"},"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}