Lithos最新文献

{"title":"Miocene adakitic monzogranites in the Northeast Pamir: Evidence for post India-Eurasia collisional evolution","authors":"Xiao-Qiang Liu ,&nbsp;Hua-Dong Ma ,&nbsp;Masumeh Sargazi ,&nbsp;Haibo Zou ,&nbsp;Muredili Mahemuti ,&nbsp;Xian-Tao Ye ,&nbsp;Chao He","doi":"10.1016/j.lithos.2024.107782","DOIUrl":"10.1016/j.lithos.2024.107782","url":null,"abstract":"<div><p>The Pamir Plateau contains critical information on the tectonic evolution of the Tethys domain. In this study, we report geochronology, geochemistry, and Sr-Nd-Hf isotopic compositions of the Cenozoic adakitic monzogranite in the Reskam and Taxkorgan areas, NE Pamir, to provide new insights into the post-collisional tectonic evolution following the India-Eurasian collision. Zircon U<img>Pb ages reveal these granitoids were emplaced at ca 12–8 Ma. Geochemically, they exhibit relatively uniform whole-rock major and trace element compositions, and share typical adakitic signatures with high SiO₂ (68.55–73.30 wt%), moderate Al₂O₃ (14.11–15.84 wt%), elevated Sr (399–1710 ppm) and La (34–182 ppm), but low Y (5.53–15.10 ppm) and Yb (0.39–1.26 ppm), and thus in high Sr/Y (32−200) and (La/Yb)_N ratios (20–236). Isotopically, these adakitic rocks show significantly enriched whole-rock Sr<img>Nd (ε_Nd(t) = −7.97 to −5.76; ⁸⁷Sr/⁸⁶Sr(t) = 0.7072–0.7110) and zircon Hf (mostly ε_Hf(t) -5 to −2) isotopic compositions. Elemental and isotope signatures indicate their origin from partial melting of mafic-intermediate sources under high pressure, with a residuum of negligible feldspar but dominant garnet. Integrating the new findings with reported data of granitoids in the Pamir, we estimate the crustal thickness variations from the Cretaceous to Miocene. The crustal thickness in the Pamir region largely remained no more than 45 km before India-Asia collision, after which a significant increase in crustal thickness occurred, reaching a peak of 80–100 km around 10 Ma. We propose that the break-off of the subducted Neo-Tethys oceanic slab (ca. 40 Ma) and lithospheric delamination (ca. 25 Ma) led to two-stage rapid continental uplift events in Pamir Syntax.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107782"},"PeriodicalIF":2.9,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142129976","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":"Fluid-rock interaction related to alpine subduction of Allalingabbro deduced from large-size μXRF element maps","authors":"Kurt Bucher ,&nbsp;Peter Thomet ,&nbsp;Rüdiger Kilian","doi":"10.1016/j.lithos.2024.107774","DOIUrl":"10.1016/j.lithos.2024.107774","url":null,"abstract":"<div><p>Alpine subduction of a block of olivine gabbro produced a plethora of different assemblages and local structures typical of high-pressure and low-temperature metamorphism. However, gabbro with the locally well-preserved igneous assemblage olivine - augite - plagioclase occurs in some domains of a 2 km long outcrop (Allalinhorn, western Alps).</p><p>A large variety of hydrate minerals including zoisite, glaucophane, talc, Mg-chloritoid, chlorite, paragonite and muscovite formed during Alpine subduction of the metagabbro. The three primary igneous minerals have been replaced by hydration reactions during Eocene subduction. Talc, omphacite, and zoisite + jadeite and are the main minerals in the local domains after olivine, augite and plagioclase respectively. The rocks preserved the coarse grained igneous texture.</p><p>An excellent overview of the complex coarse textures of the eclogite facies rocks has been provided by element distribution maps produced from up to 25 cm large polished slabs of typical samples of Allalingabbro using a μXRF instrument. The RGB images suggest that the minerals formed at the high-pressure in the presence of an aqueous fluid. The pseudomorphing reactions progressed close to volume conservation. The hydration reactions required an H₂O fluid containing dissolved solids. The mapped distribution of elements including trace elements provides important clues on the origin and mobility of these elements in the hydration fluid. The homogeneously distributed immobile Cr in omphacite portrays primary augite. The irregular patchy Sr distribution resulted from small-scale migration of components replacing plagioclase by Sr-bearing zoisite and jadeite. Coherent Ni signals are related to the presence of talc. The talc occurs as a late infill of structures produced by dissolving olivine. Mg-chloritoid, kyanite and mica coat the former grain-boundary of olivine and plagioclase suggesting that olivine dissolved at eclogite facies conditions. Talc formed at distinctly lower pressures, however, as implied by computed model reactions. The olivine replacement structures are often larger than the size thin section and can be excellently studied by the large size μXRF patterns used in this study.</p><p>The fractured surroundings of the locations of olivine provided the necessary hydraulic conductivity for hydration reactions to progress. The fractures and small veinlets contain late Ni-bearing talc. Cl is only present in very late vein amphibole suggesting that hydration fluids in the subduction zone transported dissolved components as hydrous complexes (and their dissociated ions). There is no evidence for the presence of a Cl-brine during subduction. In addition to primary olivine as a local Ni source, the element may also have partly been imported with the hydration fluid and originate from dehydration of ophiolitic serpentinites in the slab.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107774"},"PeriodicalIF":2.9,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142148260","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":"Geochemical and isotopic features of the Early Cretaceous volcanism of the Torey Volcanic Field (Eastern Transbaikalia, Russia) as a record of the transition from pyroxenite to eclogite mantle source","authors":"V.M. Savatenkov ,&nbsp;M.V. Kuznetsov ,&nbsp;L.V. Shpakovich","doi":"10.1016/j.lithos.2024.107778","DOIUrl":"10.1016/j.lithos.2024.107778","url":null,"abstract":"<div><p>The Mesozoic magmatic activation in Central and Northeast Asia resulted in the formation of a large volume of volcanic rocks with diverse compositions. The most dramatic compositional change occurred at the end of the Early Cretaceous, when mainly alkaline basaltic lavas began to erupt after subalkaline differentiated lavas. The nature of crustal and mantle processes that led to this change in volcanism remains unclear. The Torey Volcanic Field (TVF) of Eastern Transbaikalia (Russia) demonstrates a similar compositional change. Therefore, the TVF is crucial to studying the cause of the difference in geochemical and isotopic signatures of the Mesozoic volcanism in Central and Northeast Asia.</p><p>TVF belongs to the northeastern end of the Eastern Mongolia Volcanic Area (EMVA). Like other volcanic fields of the EMVA, TVF formed in two stages: early (∼121–129 Ma) and late (∼101–119 Ma). The TVF is composed of subalkaline and alkaline basaltic trachyandesites – trachyandesites. All TVF rocks are characterized by negative Ti and Sr anomalies and positive Ba and Pb anomalies. Compared to the late TVF rocks, the early TVF rocks have distinct negative Ta and Nb anomalies and are highly enriched in light rare earth elements relative to heavy rare earth elements. TVF rocks have the following isotopic characteristics: ⁸⁷Sr/⁸⁶Sr_(t) = 0.70477–0.70540, ε_{Nd(t) =} − 0.9 – +2.4, ²⁰⁶Pb/²⁰⁴Pb_(t) = 17.9–18.4, and ²⁰⁷Pb/²⁰⁴Pb_(t) = 15.5–15.6. However, older rocks mainly have higher ε_Nd(t) values and ²⁰⁶Pb/²⁰⁴Pb_(t) and ²⁰⁷Pb/²⁰⁴Pb_(t) ratios.</p><p>Geochemical and isotopic data of samples suggest that the TVF formed by melting in the continental metasomatized lithospheric mantle (CMLM). Phlogopite-amphibole-rutile-bearing pyroxenite veins played a major role in the formation of older rocks. Eclogite, represented by the recycled oceanic crust or the buried lower continental crust, was dominant in the source of younger rocks. The common source for both groups of the TVF rocks was metasomatized hydrous peridotite.</p><p>Lithospheric extension and subsequent asthenospheric upwelling led to melting in the CMLM and the formation of the TVF. At the early stage of the volcanism, melting occurred at relatively low temperatures where amphibole, phlogopite, and rutile were stable. Due to ongoing lithosphere extension, the melting of eclogite occurred at a higher temperature and/or lower pressure at the late stage of the volcanism.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107778"},"PeriodicalIF":2.9,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142130057","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":"Extra-terrestrial mantle samples: Rare Earth Element variations and evidence for melt metasomatism in ureilite meteorites","authors":"Hilary Downes ,&nbsp;David W. Mittlefehldt ,&nbsp;Aidan J. Ross ,&nbsp;Cin-Ty Lee","doi":"10.1016/j.lithos.2024.107775","DOIUrl":"10.1016/j.lithos.2024.107775","url":null,"abstract":"<div><p>Ureilites are meteorites derived from the mantle of a reduced differentiated asteroid, the “Ureilite Parent Body” (UPB), which was later disrupted by impact with another Solar System body. They have ultramafic compositions dominated mostly by olivine and pigeonite with rare orthopyroxene and augite; aluminous phases are generally absent. Ureilites vary from abundant peridotites to much rarer pyroxenites, and their core olivine compositions range from Fo₇₄ to Fo₉₇ across different samples. The UPB experienced sufficiently high temperatures to undergo silicate partial melting, as shown by depletion in the Light Rare Earth Elements (LREE) in bulk restitic ureilites. Plagioclase and merrillite were probably present in the UPB mantle but have been completely removed during silicate partial melting. Partial melts of the UPB mantle are represented by glassy melt inclusions, igneous clasts in ureilite breccias, cumulus augite in some ureilites, and rare trachyandesitic fragments. These melts are generally intermediate and sub-alkaline in composition, although a few are alkaline. They have more enriched and flatter bulk REE patterns than the restitic ureilites and often show positive Eu anomalies. Glasses (representing melts) in ureilites from this study range from 57 to 79 wt% SiO₂. One sample (AhS 22) shows petrographic and geochemical evidence for interaction between magma and the solid UPB mantle by forming metasomatic augite.</p><p>Silicate minerals in ureilites analysed by LA-ICP-MS are generally LREE-depleted, with negative Eu anomalies. Ureilitic olivines have the lowest REE contents and the smallest negative Eu anomalies. Low-Ca pyroxenes have similar patterns with slightly stronger Eu anomalies. Augites have the highest REE contents and the most negative Eu anomalies. Augites show REE disequilibrium with olivine and low-Ca pyroxene, suggesting that they were not part of the restitic assemblage but were added by silicate melts passing through the UPB mantle, i.e. they are metasomatic in origin. We also discuss the size of the original UPB, using silicate minerals as evidence for it being a typical asteroid rather than a planet-sized object.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107775"},"PeriodicalIF":2.9,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024493724002883/pdfft?md5=791f37319d7c40730209ce855060527a&pid=1-s2.0-S0024493724002883-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142095735","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":"Every intrusion has its time: New zircon U-Pb ages from the Greater Antilles Arc in the Cordillera Central, Dominican Republic","authors":"Birk P. Härtel ,&nbsp;Oliver Frei ,&nbsp;Mandy Zieger-Hofmann ,&nbsp;Klaus P. Stanek","doi":"10.1016/j.lithos.2024.107779","DOIUrl":"10.1016/j.lithos.2024.107779","url":null,"abstract":"<div><p>The Cordillera Central on the island of Hispaniola comprises a section through the crust of the Late Cretaceous phase of the Greater Antilles Arc. The gabbroic-tonalitic batholiths of the Cordillera Central are widely considered to represent the temporal main axis of this island arc. Although they have been studied extensively, the timing of batholith emplacement is not well constrained. We present new LA-ICP-MS U-Pb zircon ages and whole-rock geochemical data from diorites, tonalites, and granites of the El Río, El Bao, Jumunuco, and Loma de Cabrera batholiths, and from tonalite boulders deposited in the Eocene-Oligocene Velázquitos Formation. The sample ages range from 97 to 80 Ma with small differences between the intrusive bodies. Samples from the El Río, Jumunuco, and Loma de Cabrera batholiths cover most of the above age range, while the rocks of the El Bao pluton yield a well-defined maximum around 87 Ma. In the El Río batholith, U-Pb ages are in good agreement with the exposed contact relationships. Based on their composition and existing geochronological data, we divide the intrusive history of the Cordillera Central into four stages reflecting different magma compositions: ultramafic to dioritic magmatism lasted from 105 to 87 Ma, tonalite units formed between 96 and 84 Ma, felsic tonalites and granites intruded from 87 to 80 Ma overlapping with a younger phase of dioritic magmatism between 84 and 78 Ma.</p><p>The geochemical signatures of the felsic tonalites of the Jumunuco batholith and the granites of the El Río batholith are similar to the rhyolitic and dacitic island-arc volcanics from the Restauración Formation of the Tireo Group, thus confirming the relationship between the volcanic and plutonic units of the Greater Antilles Arc. Based on petrographical, geochemical, and geochronological data of the tonalite samples from the Velázquitos Formation, we interpret these boulders as being eroded from the Jumunuco batholith or the related Buena Vista pluton.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107779"},"PeriodicalIF":2.9,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024493724002925/pdfft?md5=15cf15feacb0bc19f46b09abcf7f636e&pid=1-s2.0-S0024493724002925-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142095843","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":"Unusual spinel in the “Verde Prato” serpentinized peridotite","authors":"Giancarlo Capitani ,&nbsp;Roberto Compagnoni ,&nbsp;Roberto Cossio ,&nbsp;Linda Pastero ,&nbsp;Roberto Conconi ,&nbsp;Marcello Mellini","doi":"10.1016/j.lithos.2024.107777","DOIUrl":"10.1016/j.lithos.2024.107777","url":null,"abstract":"<div><p>A petrographic study of “<em>Verde Prato</em>” (trade name of an ophiolitic serpentinised peridotite quarried in Tuscany) revealed, next to a relict Cr-spinel, another opaque ore mineral apparently containing ca.17 wt% SiO₂. In order to unveil the origin of this anomalous composition, detailed SEM-EDS, μ-Raman spectroscopy and X-ray μ-diffraction investigations were undertaken, which provided useful but somehow contrasting indications. Therefore, in order to definitely unveil the nature of the unusual opaque mineral, a specific TEM study was undertaken. This showed the presence of submicroscopic euhedral Mn-Cr-Fe-spinels in a matrix of a 7 Å layer-silicate (Al-lizardite). Interesting, all the submicroscopic spinel grains were found to share the same crystallographic orientation, suggesting an origin from a single, larger, former crystal. This unusual type of alteration of the mantle spinel probably occurred on the ocean floor during the pervasive polyphase process of hydrothermal peridotite serpentinization. Overall, by mapping the different serpentinite microstructures and compositions, a polyphase serpentinization history consisting of at least eight different cycles has been suggested. Moreover, the spinel composition indicates that the alteration was accompanied by Mn-metasomatism, made possible by the close proximity of Mn-rich hydrothermal vents, such as “black smokers”.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107777"},"PeriodicalIF":2.9,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024493724002901/pdfft?md5=3f685fd89464f1fb0795a50bffaa76fb&pid=1-s2.0-S0024493724002901-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142130056","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":"Revisiting the formation of lunar anorthosites via the RbSr isotope systematics","authors":"Qing Zhou ,&nbsp;Heng-Ci Tian ,&nbsp;Liyu Shan ,&nbsp;Sen Hu ,&nbsp;Wei Yang ,&nbsp;Maoyong He ,&nbsp;Lei Zhang ,&nbsp;Yangting Lin ,&nbsp;Xianhua Li","doi":"10.1016/j.lithos.2024.107780","DOIUrl":"10.1016/j.lithos.2024.107780","url":null,"abstract":"<div><p>The incorporation of KREEP (potassium, rare-earth element, and phosphorus), mantle-derived mafic melts and trapped liquid into the lunar ferroan anorthosite (FAN) suite plays a pivotal role in generating their geochemical and isotopic variations. Nonetheless, the specific involvement and distinct roles of these different components remain controversial. This study presents in-situ Sr isotopic data for 28 anorthositic clasts found within lunar feldspathic meteorites to trace their sources and post-modification processes. We find that these plagioclases exhibit substantial variations in their measured ⁸⁷Sr/⁸⁶Sr values (0.69978–0.70357), in contrast to the relatively narrow range observed in Apollo 16 FANs, thereby likely reflecting a diverse chemical composition of lunar crustal rocks. In contrast, the analyzed plagioclases have consistently low ⁸⁷Rb/⁸⁶Sr ratios (0.00185–0.03962), similar to those of Apollo samples, reflecting impact-induced loss of Rb. Detailed investigations indicate that certain elevated ⁸⁷Sr/⁸⁶Sr ratios are probably not caused by terrestrial contamination or instrumental analysis, but most likely result from the decay of ⁸⁷Rb from sources with initial ⁸⁷Rb/⁸⁶Sr higher than 0.0119–0.1380. However, such elevated ⁸⁷Rb/⁸⁶Sr values cannot solely result from crystallization of the lunar magma ocean (LMO) and likely involve KREEP components. Combined with trace element data, we estimate the maximum proportion of KREEP melt in the formation of lunar anorthosites. Future analyses of lunar anorthosites collected by China's Chang'e-5 and Chang'e-6 missions will be crucial for validating the observed Sr isotopic heterogeneity.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107780"},"PeriodicalIF":2.9,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024493724002937/pdfft?md5=6fe6594065b14f8dc43965271571baf4&pid=1-s2.0-S0024493724002937-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142095734","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":"Origin of the coeval cordierite granite, metapelite and diorite in the Qinghai Nanshan (NW China): Evidences from petrology, geochemistry, geochronology and P-T conditions","authors":"Zhen M.G. Li ,&nbsp;Juan Wang ,&nbsp;Mingwen Wang ,&nbsp;Chun-Ming Wu","doi":"10.1016/j.lithos.2024.107773","DOIUrl":"10.1016/j.lithos.2024.107773","url":null,"abstract":"<div><p>The origin of coeval magmatic and metamorphic rock associations is of great significance in tectonic interpretations. In this study, spatially associated cordierite granite (S-type), metapelite and diorite from the Qinghai Nanshan (NW China) area were dated to be coeval at ∼247–244 Ma. The cordierite granite and metapelite have almost uniform peak pressure-temperature (<em>P</em>–<em>T</em>) conditions of <em>c.</em> 3.8–5.0 kbar / <em>c.</em> 740–790 °C, indicating a geothermal gradient of higher than ∼40 °C / km. The zircon crystallization temperature of the diorite pluton is estimated to be <em>c.</em> 760 °C by Ti-in-zircon thermometer, putting a lower limit of temperature for dioritic magma. Both cotectic (phenocrysts) and restitic cordierite crystals were identified in the cordierite granite. Similar whole rock compositions of the coarse-grained cordierite granite and the metapelite in the Qinghai Nanshan area as well as the average / median pelite worldwide, imply formation of the granite was from almost complete melting of autochthonous metapelite, followed by in-situ recrystallization with negligible / without melt extraction. These data indicate that the cordierite granite and metapelite are both products of the contact aureole surrounding the diorite pluton. This study presents an example for better understanding the transition from high-grade metapelite to S-type granite.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107773"},"PeriodicalIF":2.9,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142076951","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":"Late Triassic basaltic andesites unveil inception of Neo-Tethys Ocean in Gyaca area of Tethyan Himalaya","authors":"Qinwen Gao ,&nbsp;Feng Huang ,&nbsp;Song Zhang ,&nbsp;Yunchuan Zeng ,&nbsp;Mingjian Li ,&nbsp;Shuo Wang ,&nbsp;Chenyuan Hua ,&nbsp;Hongxia Yu ,&nbsp;Yinhui Zhang ,&nbsp;Jifeng Xu","doi":"10.1016/j.lithos.2024.107765","DOIUrl":"10.1016/j.lithos.2024.107765","url":null,"abstract":"<div><p>The formation and evolution of the Neo-Tethys Ocean profoundly influenced the pre-collisional configuration of the Tibetan Plateau before the India-Asia collision. However, the timing of the Neo-Tethys Ocean's opening and the resulting magmatism remain subjects of ongoing debate. Here we present an integrated investigation of a suite of basaltic andesites exposed in the Gyaca area, eastern Tethyan Himalaya, southern Tibetan Plateau. Using zircon U-Pb-Hf isotopes, bulk rock geochemical data, and whole-rock Sr-Nd-Hf isotopic data, we attempt to temporally and petrogenetically constrain the early stages of magmatism associated with the opening of the Neo-Tethys Ocean. The Gyaca basaltic andesites were formed in the Late Triassic (ca. 217 Ma). They exhibit geochemical features resembling those of arc magmatic rocks, characterized by moderate light/heavy rare earth element fractionation ((La/Yb)_<em>N</em> = 5.16–6.57), enrichment in large ion lithophile elements, and depletion in high field strength elements. They also show variable whole-rock Sr<img>Nd (⁸⁷Sr/⁸⁶Sr_i = 0.709848–0.712233; ε_Nd(t) = −1.12 to +0.19) and zircon Hf (ε_Hf(t) = −6.2 to +3.2) isotope compositions, alongside depleted whole-rock Hf isotopes (ε_Hf(t) = +2.83 – +7.42). Compared to coeval arc magmatism in the southern Lhasa Terrane, southern Tibetan Plateau, the Gyaca basaltic andesites show higher incompatible element contents and more enriched Nd<img>Hf isotope compositions, ruling out their origin as products of northward subduction of the Neo-Tethys oceanic plate. The negative correlation between the Mg# of these basaltic andesites and ε_Nd(t) suggests that more primitive magmas have more enriched Nd isotopes, likely due to assimilation with sediments during turbulent magma ascent under high thermal conditions. Combining existing petrological and sedimentological evidence, we propose that the Gyaca basaltic andesites likely document the early interaction between the upwelling asthenosphere and the overlying sediments during the initial spreading of the Neo-Tethys seafloor. Consequently, the opening of the Neo-Tethys Ocean in the eastern Himalaya would not postdate the Late Triassic.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107765"},"PeriodicalIF":2.9,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142088795","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":"In situ geochemistry of apatite: Petrogenetic and tectonic interpretations of Jurassic felsic magmatism in the Yanbian area, NE China","authors":"Yu Li ,&nbsp;Chen-Yang Sun ,&nbsp;Wen-Liang Xu ,&nbsp;Xiao-Ming Zhang","doi":"10.1016/j.lithos.2024.107764","DOIUrl":"10.1016/j.lithos.2024.107764","url":null,"abstract":"<div><p>Geochemical analyses of individual minerals provide more detailed insights into the petrogenesis of igneous rocks than whole-rock analyses. This study conducted <em>in situ</em> geochemical and Nd isotope analyses of apatites from 10 Jurassic granitic plutons in the Yanbian area, NE China, to establish the petrogenesis and regional tectonic evolution. The results indicate that the apatite geochemistry of Jurassic granitoids in the Yanbian area was controlled primarily by the composition of parental melt. Post-magmatic alteration may lead to geochemical decoupling between apatite and parental melt, while Nd isotopes exhibit some resilience to such alterations. Apatites from Early Jurassic granitoids display characteristics that are consistent with an I-type origin, whereas those from Middle and Late Jurassic granitoids exhibit an adakitic affinity. Variations in apatite compositions indicate the fractional crystallization of other rare earth element (REE)-bearing minerals during magma evolution. The early crystallization of plagioclase and allanite led to decreases in Sr and Th contents in apatite, respectively, resulting in a negative Eu anomaly and light REE depletion. The fractional crystallization of titanite and hornblende resulted in the depletion of middle REE in apatite. Hornblende is regarded as the main residual phase in the magma source of Middle and Late Jurassic adakitic granitoids in the Yanbian area. Apatite Nd isotopic compositions suggest that the Jurassic granitoids in the Yanbian area originated from two crustal sources: the Central Asian Orogenic Belt and the North China Craton. Additionally, increasing trends in apatite Sr/Y and (La/Yb)_N ratios from the Early to Late Jurassic suggest a gradual thickening of the regional crust, which is likely driven by the continentward migration of the subduction zone associated with the Paleo-Pacific Plate.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107764"},"PeriodicalIF":2.9,"publicationDate":"2024-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142040722","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}