Zircon ages and geochemical compositions of the Manlay ophiolite and coeval island arc: Implications for the tectonic evolution of South Mongolia

Numerous small dismembered ophiolite fragments occur in South Mongolia, but they are very poorly studied. The lack of age data and geochemical analysis hampers our understanding of the Paleozoic tectonic evolution of the region. We conducted detailed studies on the Manlay ophiolitic complex and Huree volcanic rocks south of the Main Mongolian Lineament (MML) to provide some constraints on these rocks. The Manlay ophiolite consists of dunite, harzburgite, pyroxenite, gabbro, plagiogranite, basalt and chert, locally with chromite mineralization in dunite. The gabbro and plagiogranite yielded SHRIMP zircon weighted mean ²⁰⁶Pb/²³⁸U ages of 509 ± 5 Ma and 482 ± 4 Ma, respectively. The basalt and dolerite samples of this complex show enrichment in LREE and LILE and negative Nb, Ta and Ti anomalies, and the chrome spinel from the chromitite lens in the dunite is characterized by high Cr^# and low TiO₂ contents. These features suggest a supra-subduction zone (SSZ) origin for the ophiolitic complex. The Huree volcanic rocks, ranging from basalt to dacite, display enrichment in LREE and LILE, weak Eu anomalies and distinctly negative Nb, Ta and Ti anomalies, consistent with those of typical magmas in a subduction environment. An andesite sample from this arc yielded a SHRIMP ²⁰⁶Pb/²³⁸U zircon age of 487 ± 5 Ma, which is the oldest reliable age for an island arc in South Mongolia. Recognition of an Early Paleozoic ophiolitic complex and a coeval island arc indicates that South Mongolia underwent a period of active volcanism during Late Cambrian to Ordovician. Additionally, the tuff overlying the ophiolitic complex and a granite intruding the ophiolite have SHRIMP zircon U–Pb ages of 391 ± 5 Ma and 304 ± 4 Ma, respectively. Combining the available data, we propose that the Early Paleozoic subduction–accretionary complexes likely constitute the basement of the Late-Paleozoic arc formations and correlate with the Lake Zone in western Mongolia.     

The Anti-Atlas Pan-African Belt (Morocco): Overview and pending questions

Between the High Atlas and the Saharan platform, the Anti-Atlas of Morocco offers large exposures of Precambrian rocks beneath the moderately folded Paleozoic series. These inliers allow reconstructing a segment of the Pan-African Belt and of its foreland at the northern outskirts of the West African Craton (WAC). From ∼ 885 Ma to ∼ 540 Ma, three periods are recognized in the Pan-African cycle. The Tonian–Cryogenian period ends with the obduction of supra-subduction ophiolite and oceanic arc material at ∼ 640 Ma. The Early Ediacaran period is marked by the development and subsequent closure of a wide marginal basin next to a likely Andean-type arc. The Late Ediacaran period is recorded by subaerial molasse deposits associated with post-collisional high-K calc-alkaline to shoshonitic magmatism. Although a wide consensus has been reached based on the number of new robust datings, several questions still remain pending, which we address taking into account relevant African and European correlations.     

The Yanbian Terrane (Southern Sichuan Province,SW China): A Neoproterozoic arc assemblage in the western margin of the Yangtze Block

The magmatic and tectonic history of the Yangtze Block and its possible affinity with other Neoproterozoic arc terranes are important elements in the reconstruction of Neoproterozoic plate tectonics. The Yanbian Terrane in the western margin of the Yangtze Block is a typical arc assemblage composed of a flysch-type sedimentary sequence intruded by gabbroic and granodioritic plutons. The sedimentary sequence consists chiefly of tuffaceous material with interlayered chert, sandstone, and pillow basalts. Laser ablation ICP-MS U–Pb dating of detrital zircons from the sandstones yield ages as young as 840 Ma. The Gaojiacun and Lengshuiqing mafic intrusions are dated at 812 ± 3 Ma and 806 ± 4 Ma, respectively, using the SHRIMP zircon U–Pb technique. Geochemical data show that both the Gaojiacun and Lengshuiqing intrusions have arc signatures, with ɛNd(t) values of +1.5 to +6.0, initial ⁸⁷Sr/⁸⁶Sr ratios of 0.705–0.706 and pronounced negative Nb–Ta and Zr–Hf anomalies. Their geochemical variations are best explained by fractional crystallization without major crustal contamination. The Yanbian Terrane represents a typical arc assemblage formed on the western edge of the Yangtze Block during Neoproterozoic time. The sedimentary sequence was deposited in an oceanic setting, probably in a back arc basin environment. The depleted, subduction-modified lithospheric mantle wedge above the subduction zone was the source of melts from which the mafic plutons were crystallized. This scenario suggests subduction of oceanic lithosphere eastward (present-day orientation) underneath the Yangtze Block.     

Age constraints on the formation and emplacement of Neoproterozoic ophiolites along the Allaqi–Heiani Suture,South Eastern Desert of Egypt

Ophiolites are key components of the Neoproterozoic Arabian–Nubian Shield (ANS). Understanding when they formed and were emplaced is crucial for understanding the evolution of the ANS because their ages tell when seafloor spreading and terrane accretion occurred. The Yanbu–Onib–Sol Hamed–Gerf–Allaqi–Heiani (YOSHGAH) suture and ophiolite belt can be traced ∼ 600 km across the Nubian and Arabian shields. We report five new SHRIMP U–Pb zircon ages from igneous rocks along the Allaqi segment of the YOSHGAH suture in southernmost Egypt and use these data in conjunction with other age constraints to evaluate YOSHGAH suture evolution. Ophiolitic layered gabbro gave a concordia age of 730 ± 6 Ma, and a metadacite from overlying arc-type metavolcanic rocks yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 733 ± 7 Ma, indicating ophiolite formation at ∼ 730 Ma. Ophiolite emplacement is also constrained by intrusive bodies: a gabbro yielded a concordia age of 697 ± 5 Ma, and a quartz-diorite yielded a concordia age of 709 ± 4 Ma. Cessation of deformation is constrained by syn- to post-tectonic granite with a concordia age of 629 ± 5 Ma. These new data, combined with published zircon ages for ophiolites and stitching plutons from the YOSHGAH suture zone, suggest a 2-stage evolution for the YOSHGAH ophiolite belt (∼ 810–780 Ma and ∼ 730–750 Ma) and indicate that accretion between the Gabgaba–Gebeit–Hijaz terranes to the south and the SE Desert–Midyan terranes to the north occurred as early as 730 Ma and no later than 709 ± 4 Ma.     

Evidence for the Jurassic arc volcanism of the Lolotoi complex,Timor: Tectonic implications

We report the first sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon ages with geochemical data from metavolcanic rocks in the Lolotoi complex, Timor. The zircon U–Pb ages of two andesitic metavolcanic rocks yield a permissible range of the Middle Jurassic extrusion from 177 Ma to 174 Ma. The geochemical data indicate that the origins of the basaltic and andesitic metavolcanic rocks are products of prolonged oceanic crust and arc magmatism, respectively. They are originated from partial melting of lherzolites, providing an insight into the tectonic evolution of the forearc basements of the Banda volcanic arc. Thus, parts of the Banda forearc basement are pieces of allochthonous oceanic basalts and Jurassic arc-related andesites accreted to the Sundaland during the closure of Mesotethys, and are incorporated later into the Great Indonesian Volcanic Arc system along the southeastern margin of the Sundaland.     

U–Pb zircon ages,field geology and geochemistry of the Kermanshah ophiolite (Iran): From continental rifting at 79 Ma to oceanic core complex at ca. 36 Ma in the southern Neo-Tethys

The geodynamic evolution of the Zagros Mountains of Iran remains obscure. In particular, the time of formation of the Zagros ophiolites and the closure of the Neo-Tethys Ocean are highly controversial. Here we present new precise zircon U–Pb ages that show that the younger part (Sahneh–Kamyaran) of the Kermanshah ophiolite formed at 35.7 ± 0.5 Ma and the older part (Harsin) at 79.3 ± 0.9 Ma. Field relations and geochemical evidence show that the younger Sahneh–Kamyaran part is probably a fossil oceanic core complex, and the older Sahneh part is probably a continental-oceanic transition complex. Both the Sahneh–Kamyaran and Sahneh parts were later emplaced into an accretionary complex. We conclude and infer that the final closure time of the southern Neo-Tethys Ocean was after the Late Eocene. Our data and tectonic model have crucial implications for the geodynamic evolution of the Zagros region.     

The Western Sierras Pampeanas: Protracted Grenville-age history (1330–1030 Ma) of intra-oceanic arcs,subduction–accretion at continental-edge and AMCG intraplate magmatism

New U–Pb SHRIMP zircon ages combined with geochemical and isotope investigation in the Sierra de Maz and Sierra de Pie de Palo and a xenolith of the Precordillera basement (Ullún), provides insight into the identification of major Grenville-age tectonomagmatic events and their timing in the Western Sierras Pampeanas. The study reveals two contrasting scenarios that evolved separately during the 300 Ma long history: Sierra de Maz, which was always part of a continental crust, and the juvenile oceanic arc and back-arc sector of Sierra de Pie de Palo and Ullún. The oldest rocks are the Andino-type granitic orthogneisses of Sierra de Maz (1330–1260 Ma) and associated subalkaline basic rocks, that were part of an active continental margin developed in a Paleoproterozoic crust. Amphibolite facies metamorphism affected the orthogneisses at ca. 1175 Ma, while granulite facies was attained in neighbouring meta-sediments and basic granulites. Interruption of continental-edge magmatism and high-grade metamorphism is interpreted as related to an arc–continental collision dated by zircon overgrowths at 1170–1230 Ma. The next event consisted of massif-type anorthosites and related meta-jotunites, meta-mangerites (1092 ± 6 Ma) and meta-granites (1086 ± 10 Ma) that define an AMCG complex in Sierra de Maz. The emplacement of these mantle-derived magmas during an extensional episode produced a widespread thermal overprint at ca. 1095 Ma in neighbouring country rocks. In constrast, juvenile oceanic arc and back-arc complexes dominated the Sierra de Pie de Palo–Ullún sector, that was fully developed ca. 1200 Ma (1196 ± 8 Ma metagabbro). A new episode of oceanic arc magmatism at ～1165 Ma was roughly coeval with the amphibolite high-grade metamorphism of Sierra de Maz, indicating that these two sectors underwent independent geodynamic scenarios at this age. Two more episodes of arc subduction are registered in the Pie de Palo–Ullún sector: (i) 1110 ± 10 Ma orthogneisses and basic amphibolites with geochemical fingerprints of emplacement in a more mature crust, and (ii) a 1027 ± 17 Ma TTG juvenile suite, which is the youngest Grenville-age magmatic event registered in the Western Sierras Pampeanas. The geodynamic history in both study areas reveals a complex orogenic evolution, dominated by convergent tectonics and accretion of juvenile oceanic arcs to the continent.     

Structure,age, and tectonic development of the Huoshishan–Niujuanzi ophiolitic mélange,Beishan, southernmost Altaids

The Huoshishan–Niujuanzi ophiolitic mélange (HNO) is located near the central part of the Beishan Orogenic Belt in the southernmost Altaids. The HNO consists of ultramafic rocks, cumulate gabbros, gabbros, plagiogranites, diorites, diabases, basalts, andesites, rhyolitic volcaniclastic rocks and siliceous sedimentary rocks, many of which are in a schist matrix (Gongpoquan Group). Geochemical data of the mafic rocks indicate a calc-alkaline or a mixture of calc-alkaline and tholeiitic rocks with negative Nb, Ta and positive Pb, Ba and La anomalies, suggesting formation in an island arc or supra-subduction zone setting. A gabbro from a block in the mélange in the Niujuanzi area has a zircon age of 435.0 ± 1.9 Ma and a plagiogranite with an age of 444.3 ± 1.9 Ma, and another gabbro from the Huoshishan area has an age of 410.5 ± 3.7 Ma. The schist matrix has a zircon age of 512 ± 5.3 Ma and contains Silurian, Devonian and Carboniferous fossils, thus the mélange formed in the late Carboniferous or later. Our structural analysis of fault planes in the HNO, the crenulation cleavages (S₂) of the schist, and fold axial planes of early Permian sandy limestone/quartz veins and late Permian sandstones indicates that the mélange underwent a north-to-south compression, and the orientation of stretching lineations, slickensides and fold hinge lines implies that the HNO experienced top-to-the north (or -northwest) movement. The entire planar and linear structural data set suggests that the subduction polarity was probably to the south in the late Paleozoic. The emplacement age of the HNO was probably near the end-Permian based on the age of the youngest rocks in the ophiolitic mélange, and by the presence of a late Permian unconformity. From our work, integrated with published regional data, we outline a comprehensive geodynamic model for the central BOC.     

A geotraverse across two paleo-subduction zones in Tien Shan,Tajikistan

We present first LA-ICP-MS U–Pb zircon ages as well as geochemical and Sr–Nd–Pb isotope data for 14 magmatic rocks collected along ca. 400 km profile across the Chatkal-Kurama terrane in the Mogol-Tau and Kurama ranges and the Gissar Segment of the Tien Shan orogen in Tajikistan. These new data from supra-subduction and post-collisional magmatic rocks of two Late Paleozoic active margins constrain a tectonic model for terrane motions across two paleo-subduction zones: (1) The 425 Ma old Muzbulak granite of the Mogol-Tau range formed in a supra-subduction setting at the northern margin of the Turkestan Ocean. The north-dipping plate was subducted from the Early Silurian to the earliest Middle Devonian. Thereafter the northern side of the Turkestan Ocean remained a passive margin until the Early Carboniferous. (2) In the Early Carboniferous, subduction under the northern margin of the Turkestan Ocean resumed and the 315 to 305 Ma old Kara-Kiya, Muzbek, and Karamazar intrusions formed in a supra-subduction setting in the Mogol-Tau and Kurama ranges. (3) At the same time, in the Early Carboniferous, rifting of the southern passive margin of the Turkestan Ocean formed the short-lived Gissar Basin, separated from the Turkestan Ocean by the Gissar micro-continent. North-dipping subduction in the Gissar Basin is documented by the 315 Ma Kharangon plagiogranite and the voluminous ca. 321–312 Ma Andean-type supra-subduction Gissar batholith. The Kharangon and Khanaka gabbro-plagiogranite intrusions of the southern Gissar range have geochemical and Sr–Nd isotopic compositions (⁸⁷Sr/⁸⁶Sr(t) 0.7047–0.7056, εNd of + 1.5 to + 2.3) compatible with mantle-derived origin typical for plagiogranites associated with ophiolites. The supra-subduction rocks from the Gissar batholith and from the Mogol-Tau Kurama ranges have variably mixed Sr–Nd–Pb isotopic signatures (⁸⁷Sr/⁸⁶Sr(t) 0.7057–0.7064, εNd of − 2.1 to − 5.0) typical for continental arcs where mantle-derived magmas interact with continental crust. (4) In the latest Carboniferous, the Turkestan Ocean and the Gissar Basin were closed. The Early Permian Chinorsay (288 Ma) and Dara-i-pioz (267 Ma) post-collisional intrusions, emplaced in the northern part of the Gissar micro-continent after a long period of amagmatic evolution, have intraplate geochemical affinities and isotopic Sr–Nd–Pb isotopic compositions (⁸⁷Sr/⁸⁶Sr(t) 0.7074–0.7086, εNd of − 5.5 to − 7.4) indicating derivation from Precambrian continental crust which is supported by old Nd model ages (1.5 and 1.7 Ga), and by the presence of inherited zircon grains with ages 850–500 Ma in the Chinorsay granodiorite. The post-collisional intrusions in the southern Gissar and in the Mogol-Tau and Kurama ranges (297–286 Ma), emplaced directly after supra-subduction magmatic series, have geochemical and isotopic signatures of arc-related magmas. The distinct shoshonitic affinities of post-collisional intrusions in the Mogol-Tau and Kurama ranges are explained by the interaction of hot asthenospheric material with subduction-enriched wedge of lithospheric mantle due to slab break-off at post-collisional stage. Despite origination from different tectonic environments, all magmatic rocks have relatively old Nd model ages (1.7–1.0 Ga) indicating a significant proportion of Paleoproterozoic or older crustal material in their sources and their model ages are similar to those of post-collisional intrusions from the Alai and Kokshaal Segments of the South Tien Shan.     

Geochronology and Hf isotope of detrital zircons from Precambrian sequences in the eastern Jiangnan Orogen: Constraining the assembly of Yangtze and Cathaysia Blocks in South China

The Jiangnan Orogen, the eastern part of which comprises the oceanic Huaiyu terrane to the northeast and the continental Jiuling terrane to the southwest, marks the collision zone of the Yangtze and the Cathaysia Blocks in South China. Here, zircon U–Pb geochronological and Lu–Hf isotopic results from typical basement and cover meta-sedimentary/sedimentary rock units in the eastern Jiangnan Orogen are presented. The basement sequences in southwestern Huaiyu terrane are mainly composed of marine volcaniclastic turbidite, ophiolite suite and tuffaceous phyllite, whereas those in the northeastern Huaiyu consist of littoral face pebbly feldspathic sandstones and greywacke interbedded with intermediate-basic volcanic rocks. Combined with previous studies, the present data show that the basement sequences exhibit arc affinities. Zircons from the basement phyllite in the southwestern margin of the Huaiyu terrane, representing a Neoproterozoic back-arc basin, yield a single age population of 800–900 Ma. The basement greywacke from northeastern Huaiyu terrane, representing fore-arc basin, is also characterized by zircons that preserve a single tectono-thermal event during 800–940 Ma. However, the late Neoproterozoic cover sequence preserves zircons from multiple sources with age populations of 750–890 Ma, 1670–2070 Ma and 2385–2550 Ma. Moreover, Hf isotopic data further reveal that most detrital zircons from the basement sequences yield positive εHf(t) values and late Mesoproterozoic model ages, while those of the cover sequence mostly show negative εHf(t) values. The Hf isotopic data therefore suggest that the basement sequences are soured from a Neoproterozoic arc produced by reworking of subducted late Mesoproterozoic materials. The geochronological and Hf isotopic data presented in this study suggest ca. 800 Ma for the assembly of the Huaiyu and Jiuling terranes, implying that the amalgamation of the Yangtze and Cathaysia Blocks in the eastern part occurred at ca. 800 Ma.     

Late Paleozoic subduction system in the southern Central Asian Orogenic Belt: Evidences from geochronology and geochemistry of the Xiaohuangshan ophiolite in the Beishan orogenic belt

The Xiaohuangshan ophiolite of the Beishan (Inner Mongolia) is located in the southern margin of the Central Asian Orogenic Belt. It consists of several blocks composed dominantly of serpentinized ultramafic rocks, cumulative gabbros and basalts. The geochemical data of gabbros and basalts obtained from the Xiaohuangshan ophiolite are similar to tholeiitic rocks. They all have low TiO₂ and high Al₂O₃ contents. Their light rare earth elements are slightly enriched, (La/Yb)_N = 3.62–6.80, similar to the typical enriched mid-ocean ridge basalts. The mafic rocks display enrichments in large ion lithophile elements and depletions in high field strength elements, as well as significant Nb–Ta–Ti negative anomalies, similar to subduction-derived rocks. All these geochemical characteritics indicate that the Xiaohuangshan ophiolite would form in a subduction zone from a slightly enriched mantle source. Ion microprobes (SHRIMP) U–Pb dating were conducted on zircons from the basalt and gabbro. The weighted mean ages are 336.4 ± 4.1 Ma and 345 ± 14 Ma, which are considered as the crystallization ages of the basalt and gabbro, respectively. Together with other two units, the Dongqiyishan arc belt and the Yueyashan–Xichangjing ophiolite, the Xiaohuangshan ophiolite forms a Late Paleozoic arc-basin system, indicating that the Paleo-Asian Ocean did not close in the early Carboniferous. Based on the geochemical characteristics of adjacent geological bodies and their settings, the Xiaohuangshan ophiolite is considered as an indicator of a suture zone between the different epicontinental belts in the Beishan region.     

The Mesoproterozoic Guaporé suture in the SW Amazonian Craton: Geotectonic implications based on field geology,zircon geochronology and Nd–Sr isotope geochemistry

A major Mesoproterozoic paleo-plate boundary in the southwestern Amazonian Craton, the Guaporé Suture Zone, is investigated by U–Pb zircon geochronology, Sr–Nd isotope geochemistry and aeromagnetic data. This suture zone is constituted dominantly by ophiolitic mafic–ultramafic rocks of the Trincheira Complex, and minor proportion of tonalites of the Rio Galera and São Felipe complexes, Colorado Complex, amphibolites of the Rio Alegre Terrane and syn- to late-kinematic mafic to felsic plutonic rocks. The ophiolitic Trincheira Complex formed during an accretionary phase from 1470 to 1430 Ma and was overprinted by upper amphibolite–granulite facies metamorphism during the collisional phase of the Ectasian followed by syntectonic emplacement of gabbro and granite plutons (1350–1340 Ma). The ophiolites were intruded by syntectonic tonalitic–plagiogranitic plutons ca. 1435 Ma. Mafic–ultramafic rocks of the Trincheira ophiolites show moderate to highly positive initial epsilon Nd (t = 1.46 Ga) values (+2.6 to +8.8) and very low initial ⁸⁷Sr/⁸⁶Sr ratio (0.7013–0.7033). It is suggested that these magmas originated from a depleted mantle source in an island-arc–back-arc setting. The identification of a fossil ophiolite in the Guaporé Suture Zone early as 1470–1435 Ma and later collisional phase, as late as 1350 Ma, marks the impingement of the proto-Amazonian Craton against the Paragua Block, before the formation of the Rodinia supercontinent. The results provide important insights into the geodynamic history of the SW Amazonian Craton, with evidence for both accretionary orogen and subduction of oceanic lithosphere in the Mesoproterozoic, and provide information that allows other workers to evaluate the configuration of supercontinents.     

Zircon U–Pb and molybdenite Re–Os dating of the Chalukou porphyry Mo deposit in the northern Great Xing’an Range,China and its geological significance

The newly discovered Chalukou giant porphyry Mo deposit, located in the northern Great Xing’an Range, is the biggest Mo deposit in northeast China. The Chalukou Mo deposit occurs in an intermediate-acid complex and Jurassic volcano-sedimentary rocks, of which granite porphyry, quartz porphyry, and fine-grained granite are closely associated with Mo mineralization. However, the ages of the igneous rocks and Mo mineralization are poorly constrained. In this paper, we report precise in situ LA-ICP-MS zircon U–Pb dates for the monzogranite, granite porphyry, quartz porphyry, fine grained granite, rhyolite porphyry, diorite porphyry, and andesite porphyry in the Chalukou deposit, corresponding with ages of 162 ± 2 Ma, 149 ± 5 Ma, 148 ± 2 Ma, 148 ± 1 Ma, 137 ± 3 Ma, 133 ± 2 Ma, and 132 ± 2 Ma, respectively. Analyses of six molybdenite samples yielded a Re–Os isochron age of 148 ± 1 Ma. These data indicate that the sequence of the magmatic activity in the Chalukou deposit ranges from Jurassic volcano-sedimentary rocks and monzogranite, through late Jurassic granite porphyry, quartz porphyry, and fine-grained granite, to early Cretaceous rhyolite porphyry, diorite porphyry, and andesite porphyry. The Chalukou porphyry Mo deposit was formed in the late Jurassic, and occurred in a transitional tectonic setting from compression to extension caused by subduction of the Paleo-Pacific oceanic plate.     

Magmatic evolution of the Tuwu–Yandong porphyry Cu belt,NW China: Constraints from geochronology,geochemistry and Sr–Nd–Hf isotopes

The Tuwu–Yandong porphyry Cu belt is located in the Eastern Tianshan mountains in the eastern Central Asian Orogenic Belt. Petrochemical and geochronological data for intrusive and volcanic rocks from the Tuwu and Yandong deposits are combined with previous studies to provide constraints on their petrogenesis and tectonic affinity. New LA–ICP–MS zircon U–Pb ages of 348.3 ± 6.0 Ma, 339.3 ± 2.2 Ma, 323.6 ± 2.5 Ma and 324.1 ± 2.3 Ma have been attained from intrusive units associated with the deposits, including diorite, plagiogranite porphyry, quartz albite porphyry and quartz porphyry, respectively. The basalt and andesite, which host part of the Cu mineralization, are tholeiitic with high Al₂O₃, Cr, Ni and low TiO₂ contents, enriched LREEs and negative HFSE (Nb, Ta, Zr, Ti) anomalies consistent with arc magmas. Diorites are characterized by low SiO₂ content but high MgO, Cr and Ni contents, similar to those of high-Mg andesites. The parental magma of the basalt, andesite and diorite is interpreted to have been derived from partial melting of mantle-wedge peridotite that was previously metasomatized by slab melts. The ore-bearing plagiogranite porphyry is characterized by high Na₂O, Sr, Cr and Ni contents, low Y and Yb contents, low Na₂O/K₂O ratios and high Sr/Y ratios and high Mg#, suggesting an adakitic affinity. The high ε_Nd(t) (5.02–9.16), low I_Sr (0.703219–0.704281) and high ε_Hf(t) (8.55–12.99) of the plagiogranite porphyry suggest they were derived by a partial melting of the subducted oceanic crust followed by adakitic melt-mantle peridotite interaction. The quartz albite porphyry and quartz porphyry are characterized by similar Sr–Nd–Hf isotope but lower Mg# and whole-rock (La/Yb)_N ratios to the plagiogranite porphyry, suggesting they were derived from juvenile lower crust, and negative Eu anomalies suggest fractionation of plagioclase. We propose that a flat subduction that started ca. 340 Ma and resulted in formation of the adakitic plagiogranite porphyry after a period of “steady” subduction, and experienced slab rollback at around 323 Ma.     

Paleoproterozoic arc and ophiolitic rocks on the northwest-margin of the Trans-Hudson Orogen,Saskatchewan, Canada: their contribution to a revised tectonic framework for the orogen

A new lithotectonic framework for the northwestern Reindeer Zone of the Trans-Hudson Orogen divides rocks into five northwest- to north-dipping volcano-sedimentary assemblages: (1) at the structural base, the 1.92–1.87 Ga largely sedimentary Levesque Bay Assemblage (partly equivalent to former ‘MacLean Lake gneisses’), which lies within the confines of the Kisseynew Domain and is tectonically imbricated with metasedimentary rocks of the <1.85 Ga McLennan and Burntwood groups; (2) the turbiditic Duck Lake Assemblage, also located along the northern edge of the Kisseynew Domain; it contains detrital zircons ranging in age between 1.92 and 1.87 Ga; (3) the ?1.92 Ga mafic–ultramafic volcano-plutonic Lawrence Point Assemblage of the La Ronge Domain; (4) the ≥1.88 Ga felsic to intermediate volcano-plutonic Reed Lake Assemblage of the La Ronge Domain; and (5) the turbiditic Milton Island Assemblage of the Rottenstone Domain, which contains detrital zircons ranging in age between 2.83 and 1.86 Ga. The assemblages are intruded by a variety of 1.91–1.78 Ga mafic to felsic plutons.The Lawrence Point Assemblage is interpreted as a dismembered supra-subduction zone ophiolite. High-MgO refractory harzburgite (‘Group 1’ ultramafic rocks), at the structural base of the assemblage, is geochemically identical to the upper mantle section of selected supra-subduction zone ophiolites and mantle tectonites. Chromite and olivine compositions of the ‘Group 1’ ultramafic rocks are also comparable to those of ophiolitic harzburgite and mantle tectonite. Mafic metavolcanic rocks of the assemblage are classified as subalkaline tholeiitic basalts. Their trace element patterns and Hf, Ta, Th, Y, Nb, and La element ratios resemble those of modern back-arc basin basalts. The Reed Lake Assemblage represents a subduction-generated arc complex that was built on top of the Lawrence Point Assemblage; its mafic metavolcanic rocks are subalkaline basalts, with calc-alkaline trends, and elevated Th and Ce concentrations and negative Nb anomalies. Feldspar porphyry dykes intruding the Lawrence Point and Duck Lake assemblages constrain timing of Lawrence Point ophiolite emplacement onto the Duck Lake Assemblage to 1.86–1.84 Ga. The trace element geochemistry of the dykes suggests continued arc volcanism after ophiolite emplacement. Mafic metavolcanic rocks of the Levesque Bay Assemblage are geochemically similar to those of the Lawrence Point Assemblage. Other ultramafic rocks (peridotite to pyroxenite) are abundant in the Lawrence Point Assemblage, but have similar geochemistry to small ultramafic bodies intruding the Reed Lake, Duck Lake and Levesque Bay Assemblages. They represent a separate, later phase (?1.86 Ga) of ultramafic plutonism, which post-dates ophiolite emplacement.Timing of Lawrence Point ophiolite emplacement (between 1.86 and 1.84 Ga) and geochemistry of later felsic and mafic/ultramafic volcanism suggest that the Lawrence Point ophiolite and overlying Reed Lake arc assemblage were not accreted to the Hearne Craton prior to 1.86 Ga, but were first accreted to the Flin Flon–Glennie Complex after 1.86 Ga.     

The trinity pattern of Au deposits with porphyry,quartz–sulfide vein and structurally-controlled alteration rocks in Ciemas,West Java,Indonesia

The Ciemas gold mining area is located in the Sunda arc volcanic rock belt, West Java, Indonesia. Ore bodies are associated with Miocene andesite, dacite and quartz diorite porphyrite. To constrain ore genesis and mineralization significance, a detailed study was recently conducted examining these deposits, which included detailed field observation, petrographic study, petrochemistry, sulfur isotope analyses, zircon U–Pb dating, and fluid inclusion analysis. The results include the following findings. 1) Ore types have been identified as porphyry, a quartz–sulfide vein, and structure-controlled alteration rocks. 2) In host rocks, zircon LA–ICP-MS U–Pb dating of quartz diorite porphyrite, amphibole tuff breccia and andesite yield ages of 17.1 ± 0.4 Ma, 17.1 ± 0.4 Ma and 17.5 ± 0.3 Ma, respectively. 3) Fluid inclusions in the quartz from ore are given priority to liquid and gas–liquid phases, and their components are of the NaCl–H₂O system with homogenization temperatures of 240–320 °C, salinities of 14–17%, densities of 0.85–0.95 g/cm³, and fluid pressure values between 4.1 and 46.8 MPa, corresponding to metallogenic depths from 150 to 1730 m. Fluid characteristics are identified as similar to those of high sulfur epithermal deposits. 4) The sulfur isotopic compositions are notably uniform, the δ³⁴S values of wall rocks range from 3.71 to 3.85‰, and the δ³⁴S values of ores vary from 4.90‰ to 6.55‰. The sulfur isotopic composition of ores is similar to that of the wall rocks, indicating a mixed origin of mantle with a sedimentary basement. 5) The trace element patterns of different ore types are similar, which indicates that they originate from the same source. Au deposits primarily occurred during the late magmatic activity. Finally, we have set up the regional metallogenic model, confirming that this gold deposit in the Sunda arc volcanic rock belt belongs to a metallogenic system from porphyry to epithermal type.     

Geochemistry and U-Pb zircon dating constraints of some plutonic rocks along Bir Tawilah shear zone,central Saudi Arabia: Implication for magma peterogenesis and age of gold mineralization

The study area covered by this work is located along the Bir Tawilah fault zone which encompasses the Arabian Shield between Afif terrane and western oceanic terranes. The rocks are dominantly ophiolite assemblages, island arc metavolcanic and metasedimentary rocks, and dioritic to granitic intrusions. The diorite and granodiorite rocks are I-type granitoids, calk-alkaline, metaluminous to peraluminous, formed in a volcanic arc setting, whereas the monzogranite is classified as A-type granite, alkaline and highly fractionated calc-alkaline, generated in within-plate tectonic setting. Nb and Y relationships indicated that the diorites and granodiorites were generated by a mafic parental magma contaminated with crustal materials, and controlled by fractional crystallization, whereas the monzogranites were generated from a magma characterized by an enriched mantle (EM) source.Mineralization including gold is hosted by the carbonatized serpentinite (listvenite) and the syn-tectonic granodiorite along Bir Tawilah thrust zone. U-Pb zircon geochronology indicates that the granodiorite at Jabal Ghadarah is emplaced at ca. 630 ± 12 Ma, probably suggests that the metallic minerals associated with the granodiorite along Bir Tawilah thurst zone are the result of remobilization of pre-existing gold mineralization associated with listevenite that is related to arc accretion.     

Geological characteristics and genesis of the Jurassic No. I porphyry Cu–Au deposit in the Xiongcun district,Gangdese porphyry copper belt,Tibet

The Xiongcun district, located in the western segment of the Gangdese porphyry copper belt (GPCB), hosts the only known Jurassic mineralization in the GPCB, Tibet, PRC. The No. I deposit in the Xiongcun district is related to the Middle Jurassic quartz diorite porphyry (167–161 Ma) and the mineralization was formed at ca. 161.5 ± 2.7 Ma. Ore-bearing Middle Jurassic quartz diorite porphyry emplaced into the Early Jurassic volcano-sedimentary rock sequences of the Xiongcun Formation. Veinlets and disseminated mineralization developed within the Middle Jurassic quartz diorite porphyry and the surrounding metamorphosed tuff, hosting a measured and indicated resource of 1.04 Mt copper, 143.31 t gold and 900.43 t silver with an average grade of 0.48% copper, 0.66 g/t gold, and 4.19 g/t silver. The mineralization can be assigned to four stages, including three main stages of hypogene mineralization and one epigenetic stage. The main alteration associated with mineralization is potassic. Seven mineralization-related hydrothermal veins have been recognized, including quartz–sulfide, biotite–sulfide, magnetite–sulfide, quartz–molybdenite–sulfide, chalcopyrite–pyrite–pyrrhotite, pyrite and polymetallic veins. The S and Pb isotopic compositions of the ore sulfides and the Re contents of the molybdenite suggest a mantle source for the ore-forming materials with minor contamination from the subducted sediments. Hydrogen and oxygen isotope compositions of quartz in the ores suggest that both magmatic and meteoric waters were involved in the ore-forming process. The ore-bearing porphyry (167–161 Ma) and ore-forming (161.5 ± 2.7 Ma) ages of the No. I deposit correspond to the time of northward subduction of Neo-Tethys oceanic slab. The geochemical data of the ore-bearing porphyry indicate that the No. I deposit formed in an intra-oceanic island arc setting and the ore-bearing porphyry originated from the partial melting of mantle with limited contribution of subducted sediments. The genesis of the ore-bearing porphyry and No. I deposit is interpreted as being related to northward intra-oceanic subduction of Neo-Tethys oceanic slab in the Middle Jurassic time (167–161 Ma).     

In-situ LA-ICPMS trace elements and U–Pb analysis of titanite from the Mesozoic Ruanjiawan W–Cu–Mo skarn deposit,Daye district,China

In this paper, we present U–Pb ages and trace element compositions of titanite from the Ruanjiawan W–Cu–Mo skarn deposit in the Daye district, eastern China to constrain the magmatic and hydrothermal history in this deposit and provide a better understanding of the U–Pb geochronology and trace element geochemistry of titanite that have been subjected to post-crystallization hydrothermal alteration. Titanite from the mineralized skarn, the ore-related quartz diorite stock, and a diabase dike intruding this stock were analyzed using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Titanite grains from the quartz diorite and diabase dike typically coexist with hydrothermal minerals such as epidote, sericite, chlorite, pyrite, and calcite, and display irregular or patchy zoning. These grains have low LREE/HREE and high Th/U and Lu/Hf ratios, coupled with negative Eu and positive Ce anomalies. The textural and compositional data indicate that titanite from the quartz diorite has been overprinted by hydrothermal fluids after being crystallized from magmas. Titanite grains from the mineralized skarn are texturally equilibrated with retrograde skarn minerals including actinolite, quartz, calcite, and epidote, demonstrating that these grains were formed directly from hydrothermal fluids responsible for the mineralization. Compared to the varieties from the quartz diorite stock and diabase dike, titanite grains from the mineralized skarn have much lower REE contents and LREE/HREE, Th/U, and Lu/Hf ratios. They have a weighted mean ²⁰⁶Pb/²³⁸U age of 142 ± 2 Ma (MSWD = 0.7, 2σ), in agreement with a zircon U–Pb age of 144 ± 1 Ma (MSWD = 0.3, 2σ) of the quartz diorite and thus interpreted as formation age of the Ruanjiawan W–Cu–Mo deposit. Titanite grains from the ore-related quartz diorite have a concordant U–Pb age of 132 ± 2 Ma (MSWD = 0.5, 2σ), which is 10–12 Ma younger than the zircon U–Pb age of the same sample and thus interpreted as the time of a hydrothermal overprint after their crystallization. This hydrothermal overprint was most likely related to the emplacement of the diabase dike that has a zircon U–Pb age of 133 ± 1 Ma and a titanite U–Pb age of 131 ± 2 Ma. The geochronological results thus reveal two hydrothermal events in the Ruanjiawan deposit: an early one forming the Wu–Cu–Mo ores related to the emplacement of the quartz diorite stock and a later one causing alteration of the quartz diorite and its titanite due to emplacement of diabase dike. It is suggested that titanite is much more susceptible to hydrothermal alteration than zircon. Results from this study also highlight the utilization of trace element compositions in discriminating titanite of magmatic and hydrothermal origins, facilitating a more reasonable interpretation of the titanite U–Pb ages.     

Remnants of arc-related Mesoarchaean oceanic crust in the Tartoq Group of SW Greenland

The Tartoq Group, located in SW Greenland, consists of supracrustal rocks of mainly tholeiitic basaltic composition, including pillow lavas, sills/dykes and gabbros, as well as ultramafic rocks. Metamorphic grade ranges from greenschist facies to granulite facies. The Tartoq Group crops out as a series of blocks and slivers that are imbricated with originally intrusive Mesoarchaean TTG orthogneisses. The supracrustal rocks form part of a SE vergent fold and thrust belt consistent with the imbrication of TTG gneisses and supracrustal rocks along a convergent margin. LA-ICP-MS U–Pb zircon dating of an intrusive TTG sheet yields a minimum age of 2986 ± 4 Ma for the Tartoq Group. This age is consistent with MC-ICP-MS Lu–Hf and Sm–Nd isotopic whole-rock data for mafic samples from different blocks of the Tartoq Group, which yield errorchron ages of 3189 ± 65 Ma and 3068 ± 220 Ma, respectively. The mafic supracrustal rocks of the Tartoq Group have chondrite-normalized REE patterns with La_CN/Sm_CN of 0.67–1.96 and rather flat primitive mantle-normalized multi-element patterns, except for scattered LILE contents, and generally negative Nb-anomalies with Nb/Nb* of 0.26–1.31. Th/Yb varies between 0.06 and 0.47 and Nb/Yb between 0.45 and 4.4 indicative of an arc affinity when compared to rocks from modern settings. The similar geochemistry of the different lithological units, together with their coeval formation, as evident from trace element geochemical trends, supports a co-magmatic origin for the rock assemblage and their formation as imbricated relics of oceanic crust. Accordingly, we propose that the Tartoq Group represents remnants of Mesoarchaean oceanic crust, which formed in a suprasubduction zone geodynamic environment.