Granite Association Research Articles

Petrogenesis of magmatic charnockite-biotite granite suite from parts of the Chotanagpur Granite Gneissic Complex (CGGC), eastern Indian shield: Implication for the break down of the Columbia Supercontinent

A rare porphyritic charnockite that is girdled by and mineralogically grades to biotite granite occurs as a part of the Chotanagpur Granite Gneissic Complex (CGGC) in and around Massanjore, Jharkhand, India. Preservation of certain textural features, including (a) euhedral to subhedral grains of orthopyroxene, (b) low dihedral angle subtended by orthopyroxene and plagioclase grains, and (c) relict intergranular and porphyritic textures, are consistent with the view that orthopyroxene in the studied rocks has a magmatic origin. Preserved magmatic features and other petrological attributes of these rocks do not support any significant mass change beyond a few tens of microns during the overprinting high-grade metamorphism. The geochemical variation of the felsic rock suite (porphyritic charnockite and biotite granite) indicates that they are cogenetic and are derived from a ferroan A-type granitoid magma by crystal fractionation. The observed geochemical trend of the studied felsic rock suites has been simulated by phase equilibria modelling in the open system using the system components Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O2. The observed mineralogical and geochemical attributes and the results of the modelling study are consistent with a petrogenetic process in which high magma temperature (> 900 °C), low pressure, and low water activity in the parental melt favoured the separation of an orthopyroxene bearing cumulate assemblage (orthopyroxene + plagioclase + quartz + K-feldspar + ilmenite + magnetite) in the initial part of the magmatic differentiation. Removal of this anhydrous cumulitic assemblage raised the bulk H2O content in the residual melt. Orthopyroxene became unstable with respect to biotite in the evolved melt that eventually crystallised minerals that formed the biotite granite. An increase in magma fO2 also restricts the orthopyroxene stability in felsic magma. Taken together all the petrological and geochemical attributes, we demonstrate that fractionation of an orthopyroxene-bearing crystal cumulate from the melt is essential to form the charnockites, and that the biotite granite forms from the evolved melt after the fractionation. The charnockite-biotite granite association of the studied area was formed in an extensional tectonic setting, presumably during the breakdown of the Columbia Supercontinent.

Petrological insights into connections between the S- and I-type magmatic associations in metamorphic core complexes: a case study of the Çataldağ metamorphic core complex (NW Turkey)

As one of the Cordilleran-type metamorphic core complexes in the western Anatolian extensional province and the broader Aegean region, the Çataldağ metamorphic core complex is composed of a granite-gneiss-migmatite complex and a synkinematic pluton, bounded by a detachment fault zone. The plutonic rocks within the footwall of the Çataldağ metamorphic core complex consist of Eo-Oligocene anatectic S-type leucogranites associated with gneiss-migmatite complex forming the core rocks and an I-type synkinematic pluton that emplaced into the core rocks in the Early Miocene. This paper presents the petrography, mineral chemistry, major-trace element geochemistry, and Sr-Nd-Pb isotope compositions of the Çataldağ I-type synkinematic pluton. It discusses the magma source evolution from the Eo-Oligocene to the Early Miocene and their relations to the Çataldağ metamorphic core complex formation by comparing two contrasting granitic associations from a petrological perspective. The Çataldağ I-type synkinematic pluton primarily comprises porphyritic granodiorite, granite, and peripheral rocks including evolved granite and pegmatite dikes. Thermobarometry calculations estimate crystallisation conditions of approximately 795 °C at 1–2 kbar (averaging 1.5 kbar), corresponding to a shallow crustal magma chamber (⁓5 km deep). The pluton is metaluminous to slightly peraluminous and of a high-K calc-alkaline character. The 87Sr/86Sr(i) and εNd values of the studied samples range from 0.70684 to 0.70772 and from −6.1 to −2.3, respectively. Pb isotopic compositions are 18.74–19.29 for 206Pb/204Pb, 15.69–15.78 for 207Pb/204Pb, and 38.89–39.39 for 208Pb/204Pb. Geochemical modelling shows that a large amount of metasomatised lithospheric mantle-derived melt component (up to 70%) and a minor crustal component (<50%) contributed to the source region of the magma. The combination of isotopic data and thermodynamic modelling suggests that the compositional variations within the pluton were primarily the result of open system processes, predominantly the assimilation of crustal rocks with a dominance of fractional crystallisation. The Sr-Nd-Pb isotopic signatures and trace element characteristics of I-type pluton, as well as their comparisons with those of S-type leucogranites within the Çataldağ core complex, indicate heterogeneous magma sources, evolving from crust-dominated to mantle-dominated magma from Eo-Oligocene to the early Miocene, reflecting mantle upwelling beneath NW Anatolia. We infer that the long-lived, mantle-driven Eocene plutonic activity that preceded the development of core complexes may have led to thermal weakening, melting, and crustal flow in the lower-middle crust beneath NW Anatolia, facilitating the formation of the granite-gneiss-migmatite complex during the incipient phase of extension in the Eo-Oligocene. Coinciding with the rapid exhumation of the S-type granite and migmatite complex, the formation and emplacement of I-type synkinematic pluton along the detachment fault zone of the Çataldağ core complex were developed as a result of asthenospheric upwelling driven by lithospheric removal processes. This inferred lithospheric removal was triggered by Hellenic slab rollback affecting the entire western Anatolia since the Oligocene. The transition from S- to I-type granites observed in the Çataldağ core complex and other Aegean massifs may indeed be a manifestation of the intensity or accumulation of this crustal extension.

Neoproterozoic slab window in the western Yangtze Block, South China: Evidence from adakitic granodiorites, gabbro-diorites and high-K granites in the Panxi arc belt

Neoproterozoic igneous rocks are widespread along the margins of the Yangtze Block and record key information on the tectonic evolution of the South China Craton. In this paper, we present a comprehensive study of zircon U-Pb ages, whole-rock geochemistry and Sr-Nd-Hf isotopes on the Neoproterozoic granodiorites, gabbro-diorites, and high-K granites in the western Yangtze Block. The granodiorites, gabbro-diorites and high-K granites were dated at 848 ± 5.3 Ma, 824 ± 5.1 Ma and 819 ± 1.5 Ma, respectively. The granodiorites have high Sr (567 ∼ 607 ppm) contents and Sr/Y (84.4 ∼ 88.0) ratios and low alkalis (Na2O + K2O = 4.3 ∼ 4.9 wt%) and Y (6.6 ∼ 7.1 ppm) and Yb (0.7 ∼ 0.9 ppm) contents, similar to typical adakitic rocks. They show low MgO (0.9 ∼ 1.3 wt%), Cr (15.2 ∼ 26.7 ppm) and Ni (3.6 ∼ 4.4 ppm) contents and positive εNd(t) (+1.7 to + 4.2) and εHf(t) (+3.0 to + 8.2) values. The parental magmas for granodiorites were generated by partial melting of thickened juvenile mafic lower crust. The gabbro-diorites are characterized by the enrichment in LREEs, significantly negative Nb, Ta and Ti anomalies, and positive εNd(t) (+2.2 to + 4.2) and εHf(t) (+5.8 to + 10.4) values. They are inferred to be derived from partial melting of lithospheric mantle modified by subduction-related fluids. The high-K granites display high Zr + Nb + Ce + Y (208 ∼ 366 ppm) and alkali (Na2O + K2O = 7.6 ∼ 8.4 wt%) contents, high 10000*Ga/Al (2.31 ∼ 2.64) ratios and zircon saturation temperatures, similar to A-type granites. We suggest that these granites were formed by the partial melting of felsic crustal materials under low pressure and high temperature conditions. The association of granodiorites, gabbro-diorites and high-K granites indicates Neoproterozoic oceanic slab subduction in the western Yangtze Block. We suggest that a subducting oceanic slab window can account for Neoproterozoic magmatism in the western Yangtze Block.

Syn-orogenic tectonomagmatic evolution of the Qilian Orogen: Insights from the Lumanshan gabbro–granite association in the Qilian Block, Northwest China

Gabbro–granite associations provide critical geological clues for unraveling crust–mantle interactions, regional tectonics and geodynamic processes. Many Late Ordovician–Early Devonian granitoids occur in the Qilian Block, display high-K calc-alkaline affinities but have less well-constrained geodynamic mechanisms. Here, we report the newly discovered Late Ordovician-Early Devonian Lumanshan (LMS) gabbro–granite association in the Qilian Block that is composed mainly of syenogranites and alkali-feldspar granites, with minor gabbro. Zircon U Pb dating yields crystallization ages of ca. 440 Ma for the gabbros and ca. 450 Ma and 414 Ma for the syenogranite and alkali-feldspar granite, respectively. The gabbros are calc-alkaline series and display enriched mid-ocean ridge basalt ( E -MORB)-like rare earth element (REE) patterns; U, Cs, and Rb enrichments; Nb, Ta, Zr, and Hf depletions; and depleted Sr–Nd–Hf isotope compositions. The results indicate that the gabbros were possibly derived from partial melting of an asthenospheric mantle wedge metasomatized by aqueous fluids. Two granite types within the LMS pluton are peraluminous and have a transitional geochemical affinity between S- and I-type, low Mg# values, and similarly evolved Sr Nd isotope compositions, which overlap with those of Neoproterozoic basement rocks exposed in the study area. The syenogranites show adakitic geochemical characteristics with high La/Yb and Nb/Ta ratios, whereas the alkali-feldspar granites are non-adakitic granites with flat heavy REE patterns and significant Ba, Sr, and Eu depletions, suggesting that they formed at lower and middle crustal levels, respectively. The LMS ca. 450–440 Ma gabbro and syenogranite were emplaced during a back-arc extensional regime associated with roll-back of the northward-subducting South Qilian Ocean slab. Synthesized data from this and previous studies suggest that the final closure of the South Qilian Ocean and continental collision between the Qilian and Qaidam blocks likely occurred at ca. 435 Ma, and the ca. 414 Ma LMS alkali-feldspar granites generated in syn -collisional setting related with exhumation of the subducted continental crust. The LMS alkali-feldspar granites also show decoupled Nd Hf isotopic systems, which should result from significant disequilibrium melting of metasedimentary materials with the apparent abundance of inherited zircons in their source due to a less intense thermal regime. • A gabbro–granite association in the Qilian Block formed in early–middle Paleozoic. • The ca. 472–435 Ma magmatism formed in an extensional setting related to slab roll-back. • The ca. 435–400 Ma magmatism occurred in syn-collisional setting.

Ca. 2.1 Ga low-δ18O gabbro-diorite association in southern North China Craton: Implications for an intraplate rifting

Although widespread ca. 2.2–2.1 Ga igneous activities were identified through the North China Craton (NCC), their petrogenesis and implications for the Paleoproterozoic tectonic regime of the NCC are still under hot debate. Here we present the 2.18–2.14 Ga gabbro-diorite plutons in the Xiong'ershan Taihua Complex, southern North China Craton. They are dominantly gabbros with minor as gabbroic-dioritic rocks. The samples exhibit transitional geochemical characteristics from tholeiitic to calc-alkali series with enrichment in LREEs (e.g., La/Yb N = 1.90–13.9) and LILEs (e.g., Rb, Ba and Sr) but depletion in HFSE (e.g., Nb, Ta and Ti), corresponding to affinity of arc-related magmatism. The high Fe 2 O 3 (8.90–14.91 wt%), CaO (6.78–9.81 wt%) contents, and Ti/Y ratios (179–635), low Th concentrations (0.11–4.08 ppm), and consistent La/Nb and Th/Nb ratios, preclude significant crustal contamination during magma emplacement. The samples show negative zircon ε Hf (t) (−7.3–−1.6) and whole-rock ε Nd (t) (−4.0–+0.9) values with much older model ages ( T DM Hf = 2811–2606 Ma and T DM Nd = 3069–2711 Ma) than their formation ages, along with high La/Nb (1.69–6.21) and low La/Ba (0.01–0.05) ratios, indicating a refertilized Archean lithospheric mantle source. Considering that zircons of 2.18–2.14 Ga gabbro-diorite in the Xiong'ershan area lack metamict features and exhibit originally low but homogeneous δ 18 O values in the mantle source (3.04‰ to 5.07‰, 4.21‰ on average), we prefer they derived from preexisting 18 O-depleted mantle source, which might be a highly heterogeneous metasomatized SCLM by subducted-fluid during the Archean cratonization. The consistent Sm/Yb and La/Sm ratios indicate ∼5–30% partial melting of the garnet-spinel dominant source region. Combing the low δ 18 O signature and within-plate (high Zr, Zr/Y, Th/Hf and Ta/Hf) geochemical features, we suggest a thermal anomaly linked to a rift setting could account for the mantle melting. The intraplate ca. 2.1 Ga low-δ 18 O magmatism possibly resembles those during the Neoproterozoic glaciations associated with major dispersal periods of Rodinia. To better understand the Paleoproterozoic tectonic evolution of the NCC, we have also comprehensively compiled all the published ages and geochemical data of the 2.2–2.1 Ga mafic-felsic igneous rocks. The mafic suites can be divided into two groups based on ages and geochemical affinities. Mafic rocks of Group 1 (2.19–2.12 Ga) belong to rift-related basalts, together with spatially associated 2.19–2.13 Ga A-type granitic rocks and volcano-sedimentary associations, likely indicating an intraplate rift setting. Whereas mafic rocks of Group 2 (2.15–2.06 Ga) show geochemical affinity of island arc calc-alkaline basalts, together with coeval 2.18–2.05 Ga I-S type granitic associations, implying an arc-related setting and recording a possible tectonic transition from extension to subduction-collision. The rifting events in the NCC during 2.2–2.1 Ga may coincide with the global lithospheric break-up of the supercontinent, and the subsequent tectonic transition could correspond to development of the globally orogenesis at 2.1–1.8 Ga. • The Paleoproterozoic low-δ 18 O gabbro-diorite plutons were formed at 2.18–2.14 Ga. • The mafic association was derived from an ancient metasomatized SCLM source. • They were formed in an intraplate rifting system. • The extensive 2.2–2.1 Ga magmatism in the NCC corresponds to global breakup event.

Contrasting origins of A-type granites in the Late Triassic-Early Jurassic Pitou complex, southern Jiangxi province: Implications for Mesozoic tectonic evolution in South China

The origin of A-type granites is purely circumstantial. Granitic complexes are quite common and generally composed of different type granites. I- and A-type granite association in a granitic complex is often described in the literature. Here we present a granitic complex, i.e. the Pitou complex in southern Jiangxi province, South China that is composed of different varieties of A-type granites. Detailed zircon LA-ICP-MS U Pb chronology and in situ Hf isotope, mineral chemistry and whole-rock element and Sr Nd isotope data of this granitic complex are used to explore their origin and to further constrain the geodynamics of Mesozoic magmatism in South China. Our new data indicate that the Pitou complex was emplaced during the Late Triassic (237 Ma) (central to northern part) and Early Jurassic (188–185 Ma) (southern part), respectively and that both the Late Triassic and Early Jurassic granites belong to A-type but show contrasting origins. The Late Triassic granites show an association of alkali-feldspar granite-syenogranite-monzogranite and the rock type of the Early Jurassic granites is alkali-feldspar granite. All the granites are composed mainly of K-feldspar, quartz, plagioclase and biotite (ferri-biotite or annite) with biotite occurring as anhedral crystal, interstitial to quartz and feldspar. Both the Late Triassic and Early Jurassic granites have high SiO 2 (>70 wt%) and total alkalis (K 2 O + Na 2 O > 8 wt%) with high FeO T /(FeO T + MgO) and low Mg#. They are enriched in rare earth elements (except Eu) and depleted in Sr and Ba. They display Zr + Y + Ce + Nb >350 ppm, 10,000 × Ga/Al >2.6 and have high zircon saturation temperatures (>800 °C). Biotites in the granites are Fe-rich with very low Fe 3+ /Fe 2+ , indicating fairly reducing conditions. However, the Late Triassic and Early Jurassic granites also show some geochemical differences. The Late Triassic granites have lower FeO T /(FeO T + MgO) and higher Mg# than the Early Jurassic granites, with the Mg# of the former consistent with pure crustal melts and the Mg# of the latter much lower than pure crustal melts. In addition, the Late Triassic granites have lower zircon saturation temperatures (up to 843 °C, average 823 °C) than the Early Jurassic granites (up to 946 °C, average 875 °C). Furthermore, the Late Triassic granites have high 87 Sr/ 86 Sr (t) (0.7132–0.7226) and negative ε Nd (t) (−10.3 to −10.9) and ε Hf (t) (in situ zircon) (−11.5 to −11.6) that are similar to those of the early Paleozoic granitoids in the region whereas the Early Jurassic granites have low 87 Sr/ 86 Sr (t) (down to 0.7034) and positive ε Nd (t) (up to +3.0) and ε Hf (t) (in situ zircon) (up to +8.3) that are similar to those of the Early Jurassic gabbroic rocks in the region. Geochemical data and major element modeling suggest that the Late Triassic A-type granites were formed by shallow (ca. 15–20 km depth) dehydration melting of the early Paleozoic granitoids triggered by intraplating of basaltic magmas and the Early Jurassic A-type granites were produced by extensive fractionation (ca. 90% to 95%) from gabbroic magmas by removal of plagioclase, amphibole, K-feldspar, clinopyroxene and magnetite. We further suggest the origin of the Late Triassic A-type granites was related to the transtension of the regional NE–trending strike-slip faults caused by the early Indosinian continental collisions and the Early Jurassic A-type granites were emplaced in a back-arc extensional setting coupled with the slab rollback and subsequent slab break-off of the subducted Palaeo-Pacific plate. Our new data confirm that the early Mesozoic magmatism in South China was controlled by continental collisions during the Late Permian to Triassic amalgamation in Southeast Asia whereas the late Mesozoic magmatism was related to the northwestward subduction of the Palaeo-Pacific plate. A transition in the dominant tectonic regime from the Tethyan to the Pacific tectonic domain most likely took place during the Rhaetian. • The Pitou granitic complex emplaced during the Late Triassic and Early Jurassic. • Both Late Triassic and Early Jurassic granites are A-type but show contrasting origin. • Late Triassic granites formed by shallow dehydration melting of Paleozoic granitoids. • Early Jurassic granites formed by extensive fractionation from gabbroic magmas. • Origin of both A-type granites suggests different geodynamic mechanisms.

Zircon U–Pb dating and geochemistry of intrusive rocks in the Shangdan suture zone of the Qinling Orogenic Belt: petrogenesis and tectonic implications

We studied the zircon U–Pb ages, whole-rock geochemistry and Sr–Nd isotopic compositions of a Paleozoic gabbro–diabase–granite association in the Shangdan suture zone to constrain the petrogenesis of these intrusive rocks and identify their tectonic implications. These rocks have distinctive crystallization ages: the Guchenggou gabbro yielded zircon U–Pb ages of 424–423 Ma, the average age of the Yueritan diabase was 411 Ma and the Danfeng granites yielded zircon U–Pb ages of 414–411 Ma. The Guchenggou gabbro was formed by partial melting of a phlogopite-bearing garnet lherzolite modified by subduction fluids in a continental arc setting. The Yueritan diabase was generated by mixing a phlogopite-bearing garnet lherzolite modified by subduction melts with continental crustal rocks in a post-collision setting. The Danfeng granites were weakly peraluminous I-type granites formed by mixing juvenile crust with metagreywackes at high temperatures and pressures in a tectonic environment transitioning from compression to extension. We suggest that the subduction of the Shangdan Ocean induced the formation of the gabbro. The diabases and granites are related to relamination of the continental crust in response to the collision of the North Qinling Belt with the South Qinling Belt, suggesting that closure of the Shangdan Ocean may have occurred at c. 410 Ma.

Late Early Cretaceous magmatic constraints on the timing of closure of the Bangong–Nujiang Tethyan Ocean, Central Tibet

As one of the most important parts of the eastern Tethys, the evolution of the Bangong–Nujiang Tethyan Ocean (BNTO) has important geological implications for paleogeographic reconstructions of the Tethyan Realm. However, the closure time of the BNTO remains highly debated. Here, we report geochronological, petrological and geochemical data from three newly identified undeformed stitching plutons that intrude a north–south-oriented section of ophiolitic mélanges in the middle–eastern parts of the Bangong–Nujiang suture zone (BNSZ), central Tibet. The stitching plutons comprise the Chaqu diorite–granite association, the Jiang Co granite, and the Konglong diorite porphyry. Secondary ion mass spectroscopy (SMIS) zircon UPb dating suggests that these three plutons were emplaced at ca. 116–112 Ma. The stitching plutons show heterogeneous Sr–Nd–Hf–O isotopic compositions. The Chaqu diorites have initial 87Sr/86Sr ratios varying from 0.7062 to 0.7064 and εNd(t) values from −2.0 to −1.6, and slightly high zircon δ18O (6.2–6.8‰) and positive zircon εHf(t) (+2.6 to +7.4) values. The Chaqu granites show high initial 87Sr/86Sr (0.7064–0.7065) ratios and low εNd(t) (−2.3 to −2.1) values, and elevated zircon δ18O (6.2–7.3‰) values and variable zircon εHf(t) (−1.7 to +4.9) values, similar to those of the associated Chaqu diorites. The Jiang Co granites exhibit higher initial 87Sr/86Sr (0.7085–0.7094) ratios and negative εNd(t) (−8.33 to −8.27) values, and variable zircon δ18O (4.8‰ to 6.0‰) and εHf(t) (−6.9 to −2.0) values. The Konglong diorite porphyries have initial 87Sr/86Sr isotopic ratios ranging from 0.7069 to 0.7075 and negative εNd(t) values ranging from −4.2 to −4.1, and high zircon δ18O (9.0‰ to 9.8‰) and variable zircon εHf(t) (−7.3 to +0.7) values. Geochemical evidence indicates that they were derived from different magma sources that included varying proportions of mantle and crustal components. The Chaqu diorites were derived by partial melting of an ancient metasomatized mantle source, and the Chaqu granites were formed by fractional crystallization of the Chaqu dioritic magmas. The Jiang Co granites were generated by partial melting of low δ18O high-temperature hydrothermally altered ancient continental crust. The Konglong diorite porphyries were likely generated by partial melting of high-δ18O enriched lithospheric mantle. In combination with data from adjacent ophiolites, magmatic rocks, and Cretaceous sedimentary rocks, we suggest that the stitching plutons were generated in a post-collisional setting induced by upwelling of asthenospheric mantle due to slab breakoff beneath the BNSZ. Our data provide an important new upper age limit for the time of collision between the Lhasa and Qiangtang terranes, i.e., the latest closure time for the BNTO.

The OPX-Bearing and OPX-Absent granitoids of the Umarizal intrusive suite, a representative example of Ediacaran A-type magmatism in NE Brazil

Ediacaran magmatism represents one of the most prominent features of the Borborema Province (NE Brazil), with the Umarizal intrusive suite a classical example of an anorthosite - mangerite - charnockite - granite (AMCG) association. This study presents new geochemical and petrological data, discusses its magmatic evolution, and compares the outcomes with similar rocks of Western Africa. The Umarizal suite displays mineral associations that crystallizated under high temperature (<900 °C) and pressure (up to 8 kbar) and low oxygen fugacity conditions that favored the formation of fayalite, magnetite, hypersthene, Fe-hornblende and annite. This generated transitional alkaline to calc-alkaline A-type magmas, which have been emplaced at intermediate to upper crust. Based on our results, we concluded that the several lithological componentes of the Umarizal suite resulted from varying degrees of interaction of melts derived from granulite-facies protoliths with crustal materials. It is considered a late-to post-tectonic Brasiliano/Pan-African orogenic context for the emplacement of this AMCG association along extensional shear zones.

Geochronology and geochemical characteristics of Paleoproterozoic syn-orogenic granitoids and constraints on the geological evolution of the Jiao-Liao-Ji orogenic Belt, North China Craton

A suite of Paleoproterozoic syn-orogenic magmatism with distinctive natures in the Jiao-Liao-Ji Belt (JLJB) of North China Craton is studied, including I-type monzogranite, related quartz gabbro, S-type granites, and adakitic granites. The Caiyuan monzogranite and quartz gabbro intrusions yield zircon U-Pb ages of 1881 ± 31 Ma and 1889 ± 19 Ma, respectively. They exhibit light rare earth element enriched patterns, and are rich in Rb, Ba, and K, but depleted in Nb, Ta, and Ti. These granites have relatively low (87Sr/86Sr)i ratios of 0.701985–0.706703, εNd(t) values of −13.0 to −0.3 and dominantly negative zircon εHf(t) values. Two Siping porphyritic granite samples give U-Pb ages of 1877 ± 11 Ma and 1881 ± 11 Ma respectively. They display enriched REE patterns, characterized by high Al2O3 and A/CNK ratio (>1.1), similar to S-type granites, with high (87Sr/86Sr)i ratios up to 0.711142 and negative εNd(t) values of −8.0 to −2.2. The Wafang and Xujiapu granites intrusions yield zircon U-Pb age of 1887 ± 11.0 Ma and 1885 ± 9.7 Ma and have high Sr/Y, (La/Yb)N and strikingly positive Eu anomalies, likely belonging to adakite. The association of quartz gabbro, I-type, and S-type granites in the Caiyuan region indicate that they were derived from mafic parental magma triggered by slab subduction. Crustal materials mixed in further AFC processes of the magma, before the monzogranite and porphyritic granite crystallized. The Wafang adakitic granite was probably related to the partial melting of a thickened crust. A complex syn-orogenic evolution model is thus proposed in the Late Paleoproterozoic of the JLJB, as slab subduction and partial melting of thickened crust simultaneously occurred at ~1885 Ma.

Neoarchean–early Paleoproterozoic crustal evolution in the Jiapigou terrane in the northeastern part of the North China Craton: Geochemistry, zircon U–Pb dating and Hf isotope constraints from the potassic granitic complex

Neoarchean granitic rocks are important components of Precambrian cratons, and their petrogenesis can provide constraints for understanding the evolution of continental crust. The Neoarchean potassic granites are widely distributed in southern Jilin Province, which is located in the northeastern part of the North China Craton. Newly obtained field geology observations and petrological, geochemical and geochronological data reveal that the Jiapigou potassic granitic complex is mainly composed of biotite granitic gneiss and medium- to coarse-grained granite. All the granitic gneisses and granites are high-K calcium–alkaline to shoshonite, metaluminous to peraluminous (A/CNK = 0.95–1.13; molar Al2O3/(CaO + Na2O + K2O)), enriched in LILEs and LREEs with strongly fractionated REE patterns ((La/Yb)N = 21–179), and depleted in Nb, Ta, Ti and P. The biotite granitic gneisses have low Rb/Sr ratios (∼0.06) and weak positive Eu anomalies (δEu = 1.26–1.51), while the granites have low Th, U and REEs and strong positive Eu anomalies (δEu = 7.27–16.92). The zircons of these granitic rocks generally have core–rim structures based on cathodoluminescence images and show inherited ages of 2729 ± 10 Ma, crystallization ages of 2523 ± 11 Ma to 2526 ± 15 Ma, and crystallization/metamorphism ages of 2480 ± 15 Ma to 2485 ± 9 Ma. The zircon Hf isotope results of the medium-grained monzogranite show that the εHf(t2) values vary from –2.2 to +5.3, and the two-stage model ages (TDM2) are 2.9–3.0 Ga. The magmatic zircons of the early Neoarchean (∼2.73 Ga) and the late Neoarchean (∼2.52 Ga) crystallized in high-temperature magmas (738–890 °C), whereas those of the early Paleoproterozoic (∼2.48 Ga) crystallized in relatively low-temperature (646–702 °C) magmas. These results indicate that the Jiapigou granitic rocks were products of intracrustal recycling during the late Neoarchean and the early Paleoproterozoic. The protoliths of the Jiapigou granitic gneisses were derived from the remelting of the early Neoarchean juvenile crustal rocks in the lower crust during the late Neoarchean. Subsequently, these granitic rocks underwent amphibolite-facies metamorphism and water-fluxed melting in the early Paleoproterozoic, resulting in the association of migmatic granitic gneisses and potassic granites at the shallow crust level. The cratonization in the Jiapigou terrane involved early Neoarchean (∼2.73 Ga) juvenile crust growth and late Neoarchean (∼2.53–2.52 Ga) to the early Paleoproterozoic (∼2.48 Ga) intracontinental reworking.

Valorization of powder of volcanic rocks used as cement substitution in self-compacting concrete

Self-compacting concrete undergoes incessant evolutions both in the improvement of its intrinsic performances and in its uses when it is combined with other materials which give it desired properties. These concretes interest more and more industrial because they have several advantages: reduce the cost, build elements with complex geometry or heavily scraped and offers a unique solution to architectural creativity. The objective of this study is to introduce as cement substitution, powder of natural volcanic rock such as granite and perlite from west of Algeria in self-compacting concretes. This is to study their performance on workability, physical-mechanical properties by destructive (compression flexure) and non-destructive tests (ultrasound, Smidth rebound hammer). Six formulations of self-compacting concretes have been developed. One control concrete without addition and four concretes containing 10% and 20% of granite powder or perlite and one concrete containing 5% of granite combined with 5% of perlite. Association of granite and perlite has generated satisfactory workability and mechanical properties which approach those of the reference concrete.

U-Pb Age, by Zircon, of the Pre-Klesiv Breed Association of the Osnytsky Block

The Osnytsky block is an integral part of the Osnytsky-Mikashevytsky volcanic-plutonic belt, represented by early proterozoic igneous rocks of different compositions. This is a new type of igneous belts for the early precambrian – a paleotypical analogue of intracontinental volcanic-plutonic belts by the phanerozoic, which was formed in the conditions of mature continental crust in the initial stage of radical structural rearrangement of the cratonized gneiss base of the Eastern European platform. Volcanogenic formations have undergone regional metamorphism at a level not higher than the epidote-amphibolite facies, classified in the klesiv series, which combines effusives of basic, acidic and medium composition and occupies a higher stratigraphic position compared to the metamorphites of the teteriv series. Intrusive rocks (gabbro-diorite-granodiorite granite association) – to the osnitsky complex. Rocks of the osnitsky complex are widespread, they account for 80-85% of the area of the Osnitsky block. The pre-klesiv association, represented mainly by gneisses of the teteriv series and plagiogranitoids of the sheremetivsky complex, has a limited distribution. The LA-ICP-MS U-Pb method was applied to date zircon from plagiogranite and plagiomigmatite of the sheremetivsky complex, and from gneiss and amphibolite. The plagiogranite yielded an age of 2110 ± 8, and plagiomigmatite of 2165 ± 22 Ma. Hence, granitoids of the sheremetivsky complex in the Osnitsk block were formed between 2.16 and 2.11 Ga. The age of the metamorphism of gneisses was defined as 2198 ± 29 Ma, whereas zircon from amphibolite crystallized at 1981 ± 36 Ma. Correspondingly, gneiss can be attributed to the teteriv series, whereas amphibolite can belong to either osnitsky complex, or nartsyzivsky complex.

Цирконология сиенитов Северного Тимана

Northern Timan is an uplifted block of the Upper Precambrian basement of the Timan Ridge, where intrusive rocks of various compositions cut Neoproterozoic metaterrigenous rocks of the Barmin Group and are overlain by Lower Silurian limestone. Syenites are widespread in the Cape Bolshoy Rumyanichny pluton and compose the Krayny Kameshek and Malyi Kameshek plutons. To determine the age of the syenites, U—Pb dating of zircons was carried out using secondary ion mass spectrometry (SIMS). The age of zircons from syenite of the Cape Bolshoy Rumyanichny pluton is 613 ± 7 Ma, Krayny Kameshek pluton — 602 ± 5 Ma, and Malyi Kameshek pluton — 598 ± 17 Ma. Similar zircon ages are known for other alkaline igneous rocks that occur within the Cape Bolshoy Rumyanichny pluton: olivine-kersutite gabbro — 614 ± 2 Ma, granites — 614 ± 11 Ma. Zircons from subalkaline granites of the Bolshoy Kameshek pluton are of the same age — 613 ± 6 Ma. The location of the plutons in the area of the Late Riphean passive margin of Baltica, the close association of subalkaline and alkaline granites, syenites, and alkaline gabbros indicate the anorogenic nature of these magmatic rocks and possible relationship with mantle plume activity. Ediacaran magmatic rocks of 614—600 Ma located in the Northern Timan could be associated with the final stages of Rodinia breakup, accompanied by plume-related magmatism, the products of which are also known in the eastern part of Laurentia and in the Scandinavia.

Delineation of the early Neoarchean (2.75 to 2.70 Ga) crustal growth and reworking processes in the southeast base of Taihang Mountain, North China Craton

Numerous studies suggest that various secular geologic and geochemical transitions occurred between ~3.2 Ga and 2.5 Ga. During this age-window, the ~2.70 Ga tectono-thermal event of the Neoarchean is by far the most influential, and is unusual in terms of coeval mafic-felsic magmatic rocks which were interpreted to reflect widespread crustal accretion. Here we report the early Neoarchean TTG and potassic granite association preserved in the Yunmengshan area, Taihang Mountain, North China Craton (NCC). TTG and potassic granites emplaced at 2712 ± 65 to 2644 ± 25 Ma, followed by ~2.57 to 2.50 Ga metamorphism and partial anatexis. TTG has geochemical features corresponding to high-Al medium-pressure (MP) TTG. Their high CaO, low to moderate Al2O3/(FeOT + MgO), and positive εHf (t) values (+3.8 to +7.2) with TDM2 of 2.96 to 2.75 Ga, indicate that they formed by partial melting of juvenile low-K mafic rocks, representative of crustal accretion. Besides, TTG can be subdivided into two groups based on Eu anomalies. Those with Eu/Eu* < 1.0 underwent advanced amphibole and plagioclase fractionation. The possible reason for their weakly negative Eu anomalies is that plagioclase has negated the effects of amphibole fractionation which is theoretically accompanied by plagioclase removal. Those with positive Eu anomalies accord with “slab-melt” identification criterion (Sr > 300 ppm plus elevated Sr/Y > 40, (La/Yb)N > 12 and Eu/Eu* > 1.0). The high Eu/Eu*, Sr/Y and low Yb probably represent the contribution of amphibole fractionation and plagioclase accumulation during the magma evolution. The evidence favors an arc-related setting for the TTG. The early Neoarchean potassic granites are monzogranite to syenogranite, and formed shortly after TTG. They belong to high-K calc-alkaline to shoshonitic I-type granite, and display depleted and concave-upward REE patterns between middle and heavy REEs and higher Zr/Sm ratios (69.6 on average) than TTG (45.4). The calculated εHf (t) values are mainly positive (+1.4 to +7.0) with TDM2 from 3.03 Ga to 2.72 Ga, together with low Al2O3/(FeOT + MgO), low to moderate CaO and high K2O/Na2O ratios, indicating a high-K mafic crustal source with metapelite involvement. Meanwhile, we reviewed geochemical data of the early Neoarchean TTGs published in the NCC and other cratons abroad. The results show that samples from Trans-North China Orogen in NCC have lower Y contents, higher Sr/Y and (La/Yb)N ratios, and more depleted HREE than those from Eastern Block, which could be interpreted to reflect an increase in the depth of melting. Alternatively, according to previous studies and comparison globally, elevated Sr/Y values could also reflect increased consumption of plagioclase in melting reactions due to higher temperatures, or magma fractionation. Therefore, it mostly lacks a clear distinction between the “arc” and “non-arc” settings based on geochemistry. However, many researchers put forward evidence that subduction was well attested in the late Archean (3.0 to 2.5 Ga), but it might be unstable.

Petrography and geochemistry of Neoproterozoic charnockite–granite association and metasedimentary rocks around Okpella, southwestern Nigeria

The Neoproterozoic charnockite–granite association of Okpella intrudes metasedimentary and migmatite-gneiss complex rocks in the eastern Igarra Schist Belt, southwestern Nigeria. In order to unravel the complex processes involved in the formation and tectonic evolution of the Igarra Schist Belt during the Neoproterozoic, detailed field, petrographic and whole-rock geochemical study of the charnockite–granite association and metasedimentary rocks around Okpella was conducted. Published data on the metasedimentary rocks and Pan-African granitoids in different sectors of the belt were also compiled for detailed interpretations. The charnockites and granites of Okpella show primary magmatic mineralogy and geochemical characteristics. They are silicic (> 63 wt% SiO2), metaluminous to peraluminous, high-K calc-alkaline, ferroan, post-collisional granitoids. The garnet-biotite schist, calc-silicate gneiss and quartzite in the area are low–medium grade metasedimentary rocks. The mineralogy and geochemistry of the charnockites suggest that the charnockitic melt was derived from mafic lower continental crust through partial melting and assimilation-fractionation processes. The granites probably originated from mixed melts derived from lower- to mid-crustal tonalites-trondhjemites-granodiorites and/or subducted metagreywackes and mantle-derived magmas (probably the charnockitic melt and/or its progenitor). The granites and charnockites are coeval and were presumably emplaced during the post-collisional stages of the Pan-African Orogeny. The garnet-biotite schist, calc-silicate gneiss and quartzite represent metamorphosed immature to slightly mature sedimentary rocks, probably greywacke, marl and subarkose, respectively, that were sourced from intermediate–acid rocks which underwent low–moderate chemical weathering with minor contribution from recycled sediment sources and deposited in active continental environments. The Neoproterozoic evolution of the Igarra Schist Belt, therefore, involved deposition and infolding of sediments in active continental margin during the early Pan-African followed by upwelling of basaltic magma from the mantle which underplated and crystallized in the lower continental crust and was subsequently partially melted to generate the charnockitic and granitic melts through mantle-crust interaction during the late Pan-African.

Aeromagnetic modelling of Precambrian subsurface structures of the Tasiast area, NW Mauritania

Abstract The NW sector of Mauritania represents the Archaean province of the Reguibat Shield. It is mainly composed of the typical Archaean cratonic association of granitoid gneisses, greenstone belts and granites. The greenstone belts contain high mineral potential, mainly gold. This is particularly the case of the Chami Greenstone Belt, which hosts the large Tasiast gold mine. The gold deposits are hosted along a NS oriented shear zone with a surface of 70 × 15 km 2 . In this study, a subsurface structural model is proposed based on the application of suitable computations on a high-resolution reduced-to-the-pole aeromagnetic anomaly map of the northern Chami area. Upward continuations, apparent magnetic susceptibility, directional derivatives, analytical signal, 3D Euler deconvolution and spectral analyses were performed to build this model. They were used to decipher the main evidenced structural features with the main NNE–SSW, NW–SE and ∼120° N directions, identified on most all computed maps combined with in situ measurements. They probably correspond to mafic dykes, faults and shears rooted up to 5 km in depth, particularly to the north, SW and NE, and southwards and westwards by spectral analyses and 3D Euler deconvolution, respectively. The basement is deeper towards the west and south and crops out towards the NE in agreement with the geological observations. In addition, the high values of magnetic susceptibility ( χ m ) measured in situ on banded iron formations (25.7–35 × 10 −3 SI) SW of Akjoujt could be the origin of metallotect sources associated with magnetic minerals for exploration of gold-bearing and base metals.

Neoproterozoic magmatic evolution of the southern Ouaddaï Massif (Chad)

This paper presents new petrological, geochemical, isotopic (Nd) and geochronological data on magmatic rocks from the poorly known southern Ouaddaï massif, located at the southern edge of the so-called Saharan metacraton. This area is made of greenschist to amphibolite facies metasediments intruded by large pre- to syn-tectonic batholiths of leucogranites and an association of monzonite, granodiorite and biotite granite forming a late tectonic high-K calc-alkaline suite. U-Pb zircon dating yields ages of 635 ± 3 Ma and 613 ± 8 Ma on a peraluminous biotite-leucogranite (containing numerous inherited Archean and Paleoproterozoic zircon cores) and a muscovite-leucogranite, respectively. Geochemical fingerprints are very similar to some evolved Himalayan leucogranites suggesting their parental magmas were formed after muscovite and biotite dehydration melting of metasedimentary rocks. A biotite-granite sample belonging to the late tectonic high-K to shoshonitic suite contains zircon rims that yield an age of 540 ± 5 Ma with concordant inherited cores crystallized around 1050 Ma. Given the high-Mg# (59) andesitic composition of the intermediate pyroxene-monzonite, the very similar trace-element signature between the different rock types and the unradiogenic isotopic signature for Nd, the late-kinematic high-K to shoshonitic rocks formed after melting of the enriched mantle and further differentiation in the crust. These data indicate that the southern Ouaddaï was part of the Pan-African belt. It is proposed that it represents a continental back-arc basin characterized by a high-geothermal gradient during Early Ediacaran leading to anatexis of middle to lower crustal levels. After tectonic inversion during the main Pan-African phase, late kinematic high-K to shoshonitic plutons emplaced during the final post-collisional stage.

Petrogenesis of Middle Triassic granite association in the Gonghe basin, Qinghai: Constraints from geochemistry, U-Pb ages and Hf isotopic

青海共和盆地位于青藏高原东北缘，以往有关共和盆地及邻区早-中三叠世岩浆岩成因机制的认识分歧较大，且研究主要集中在露头岩石方面。本文以共和盆地干热岩GR1井深部花岗岩岩芯样品作为研究对象，对其进行岩石学、长石电子探针、主微量元素地球化学、锆石U-Pb年代学及Lu-Hf同位素研究。矿物组成及长石电子探针测试结果显示花岗岩主要为奥长花岗岩、英云闪长岩及花岗闪长岩。锆石U-Pb测年结果表明，奥长花岗岩的结晶年龄为236.5±1.7Ma，英云闪长岩的岩浆结晶年龄为241.6±3.0Ma。主、微量元素地球化学显示这些花岗岩主要为准铝质，属于高钾钙碱性系列。全岩Ta-Nb-Hf等不相容元素图解及锆石Hf同位素数据表明共和盆地的236.5~241.6Ma花岗岩显示火山弧及同碰撞花岗岩成分特征，说明中三叠世共和地区发生俯冲-碰撞转换。结合本文数据与区域背景资料，作者认为：共和盆地早-中三叠世花岗岩组合的形成与印支期宗务隆洋的南向俯冲作用密切相关，此时，在宗务隆-青海南山-西秦岭北缘存在统一的大陆边缘弧环境；在236~241Ma时发生俯冲-碰撞转换；晚三叠世时宗务隆-青海南山-西秦岭北缘已处于碰撞期和后碰撞期。

Isotopic-Geochemical Systematics (Sm–Nd, Lu–Hf) of Neoarchean Subalkaline and Alkaline Rocks of the Keivy Structure (Kola Peninsula): Their Age and Genetic Relations

The Neoarchean subalkaline magmatism of the Keivy structure is expressed in the formation of the volcanoplutonic latite–monzonite–granite association (LMGA). The formation of LMGA magmas is assumed to occur due to melting of metasomatically altered mafic rocks during intrusion into the lower crust of basaltic melts initial for rocks of the dike complex and gabbro–labradorite massifs. The alkaline granites associated with LMGA have a close U–Pb age but a later formation time based on the geological data. With respect to LMGA, alkali granites have increased concentrations of SiO2, alkalis (K2O/Na2O = 1.1–1.4), iron (F# = 84–98%), a high agpaitic index (Kagp = 0.86–1.2), and lower quantities of TiO2, MgO, Fetot, and Al2O3, which probably resulted from the higher degree of differentiation of their initial melts compared to LMGA.