Lithos最新文献

{"title":"Contribution of alkaline magmas to the petrogenesis of Triassic aluminous A-type granites on Liaodong Peninsula, Northeastern China","authors":"Yu-Sheng Zhu ,&nbsp;Jin-Hui Yang ,&nbsp;Jin-Feng Sun ,&nbsp;Jing-Yuan Chen ,&nbsp;Lei Xu ,&nbsp;Rui Li ,&nbsp;Bao-Quan Zhou","doi":"10.1016/j.lithos.2024.107834","DOIUrl":"10.1016/j.lithos.2024.107834","url":null,"abstract":"<div><div>Aluminous A-type granites are not typically associated with mantle-derived rocks. Their generation is usually linked to crustal melting with mantle-derived magmas primarily acting as a heat source. However, the Triassic Bolinchuan A-type granites on Liaodong Peninsula, northeastern China, coexist with a large mantle-derived alkaline igneous complex, indicating a close genetic relationship that provides new insights into the petrogenesis of aluminous A-type granites. The Bolinchuan granites were formed during 230–226 Ma, coeval with syenites in the alkaline complex (230–224 Ma). The granites are metaluminous to weakly peraluminous, but have relatively high alkali contents (8.61–9.40 wt%). Their high Ga/Al ratios, elevated Nb, Zr, Ce, and Y contents, and high magmatic temperatures (&gt;875 °C) indicate an affinity with aluminous A-type granites. However, the Bolinchuan granites have relatively high MgO contents at intermediate SiO₂ contents, with Mg# values of up to 47; these features are inconsistent with the melting of only crustal rocks. Instead, these granites contain mineral phases similar to those of the syenites and exhibit major and trace element trends that are continuous with those of the syenites. Their geochemical features include enrichments in large-ion lithophile elements (e.g., Ba and Sr), depletions in high-field-strength elements (e.g., Nb and Ta) and heavy rare earth elements, and small negative Eu anomalies, which are also consistent with the features of the associated syenites. Furthermore, the granites and their accessory minerals have high initial ⁸⁷Sr/⁸⁶Sr ratios, and low ε_Nd(t) and ε_Hf(t) values, which are similar to the syenites, apart from being slightly less isotopically enriched. These geochemical and isotopic features suggest the Bolinchuan granites formed from the syenitic magmas by fractional crystallization of alkali feldspar, amphibole, and apatite, in combination with the addition of ∼30 % juvenile crust-derived materials, as indicated by modeling. Our study reveals that differentiation of mantle-derived alkaline magmas can generate magmas parental to aluminous A-type granites. As such, the mantle not only provides the heat for the formation of aluminous A-type granites, but can also be the main source of the magmas.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107834"},"PeriodicalIF":2.9,"publicationDate":"2024-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142446361","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":"Constraints of in-situ elemental compositions and U–Pb ages of cassiterite on the origin of the Cretaceous Gejiu and Dulong tin deposits, SW China: Implications for the linkage of tin belts in SE Asia","authors":"Zhi Zhang ,&nbsp;Jie-Hua Yang ,&nbsp;Rui-Zhong Hu ,&nbsp;Bin Fu ,&nbsp;Qian Hu ,&nbsp;Mei-Fu Zhou","doi":"10.1016/j.lithos.2024.107832","DOIUrl":"10.1016/j.lithos.2024.107832","url":null,"abstract":"<div><div>The western Yunnan tin belts in SW China and the southern Myanmar tin belt in SE Asia are traditionally thought to be part of the SE Asian tin metallogenic province. However, the tectonic setting of the Youjiang tin belt in SW China and its genetic relationship to the other tin belts are poorly documented. In this belt, the giant Gejiu and Dulong tin deposits are typical of skarn-type deposits and both contain contact and distal skarn orebodies. Tin ores of distal orebodies in these two deposits are composed of cassiterite, sulfide and calcite. In both deposits, most cassiterite grains from these ores are rich in Fe and W and depleted in Nb and Ta. They have ²³⁸U/²⁰⁶Pb ages between 81.4 and 84.1 Ma, similar to hosting granitic plutons. Two generations of cassiterite with distinctly different microtextures and trace elemental compositions can be recognized. The first generation (Cst-I) is compositionally and texturally homogeneous, but the second generation (Cst-II) displays distinctly oscillatory zoning. Cst-II contains Nb, W, and U lower, and Fe, Ta, Zr and chalcophile elements (Ga, Ge, In, and Sb) higher than Cst-I. These textural and compositional variations reflect the potential involvement of meteoric water in the magmatic-hydrothermal system. In this system, ore-forming fluids were evolved to more alkaline and oxidized to facilitate the precipitation of cassiterite. Our study indicates that these two deposits in the Youjiang tin belt have mineralization styles similar to those in the adjacent western Yunnan and southern Myanmar tin belts and all these tin belts belong to the SE Asian metallogenic provinces. A westward-younging trend of tin mineralization in these three belts can be explained by the rollback of the subducted Neo-Tethyan oceanic slab. This setting is different from the one related to the subduction of the Paleo-Pacific plate.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107832"},"PeriodicalIF":2.9,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142536317","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":"Petrogenesis of the Zenong Group volcanics in the central Lhasa subterrane, Tibet: Geodynamic implications of the scissor-like southward subduction of the Shiquanhe-Jiali Tethyan Ocean","authors":"Jia-jia Yu ,&nbsp;Wei Chen ,&nbsp;Ju-Xing Tang ,&nbsp;Cheng-Yang Wang ,&nbsp;Xu-Dong Ma ,&nbsp;Qing-Ping Liu ,&nbsp;Meng-Xiang Di ,&nbsp;Chang Liu","doi":"10.1016/j.lithos.2024.107831","DOIUrl":"10.1016/j.lithos.2024.107831","url":null,"abstract":"<div><div>The widespread Mesozoic volcanics in the central Lhasa subterrane have been a subject of debate concerning their genetic mechanisms. Leveraging geochronology, element geochemistry, and Hf isotopes, we have systematically investigated the origin and dynamic mechanisms of the Zenong Group volcanics in the Bengnazangbu and western Dangreyongcuo areas in the east-middle part of the central Lhasa subterrane. Comprising primarily of andesites, dacites, and rhyolites, the Zenong Group volcanics display distinct geochemical signatures. In the Dangreyongcuo and Bengnazangbu areas, the andesite, dacite, and rhyolites show medium to high-K calc-alkaline characteristics. These rocks share similarities in trace element distribution, exhibiting enrichment in Rb, U, Th, Pb, and K, but depletion in Nb, Ta, Ti, Ba, and Sr. These characteristics accord with the typical composition of arc volcanic rocks. Zircon U<img>Pb dating has revealed that the volcanic rocks in the Dangreyongcuo and Bengnazangbu areas have ages of 127–126 Ma and 112–103 Ma, respectively. Further, the distribution of zircon U<img>Pb ages suggests a west-east younging trend both in the Zenong Group and the Shiquanhe-Jiali suture zone. The ε_Hf(t) values of andesite, dacite, and rhyolite are all below the chondrite standard line, ranging from 0 to −15, and the crustal model ages range from 2.0 to 1.2 Ga. Our data, combined with the geological setting, whole-rock geochemistry, Hf isotopes, and geochronology, suggest that the Zenong Group volcanic rocks are the result of the mixing of mantle wedge melts formed by the subduction of the Shiquanhe-Jiali Ocean with the lower crust of the Lhasa terrane, and undergoing fractional crystallization of amphibole ad plagioclase. And we believe that the Shiquanhe-Jiali Ocean was sequentially closed from west to east in a scissor-like fashion during southward subduction.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"490 ","pages":"Article 107831"},"PeriodicalIF":2.9,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142658367","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":"Timing of the subduction initiation and ophiolite emplacement of the inner Tauride Ocean: Insight from the Pınarbaşı ophiolite in Central Türkiye","authors":"Rahmi Melih Çörtük ,&nbsp;Ömer Faruk Çelik ,&nbsp;Mutlu Özkan ,&nbsp;Joshua H.F.L. Davies ,&nbsp;Andrea Marzoli","doi":"10.1016/j.lithos.2024.107833","DOIUrl":"10.1016/j.lithos.2024.107833","url":null,"abstract":"<div><div>Late Cretaceous ophiolites are widespread in southern Türkiye, including the Tauride Belt Ophiolites and the Central Anatolian Ophiolites. Here, we report new geological, geochemical, geochronological, and zircon isotopic data from ophiolitic rocks of the Pınarbaşı ophiolite (Eastern Tauride Belt). The Pınarbaşı ophiolite forms incomplete sequences, with its mantle section dominated by serpentinized harzburgite and chromitites, while the crustal section comprises ultramafic and mafic cumulates. Whole-rock and mineral chemistry data suggest a supra-subduction zone origin. LA-ICP-MS zircon U-Pb age of 88.2 ± 0.4 Ma (MSWD = 0.84) was obtained from a plagiogranite dyke cutting serpentinized peridotite of the Pınarbaşı ophiolite. Another, U-Pb zircon crystallization age of 96.8 ± 0.6 Ma (MSWD = 1.53) was obtained from a plagiogranite dyke within the mélange of the Pınarbaşı ophiolite. Hafnium isotope compositions of these zircons (εHf(t) = +26.4 to +3.1) suggest a depleted to slightly enriched mantle source. The formation ages of the crustal rocks (gabbro, plagiogranite, and dolerite) of the Cretaceous ophiolites in the Tauride Belt from this and previous ophiolite occurrences, suggest that supra-subduction zone ophiolites in the Inner Tauride Ocean formed during the period ∼101–87 Ma. On the other hand, the peak metamorphism of the metamorphic sole rocks is reported to have occurred around ∼104 Ma. According to all available petrogenetic and geochronological data, it is considered that the supra-subduction zone crust developed shortly (∼ 3–4 Myr) after the initiation of intra-oceanic subduction and this lasted ∼10–15 Myr.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107833"},"PeriodicalIF":2.9,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142442934","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":"Constraints of upper crust magmatic processes on the formation of Saindak porphyry Cu deposit: Insights from mineral geochemistry","authors":"Lu Wang ,&nbsp;Zi-xuan Wang ,&nbsp;Yuan-chuan Zheng ,&nbsp;Zeng-qian Hou ,&nbsp;Zhu-sen Yang ,&nbsp;Chang-da Wu ,&nbsp;Xin Li","doi":"10.1016/j.lithos.2024.107829","DOIUrl":"10.1016/j.lithos.2024.107829","url":null,"abstract":"<div><div>Upper crustal magmatic processes play a crucial role in linking the magmatic and hydrothermal systems of porphyry deposits, ultimately controlling the generation of ore-forming fluids. Understanding these processes within a magma chamber is essential for deciphering the formation of porphyry deposits. The Saindak deposit, a large porphyry Cu system in the western Chagai belt, features coeval ore-forming and barren magma pulses, providing key insights into the characterization of porphyry systems. In this study, detailed petrographic observations and geochemical analyses of amphibole, plagioclase, and apatite were conducted to unravel the magmatic evolution at Saindak. Based on textural relationships and crystallization sequences, three distinct populations of amphibole in the ore-forming magma were identified. These amphiboles record the entire fractional crystallization process of magma that initially emplaced at a depth of ∼5 km to the connected magma system at ∼2 km. The study of amphibole and apatite reveals that the fertile magma underwent large-scale fluid exsolution in an open system. The simultaneous and rapid depletion of Cu, Cl, S, and H₂O in the magma indicates that Cl and S were highly partitioned into the exsolved fluid phase. These elements formed complexes, which effectively concentrated metals in the fluid. Conversely, the barren magma was characterized by either low metal content or limited fluid exsolution within the magma chamber. Overall, we reconstruct the upper crustal magmatic processes at Saindak and conclude that efficient extraction of Cu through fluid exsolution is the key to porphyry deposit formation.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107829"},"PeriodicalIF":2.9,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142438344","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":"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}