Post-collisional Tectonic Setting Research Articles

Geochemical and geochronological evidences from Cambrian to Ordovician protracted magmatism in the Istranca Massif, NW Türkiye

Plutonic rocks in different ages are cropted out and form the basement rocks in the Istranca Massif. One of the plutons located at the basement is the Cambrian-Ordovician Vize pluton (Vize-Kırklareli) and is distinguished from other plutons by some of its characteristic features. This pluton intruded into the high-grade metamorphic sedimentary rocks, and is unconformably overlay by Triassic low-grade metamorphic rocks and Eocene aged coral reef limestones (Soğucak Formation). Based on new whole rock geochemical and zircon UPb data concentrated in two different ages, it can be said that the Vize pluton was affected by protracted magmatic activity. The igneous minerals and texture of Vize pluton are partly preserved, It has a mylonitic texture, a distinct foliation consisting of light and dark zones. In addition, metagranites contain mafic magmatic enclaves (MMEs) in some places.The Vize pluton is an I-type pluton with predominantly peraluminous and slightly metaluminous character. It is also High-K, calc-alkaline, and reflecting volcanic arc and post-collisional tectonic settings. Mineral chemical analyses show that the mafic minerals in the Vize pluton consist of Fe-biotite and calcic amphibole (hornblende). Ti-in biotite thermometry shows that the temperature of the pluton in the final crystallization temperatures are between 834 and 850 °C (mean = 845 ± 4 °C), while the crystallization temperatures of amphiboles are between 876 and 910 °C (mean = 893 ± 22 °C). Crystallization depths are estimated to be a range of 6.5 to 7.9 km. It can be assumed that the oxygen fugacity of calcic amphiboles (logƒO2) is stabilized between −10.7 and − 11.3 bar (mean = −11.05 ± 0.4 bar). ∆NNO values are between 0.72 and 1.11 (mean = 0.96 ± 0.12) and H2O melt content is between 4.63 % and 5.43 % (mean = 5.04 ± 0.4 %). Oxygen fugacity values are among the typical values of calc-alkaline magma crystallization.The Vize pluton was crystallized in Cambrian to Ordovician times according to zircon UPb dating is concentrated in two different populations as 526.16 ± 3.26 Ma and 452.93 ± 2.76 Ma. All data obtained are consistent with the ages of the magmatism that produced the Vize Pluton in the Balkanides and Istranca Massif of 420–470 Ma (mean 447.17 ± 3.24 Ma) and indicate that it probably formed in the northern Gondwana. It was affected by the magma-mixing processes of coeval felsic and mafic magmas, and anatexis processes. Geochronological and geochemical data indicate the existence of a protracted magmatic activity related to convergent setting (long-lived magmatic arc) that forced the Vize-Pluton to undergo multi-stage melting-crystallization processes.

Geochemical characteristics and genesis of niobium–yttrium–fluorine granite pegmatite from Hmrat El Sorwhyia area, North Eastern Desert, Egypt

The granite pegmatites of Hmrat El Sorwhyia, situated in the northern Egyptian-Nubian Shield, are predominantly hosted within the central areas of syenogranitic bodies, with limited occurrences noted along the marginal sites. The Hmrat El Sorwhyia granitic pegmatites represent a notable example of rare-metal mineralisation. This study introduces novel bulk- rock compositions, including major, trace, and rare earth elements, to investigate and constrain the origin and mechanisms influencing the genesis of the Hmrat El Sorwhyia granitic pegmatites and their rare-metal mineralisation. The studied pegmatites exhibit diverse morphologies, featuring lenticular pockets that contain the highest radioelement concentrations. The maximum (equivalent uranium) eU value is 760 ppm while the maximum (equivalent thorium) eTh value is 5552 ppm. These pegmatites have granitic composition and peraluminous characteristics, indicative of A-type affinity associated with post-collisional tectonic settings, and are categorised as niobium–yttrium–fluorine-type pegmatites. The formation of granite pegmatites through fractional crystallisation during the late-stage magmatic processes involved the concentration of U, Th, rare earth elements, Zr, Y, and Nb. This concentration facilitated the crystallisation of thorite, uranothorite, columbite, cerianite, and zircon. Additionally, assimilation-fractional crystallisation mechanisms led to the exchange of accessory phases between successive injections of pegmatite and the surrounding wallrock, resulting in variable mineral concentrations. These open-system processes were responsible for the development of these pegmatites.

Final closure of the Paleo-Tethys Ocean: Insights from Triassic granitoids in the central Qiangtang area, northern Tibetan Plateau

The geodynamic evolution during the closure of the Paleo-Tethys Ocean in the Tibetan Plateau remains to be fully understood. The Longmu Co−Shuanghu suture zone in the northern Tibetan Plateau has usually been considered to represent the main ocean basin of the Paleo-Tethys Ocean, so it plays a key role in understanding the evolution of the Paleo-Tethys Ocean. In this study, we focused on the Gacuo and Bensong batholiths on the north and south sides of the Longmu Co−Shuanghu suture zone, respectively. We conducted detailed zircon geochronology and whole-rock geochemical and Sr-Nd isotopic analyses, as well as zircon Hf isotope studies. Zircon U-Pb dating indicates that the Gacuo batholith was formed ca. 223−209 Ma, and the age of the Bensong batholith is ca. 213−203 Ma. The Gacuo batholith is mainly composed of I-type granitoids, which are most likely attributed to partial melting of ancient sedimentary materials of the North Qiangtang terrane with a mixture of ∼0%−30% amounts of mantle-derived components. In contrast, the Bensong batholith has granitoids of A-type affinity, and it was probably generated by partial melting of Mesoproterozoic crust of the South Qiangtang terrane with limited mantle contribution (<5%). Finally, we suggest that the Gacuo batholith was probably generated by the break-off of the oceanic slab beneath the North Qiangtang terrane, while the Bensong batholith was related to a possible lithospheric delamination process of the South Qiangtang terrane after continental collision. Therefore, the Gacuo and Bensong batholiths both developed in a postcollisional tectonic setting, and they recorded the evolutionary process of the subduction and closure of the Paleo-Tethys Ocean during the Late Triassic.

Petrogenesis of granitoids in the southern Anhui Province, China: Implications for the Neoproterozoic tectonic evolution of the eastern Jiangnan orogenic belt

The Jiangnan orogenic belt is a key component of the South China Block, yet the tectonic-magmatic evolution of the orogenic belt remains widely debated. The eastern segment of the Jiangnan orogenic belt experienced Neoproterozoic magmatism evidenced by widespread granitoids, which is key to understanding the tectonic evolution of the orogenic belt. In this study, we conducted detailed field, petrographic, geochemical, and geochronological studies of the Neoproterozoic Xucun pluton and adjacent magmatic rocks in the southern Anhui province of the eastern Jiangnan orogenic belt. Zircon LA-ICP-MS U-Pb dating of two samples yields interpreted crystallization ages of 830.3 ± 2.9 Ma and 831.2 ± 3.3 Ma. The Xuun pluton is an S-type, peraluminous biotite granodiorite that belongs to the calc-alkaline to high-K calc-alkaline series. εNd(t) values for the pluton range from −2.53 to −0.49, and the TDM2 model ages range from 1.66 to 1.83 Ga. The whole-rock, major and trace element and Sm-Nd isotopic compositions of the Xucun pluton suggest petrogenesis in a magmatic arc-related tectonic setting. These new constraints, combined with previous results, indicate that the Xucun pluton formed in a post-collisional tectonic setting. The source for the Xucun pluton was mainly juvenile crust mixed with some Mesoproterozoic continental crust. The juvenile crustal rocks were generated during arc magmatism before ca. 860 Ma. We interpret that the the eastern Jiangnan orogenic belt was generated during the ca. 860–830 Ma collision of the Shuangxiwu arc and a continental terrane. Subsequent collapse of the Jiangnan orogenic belt resulted in erosion and partial melting of juvenile crustal rocks to form S-type granitoids, including the Xucun pluton.

The Neoproterozoic Agudos Grandes granitic batholith, SE Brazil: Inferences on source areas from elemental and Sr-Nd-Pb isotope geochemistry

I-type, K-rich calc-alkaline hornblende-biotite granitoids (HKCA) suites are typical of both pre- and post-collisional tectonic settings, and their petrogenesis is challenging, since they are dominated by rocks with intermediate composition (e.g., 60–68 wt% SiO2; 10–20 vol % mafic mineral) that are neither typical products of crust nor of mantle partial melting. These granitoids are particularly abundant as the main components of Ediacaran batholiths intruding the Neoproterozoic Ribeira Fold Belt in SE Brazil, e.g. constituting ∼70% of the exposition of the Agudos Grandes Batholith, where they were emplaced at 620-610 Ma, as indicated by U–Pb zircon dating from our previous work and new data presented here. Two types of coeval granitoids comprise an expanded suite of mafic to felsic titanite and allanite-rich biotite granitoids (Itapevi-type) and a single occurrence of biotite-muscovite leucogranite (Turvo-type). Elemental and isotope whole-rock data indicate that different sources were involved in the genesis of their parent magmas, with crust with old residence predominating for the HKCA and Itapevi types, as indicated by very negative (−16 to −20) εNd(t) and low initial 206Pb/204Pb (16.4–16.7), and younger metasedimentary rocks as the source of the Turvo leucogranite (εNd(t) (∼-14); initial 87Sr/86Sr = 0.717). This “syn-orogenic” magmatism was immediately followed, as demonstrated by field and geochronological data, by ∼605-600 Ma circumscribed plutons dominated by more fractionated (±muscovite)-biotite granites that derive from melts generated in the middle crust from sources that are slightly younger than those of the HKCA granitoids, as indicated by slightly less negative (εNd(t) (similar to those of the Turvo leucogranite) and higher 206Pb/204Pb (17.1–17.3). After a ∼15 Myr lull, A-type plutons were emplaced in a post-orogenic setting, probably from mantle and crust sources. The syn-to late-orogenic (620-600 Ma) magmatism of the Agudos Grandes was produced by a thermal anomaly, probably associated with a continental arc. A combination of elemental and isotope geochemistry and inherited zircon data suggests that crustal melting was probably induced by ascension of mantle-derived basic magmas, and initiated in hot zones at the lower portions of a previously thickened crust, formed by old Paleoproterozoic to Archean material (the basement of the Apiaí-São Roque Domain of the Ribeira Belt?), and progressed to the middle portions of the crust, where it provoked partial melting of a different crustal domain with younger age and crustal residence (Embu Complex orthogneisses and metasediments).

Physico-mechanical properties and shielding efficiency in relation to mineralogical and geochemical compositions of Um Had granitoid, Central Eastern Desert, Egypt

The current work aims to describe the physico-mechanical characteristics and shielding efficiency with reference to the mineralogical and geochemical compositions of the Neoproterozoic Um Had composite granitoid pluton in order to deduce their favorability as dimension stones. The Um Had granitoid pluton has an elliptical outline with a mean diameter of about 10 km. This pluton is a composite (ranging from white to reddish pink color), hard, massive, and medium- to coarse-grained granitoid body. It is classified as syenogranite according to their modal and bulk chemical compositions. Geochemically, the granitoid pluton is a highly calc-alkaline, peraluminous granite, formed by low degree partial melting of tonalitic source rock in a post-collisional tectonic setting. The physico-mechanical properties of the granitoid pluton under study satisfy the requirements of dimension stone in terms of their bulk density (from 2561 to 2564 kg/m3), and to some extent water absorption capacity (from 0.38% to 0.55%). However, their compressive strength values (50.4–113.4 MPa) do not achieve the minimum requirement for interior use and light duty exterior use. This study delves into the potential of some of our syenogranite samples (I, IIA, IIS, and 10) as gamma radiation shielding materials. We have assessed the mass attenuation coefficient (GMAC), effective atomic number (Zeff), exposure build-up factor (EBF), and energy absorption build-up factor (EABF) for each of these samples. The GMAC and Zeff calculations were performed using the Phy-X online software, across a photon energy range of 0.015–15 MeV. Our findings suggest an inverse relationship between photon energy and GMAC, with the highest values observed for the (I) granite sample (∼18). This study shows the promising radiation shielding capacity of our samples. The insights derived from GMAC, Zeff, EBF, and EABF can serve as a guide for the development of effective, naturally sourced radiation shielding materials.

Geochemistry and origin of felsites and associated A-type granites at Wadi Atalla area, Central Eastern Desert, Egypt: Implication for genesis of Neoproterozoic post-collisional highly silicic melts

Alkaline volcanics (felsites) and A-type granites are spatially and temporally associated in the Wadi Atalla area, Central Eastern Desert, Egypt. These rocks represent final Neoproterozoic magmatic activity in the Northern Nubian Shield. Wadi Atalla felsites form NW-trending elongate mass consisting of silicic volcanics, which is intruded by A-type granites of Um Had and Um Effein plutons. Field relations indicate that both felsites and A-type granites were emplaced in a series of magmatic pulses. Felsites include tuffaceous, porphyritic and hypabyssal varieties, while A-type granites comprise syenogranite and alkali feldspar granite. Geochemically, they are highly silicic rocks and display a narrow range of SiO2. They have high-K alkaline nature with metaluminous to peraluminous character and were erupted in a post-collisional tectonic setting. Mineral chemistry of biotite supports the alkaline and A-type characters of the studied rocks. Atalla felsites and associated A-type granites show light REE enrichment relative to heavy REE [(La/Lu)n = 2.67–5.72] with pronounced negative Eu anomalies (Eu/Eu* = 0.15–0.52). Compositional similarities between Atalla felsites and A-type granites in the studied area suggest that the intrusive and extrusive events are broadly related. The systematic variation of major- and trace-element contents of the felsites and A-type granites indicates derivation from similar sources through partial melting of juvenile crustal rocks, followed by extensive fractional crystallization. The main fractionated phases are feldspars, with minor role of fractionation of amphibole, biotite, apatite and FeTi oxides. Multiple saturation calculations indicate water-saturated storage and final equilibration conditions for the felsites ranging from 788 °C at 90 MPa to 740 °C at 255 MPa. The parental magmas of the felsites and A-type granites were linked to lithospheric delamination and upwelling of asthenospheric mantle material. This process led to generation of mantle melts that supplied heat to melt the juvenile crust of the Arabian-Nubian Shield (ANS), along with crustal uplift recorded by intersecting strike-slip faults and shear zones. Atalla felsites represent a distinctive post-collisional alkaline volcanic phase in the Nubian Shield that has been emplaced in an extensional tectonic regime, during a phase of fracturing and crustal uplift, which followed the end of the Pan-African orogeny. This volcanic phase is younger than the Dokhan volcanics in the Eastern Desert and older than the typical Katherina volcanics in southern Sinai.

Geochronology and skarn mineralogy of the Akesayi Fe deposit in the Western Kunlun, Xinjiang: Implications for mineralization process

The Akesayi deposit, located in the eastern part of the Tianshuihai terrane of the Western Kunlun Orogenic Belt, Xinjiang, China, is a recently discovered medium-sized magnetite deposit containing approximately 51 million tons of ore with an average grade of 41 wt%. This deposit is hosted by skarns at the contact between monzonitic granite, diorite porphyry, and medium to low-grade metamorphic clastic rocks of the Permian Huangyangling Group. The ore types include banded, disseminated, and massive ores. The metallogenic process can be divided into prograde skarn, retrograde skarn, oxide, quartz-sulfide, and carbonate stages. The metallic minerals include magnetite and pyrite, and the gangue minerals include olivine, garnet, hedenbergite, hornblende, actinolite, biotite, cummingtonite, chlorite, quartz, and calcite. The zircon U–Pb dating of biotite adamellite intrusion and schist together constrains the formation age of the host rocks in the Akesayi Fe deposit to 217–272 Ma. Rb–Sr dating of eight garnet samples yields an isochron age of 12.41 ± 0.31 Ma, which is almost identical to the 12.56 ± 0.50 Ma age obtained via Sm–Nd dating of eight garnet samples. Furthermore, zircon U–Pb dating yields ages of 12.76 ± 0.12 Ma and 12.37 ± 0.18 Ma for diorite porphyry and monzonitic granite near the Fe orebodies, respectively. The initial Sr isotopes of garnet ((87Sr/87Sr)i = 0.710901) prove that the diorite porphyrite ((87Sr/87Sr)i = 0.709283) is related to skarn mineralization. Thus, the Akesayi deposit is a skarn-type iron ore related to the middle Miocene diorite porphyry. The mineral assemblage indicates the extensive development of manganese-skarn in the Akesayi mining area. The manganese content of host rocks of the deposit is low, and the source of manganese in the skarn may mainly come from the hydrothermal fluids associated with Miocene diorite porphyry emplacement. The compositional variations between the cores and rims of single garnet grains and different stages of tephroite indicate the concentration characteristics of the hydrothermal system, particularly manganese content, which evidently changed during hydrothermal activity. The endmembers of garnet and pyroxene suggest that the ore-forming environment transformed from a relatively reduced acidic environment to an alkali-rich, high-oxygen fugacity environment. The widely developed chlorine-rich amphiboles and biotite indicate that the hydrothermal fluids were rich in chlorine and may have been related to the diorite porphyrite intrusion near the ore bodies. The iron mineralization of the Akesayi deposit is analogous to the Gangdese Miocene porphyry–skarn polymetallic mineralization, which occurred during the Miocene in a post-collisional tectonic setting. Considering the series of Miocene intrusives discovered in West Kunlun, we propose that Miocene skarn Fe mineralization events occurred in West Kunlun, and that this area has great prospecting potential.

Late Carboniferous bimodal volcanic rocks of the West Junggar Terrane, NW China: Implications for the postcollisional tectonic setting of the southwestern CAOB

ABSTRACT The West Junggar terrain (WJT), as a crucial part of the Central Asian Orogenic Belt (CAOB), is distributed with numerous igneous rocks, which provide critical information for crustal growth. However, the closure of the Junggar Ocean (JO) and the beginning of the postcollisional tectonic stage of the WJT have been controversial. This study delimited the regional lithologic units based on remote sensing geological mapping and recognized a series of bimodal volcanic rocks (BVR) in Hala’alate Mountain of the WJT. LA-ICP‒MS zircon U‒Pb geochronology and geochemistry were used to discuss the petrogenesis of the BVR and determine the stage of regional tectonic evolution. Geochronological results yield crystallization ages of 302 ± 4 Ma, 298 ± 2 Ma, 304 ± 1 Ma, and 303 Ma± 2 Ma for the basaltic andesite, basalt, and two rhyolitic samples, respectively. Basalts and basaltic andesites are calc-alkaline, and display enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depletion in high field strength elements (HFSEs). Notably, basaltic andesites in this area were once misjudged as sanukitoids owing to their low contents of Mg#, Ni, Cr, and other characteristics that are inconsistent with the typical definition of sanukitoids. The rhyolites are A2-type granitoids with high SiO2 contents and are depleted in Nb, Ta, P, Ti, and Sr, showing enriched LREE patterns with negative Eu anomalies. These features indicate that the magma of the mafic end-member of the BVR is derived from the partial melting of the depleted lithospheric mantle, whereas the felsic end-member magma can be associated with the remelting of the lower crust due to the upwelling and underplating of mafic magma. In combination with previous studies of simultaneous basic dikes and felsic rocks, a postcollisional tectonic stage was proposed for the WTJ during the late Carboniferous, suggesting that the JO was closed.

The Carboniferous shoshonitic (s.l.) gabbro–monzonitic stocks of Veiros and Vale de Maceira, Ossa-Morena Zone (SW Iberian Massif): Evidence for diverse subduction-related lithospheric metasomatism

Post-collisional potassium-rich rocks are a critical petrogenetic and geodynamic marker across the European Variscan Belt. We present a detailed characterization of the only potassium-rich mafic intrusions identified so far in the Ossa-Morena Zone (Iberian Massif). Using new major, trace and SmNd isotopic whole-rock analyses, as well as mineral chemistry analyses, we discussed the petrogenesis of the early Carboniferous potassium-rich Veiros and Vale de Maceira (Portugal) stocks in the geotectonic framework of the southern Iberia, marked by the collision of the Ossa-Morena Zone, a Gondwanan terrane, with the South Portuguese Zone, a Laurussian terrane. The Veiros and Vale de Maceira shoshonites (s.l.) range from gabbros to syenites, with a predominance of monzonites and monzogabbros, characterized by different proportions of olivine, clinopyroxene, orthopyroxene, plagioclase, alkali feldspar, phlogopite and brown hornblende. The Veiros stock is mainly composed of fine-grained ultrapotassic rocks, and the Vale de Maceira stock is composed chiefly of medium-grained shoshonite rocks. A small group of hornblende-bearing medium-grained calk-alkaline rocks was also identified. The stocks have high contents of K2O, MgO, total alkalis, Th and other LILE, high ratios of LREE/HREE and LREE /HFSE, and show a Nb-Ta-Ti negative anomaly, typical of orogenic settings. Sr and Nd isotopes yielded moderate radiogenic Sr and unradiogenic Nd, that might suggest the involvement of a crustal component. However, the combined use of isotopic and elemental compositions rules out significant contamination by crustal materials upon ascent and emplacement. Instead, a source metasomatised by subduction-related fluids and hydrous melts from the slab is proposed. This diversely metasomatised source was a phlogopite-amphibole-bearing and (phlogopite-free) amphibole-bearing lherzolite at the upper part of the garnet stability field in the sub-continental lithospheric mantle. The Devonian mafic volcanic rocks point to a northward dipping (present coordinates) subduction of the Rheic oceanic plate underneath the Ossa-Morena Zone during the Variscan Orogeny. However, the Veiros and Vale de Maceira magmas originated during the post-collisional stage from the partial melting of the supra-subduction metasomatized lithosphere. The melting occurred during a period of enhanced heat due to asthenospheric upwelling related to the slab break-off of the Rheic's slab. The stocks are concomitant with the profusion of granitoid intrusions, which is compatible with a post-collisional tectonic setting. They are also coeval with the opening of the Beja-Acebuches back-arc, likely related to slab roll-back of a segment of the Rheic oceanic crust, implying polyphasic subduction and a complex geodynamic setting for the late stages of oceanic closure in southern Iberia.

Zircon U-Pb ages and Hf isotope characteristics of granitic rocks from the Shapinggou molybdenum deposit, Dabie Shan, China

The giant Shapinggou porphyry molybdenum deposit in Jinzhai county, Anhui province is located in eastern Dabie Shan, but its genesis, genetic type and tectonic setting are still debated. New zircon U − Pb age data presented in this contribution show that the granitic rocks at Shapinggou area have been episodically formed at ∼ 135 Ma, ∼127 Ma, ∼117 Ma and ∼ 113 Ma in Early Cretaceous, and can be classified into the early-stage (135–127 Ma) granodiorite and monzogranite plutons, and the late-stage (117–113 Ma) quartz-orthophyre stock and cryptoexplosive breccia pipes. Mo mineralization is closely associated with the late-stage shallow-seated granitic stock or pipes. Granitic rocks of both stages have high contents of SiO2, K2O + Na2O and Al2O3, low contents of TiO2, CaO and MgO, showing a metaluminous to peraluminous, high-K calc-alkaline to shoshonite affinity. They are generally featured by enrichments of LILE (Rb, U, Th) and LREE, and depletions of HFSE (Nb, Ta, Ti) and HREE, with high (La/Yb)N ratios. The early-stage granitic plutons show trace element geochemical signatures of partial melting of over-thickened continental crust (>50 km), whereas element geochemistry of the late-stage small-sized granitic intrusions suggests a shallow source depth (ca. 35 km) under post-collisional extension setting. The Hf isotope data indicate that the Shapinggou granitic rocks are originated from a crustal source predominated by the Kuanping Group mixed with other components such as the mantle. The southward subduction and partial melting of the southern North China Block (including Kuanping Group) beneath the Dabie Shan lead to the generation of the Shapinggou porphyry Mo system in the post-collisional extension setting. Hence the Shapinggou Mo system distinguishes for its crustal source and post-collisional tectonic setting from the porphyry Mo deposits of Climax- or Endako-types, and should belong to collision-type or Dabie-type porphyry Mo deposit.

Petrogenesis and tectonic significance of Late Paleozoic magmatism in the Xilinhot micro-continent, central Xingmeng orogenic belt

ABSTRACT The evolution history of the Hegenshan Ocean is an important part of studying the evolution of the Xingmeng orogenic belt, but it is still controversial. Here we present an integrated study of petrology, zircon U–Pb geochronology, whole-rock geochemistry, and Sr–Nd isotopes on a series of intrusive rocks from the Baiyinguole area, Xiwuqi, central Inner Mongolia, NE China. Chronological data indicate that the intrusive rocks can be divided into three stages: 326–317, 297–295, and 259–254 Ma. The 326–317-Ma gabbros and diorites belong to the calc-alkaline series, and are characterized by positive whole-rock εNd(t) values (+1.1–+6.7), relatively low La/Ba ratios (0.04–0.10), and high La/Nb ratios (1.82–3.18), indicating that the magma source is from a subduction-modified lithospheric mantle. These samples have arc features owing to the southward subduction of the Hegenshan oceanic crust. The 297–295-Ma granodiorites and monzogranites show positive εNd(t) values (+1.9–+2.4), low 87Sr/86Sri ratios (0.704185–0.705234), and young Nd two-stage model ages (TDM2), which is consistent with typical I-type granites. On various tectonic setting discrimination diagrams, the granodiorites and monzogranites are plotted in the syn-collisional field. The 259–254-Ma syenogranites have low abundances of mafic minerals, low contents of Zr/Hf (18.31–31.35) and Nb/Ta (6.80–11.80) values, high SiO2 (76.36–78.54 wt.%) content, A/CNK (1.08–1.76), and D.I. of 96.8–97.4 (average 97.1), and notable negative Eu anomalies (δEu* = 0.07–0.17) and weakly tetrad-effects in REE pattern, which is affinity to the characteristics of highly differentiated granites. Moreover, they have positive εNd(t) values (+2.0–+2.1) with scattered TDM2 of 730–1217 Ma and low Nb/U ratios. This study suggests that the syenogranites are formed in a post-collisional tectonic setting, which is related to the closure of the Hegenshan Ocean. In addition, based on a review of the pre-existing literature data, a model of southward ridge subduction is proposed to explain the tectonic evolution of the Hegenshan Ocean.

Early Mesozoic polyphase contractional deformation in the Yanshan belt: Implications for the destruction of the north China Craton

• The northern North China Craton was in a contractional setting in early Mesozoic. • Post-collisional contractional deformation was due to the lithosphere delamination . • A decoupling process dominated the early stage of the destruction of the NCC. After the collision of the Mongolian arc terranes with the amalgamated Bainaimiao arc and North China Craton in the latest Permian to earliest Triassic, the northern North China Craton ended the Andean-type accretionary orogenesis. The nature of the subsequent post-collision tectonic setting in early Mesozoic in the northern North China Craton remains controversial. Some workers proposed that the northern North China Craton evolved into a post-orogenic extensional stage. However, this view was mainly built on geochemistry studies of Triassic plutonic rocks in northern North China Craton while it had never received support from studies of tectonic deformation. In contrast, our recent field mapping combining with geochronological studies in the Yanshan belt suggest that the northern North China Craton was in an overall polyphase multi-directional contractional settings in early Mesozoic. We have identified four stages of contractional deformation (D 1 -D 4 ) in this region. D 1 (250–231 Ma) is the intracratonic response to the collision of the Mongolia arc terranes with the NCC. D 2 (214 ∼ 207 Ma) and D 3 (204 ∼ 195 Ma) are post-collisional intracratonic contractional deformation which occurred synchronously with the lithosphere thinning. D 2 and D 3 and the intervened plutonism might be a crustal response to the delamination and sinking of the over-thickened lithosphere of the northern North China Craton. D 4 is the result of the west-ward subduction of the Izanagi plate beneath the eastern Asian continent plate in the Early Jurassic. These findings together with previous studies indicate that the northern North China Craton experienced a long period of polyphase contractional deformation before its final destruction in the Early Cretaceous. The early stage of the destruction of the North China Craton is characterized by coeval lithosphere thinning and crustal thickening.

LA-(MC)-ICP-MS U-Th-Pb dating and Nd isotopes of allanite in NYF pegmatite from lesser qingling orogenic belt, central China

U-Th-Pb dating and Sm-Nd isotopes of magmatic allanite from the Huangjiagou NYF pegmatites (lesser Qinling orogenic belt, China) were precisely measured and compared with zircon U-Pb dating and Lu-Hf isotopes to demonstrate the suitability and robustness of the U-Th-Pb and Sm-Nd system in allanite as a note-taker of formation age and magma sources for pegmatites. Allanite crystals from the Huangjiagou NYF pegmatites exhibit complex chemical zoning with a homogeneous primary internal domain, which has a typical magmatic origin with high La/Sm, Th/U, and low Eu/Eu*. The allanite has low La/Ce ratios (0.48–0.62) and thus is classified as allanite-(Ce). We used time-depended element fractionation and the changing of NAI with ablating different matrices to test the matrix differences between allanite and zircon standard 91500, and achieved excellent allanite U-Th-Pb date using zircon 91500 as external standard. Magmatic allanite-(Ce) yields a lower-intercept age of 1829 ± 23 Ma on the Tera-Wasserburg plot and a 208Pb/232Th weighted average age of 1840 ± 17 Ma, both of which are consistent with the zircon 207Pb/206Pb weighted mean age (1826 ± 11 Ma) within uncertainty, supporting the reliability and accuracy of non-matrix matched allanite U-Th-Pb dating. We used titanite standard (MKED1) to correct the time-drift in allanite Nd isotope analysis. And by integrating the zircon Lu-Hf isotopes and allanite Sm-Nd isotopes, together with field investigation and mineralogy, we suggest that the Huangjiagou NYF pegmatites belong to an abyssal class, formed in the late Paleoproterozoic, and likely related to the partial melting of the dehydrated Taihua Group (amphibolite and TTG granites) in the post-collisional tectonic setting between the Eastern and Western blocks along the trans-North China Orogen (TNCO). This study confirms the talent of allanite serving as a good indicator for the crystallization age and magma sources of NYF pegmatites using non-matrix matched U-Th-Pb dating and in situ Sm-Nd isotope analysis.

Evidence of gold related to Neoarchean alkaline magmatism in the Abitibi greenstone belt (Canada) from mineral parageneses and microscale trace element geochemistry on pyrite

Most of Archean gold deposits are classified as orogenic gold systems (OGS), precipitated by metamorphic fluids during compressional deformation at convergent plate margins. However, Neoarchean gold deposits are also found spatially related to post-collisional alkaline intrusions such as syenites, suggesting a genetic link between gold and magmas. To bring novel evidence on this relation, ore parageneses related to Bachelor/O’Brien, Beattie, Douay and Golden Arrow gold deposits were studied together with trace elements distribution at micron-scale in Au-bearing pyrites. Further, the δ34Spyrite signature in the Beattie deposit were compared to epithermal Phanerozoic analogues in post-collisional tectonic settings. Except for Golden Arrow, results show a paragenetic assemblage of K-feldspar-albite-anhydrite-barite-celestite-apatite-rutile-calcite-dolomite which is also common in Phanerozoic magmatic-hydrothermal systems. Gold-bearing pyrites are characterized by a higher abundance of most trace elements compared to OGS. Positive Au-Ag-Bi-Te-Tl-W-anomalies – which are not observed in OGS – suggest deposition from highly oxidized fluids, while Au precipitation in OGS is mainly controlled by reduced fluids. The presence of highly oxidized environments is also confirmed by very low δ34Spyrite values ranging from −17.3‰ to −13.9‰ VCDT found at Beattie, in the range of those found in Phanerozoic deposits of Tuvatu and Emperor in Fiji. It is proposed that Archean gold related with late alkaline continental magmatism is deposited both at the top of porphyritic system and in epithermal environment, before the acme of deformation and metamorphism.

Petrology, zircon U–Pb geochronology and tectonic implications of the A1-type intrusions: Keban region, eastern Turkey

The Southeast Anatolian Orogenic Belt (SAOB), the most extensive segment of the Alpine-Himalayan Orogenic Belt, resulted from the northward subduction of the southern branch of the Neotethys oceanic crust beneath the Anatolian micro-plate. We present new whole-rock geochemistry, zircon U–Pb ages, and Lu–Hf isotope data from the stocks and dykes with a length of up to tens of meters belonging to the Keban magmatic rocks, eastern Turkey. These rocks are represented by syenite and quartz monzonite intruded into the Keban metamorphic complex. The geochemistry data indicates that the samples bear mostly metaluminous, variably high alkalines (K2O + Na2O), Ga/Al ratios and zircon saturation temperature, and typically the A-type granite characters. According to the Y/Nb vs Yb/Ta diagram, the Keban magmatic rocks show A1-type geochemical signatures modified by crustal melts. Syenite and quartz monzonite samples from Keban magmatic rocks give zircon U–Pb ages of 77.4 ± 0.34 Ma, 76.3 ± 0.3 Ma and 76.36 ± 0.34 Ma, respectively. On the primitive mantle-normalised trace element patterns, the Keban magmatic rocks show enrichment in large-ion lithophile elements (LILEs) relative to high field strength elements (HFSEs). They are coupled with slightly negative Nb–Ta anomalies. Chondrite-normalised rare earth-element patterns show strong enrichment in LREEs relative to HREEs, a typical A-type granites feature. The zircons have negative εHf(t) values that vary from −2.68 to −0.41, and Hf model ages (TDM2) range from 1171.54 to 1329.26 Ma, indicating the enriched lithospheric mantle sources and crustal contribution. The sources and evolution of the alkaline magmas might be related to the post-collisional tectonic setting.

Paleoproterozoic tectonic evolution of the Khondalite Belt in the North China Craton: Constraints from the geochronology and geochemistry of 1.9–2.3 Ga felsic and basic intrusive rocks in the Jining area

Although the Paleoproterozoic Khondalite Belt is one of the most important delineation boundaries in the North China Craton, its tectonic evolution remains controversial. Here, we present new geochronological and geochemical data for Paleoproterozoic granodiorite gneiss, amphibolite, and gabbro and monzogranite dykes in the Jining area in order to constrain the tectonic evolution of the Khondalite Belt. Zircon U–Pb dating indicates that the granodiorite gneiss, amphibolite and monzogranite were emplaced at ca 2.3 Ga, 2.0 Ga and 1.9 Ga, respectively. The 2.3 Ga granodiorite gneisses have positive εNd(t) values (+0.6 to +1.3) and high zircon saturation temperatures (864–873 °C), and show geochemical characteristics of A2-type granites, probably indicating extension background related to subduction. The 2.0 Ga amphibolites have high Nb contents and their protoliths display geochemical features of Nb-enriched basalts. The low MgO, Cr, Ni, LREE-enriched patterns, and negative εNd(t) values (−5.5 to −6.3) with relatively old Nd model ages suggest that the protoliths were derived from a fertile mantle source metasomatized by slab-derived melts. The distinct geochemical characteristics suggest that the formation of the amphibolites were attributed to the upwelling asthenosphere triggered by the opening of slab window. Based on the U-Pb ages of zircons and the contact relationship in the outcrops, the intrusive age of the gabbros was constrained to be 2.0–1.9 Ga. These gabbro dykes have high Mg#, Cr, and Ni contents, and show E-MORB-like REE patterns with high contents of large ion lithophile elements and negative Nb-Ta anomalies, indicating a subducting tectonic setting. Their high Ba/Th and Rb/Y ratios, low Th/Ta and Nb/Y ratios imply a mantle source metasomatized by slab-derived fluids. The 1.9 Ga monzogranite dykes have high Sr and Sr/Y ratios, low Yb and HREE, similar to those of typical adakitic rocks. Their low MgO, Cr, Ni, Mg# and negative εNd(t) suggest that the dykes were generated by partial melting of thickened lower continental crust. These different rocks, therefore, indicate a convergent margin occurred along the Khondalite Belt before the collision between the Yinshan Block and the Ordos Block, followed by extension event at ca. 2.3 Ga and closed with a collision at ca. 2.0–1.9 Ga, and then changed to post-collisional tectonic setting with the adakitic monzogranite dykes formed at ca. 1.9 Ga.

The Karavansalija Mineralized Center at the Rogozna Mountains in SW Serbia: Magma Evolution and Time Relationship of Intrusive Events and Skarn Au ± Cu–Pb–Zn Mineralization

The Karavansalija Mineralized Center (KMC) with its Au–Cu skarn mineralization associated with the Rogozna Mountains magmatic suite in southwestern Serbia belongs to the Oligocene Serbo-Macedonian magmatic and metallogenic belt (SMM-MB). Samples from intrusive and volcanic rocks at the KMC show typical arc signatures of subduction-derived magmas through enrichment in large-ion lithophile elements (LILE) and depletion of high–field strength elements (HFSE). The magmas developed a high-K (calc-alkaline) fractionation trend and evolved toward shoshonitic compositions. Whole-rock trace element data suggest plagioclase-absent, high-pressure amphibole ± garnet fractionation that generates adakite-like hydrous magmas during evolution in lower crustal magma chambers. Zircon LA–ICP–MS and high-precision CA–ID–TIMS dating together with zircon trace elements and Hf isotope measurements were carried out in order to couple the geochronologic and geochemical evolution of the KMC. The results suggest that magmatism starts around 29.34 Ma with granitic to rhyodacitic subvolcanic intrusions followed by a more evolved magmatic intrusion that was emplaced into Cretaceous limestone, generating a widespread skarn alteration at ca. 28.96 Ma. After a period of quiescence of about 1.2 My, either another magma body evolved or the same upper crustal magma chamber was recharged and also likely partly reactivated older plutonic rocks as indicated by xenocrysts. The REE ratios shift from apatite, titanite ± amphibole-dominated fractionation of the older magmatic event to crystallization of allanite, efficiently depleting the LREE and Th/U in the younger upper crustal magma. After a lamproite-like melt was injected, the increased heat and fluid pressure led to the expulsion of a quartz-monzonite porphyritic stock at ca. 27.72 Ma, strongly interacting with the skarns and established a fertile hydrothermal system. Soon after a non-mineralized second pulse of some porphyry dykes cut the previous phenocryst-rich “crowded” porphyries and skarns at ca. 27.60 Ma, thus bracketing the maximum timespan of ore mineralization to about 112 ± 45 Ka. Increased contribution of a lamproite-like melt is inferred from the presence of phlogopite micro-phenocrysts, phlogopitization of biotite, and diopside clusters in the latest porphyry dykes. There is a trend of increased crustal assimilation from the oldest volcanic phase to the emplacement of the youngest porphyry dykes recorded by ɛ-Hf of the zircons. Oligocene occurrences of significant base metal mineralization within Serbia, northern Macedonia, and Greece, e.g., Crnac, Rudnik, Veliki Majdan, Stratoniu, or the Cu–Au porphyry at Buchim (northern Macedonia), are all associated with trachy-andesitic (quartz latitic) porphyry dykes, which originated through post-collisional tectonic settings or upper plate extension involving reworking of crustal arc-derived rocks and partial melting of the mantle wedge. This study demonstrates that on the basis of field relationships and the application of high-precision CA-ID-TIMS zircon age data, pulses of porphyry dykes of a 10ka age range can be distinguished, and the timing of mineralization can be parenthized.

An appraisal of the geochemistry and geotectonic settings of the pan african rocks around akure and are-ekiti and environments, Southwestern, Nigeria

The geochemical characteristics of the Pan-African rocks from Akure and Are –Ekiti and Environs show a minor variations in the contents of silica (SiO2 50.18-98.92 wt%,), alumina, Al2O3 (0.26-17.26wt%), potash (K2O, 0.07-5.98wt%), and iron F2O3 (0.52-10.77wt%) respectively. The rocks suites from both areas are also characterized by high alumina, high silica, and presence of biotite, microcline, monzogranite, syenogranites, diorite, granodiorite as well as granites. The rocks from both studied areas plotted into the S-Type and I-Type granites suggestive of their derivation from mixed sources. The presence of shoshonitic series suggests rock association characterized by k-rich, high Na2O + K2O and low TiO2. The granites from b Akure and Are Ekiti and environs are characteristically potassic with metaluminous I-Type and peraluminous S-Type affinity and elong to high-K calcalkaline to shoshonitic series. The rocks are strongly enriched in Ba-Sr with pronounced negative Eu anomaly, belonging to syn-to post collisional tectonic setting. However, the plots of Rb versus Y+Nb, Rb versus Ta + Yb, Ta versus Yb, Nb versus Y, as well as Ta versusYb respectively showed that the granitic rocks of Akure and Are Ekiti and environs were formed in the tectonic environments of volcanic arcs, syn-collisional and post collisional as well as within plate settings, suggesting their derivation from fractional crystallization and partial melting.

Trace element geochemistry of Bitlis ignimbrites sourced by Quaternary Nemrut Volcano: inferences for A2-type magma generation in Eastern Anatolia post-collisional extensional setting

In the study presented here, we investigated the K-Ar age determination and petrological significance of trace element compositions of Bitlis (Eastern Anatolia) ignimbrites associated with explosive activities of the well-known Nemrut volcano. K-Ar geochronological dating of Bitlis ignimbrite flow deposits gave the age of 790 ka which corresponds to the first products of pre-caldera stages of Nemrut stratovolcano. Bitlis trachydacitic ignimbrites with shoshonitic affinity are characterized by the typical negative anomalies of Eu, Nb-Ta, and Ti in chondrite-normalized spider and multi-element variation diagrams, and plot in the fields of within-plate and post-collisional tectonic setting in Rb vs Y+Nb discrimination diagram. Accordingly, similar to that of Nemrut volcanic products, trace element signatures (e.g., high Nb, Ce, Y, and Zr contents) of Bitlis ignimbrites show coincidence with geochemical characteristics of A2-type silicic magmas. Relative to the upper crust, higher La/Ba and Nb/La, and lower Ba/Ta and La/Ta ratios of Bitlis ignimbrites, which are close to that of Nemrut basalts, suggest an interaction between OIB-like basaltic magma and upper crust. Our results point to A2-type silicic magma generation in Eastern Anatolia post-collisional extensional setting, and Nemrut volcanic and pyroclastic rocks (e.g., Bitlis ignimbrites) formed by partial melting of upper crustal rocks at shallow level via interaction with OIB-like basaltic magma derived from a common mantle source.