Geosystems and Geoenvironment最新文献

{"title":"Constraints on tectonic processes in subduction mélange: A review of insights from the Catalina Schist (CA, USA)","authors":"Sarah C. Penniston-Dorland ,&nbsp;Kayleigh M. Harvey","doi":"10.1016/j.geogeo.2023.100190","DOIUrl":"https://doi.org/10.1016/j.geogeo.2023.100190","url":null,"abstract":"<div><p>Subduction mélange, with its distinctive block-in-matrix structure, is documented in exhumed fossil subduction zones worldwide. Rocks from these terranes preserve features that record tectonic processes from the time that the rocks were at the subduction interface. Careful study of these features allows for connections to be made with tectonic processes occurring in active subduction zones. The Catalina Schist mélange has served as an exhumed analog in such studies as it records abundant evidence for tectonic processes occurring at the subduction interface. Focusing of fluids in mélange matrix at the subduction interface is documented, and this fluid-rich environment may have contributed to seismic activity. Deformation and tectonic mixing juxtaposed disparate materials (mafic, ultramafic, and sedimentary rocks) over length-scales of 10s of km along the interface, occurring in concert with metasomatism and mass transport by fluids to create mineralogically, chemically, and rheologically distinct compositions. These processes may have impacted seismic behavior and plate geodynamics along with influencing the chemistry of arc magmas that form above the subduction interface. Evidence suggests that the duration of tectonic formation of mélange may be variable from one locality to another, with relatively small differences in peak ages of blocks of &lt;10 Myrs recorded in the amphibolite facies rocks of the Catalina Schist.</p></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"2 3","pages":"Article 100190"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49747092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Detrital zircon U–Pb geochronology and fluvial basin evolution of the Liuqu Conglomerate within the Yarlung Zangbo Suture Zone: A critical geochronometer for the collision tectonics of the Tibetan-Himalayan Orogenic Belt","authors":"Yanxue Xie,&nbsp;Yildirim Dilek","doi":"10.1016/j.geogeo.2023.100178","DOIUrl":"https://doi.org/10.1016/j.geogeo.2023.100178","url":null,"abstract":"<div><p>We present new U-Pb detrital zircon ages, depositional history and tectonic model for the Liuqu Conglomerate (LQC) in southern Tibet that represents a critical geochronometer for the collision history of the Tibetan-Himalayan Orogenic Belt. LQC is a ∼5 km–thick, late Mesozoic–Cenozoic molasse deposit occurring strictly within the Yarlung Zangbo Suture Zone (YZSZ) and is tectonically overlain to the north by the Cretaceous Xigaze ophiolite and to the south by the Mesozoic Tethyan Himalaya sequence. It consists of matrix- and clast-supported conglomerates with sandstone intercalations, and its matrix includes poorly to moderately sorted sandstone and mudstone. New U–Pb detrital zircon dating of LQC sandstones has revealed a youngest zircon age of 307 ± 13 Ma and an oldest zircon age of 3362 ± 51 Ma. The age spectrum of zircons displays a prominent peak of ∼935 Ma, two large peaks at ∼516 Ma and 1474 Ma, and two small clusters of ∼2429 Ma and ∼2772 Ma that point to East Gondwana as the likely provenance for the LQC depocenter. The LQC represents fluvial deposits of an axial river system, which developed in an orogen-parallel, transtensional accommodation space within the YZSZ, after the collision of the Late Jurassic-Early Cretaceous Trans–Tethyan arc–trench system with the northern edge of India in the latest Cretaceous. The Indian subcontinent with the accreted Tethyan ophiolites and the intra–suture LQC depocenter arrived at and collided with the active margin of Eurasia during the latest Oligocene (∼23 Ma). The LQC depocenter started receiving clastic material and zircons for the first time from the Gangdese Magmatic Belt and the Xigaze forearc basin to the north by ∼20 Ma. The ensuing continent–continent collision resulted in significant crustal uplift across the collision zone, and in the inversion and rapid exhumation of the LQC strata by the early–Middle Miocene. The depositional and exhumation history of the fluvial LQC formation within the YZSZ involved two discrete collision events during the evolution of the Tibetan-Himalayan Orogenic system.</p></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"2 3","pages":"Article 100178"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49747174","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Architecture of ophiolitic mélanges in the Junggar region, NW China","authors":"Ji'en Zhang ,&nbsp;Yichao Chen ,&nbsp;Wenjiao Xiao ,&nbsp;John Wakabayashi ,&nbsp;Shuaihua Song ,&nbsp;Jun Luo ,&nbsp;Yulong Zhao","doi":"10.1016/j.geogeo.2022.100175","DOIUrl":"https://doi.org/10.1016/j.geogeo.2022.100175","url":null,"abstract":"<div><p>Ophiolitic mélanges, units that contain components of an ophiolite suite, provide crucial information on earth history and orogenic evolution. In this paper, four ophiolitic mélanges are characterized, including the Baijiantan-Yeyagou, Hebukesair, Zhaheba and Hongguleleng mélanges in the Junggar region (NW China), southern Altaids. Detailed geological mapping, structural, geochronological, and geochemical analyses constrain ages, geochemical affinities and relationships of magmatic with clastic rocks. MORB-/OIB-type (meta)gabbros and plagiogranite are the oldest mélange components, slightly older or coeval with associated chert and MORB-/OIB-type basalt; these rocks collectively constitute an ophiolite suite. Ophiolitic rocks predate associated clastic sedimentary rocks (conglomerate and turbidite) by ∼90-25 My, and associated SSZ-type hornblende gabbro, basaltic andesite, diabase, diorite and rhyolite by ∼78-37 My, except in the Hongguleleng mélange, where ophiolitic rocks predate latter units by ∼9-25 My. The ophiolitics are repeated by imbricate thrusts and duplexes, and folded. Ophiolitic blocks in mélanges locally preserve similar structures. Such blocks commonly have MORB and/or OIB geochemical affinities. Significantly older ages of MORB/OIB igneous rocks compared to ages of associated clastic sedimentary/SSZ-type igneous rocks shows that the former rocks formed as part of the crust of a large ocean, far from a convergent margin. The far-traveled oceanic crustal slices were imbricated and disrupted into block-in-matrix structures during accretion and incorporation into a subduction complex. SSZ-type magmatic rocks locally intrude into and extrude onto clastic rocks, demonstrating that a mélange contains multi-stage magmatic rocks. Folds, tilted structures and shear band cleavages are locally cross-cut by dikes, and these rocks are themselves have been dismembered into blocks. An intruded conglomerate in the Hongguleleng mélange contains pebbles of gabbro and basaltic andesite, the latter of which overlies sandstone. Superimposed folds in clastic rocks and chert record the polydeformation of the mélanges. Determination of the complex relationships of multi-stage magmatism and deformation illuminates the tectonic history of ophiolitic mélanges in the Junggar region. This history includes formation and subduction-accretion of the crust of a large ocean and post-subduction intracontinental deformation.</p></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"2 3","pages":"Article 100175"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49746937","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Suprasubduction ophiolite (SSZ) components in a middle to lower upper Jurassic Hallstatt Mélange in the Northern Calcareous Alps (Raucherschober/Schafkogel area)","authors":"Sebastian P. Drvoderic ,&nbsp;Hans-Jürgen Gawlick ,&nbsp;Hisashi Suzuki ,&nbsp;Felix Schlagintweit","doi":"10.1016/j.geogeo.2022.100174","DOIUrl":"https://doi.org/10.1016/j.geogeo.2022.100174","url":null,"abstract":"<div><p>The Northern Calcareous Alps in the Western Tethys realm were affected in Middle to Late Jurassic times by a mountain building process triggered by ophiolite obduction similar to that in the Inner Western Carpathians or Inner Dinarides. In contrast to these other mountain ranges, in the Northern Calcareous Alps the obducted ophiolites or ophiolite derived components in the Bathonian-Oxfordian mélanges are missing. Cr-spinels in Kimmeridgian basinal deposits are the oldest known relics of a Jurassic ophiolite obduction. This study reveals new data from a newly detected Hallstatt Mélange below the Late Jurassic Plassen Platform in the southeastern Northern Calcareous Alps (Raucherschober/Schafkogel area). Upper Triassic Hallstatt Limestone blocks from the former distal northwestern continental margin of the Neo-Tethys Ocean, as well as ophiolite and radiolarite blocks from the Neo-Tethys Ocean floor rest within an upper Middle to lower Upper Jurassic radiolaritic-argillaceous matrix. Ophiolitic blocks show calc-alkaline volcanic arc affinity, defining the rocks as the product of intra-oceanic subduction and the formation of an early arc during stacking of the oceanic crust. Resedimented ribbon radiolarite blocks deposited above the newly formed suprasubduction (SSZ) ophiolites in the Neo-Tethys Ocean east of the island arc have a Middle Jurassic age. Later, at a time of decreasing tectonic activity, the Hallstatt Mélange was sealed by the Kimmeridgian-Tithonian Plassen Carbonate Platform, showing a shallowing-upward trend.</p></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"2 3","pages":"Article 100174"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49747010","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemistry of volcanic rocks and dykes from the Remeshk-Mokhtarabad and Fannuj-Maskutan Ophiolites (Makran Accretionary Prism, SE Iran): New constraints for magma generation in the Middle East neo-Tethys","authors":"Emilio Saccani ,&nbsp;Morteza Delavari ,&nbsp;Asghar Dolati ,&nbsp;Luca Pandolfi ,&nbsp;Edoardo Barbero ,&nbsp;Valentina Brombin ,&nbsp;Michele Marroni","doi":"10.1016/j.geogeo.2022.100140","DOIUrl":"https://doi.org/10.1016/j.geogeo.2022.100140","url":null,"abstract":"<div><p>The Remeshk-Mokhtarabad and Fannuj-Maskutan ophiolites represent two major ophiolitic units in the North Makran Domain (Makran Accretionary Prism). Volcanic rocks and dykes of these ophiolites mainly consist of basalts and rare basaltic andesites, andesites and dacites. No chemical distinction can be seen in basalts from these two ophiolitic units, or between volcanic rocks and dykes. Basaltic rocks show a broad MORB-type nature but variable chemical composition (e.g., SiO₂= 42.64–52.63 wt%; TiO₂= 0.98–2.43 wt%; Mg# = 71–50). They show both N-MORB (Type 1) and E-MORB (Type 2) compositions (MORB: mid-ocean ridge basalt; N: normal; E: enriched). Type 1 rocks are very rare in both ophiolitic units, whereas Type 2 rocks are predominant. Type 1 rocks show low Th (0.10–0.16 ppm), Nb (1.86–2.82 ppm), Ta (0.09–0.17 ppm) abundance and low (La/Yb)_N (0.50–0.75), (La/Sm)_N (0.48–0.72) ratios. Compared to N-MORBs, Type 2 basalts show slight enrichment in Th (0.42–1.60 ppm), Nb (6.09–14.6 ppm), and Ta (0.227–0.792 ppm), as well as (La/Yb)_N and (La/Sm)_N ratios &gt;1 like those observed in typical E-MORB. Trace element petrogenetic models indicate that primitive basalts derived from partial melting of a heterogeneous sub-oceanic mantle variably metasomatized by plume-type (OIB-) components. Type 1 basalts derived from partial melting of mantle regions with no enrichment in OIB-type components, whereas Type 2 basalts derived from partial melting of DMM sources variably enriched by OIB-components. These rocks formed in an oceanic basin that was strongly affected by mantle plume activity and different extents of plume-ridge interaction.</p></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"2 3","pages":"Article 100140"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49746930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Early Cambrian forearc ophiolite-hosted VMS-type Cu deposit in the North Qaidam belt, northern Tibetan Plateau","authors":"Changlei Fu ,&nbsp;Bingzhang Wang ,&nbsp;Zhen Yan ,&nbsp;Jonathan C. Aitchison ,&nbsp;Wenjiao Xiao ,&nbsp;Solomon Buckman ,&nbsp;Wufu Li","doi":"10.1016/j.geogeo.2022.100172","DOIUrl":"https://doi.org/10.1016/j.geogeo.2022.100172","url":null,"abstract":"<div><p>The North Qaidam belt is an important polymetallic metallogenic belt in the northwestern region of China. However, the tectonic setting and age of related VMS deposits remain debated. Here we performed an integrated analysis of field relationship, geochemistry, and geochronology for hosting rocks of the Lüliangshan VMS-type Cu deposit and surrounding mafic-ultramafic rocks. These rocks, including serpentinite, pyroxenite, chromitite, mafic dykes with associated meta-plagiogranite, lava, chert, and limestone, constitute a relatively complete ophiolite complex, indicating that the Lüliangshan Cu deposit can also be introduced as an ophiolite-hosted VMS deposit. Geochemical data show that the meta-dolerite and ore-hosting lava exhibit geochemical features similar to tholeiitic forearc basalt and are probably generated by partial melting of a depleted mantle source metasomatized by hydrous fluids. Some lavas have boninitic compositions and are formed by partial melting of residual mantle after extraction of forearc basalt. Some ore-hosting lavas also have geochemical affinities to island arc tholeiites as a result of more SSZ components involved in their magma source. The chert samples have remarkably high Fe₂O₃^T contents and are classified as iron-rich one of hydrothermal origin, which is deposited in a ridge-proximal environment. These rocks, together with chromitites with subducted-related geochemical features, collectively indicate that the ophiolite-hosted VMS-type Cu deposit was formed in the forearc setting. Meta-gabbros intruding the ore-hosting lavas yield zircon U-Pb ages mainly ranging from 527 Ma to 518 Ma. The new ages of forearc ophiolite and the oldest age of island-arc rocks (514 Ma) suggest that the Lüliangshan Cu deposit formed in the early Cambrian during early-stage subduction of Proto-Tethys Ocean.</p></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"2 3","pages":"Article 100172"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49746506","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ion-probe (SIMS) U-Pb geochronology and geochemistry of the Upper Cretaceous Kızıldağ (Hatay) ophiolite: Implications for supra-subduction zone spreading in the Southern Neotethys","authors":"Emrah Şimşek ,&nbsp;Osman Parlak ,&nbsp;Alastair H.F. Robertson","doi":"10.1016/j.geogeo.2022.100165","DOIUrl":"https://doi.org/10.1016/j.geogeo.2022.100165","url":null,"abstract":"<div><p>The Kızıldağ (Hatay) ophiolite in southern Turkey represents a complete, although fault-dissected, remnant of oceanic lithosphere that formed within the South Tethyan ocean during the late Cretaceous. The Kızıldağ forms part of the Upper Cretaceous belt which includes the Troodos (Cyprus), Baer-Bassit (Syria), Amanos (S Tukey), S Iran and Semail (Oman) ophiolites. Ion-probe (SIMS) dating of seven samples of crustal rocks (cumulate gabbro, isotropic gabbro and isolated dykes in mantle tectonite), and a plagiogranite intrusion provides important clues concerning the temporal development of the emplaced oceanic crust. Single grain ²⁰⁶Pb/²³⁸U dates that overlap within analytical uncertainty for four samples, including the plagiogranite (93.83 ± 0.46 Ma), the isotropic gabbro (92.9 ± 0.52 Ma) and the isolated dykes (92.54 ± 0.44 Ma to 93.6 ± 0.75 Ma), are interpreted as magmatic crystallisation ages, and suggest that the Kızıldağ ophiolite formed within 1-2 Ma. Three other samples with single grain ²⁰⁶Pb/²³⁸U dates that are outside the range of analytical uncertainty yielded nearly identical lower intercept ages of 94.2 ± 2.5 Ma to 94.4 ± 0.97 Ma for two cumulate gabbros and 90.0 ± 6.4 Ma for an isotropic gabbro. Comparison of the new and published radiometric ages of the Kızıldağ suggest that this ophiolite is ∼1.5 Ma older than previously believed, and is similar to the crystallisation ages of plagiogranites from the Troodos (Cyprus) and the Semail (Oman) ophiolites. The new age data emphasise the value of dating a range of ophiolitic rocks. Geochemically, the crustal rocks of the Kızıldağ ophiolite formed from boninitic magmas (cumulate gabbros and isolated dykes) and from island arc tholeiitic magmas (isotropic gabbro). The new whole-rock chemical data support a subduction-initiation (fore-arc) setting for the Kızıldağ ophiolite, in common with the Troodos, Semail, Baër-Bassit and other Upper Cretaceous ophiolites of the South-Tethyan region.</p></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"2 3","pages":"Article 100165"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49764638","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Skarns at a peridotite contact, Neyriz, Iran: High-temperature melting and metamorphism in a forearc setting","authors":"Robert Hall ,&nbsp;Rainer Thomas","doi":"10.1016/j.geogeo.2022.100149","DOIUrl":"https://doi.org/10.1016/j.geogeo.2022.100149","url":null,"abstract":"<div><p>In the Neyriz area of southern Iran unusual skarns are found above serpentinised peridotites at the contact with crystalline limestones. They have been interpreted as the high-temperature product of intrusion by hot peridotite into limestones, as low-temperature rodingites (the product of calcium metasomatism associated with serpentinisation), or a fortuitous juxtaposition of unrelated rocks. Their age is not known. The skarns are wollastonite-pyroxene-calcite rocks in which dark green pyroxenes are fassaites with high Al, Fe and Ti with high Ca-Tschermak's components. The field relations, textures, mineral assemblages and compositions, and melt inclusions in wollastonite and fassaite indicate the skarns formed by melting at the contact between peridotites and limestones with retrograde reactions during cooling forming garnet and anorthite. There are uncertainties in temperature estimates since pressure, X_CO₂ and other compositional variables are unknown, but melting temperatures were likely to have been close to 1100°C with garnet formation at approximately 900°C. Later alteration of some skarns and formation of rodingites close to the limestone-peridotite contacts occurred during low-temperature Ca metasomatism, probably after emplacement of the ophiolite during Zagros collision. A hot intrusive origin for the skarns appears incompatible with an arc-related supra-subduction origin of the ophiolite inferred from geochemical studies, but recent work in eastern Indonesia shows that during late Neogene subduction rollback, melts formed above hot mantle that intruded highly extended continental crust in a forearc setting. The scale, timing and temperatures of melting and metamorphism are very similar to those of the Late Cretaceous Neyriz ophiolite.</p></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"2 3","pages":"Article 100149"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49764648","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Relics of ophiolite-bearing accretionary wedges in NE Brazil and NW Africa: Connecting threads of western Gondwana´s ocean during Neoproterozoic times","authors":"Lauro Cézar M. de Lira Santos ,&nbsp;Fabrício A. Caxito ,&nbsp;Merlain H. Bouyo ,&nbsp;Sonia Ouadahi ,&nbsp;Kawther Araïbia ,&nbsp;Geysson A. Lages ,&nbsp;Glenda L. Santos ,&nbsp;João Paulo A. Pitombeira ,&nbsp;Peter A. Cawood","doi":"10.1016/j.geogeo.2022.100148","DOIUrl":"https://doi.org/10.1016/j.geogeo.2022.100148","url":null,"abstract":"<div><p>Neoproterozoic breakup of Rodinia resulted in the formation of several oceanic realms between dispersing cratons, which were later consumed during the assembly of Gondwana. In its western portion, the interior orogenic belts of Gondwana formed during the Brasiliano-Pan African Orogeny in the late Neoproterozoic-early Cambrian. Available geophysical, structural and petrological data suggest that the complex network of shear zones that once connected the Borborema province (NE Brazil), Tuareg shield (Hoggar) and Central African domain (NW Africa) likely represent ancient sutures that mark collisional episodes between Archean-Paleoproterozoic paleocontinents such as Amazonian-West African and São Francisco-Congo. Mafic, ultramafic and sedimentary sequences associated with this set of structures respresent dismembered ophiolite slices interpreted as oceanic remnants (<em>sensu lato</em>) that were emplaced during the late stages of the Gondwana assembly. For instance, the composite Transbrasiliano-Khandi-In-Tedeini-Silet shear system crosscuts rock assemblages preserving a complex history of oceanic-crust-transition development (Novo Oriente complex) in association with primitive to evolved magmatic arcs and UHP rocks both in the Borborema province and NW Africa. In the central Borborema province, preserved ophiolitic slices are strongly overprinted by ductile and brittle deformation events, but partially preserved MORB-like amphibolites are akin to subduction-related-types that crystallized in early- and late Neoproterozoic times docked via terrane accretion and dispersed by strike-slip shear zones. In the southern Borborema province, an example of a Neoproterozoic ophiolitic assemblage is the Monte Orebe complex, that encompasses T-MORB mafic rocks, ultramafic lenses, and exhalative sedimentary rocks akin to early to late stages of oceanic basin spreading, emplaced during convergent plate motions between the Pernambuco-Alagoas superterrane and the São Francisco craton. Correlative units are found in Cameroon, including the strongly hydrotermalized ultramafic rocks of the Lomié and Boumnyebel complexes, that are structurally controlled by top-to-the-south verging nappes found in the N-NW margin of the Congo craton. In all scenarios, the ophiolitic complexes are related to intra-oceanic and continental magmatic arcs as well as to geophysical signatures comparable to Phanerozoic suture zones. Although strongly dismembered, scrapped off Neoproterozoic oceanic crust partially preserved within the major belts of western Gondwana demonstrate the role of accretion-collisional orogenesis during its assembly.</p></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"2 3","pages":"Article 100148"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49747080","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Insights into the Tethyan mantle heterogeneity: Trace element evidence from the Karakaya Complex, Central Anatolia","authors":"Kaan Sayit","doi":"10.1016/j.geogeo.2022.100139","DOIUrl":"https://doi.org/10.1016/j.geogeo.2022.100139","url":null,"abstract":"<div><p>The Nilüfer Unit of the Karakaya Complex (northern Turkey) preserves the remnants of the voluminous Triassic Tethyan magmatism. In the Imrahor area (Ankara), the Nilüfer Unit is characterized by a megablock consisting of hydrothermally altered basalts, gabbros, and subordinate wehrlitic cumulates. These lithologies display marked positive Nb anomalies with depleted Th/La ratios and varying degrees of LREE enrichment. They can be subdivided into two groups based on Nb/Nb*, which are not related to each other via fractional crystallization or extent of partial melting. With their strong Nb-kick and broad La/Sm range, the Imrahor lithologies are more akin to FOZO (Focus Zone)- or C (common component)-type melts than EM (Enriched Mantle) and HIMU (high μ). The Zr-Nb systematics reveals that melt mixing was an essential process in the petrogenesis of these mafic rocks. Based on geochemical modeling, the trace element systematics of the İmrahor lithologies can be explained by melting metasomatized oceanic lithospheric mantle (OLM) infiltrated by very low-degree melt fractions. The metasomatized OLM may represent a recycled, plume-related material that has generated Nb-enriched melts during the Triassic Tethyan magmatism.</p></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"2 3","pages":"Article 100139"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49764635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}