Search

It is generally believed that adakites are produced by slab melting under young and hot condition in plate convergent margins. However, other rocks that are not associated with slab melting but display the geochemical characteristics of an adakite, are termed "adakitic" or "adakite-like" rocks in present paper. Although formation mechanism of adakitic rocks is different from that of adakites, they are all generated by the crystallization of melts (magmas), which are termed "adakitic melts". The unique geochemical features of adakitic melts arise from mafic rock melting in the specific environments including 800–1000 °C, 1.5–3.0 GPa, and 1.5–6.0 wt% H 2 O, with the superfluous garnet and/or rutile and minor plagioclase within the source. Adakitic rocks can be formed in continental-collision zones and intraplate settings, and thus have no specific indicative significance for tectonic setting. This paper divides adakitic rocks into four genetic types formed by (1) direct partial melting of thickened lower rocks, (2) partial melting of delaminated lower crust, (3) differentiation of mafic magma under high-pressure conditions, and (4) magma mixing. The adakitic rocks may coexist with coeval ultrapotassic-potassic volcanic rocks, Nb-enriched basalts or shoshonitic igneous rocks, which hints that the adakitic rocks have a genetic relationship to the mantle-derived rocks when the both form a magmatic association. Most host rocks of porphyry Cu–Mo–Au deposits show adakitic feature geochemically in both continental collision zones and subduction zones, but a few of the host rocks from subduction zone are not adakitic. This paper firstly identifies that the adakitic porphyries in collision zones show trace-element contents (e.g., Sc, Th, and Y) and ratios (e.g., Th/Yb, Sr/Y, and La/Yb) clearly different from those in subduction zone. The magmatic sources of adakitic porphyries from a continental crust have higher Th and lower Sc contents, and more garnet and rutile remains than those of adakites from a subduction zone. The higher Th/Yb, Sr/Y, and La/Yb ratios indicate that the source depth of porphyric rocks from collision zones is probably deeper; whereas the depth of porphyric rocks from subduction settings is variational and relatively shallow, therefore a few of them don't display adakitic signature. Further investigations into the genetic link between adakitic melts and porphyry Cu–Mo–Au deposits are required. • Adakite not related to slab melting are termed "adakitic" or "adakite-like" rocks. • They are formed by melting of thickened lower rocks or delaminated lower crust. • They are also formed by differentiation of mafic magma or magma mixing. • Most porphyry deposit in collision and subduction zones show adakitic feature. • Sources of Porphyry deposits in collision zones are deeper than in subduction settings. [ABSTRACT FROM AUTHOR]

The Gharebagh area consists of a suite of mafic to acidic rocks located in northwestern Iran, in the Sanandaj-Sirjan zone (SSz), which is part of the Zagros orogenic belt. In this paper, we present a detailed petrological, geochronological, and isotopic study of representative rocks of Late Paleozoic igneous activity in NW Iran. LA-ICP-MS dating of zircons shows that the Gharebagh intrusive body (GIB) was formed in a tight time frame of 300 Ma. Geochemical analyses as well as isotopic studies of Lu Hf on zircon and Sm Nd on whole-rock were used to determine the petrogenesis of these rocks and develop a tectonic model. Crustal-model ages (Hf-t NC) of 0.57 to 1.02 Ga indicate the contribution of older Neoproterozoic crust to the formation of these rocks. The partially melted lower crust was one part of the magma together with a mafic melt formed by differentiation of the depleted mantle. The GIB suite was presumably formed by an anorogenic magmatic event (continental rift) that included extensive mantle upwelling and partial melting of the lower crust. So the gabbroid and granitoid rocks are coeval with the 300 Ma but not co-magmatic origin. • A bimodal magmatism event took place at around 300 Ma in the NW of SSz. • Gabbros were likely derived from a depleted mantle with partial crustal contamination. • A-type granite, were likely formed by crustal partial melting. • Intermediate rocks resulted from mixing of crust and mantle derived magma. • Bimodal magmatism suites were generated at a anorogenic (crustal rifting) setting. [ABSTRACT FROM AUTHOR]

Adakites formed at the oceanic subduction zones are sodic, whereas adakitic rocks in continental collision zones are generally potassic. Many orogenic belts also contain sodic adakitic rocks which formed during continental collision. The source and petrogenesis of these sodic adakitic rocks are debated. In this paper, we present whole-rock geochemical and Sr Nd isotope, and zircon U–Pb–Hf–O isotope and trace element data for the newly identified Early Devonian granitic pluton from the Balong area in the East Kunlun Orogen (EKO), China. The Balong granites are characterized by low K 2 O/Na 2 O (0.40–0.84), high Sr/Y (33–53), and variable (La/Yb) N (6–40) ratios coupled with low Yb (0.71–1.05 ppm) and Y (7.80–12.8 ppm) concentrations. They display low MgO contents (0.60–1.23 wt%) and Mg# values (38–45), as well as low Cr (2.57–5.08 ppm) and Ni (1.10–1.90 ppm) concentrations. They have whole-rock (87Sr/86Sr) i = 0.7101–0.7123 and ε Nd (t = 418 Ma) = −6.8 to −5.8. Autocrystic zircon rims yield U Pb ages of 420–417 Ma, whereas relict zircon cores have Neoproterozoic ages of 918–909 Ma. The zircon rims have low P contents, variable ε Hf (t = 418 Ma) values of −6.4 to +2.2, and δ18O values of 5.4‰–7.5‰, whereas the zircon cores have elevated P contents, variable ε Hf (t) values of −5.5 to +5.3, and relatively high δ18O values of 8.2‰–9.8‰. These whole-rock and zircon geochemical characteristics suggest a genetic link with the Neoproterozoic S-type orthogneisses and MORB-like (mid-ocean ridge basalt) eclogites in the EKO. Two end-member mixing calculations show that the whole-rock Sr Nd and autocrystic zircon Hf isotopic compositions of the Balong granites can be produced by mixing 60–50 wt% orthogneiss-derived melt and 40–50 wt% eclogite-derived melt. Given that the P–T paths of the exhumed continental eclogites did not intersect the wet solidus of mafic rocks, we suggest the Balong granites formed by partial melting of ultrahigh-pressure metamorphic rocks of the subducted plate trapped beneath the lower crust of the overlying plate. These results, combined with existing data from adjacent regions, suggest the partial melting of ultrahigh-pressure metamorphic terranes was related to slab breakoff at the terminal stage of continental collision. This study provides a novel model for the origin of sodic adakitic rocks in the continental collision zones. [ABSTRACT FROM AUTHOR]

Numerous studies have focused on the effects of subduction zones on the development of back-arc basins. However, few have considered whether or how back-arc extension affects subduction zones. Back-arc spreading is thought to have resulted in reduced arc magma production in many Cenozoic subduction systems, but there are no documented pre-Cenozoic examples of this process. This paper reports new geochronological, mineralogical, geochemical, whole-rock Nd, and zircon Hf O isotope data for Carboniferous mafic dikes (diabase and gabbro) from the Tuotuo River area, Northern Qiangtang terrane (NQT), central Tibet. The dikes were intruded during the middle Carboniferous (330–325 Ma). The dikes are typical arc-like basalts with enrichments of large-ion lithophile elements and depletions of high-field-strength elements. Depleted mantle-like Nd − Hf − O isotopes indicate the mafic rocks were formed by partial melting of metasomatized asthenospheric mantle. Clinopyroxene compositions follow the trends of both back-arc basin basalts (BABBs) and rift cumulates, and the whole-rock compositions are also similar to BABBs. Based on the tectonic evolution of the Paleo-Tethys Ocean in the Tibet segment, we propose that this Carboniferous mafic magmatism was caused by back-arc extension during a period of magmatic quiescence of the main Paleo-Tethyan subduction system. This back-arc extension may have led to the opening of the Xijir Ulan Ocean. • The 330–325 Ma mafic dikes in Northern Qiangtang occurred in back-arc setting. • Back-arc extension coeval with Paleo-Tethys arc magmatic quiescence. • Slab-roll back or mid-ocean ridge subduction caused back-arc extension. • This back-arc extension may represent initial opening of Xijir Ulan Ocean. [ABSTRACT FROM AUTHOR]

In central-western Argentina, an Early Paleozoic belt including mafic-ultramafic bodies and marine metasedimentary rocks occurs along the western margin of the Precordillera and in the eastern Frontal Cordillera. In this paper, we present the analysis of aeromagnetic data and its processing focused on mapping geological limits, structures and the relation at depth of the southern Precordillera. With this main objective were applied filtering algorithms, reduction to the pole, tilt derivative, analytic signal, and particularly, the use of Improved Logistic Function (IL) as a new method of edge detection, in combination with the inversion map obtained from the Magnetization Vector Inversion (MVI) method. The results allow us to describe at depth the main trend of the Southern Precordillera Mafic Ultramafic Belt as two separated bocks, one in Peñasco and another in Cerro (Co.) Cortaderas, passing through Cerro (Co.) Pozos with a possible NNE-SSW direction. The combination of this techniques also can be used as prospecting guide to Pb–Zn–Ag vein deposits and High sulfidation Au-Epitermal deposits. • Determination of the Precordillera Mafic-Ultramafic Belt. • Linkage of maximum susceptibility, IL filter, outcrops of Mafic Ultramafic rocks and structural lineaments. • Magnetic Susceptibility 3D Model. [ABSTRACT FROM AUTHOR]

[Display omitted] • A water-rich mafic magmatic event, which was dated in the Middle Jurassic period, has been identified in the Jidong district. • The mafic dikes were likely originated from partial melting of subduction-related metasomatized lithospheric mantle. • The formation of these dikes was related to the westward subduction of the Paleo-Pacific plate. The westward subduction of the Paleo-Pacific plate had a significant effect on the evolution of the eastern margin of the Eurasian continent during the Mesozoic. However, records for the initial subduction of the Paleo-Pacific plate from mafic rocks are still lacking. In this paper, we deal with Middle Jurassic mafic rocks and coeval granites in the eastern Hebei district to constrain the impact of the subduction on the igneous event. Our new U-Pb ages of zircon grains confirm the emplacement of these rocks during the Middle Jurassic. These mafic dikes are composed of appinites and lamprophyres with high MgO (7.8–12.2 wt%), Cr (>500 ppm) abundances relative to high-Ti mafic rocks. They display large ion lithophile element enrichment, high field strength element depletion, and enriched isotopic components (ε Hf (t) = -9.6 – –22.7), indicating arc-like geochemical signatures. These mafic dikes were likely formed from mafic magmas derived from subduction-related metasomatized subcontinental lithospheric mantle sources under the spinel- garnet transition zone. The coeval Shijiatai (SJT) granitic pluton, which is suggested as the appinite-granite suite, is high-silica granites with low Mg# (<30) values. The SJT granitic magmas were likely sourced from the chemically modified lower crust caused by underplating of mafic magmas derived from hydrated lithospheric mantle. More importantly, the new identification of Jurassic, rather than Triassic water-rich appinitic rocks in eastern China strongly points to the subduction of the Paleo-Pacific plate. Accordingly, our study provides new geochemical evidence for westward subduction of the Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Early Carboniferous magmatic rocks in rift basins were reported in SW Yunnan. • They are products of Paleo-Tethys rifting & Proto-Tethys post-collision extension. • Late Devonian–early Carboniferous magmatic belt exists in SW China and SE Asia. • The Paleo-Tethys probably opened on one of the rift basins of the Proto-Tethys. Western Yunnan in SW China preserves abundant rock records related to the eastern Proto- and Paleo-Tethys oceans, yet the transition between the two oceans remains poorly understood. This paper presents new zircon U–Pb ages and Lu–Hf isotopic data, together with whole-rock elemental and Nd isotopic data for the magmatic rocks from Mengding and Menglong in western Yunnan. The Mengding basaltic rocks show oceanic island basalt geochemical features and have similar whole-rock Nd isotopic compositions with ε Nd (t) values of +3.5–+4.4 and uniform zircon Lu–Hf compositions with ε Hf (t) values of +6.1–+8.0, similar to the modern Hainan oceanic island basalts. These rocks yielded a zircon U–Pb age of 341 ± 2 Ma, indicating their eruption in a passive continental rift basin setting during the early Carboniferous. The Menglong mafic rocks yielded a similar zircon U–Pb age of 343 ± 3 Ma. The Menglong mafic–ultramafic rocks display E-MORB geochemical signatures, suggesting a within-plate extensional setting. They exhibit uniform Nd isotopic compositions with ε Nd (t) values of +4.1–+4.4, whereas their zircon Ɛ Hf (t) values vary from −19.5 to +11.1, indicating a mixed magma source with contributions from asthenosphere mantle and decompression melting of the metasomatized mantle wedge. Our results, together with the regional geological and stratigraphical evidence, suggest that the Menglong mafic–ultramafic rocks are comparable with the Late Devonian–early Carboniferous magmatic rocks in northern Tibet, eastern Myanmar and northern Thailand, likely formed in a post-collision extensional setting in the aftermath of Proto-Tethys closure. Taking account of the zonal distribution of the Late Devonian–early Carboniferous magmatic rocks, we propose that slab detachment of the Proto-Tethys led to an overall extensional tectonic setting, resulting in a series of rift basins in western Yunnan during the Late Devonian to early Carboniferous. The Paleo-Tethys probably opened on one of the rift basins of the Proto-Tethys. [ABSTRACT FROM AUTHOR]

[Display omitted] • The volcano-plutonic complex was mainly generated by the partial melting of lower crust. • Mantle delamination generated heterogeneous magma and thus a variety of deposits. • Intracontinental tectonic transformation controlled the porphyry emplacement. The Yao'an Pb–Ag–Au deposit is located far from the present-day margin of the Yangtze Craton, providing an excellent example for studying the genesis of porphyries and associated polymetallic mineralization in intracontinental transpression settings. In situ zircon U–Pb ages and Sr–Nd–Hf–O isotopic data of the Yao'an porphyries in the intracontinental zone, combined with research data published for the Machangqing and Beiya ore-bearing porphyries in the cratonic margin, were used in this paper. Four-phase felsic rocks (∼33 Ma) and later mafic rock (∼31 Ma) were recognized in the Yao'an district. Of these, the third-phase syenite porphyry had a genetic link with Pb–Ag–Au mineralization, which occurred within the second-phase volcanic rocks and Mesozoic strata. In addition, the Yao'an porphyry showed high initial 87Sr/86Sr ratios (0.7087–0.7094) and enriched Nd (ε Nd (t) = −10.53 to −12.60) isotopic composition, with a wide range of zircon Hf (ε Hf (t) = −8.39 to −13.2) and δ 18O values (6.28 ‰–9.20 ‰). These features suggest that the Yao'an porphyries were produced by partial melting of an ancient lower crust mixed with continental lithospheric-mantle-derived melt, which are differed from the magma source of the Beiya and Machangqing porphyries. Given the nature sources of the porphyries, we conclude that the spatial variation of metal associations changing from the Cu ± Au ± Mo system at the cratonic margin to the Pb–Ag–Au deposits in the intracontinental zone in the western Yangtze Craton was likely controlled by different magma sources. The delamination of an overthickened continental lithospheric mantle in an intracontinental transpression setting was a geodynamic trigger for porphyry magma generation, ascent, and emplacement. [ABSTRACT FROM AUTHOR]

The paper presents new geological and geochemical data on the Perseverance komatiite complex (PK) that hosts the Perseverance Ni-sulphide deposit and the volcanic and sedimentary rocks forming the footwall of the PK. Using the 3D reconstruction of the PK and its' footwall volcano-sedimentary succession the heterogeneity of the komatiite channel has been characterised on the basis of spatial distribution of the geochemical petrogenetic indicators. The study shows that the komatiite facies proximal to the mineralised bodies and the main pathway are expressed in the 3D models as the segments with anomalously high MgO concentrations coupled with low contents of Al 2 O 3 , TiO 2 and CaO (Fig - abstract). The geochemical indicators of komatiite fertility, Ni/Cr and Ni/Ti ratios, are commonly in the range of 1 to 3 for Ni/Cr and 2 to 5 for Ni/Ti within the main pathway. The Ni/Cr exceeds 5 and Ni/Ti 20 in the mineralised parts of the channel. In the peripheral zone komatiites these values commonly drop to less than 1, corresponding to barren komatiites. Similarly large variations are exhibited by the ratios of mantle normalized Pt and Pd to Al and Ti over short distances from 1 to 25. Closely spaced high and low values of these ratios hinder their use for discriminating fertile from barren komatiites. However, within the komatiite main lava pathway they can be used as geochemical pathfinders for magmatic sulphides. Reconstruction of the structurally complex komatiite sequences can be facilitated by using lithogeochemical correlation of the host volcano-sedimentary successions and particularly tracing geochemically distinctive marker units. For these purposes a special reference in this study was made to the geochemical systematics of rocks that make up footwall succession of the PK complex. It was shown that amphibolites of the host sequence can be geochemically subdivided into different types, including mafic volcaniclastics (mafic-1) and intrusive gabbro (mafic-2). The mafic volcaniclastics are strongly enriched in LREE, possibly due to presence of sedimentary epiclastic material or reflecting magma contamination by the crustal material during ascent through the crust. Additionally, they have notably high-Th contents, allowing them to be classified as having high-Th geochemical affinities. The second group (mafic-2), interpreted as coherent in origin, are characterised by flat REE patterns and lower overall abundances of the rare earths and Zr corresponding to a tholeiitic composition. Contents of Th and TiO 2 of these rocks are clustered in the two narrow intervals of compositions, corresponding to low-Th and intermediate-Th basalts, which form different amphibolite bodies. Mafic volcanics intercalate with the felsic volcanics, and quartz-feldspar-biotite-amphibole (QFBA) schists. It is shown that QFBA schist composition corresponds to metamorphosed clastic sedimentary and volcaniclastic rocks of mixed composition, which contain both clastic material derived from an Archaean provenance and volcaniclastics material derived from mafic and felsic tuffs. In conclusion, abundances and ratios of the trace elements in composition of the mafic rocks are matching to that of the different parts of the Agnew Wiluna greenstone belt and can be used for overall stratigraphic correlations. [Display omitted] • The paper presents new geological and geochemical data on the Perseverance komatiite complex (PK) that hosts the Perseverance Ni-sulphide deposit and the volcano-sedimentary succession forming the footwall of the PK. • The 3D reconstruction of the PK and its' footwall volcano-sedimentary succession has been undertaken that has allowed to enhance the heterogeneity of the komatiite channel on the basis of spatial distribution of the geochemical petrogenetic indicators. • The study shows that the komatiite facies proximal to the mineralised bodies and the main pathway are expressed in the geochemical 3D models as the segments with anomalously high MgO concentrations coupled with the anomalous values of the geochemical indicators of komatiite fertility, including Ni/Cr, Ni/Ti ratios and the ratios of mantle normalized Pt and Pd to Al and Ti. • Reconstruction of the structurally complex komatiite sequences can be facilitated by using lithogeochemical correlation of the host volcano-sedimentary successions and particularly tracing geochemically distinctive marker units. It was shown that amphibolites of the host sequence can be geochemically subdivided into different types, including mafic volcaniclastics (mafic-1) and intrusive gabbro (mafic-2). • Mafic volcanics intercalate with the felsic volcanics, and quartz-feldspar-biotite-amphibole (QFBA) schists. It is shown that QFBA schist composition corresponds to metamorphosed clastic sedimentary and volcaniclastic rocks of mixed composition, which contain both clastic material derived from an Archaean provenance and volcaniclastics material derived from mafic and felsic tuffs. The paper presents new geological and geochemical data on the Perseverance komatiite complex (PKC) that hosts the Perseverance Ni-sulphide deposit and the volcanic and sedimentary rocks forming the footwall of the PKC. Using the 3D reconstruction of the PKC and its' footwall volcano-sedimentary succession the heterogeneity of the komatiite channel has been characterised on the basis of spatial distribution of the geochemical petrogenetic indicators. The study shows that the komatiite facies proximal to the mineralised bodies and the main pathway are expressed in the 3D models as the segments with anomalously high MgO concentrations coupled with low contents of Al 2 O 3 , TiO 2 and CaO. The geochemical indicators of komatiite fertility, Ni/Cr and Ni/Ti ratios, commonly are in the range of 1 to 3 for Ni/Cr and 2 to 5 for Ni/Ti within the main pathway, The Ni/Cr exceeds 5 and Ni/Ti 20 in the mineralised parts of the channel. In the peripheral zone komatiites these values commonly drop to less than 1, corresponding to barren komatiites. Similarly large variations are exhibited by the ratios of mantle normalized Pt and Pd to Al and Ti over short distances from 1 to 25. Closely spaced high and low values of these ratios hinder their use for discriminating fertile from barren komatiites. However, within the komatiite main lava pathway they can be used as geochemical pathfinders for magmatic sulphides. Reconstruction of the structurally complex komatiite sequences can be facilitated by using lithogeochemical correlation of the host volcano-sedimentary successions and particularly tracing geochemically distinctive marker units. For these purposes a special reference in this study was made to the geochemical systematics of rocks that make up footwall succession of the PKC complex. It was shown that amphibolites of the host sequence can be geochemically subdivided into different types, including mafic volcaniclastic rocks (mafic-1) and intrusive mafic rocks, apparently metagabbro sills (mafic-2). The mafic volcaniclastic rocks are strongly enriched in LREE, possibly due to presence of sedimentary epiclastic material or reflecting magma contamination by the crustal material during ascent through the crust. Additionally, they have notably high-Th contents, allowing them to be classified as having high-Th geochemical affinities. The second group (mafic-2), interpreted as coherent in origin, are characterised by flat REE patterns and lower overall abundances of the rare earths and Zr corresponding to a tholeiitic composition. Contents of Th and TiO 2 of these rocks are clustered in the two narrow intervals of compositions, corresponding to low-Th and intermediate-Th basalts, which form different amphibolite bodies. Mafic volcanics intercalate with the felsic volcanics, and quartz-feldspar-biotite-amphibole (QFBA) schists. It is shown that QFBA schist composition corresponds to metamorphosed clastic sedimentary and volcaniclastic rocks of mixed composition, which contain both clastic materials derived from an Archaean provenance and volcaniclastics material derived from mafic and felsic tuffs. The different geochemical affinities of the mafic rocks distributed in the footwall succession of the PKC apparently suggests different magma sources and, possibly, can also reflect the position of the rocks within the mantle plume structure. In conclusion, abundances, and ratios of the trace elements in composition of the mafic rocks matches that of the different parts of the Agnew Wiluna greenstone belt and can be used for overall stratigraphic correlations. [ABSTRACT FROM AUTHOR]

Due to the unclear tectonic setting of the Jurassic ophiolites within the Bangong-Nujiang suture, how and when intra-oceanic subduction initiated within the Bangong Meso-Tethys remain controversial. Based on the new petrological, geochemical, and geochronological data reported in this paper, ∼190–180 Ma MORB-like ophiolites and OIB-like mafic rocks were identified from the Shiquanhe ophiolitic complex in the western Bangong-Nujiang suture. The MORB-like gabbros exhibit strong light rare earth elements (LREEs) and heavy rare earth elements (HFSEs) depletion and were derived from partial melting of a highly refractory depleted mantle source with limited slab-derived fluids. The OIB-like mafic rocks are enriched in LREEs and HFSEs and were originated from the melting of upwelling asthenospheric mantle without subduction additions. The data for the MORB-like ophiolites reported in this paper and previously published data demonstrate the formation of Early Jurassic fore-arc ophiolites in response to the Early Jurassic intra-oceanic subduction initiation within the Bangong-Nujiang suture. The Early Jurassic OIB-like rocks formed in the extensional tectonic setting, together with regional geological evidence, suggest that the Early Jurassic initial subduction event within the Bangong Meso-Tethys resulted in broad upper plate extension. Our study not only reveals the intra-oceanic subduction initiation age of the Bangong Meso-Tethys but also implies that subduction initiation can cause strong extension in a wider region of the upper plate in the Tethys oceanic system, not just in the fore-arc region. • Discovery of MORB-like fore-arc ophiolite (190–185 Ma) in the Shiquanhe area. • Identifying of OIB-like gabbro-monzonite (185–180 Ma) in the Shiquanhe melange. • Confirming Early Jurassic intra-oceanic subduction initiation in Bangong Ocean. [ABSTRACT FROM AUTHOR]

[Display omitted] • Deciphering the Eoarchean geological record must come from observation, not modelling. • Tectonic interleaving (including mantle over crustal rocks) shows crustal shortening. • Greenland's Eoarchean mafic rocks formed by fluid-fluxing of depleted upper mantle. • Formation of Greenland's Eoarchean crust matches convergent plate boundary processes. • Greenland's Eoarchean geology is inconsistent with stagnant-lid/heat-pipe models. It is 50 years since the landmark paper where Black et al. (1971) presented whole-rock Pb-Pb and Rb-Sr isotopic evidence for some rocks in Greenland surviving from Earth's first billion years; the ≥ 3700 Ma Amîtsoq gneisses. This overturned ideas prevalent at that time that the young Earth was far too violent for such ancient rocks to survive. In the following few years it emerged how 'normal' this early Earth appeared to be, with a retained hydrosphere (oceans) by 3700 Ma and 'continental' crust dominated by rather normal granitic sensu lat o rocks. By several decades ago this led to a vision of Eoarchean lithosphere development being controlled by a geodynamic regime with definite similarities to that in the Phanerozoic, particularly with evidence for lateral lithosphere movement (mobile lid) such as exemplified by arc-like magmatism and Barrovian metamorphism (the latter requiring tectonic crustal thickening). However, the literature in recent years is increasingly emphasising model-driven non-uniformitarian stagnant lid geodynamic scenarios to explain the Eoarchean geological record. This paper reviews the broad range of field and laboratory evidence extracted from the Eoarchean geological record in Greenland. We argue that the non-uniformitarian sagduction within a stagnant lid regime interpretation does not fit Eoarchean facts. [ABSTRACT FROM AUTHOR]

• Underground crosscut faced abrupt rock fragment ejection ascribed to strainburst. • Fragment ejection due to extra stress from seismic wave onto initial stress. • Wave raised the tangential stress thus triggered the rock fragment ejection. • Rockmass exhibited post peak brittleness response resulted in energy dissipation. • Suitable critical plastic strain multiplier value was 0.3 in the Mafic rock unit. Deep, highly stressed hard rock underground mines tend to experience elevated elastic strain energy which can dissipate around excavations causing rock fragment ejections and damage attributed to strainbursts. Prediction of this mechanism is challenging as its occurrence leads to operation delays, a high possibility of excavation collapse and fatalities. This paper outlines the back analysis of a strainburst associated rock fragment ejection displayed in an underground crosscut. This investigation is based on the preliminary rockmass structure review, an Institute of Mine Seismology (IMS) microseismic spectral analysis, mXrap stope blast event monitoring, the rock fragment ejection velocity and elastic strain energy computation. Coupled with an explicit finite volume numerical simulation to identify the initial and modified tangential stress around the crosscut. This FLAC3D numerical simulation employs an advanced strain-softening IMASS constitutive model governed by the peak and residual bounding Hoek-Brown (HB) strength envelopes. In this simulation, a plastic multiplier takes into account the rockmass's post-peak brittle behaviour, characterised by the dynamic response to strainbursts. For this post-peak brittleness behaviour, the critical plastic shear strain multiplier is varied between 0.0 and 1.0. It is deduced from this study that the strainburst associated rock fragment ejection was not fault-slip linked only triggered by a dynamic disturbance from the seismic event. It was ascribed to a tangential stress component overlaid with a stress pulse which emanated from the 1.6 M L seismic event 30 m above the crosscut. The shear wave from the event created a dynamic stress pulse that modified the initial static tangential stress that exacerbated the rock fragment ejection process. In addition, the deviatoric stress increment (45 MPa to 58 MPa) measured from the seismic source was directly proportion to the strainburst potential and its increment raised the brittle shear ratio (BSR) from 0.22 to 0.42. [ABSTRACT FROM AUTHOR]

• Models advocating continental crust formation in a stagnant lid regime are not viable. • Archean continental crust was generated in subduction zones. • Changes at the end of the Archean resulted from the combined effects of several ongoing processes. The process that generated the continental crust has long been debated. One school argues that, through most of geological time, the crust formed at convergent margins like most modern granitoids. The other school promotes a model in which, from the Hadean to at least 2.5–3.0 Ga, the continental crust grew within a stagnant or sporadically mobile lid. In one version of this model, the lower part of thick mafic crust partially melts to produce felsic magma. In another, a process called sagduction operates: the lower part of a thick pile of mafic rocks converts to eclogite, sinks into the mantle, and partially melts to form the felsic magmas that build the continental crust. In this paper, I argue that the latter processes are implausible. The lower part of thick oceanic crust consists of ultramafic cumulates and these rocks are dry. Missing is basalt and water, both of which are needed to produce granitic melt. Hydrated volcanic rocks never are deeply buried, and any water released during their dehydration migrates upwards into cooler rocks where it cannot trigger partial melting. Subduction probably operated on Earth from at least 3.8 Ga. Archean subduction zones may have been shallow, short-lived and transient but they were capable of transporting hydrated oceanic crust to depths of 100 km, which is all that is needed for the formation of granitoid magmas. The presence of subduction zones does not necessary imply the operation of plate tectonics. A hybrid situation is possible in which a mobile or partially mobile lid covered most of the planet, but localized, shallow, transient subduction zones operated to generate the felsic magmas that built the continental crust. All the changes that are said to signal a major change in geodynamic regime around 3 Ga are better explained as the nexus of several ongoing processes: (1) progressive growth of felsic crust, particularly during major mantle-generated pulses at 2.7 and 2.5 Ga; (2) the emergence of land that allowed erosion and generation of detrital sediments; and (3) a decline of temperatures in mantle and crust, which changed the style of intracrustal deformation. [ABSTRACT FROM AUTHOR]

The Pamir–Karakoram terrain contains abundant Cretaceous granitoids, and minor coeval volcanic rocks and mafic intrusions, which represent a wide (ca. 400 km) continental arc developed during northward subduction of Neo-Tethys oceanic lithosphere. However, little is known of the tectonic controls on the magmatic flare-ups and their implications for crustal thickening. In this paper, we report new zircon U Pb age and Hf isotope data for Cretaceous biotite granites, two-mica granites and mafic microgranular enclaves (MMEs) from the large-scale granitic batholiths in Pamir. These and previously published results show there were four episodes of Cretaceous magmatism (124–108, 107–103, 102–92, and 80–70 Ma). The Cretaceous arc migrated progressively landward from Karakoram to Central Pamir with a maximum arc–trench distance of ca. 400 km during the first magmatic episode (124–108 Ma). The igneous rocks are mainly S-type granites with enriched zircon Hf isotopic compositions (ɛ Hf (t) = −19.8 to −5.4), indicating derivation by partial melting of metasedimentary units. A magmatic flare-up at 105 ± 2 Ma generated voluminous I-type granites and minor mafic igneous rocks that cover ca. 30% of the study area. The I-type granites have higher zircon ɛ Hf (t) values (−19.0 to −2.0) as compared with those of the earlier S-type granites, which reflect the addition of mantle-derived materials (ca. 30%). The third episode of magmatism (102–92 Ma) generated mainly intermediate–silicic volcanic rocks, which are geochemically similar to I-type granites and have ɛ Hf (t) values of −15.0 to −1.5. The final episode of magmatism (80–70 Ma) was dominated by alkaline and mafic igneous rocks formed in a post-collisional setting, which have variable ɛ Hf (t) values of −6.6 to 10.5. Our study highlights that the Early Cretaceous magmatic flare-up in the Pamir–Karakoram terrain was related to foundering of the flat-slab of Neo-Tethys oceanic lithosphere that was previously subducted, which induced voluminous underplating of mantle-derived magma in the lower crust. This process had a key role in crustal thickening in the Pamir–Karakoram terrain prior to the Cenozoic India–Asia collision. • There are four episodes of Cretaceous magmatism in Pamir (124–108, 107–103, 102–92 and 80–70 Ma). • Landward arc migrated during the first episode related to flat subduction. • The magmatic flare-up occurred at ca. 105 ± 2 Ma, driven by flat-slab foundering. • Magmatic flare-up in Pamir–Karakoram played a key role in crustal thickening. [ABSTRACT FROM AUTHOR]

In this paper, we present zircon U Pb dating, elemental geochemistry, and Sr–Nd–Hf isotopic compositions for Late Carboniferous intrusive rocks in the northern Great Xing'an Range, northeast China. We decipher the mechanisms which triggered lithospheric thinning under microblock-microblock collision and provide a new perspective on the Late Paleozoic evolution of the eastern Central Asian Orogenic Belt. Zircon U Pb dating indicates that Jifeng gabbroic diorites and Xinlin granites were formed during a short time interval at 322–321 Ma, whereas the Xinlin gabbros were crystallized at 300 ± 2 Ma. The Jifeng gabbroic diorites exhibit typical arc characteristics, depleted in HFSEs and enriched in Pb and have positive ε Nd (t) (+1.88 to +2.00) and ε Hf (t) (+6.6 to +10.7) values, suggesting they originated from the partial melting of depleted lithospheric mantle modified by slab fluids. The Xinlin gabbros belong to alkaline series and are characterized by the enrichment in HFSEs with positive Nb and Ta anomalies and depleted Nd Hf isotopic compositions (zircon ε Hf (t) = +12.5 to +18.9, whole rock ε Nd (t) = +8.0 to +8.1). High Nb concentrations and low La/Nb (0.81–0.83) and La/Ta (12.50–14.61) ratios of the Xinlin gabbros indicate an origin from a depleted asthenospheric mantle. The Xinlin granites have high-K calc-alkaline compositions, belonging to I-type granites. These granites have positive ε Hf (t) values (+0.2 to +15.1) and juvenile two-stage model ages (1314–506 Ma) with low Sr and high Yb contents, indicating they were formed by the partial melting of a juvenile lower crust under low-pressure conditions. These data, together with the temporal and spatial distribution and the geochemistry characteristics of the Carboniferous igneous rocks in the Great Xing'an Range, suggest that the amalgamation between the Erguna–Xing'an and Songnen blocks occurred before the Late Carboniferous. The occurrence of asthenospheric mantle-derived mafic rocks indicates localized thinning process of lithosphere. Late Carboniferous magmatism on the Erguna–Xing'an Block attributed to dripping or piece removal of the lithosphere due to asthenospheric fluctuation triggered by slab break-off. • Lithospheric and asthenospheric sources of mafic rocks represent the different stage of post-collisional magmatism. • The amalgamation of the Xing'an and Songnen blocks occurred before late Early Carboniferous. • Lithospheric dripping triggered by slab break-off generated the planar Late Carboniferous post-collisional magmatism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Depleted continental mantles occur with different mineral chemistry and occurrence. • Mafic dikes were formed from melts via low-degree melting of asthenosphere mantles. • Orthopyroxenites were formed from reaction between SiO 2 -rich melts and peridotites. • Ophiolites were formed in a continental margin that was related to the Meso-Tethys. Whether the ophiolites in the southeast margin of the Gaoligong tectonic belt are related to subduction or rift is hotly debated. The aim of this paper is to present the geological and geochemical data of these ophiolitic blocks in order to understand the significance of these in the tectonic evolution of the Meso–Tethys. The peridotites in the ophiolites are dominantly harzburgites with high Mg# (88.7–92.2) and low Al 2 O 3 (<0.8 wt%) and CaO (<0.5 wt%) contents, and display U-shape chondrite-normalized rare-earth element patterns. However, they show two different groups of mineral chemistries and occurrences. Group I are with olivine Fo 90.6–92.3, orthopyroxene Mg# 91.0–92.6, clinopyroxene Mg# 91.1–93.3, and spinel Cr# 42.1–67.4 and Mg# 62.8–71.6. They exhumed adiabatically and were intruded by mafic dikes from the melts through low-degree melting of asthenospheric mantles and by orthopyroxenites in the Early Jurassic. Group II are with olivine Fo 89.8–95.3, orthopyroxene Mg# 91.3–94.6, and spinel Cr# 62.4–94.1 and Mg# 19.5–51.0. They underwent brittle deformation and medium- to low-temperature fluid replacement. The two group's peridotites have experienced the similar partial melting degrees and are the fragments of subcontinental lithospheric mantles. Extensive continental affinity tholeiites erupted in the Middle Jurassic, coeval with the primary spreading time of the Bangonghu–Nujiang Ocean in the central Tibet. The peridotites, mafic rocks, and marine-facies sediments represent the opening products of the Meso–Tethys in the Jurassic as ophiolites in a continental margin. [ABSTRACT FROM AUTHOR]

When impinging on the lithosphere in spreading ridges or intra-plate settings, the asthenospheric mantle can significantly influence plate tectonics. However, the active role of the asthenospheric mantle on subducting slabs remains poorly understood. The main reason for this dispute is the lack of typical geochemical mafic rocks in the subduction zone. In this paper, we first report the Early Jurassic (187 Ma) Yurongguo Nb-enriched basalts in the western segment of the Bangong-Nujiang suture zone. These samples show typical Nb-enriched basaltic features with high Na 2 O, TiO 2 , Nb (>7 ppm), high Nb/Th (average = 11.05), Nb/La (average = 1.37) and Nb/U (average = 72.98) ratios. Unlike the adakite-related Nb-enriched basalts, the Yurongguo Nb-enriched basalts formed from the mixture of magmas derived from upwelling asthenosphere (20–30%) and depleted mantle (70–80%) in the spinel lherzolite region (<70 km). We conclude the Yurongguo Nb-enriched basalts were formed in the fore-arc basin setting with the influence of slab rollback, which occurred under the intra-oceanic subduction. Two southward intra-oceanic subductions may exist in the western part of the Bangong-Nujiang Tethyan Ocean in the Jurassic. The Early Jurassic (200–180 Ma) intra-oceanic subduction formed the fore-arc basin, probably accompanied by asthenospheric mantle activity at the same time, followed closely by flat subduction due to the oceanic plateau. After a period of geological stabilization, the Late Jurassic (170–150 Ma) was the period when the spreading of the little ocean basin ceased, and the second intra-oceanic subduction occurred. We proposed an oceanic plateau-subducted oceanic slab interaction and overriding intra-oceanic subduction model for the Meso-Tethyan subduction in the western Tibetan Plateau. • Yurongguo rocks were formed in 187 Ma, which are the typical Nb-enriched basalts. • OIB (20–30%) and MORB (70–80%) mixed to form the Yurongguo Nb-enriched basalts. • Yurongguo Nb-enriched basalts are the consequence of intra-oceanic subduction. • Oceanic plateau played an important role in the intra-oceanic subduction. [ABSTRACT FROM AUTHOR]

Granitic rocks derived by sequential partial melting are not well-documented worldwide. This paper provides another new important case in southern Tibet. The Yardoi gneiss dome within the Southern Tibet Rift System (STRS) consists of at least four suites of Miocene high-Sr/Y granites, formed at 20.4 Ma, 18.9 Ma, 17.7 Ma, and 17.1 Ma, respectively. Geochemical data indicate that they are Na-rich and peraluminous granites with high Sr/Y and La/Yb ratios. These granites show relatively radiogenic 87Sr/86Sr(t) (0.7091–0.7149) and unradiogenic ε Nd (t) (−11.1 to −7.7) isotopic signatures. As crystallization ages become younger, they are characterized by decreases in ε Nd (t) and Sr/Y but increases in 87Sr/86Sr(t) and Rb/Sr. Such temporal trends could be explained by sequential partial melting of first the mafic lower crustal rocks and then progressively shallower metasedimentary rocks. These findings together with literature-derived data, suggest that from north to south along the STRS, as extension proceeded with a heat source from the upwelling of asthenospheric mantle, sequential partial melting produced different Miocene magmatic rocks. This provides new insight into the mechanisms for the generation of geochemical and isotopic variations in spatially confined but temporally progressed granitic rocks. • The granites are Na-rich peraluminous ones with high Sr/Y and La/Yb ratios. • The granites have lower 87Sr/86Sr(t) but higher ε Nd (t) than other Miocene ones. • As crystallization ages become younger, ε Nd (t) decreases, 87Sr/86Sr(t) increases. • Data suggest sequential partial melting of first mafic and then metapelite rocks. • The E–W extension was active at ∼20 Ma. [ABSTRACT FROM AUTHOR]

Ophiolite-related rocks and volcanic-arc rocks are the main geological components in Cuba; deciphering their origin and evolution is fundamental in interpreting and reconstructing the tectonic processes for the Caribbean region. In this paper, we report new zircon U Pb chronology, mineralogy, and geochemistry of ophiolitic metadiabase dikes and island-arc rocks in central Cuba, and discuss their origin and petrogenesis. The metadiabase dikes have a zircon U Pb age of 135.0 ± 1.7 Ma; they are low-K tholeiites , and have geochemical characteristics intermediate between those of typical normal mid-ocean ridge basalt (N-MORB) and island-arc tholeiites (IAT), suggesting that they were formed in a back-arc basin. The investigated island-arc rocks, including amphibolite from the Mabujina amphibolite complex (MAC), plutonic diorite and their mafic enclaves, and volcanic dacite, have zircon U Pb age of 93.53 Ma, 92.31 Ma, 94.35 Ma and 83.60 Ma, respectively, recording different phases of island-arc magmatism. The amphibolite samples have geochemical compositions suggesting that the protolith of the amphibolite was basaltic igneous rocks that originated from a depleted mantle source mildly modified by fluids from a subducting slab, and that the mantle source might be deep and garnet-bearing. Microstructures and elemental geochemical data reveal that the mafic enclaves and diorites represent distinct island-arc magma pulses that originated from partial melting of depleted mantle which had been previously modified by subduction-related mobile elements. The dacites are evolved island-arc volcanic rocks that formed through fractional crystallization of hydrous basaltic magmas that originated from a strongly depleted mantle source. Above data support such a tectonic model, that is, during the Early Cretaceous (from ∼135 Ma or even earlier), a typical trench–arc–basin system developed in the Caribbean region as a result of southwest-directed subduction of the Proto-Caribbean plate beneath the Caribbean plate; after that time, uninterrupted Proto-Caribbean plate subduction occurred, generating quasi-continuous arc magmatism from before ∼135 to 81 Ma, and gradually consuming the Proto-Caribbean Ocean. • A diabase dike in the ophiolite in central Cuba has a zircon U Pb age of 135.0 ± 1.7 Ma. • A typical trench–arc–basin system developed in the Caribbean region during the Early Cretaceous. • The arc rocks have highly diverse major and trace elemental and isotopic compositions. [ABSTRACT FROM AUTHOR]

• Identification of the ca. 1.23–1.21 Ga dolerite sills and flood basalts from Fanhe Basin in the northeastern North China Craton. • The ca. 1.23–1.21 Ga mafic rocks can be divided into alkaline and sub-alkaline series and exhibit distinct trace element and Nd isotopic compositions. • The alkaline rocks were derived from an OIB-like asthenospheric mantle source. • The sub-alkaline rocks were derived from a subduction-modified subcontinental lithospheric mantle. The Ectasion Period (1400–1200 Ma) represents a transition stage from Columbia (Nuna) to Rodinia supercontinents. LIPs and mafic magmatic events during this period can provide important constraints on deep processes and paleogeographic reconstructions during this transition. In this paper, we firstly reported some ca. 1.23–1.21 Ga flood basalts coeval with mafic sills from the Fanhe Basin in the northeastern North China Craton (NCC). New zircon/baddeleyite U-Pb/Pb-Pb dating on dolerite sills emplaced into the Fanhe Group yields emplacement ages from 1231 ± 9 Ma to 1206 ± 20 Ma. Whole-rock 40Ar/39Ar dating of two basalts from the Erdaogou Formation yields approximate total gas ages of ca. 1250 Ma and ca. 1210 Ma. These new geochronological results revealed that the Erdaogou basalts are coeval with some dolerite sills emplaced into the Kuangzhuangzi, Guanmenshan and Tongjiajie Formations and the dolerite sills emplaced into the Hutouling and Erdaogou Formations. These newly recognized ca. 1.23–1.21 Ga mafic rocks can be linked to the broader Licheng LIP of the previous studies. The ca. 1.23–1.21 Ga mafic rocks in the Fanhe basin can be divided into alkaline and sub-alkaline series and these two series exhibit distinct trace element and Nd isotopic compositions. The alkaline rocks show strongly fractionated chondrite-normalized REE patterns with high La N /Yb N values of 12.69–15.05. The sub-alkaline samples display less fractionated REE patterns with lower La N /Yb N values of 2.74–10.13. The alkaline rocks have OIB-like trace element patterns and slightly negative to positive ε Nd (t) values from −0.7 to 0.7. An OIB-like, asthenospheric mantle source is suggested as the source of the alkaline rocks. In contrast, the sub-alkaline rocks exhibit low negative ε Nd (t) values from −10.9 to −4.6 and are interpreted to be derived from a subduction-modified subcontinental lithospheric mantle. By comparisons with the coeval mafic magmatism in other parts of the NCC and other cratons, we suggest that the ca. 1.23–1.21 Ga mafic magmatism or LIP in the NCC was either related to the mantle plume that resulted in the Marnda Moorn LIP in Western Australia or related to a back-arc extension prior to the formation of a Grenvillian orogen located in another continent connected to the southeastern margin of the NCC during assembly of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]

Inverted metamorphic gradients are recognized in several Proterozoic to Phanerozoic orogens. However, the mechanisms that are responsible for the formation of these gradients are still a matter of discussion. In the southern Brasília Orogen, an inverted metamorphic gradient is recorded in the Passos Nappe, that comprises a sequence of metasedimentary rocks with minor intercalations of tholeiitic metamafic rocks, metamorphosed under greenschist facies (biotite zone) at the bottom and high-pressure granulite facies at the top. This paper presents a detailed investigation of pressure and temperature conditions along the Passos Nappe by integrating conventional geothermobarometry in metamafic rock and single-trace elements geothermometry (Zr-in-rutile and Ti-in-quartz) in quartzite. Nine lithostratigraphic units are identified in the Passos Nappe, which are informally named A to I, from the bottom to top, adding up to a minimum thickness of 4.56 km. In mafic rocks, the increase of metamorphic conditions is indicated by: (1) chemical variation of amphiboles, from actinolite/edenitic hornblende in Unit C, to pargasitic hornblende in Units E and G, and Fe-pargasite in Units H and I; (2) plagioclase composition varying from An1-13 in Unit C, An15-27 in Unit D to andesine at upper units; and (3) occurrence of clinopyroxene from the top of Unit E upwards. Additional petrographic features in quartzite also corroborate these insights, such as: the increase of grain size of both quartz and rutile, from bottom to top; the morphology of rutile crystals; the mechanism of quartz recrystallization (subgrain rotation dominates in lower units while grain boundary migration dominates in upper units) and the occurrence of rutile needles in quartz in the upper units, which suggest a continuous gradient. Combined application of Zr-in-rutile and Ti-in-quartz geothermometers in quartzite provided the following average temperature and pressure values for each unit: 673 °C and 11.7 kbar for Unit E, 690 °C and 9.5 kbar for Unit G, 747 °C and 11.6 kbar for Unit H and 758 °C and 11.3 kbar for Unit I. Our data indicate that the Zr-in-rutile and Ti-in-quartz systems do not re-equilibrate in metamorphic conditions lower than 600 °C. The extrapolation of these results to the low-grade units indicate: 496 °C and 4.8 kbar at Unit A, 504 °C and 4.8 kbar at Unit B, 502 °C and 4.4 kbar at Unit C. The results obtained with the geothermometer hornblende-plagioclase and the geobarometer garnet-rutile-ilmenite-plagioclase-quartz in metamafic rocks yielded the following average values for each unit: 486 °C and 5.0 kbar at Unit C, 568 °C and 6.0 kbar at Unit D, 622 °C and 8.1 kbar at Unit E, 650 °C and 8.4 kbar at Unit G, 743 °C and 9.4 kbar at Unit H and 723 °C and 11.2 kbar at Unit I. Since the two geothermobarometric approaches are based on independent chemical systems, the results obtained represent robust estimates for the temperature and pressure conditions for the inverted metamorphic gradient of the Passos Nappe. Comparing the inverted metamorphic gradient at the Passos Nappe with classical occurrences at the Himalaya Orogen, it is possible to assume that both origins were similar, which probably involved isotherm inversion due to subduction, channel flow process associated with shear heating and transport of higher pressure rocks over low-pressure rocks by reverse ductile shearing. • Characterization of the inverted metamorphism at the Passos Nappe (SW, Brazil), by combining multiple geothermobarometers. • Geodynamic processes that could produce inverted metamorphic sequences in orogenic systems. • Correlation between tectonostratigraphic dominant in the Southern Brasília Orogen. [ABSTRACT FROM AUTHOR]

Basalts are ubiquitous, mantle-derived mafic rocks found within all tectonic settings. Studying the chemical composition of basalts has proven to be an effective way to understand tectonics-related mantle processes for more recent periods of Earth history when other geological and tectonic records are still well preserved. However, using basalt geochemistry to decipher ancient tectonic environments and mantle processes on Earth remains a significant challenge; interpretations are often non-unique, and weathering, erosion, and orogenic processes can modify the chemical composition of basalts, and eliminate or obscure other complementary geotectonic records. This is most apparent in the oceanic realm, where subduction-related processes have erased much of the geological record for times older than ∼200 Ma, only leaving small and rare dismembered blocks of oceanic lithosphere as ophiolite mélanges along tectonic sutures. As a result, workers must rely heavily on analyzing the chemical composition of preserved basalts to identify the tectonic settings of their original melt extraction from the mantle using various tectonic discrimination diagrams from the literature (e.g., Pearce and Cann, 1973). In this paper, we demonstrate that such widely used classic discrimination diagram approaches often suffer from the intrinsic shortfall of large ambiguity. Instead, we apply here a big-data approach to characterize basalts generated in some typical tectonic settings. We start with a bespoke data correction and machine learning workflow. Our results show that mid-ocean ridge basalts, ocean island basalts, continental flood basalts, arc basalts (from both the oceanic and continental realm), and oceanic flood basalts are statistically chemically different, thus presenting a novel and unique chemical 'fingerprinting' approach to more accurately discriminate basalts. The method successfully predicts the tectonic settings of basalt emplacement at a prediction accuracy of >96%. [ABSTRACT FROM AUTHOR]

Strong post-collisional deformation and contemporaneous magmatic flare-ups during the Cenozoic indicate large-scale continental lithospheric modification in the southeastern (SE) Tibetan Plateau. However, the relationship between regional deformation and magmatism is poorly understood. In this paper, we report for the first time the presence of 32–17 Ma mafic rocks within the Ailaoshan-Red River shear zone (ARSZ) and provide new insights into the correlation between deformation and magmatism. Using 369 Cenozoic mafic and felsic rocks (this study and literature data) in and around the ARSZ, we document a continuous magmatic record that delineates a consecutive depletion of their mantle sources through time, which is correlated with the development of regional deformation. The spatial distributions, rock associations, and geochemical features of these rocks indicate a three-stage magmatic evolution in the SE Tibetan Plateau. During the earliest episode (40–32 Ma), the strong emplacement of both mafic and felsic rocks shows a planar-shaped geographic distribution. The second episode (32–17 Ma) is characteristic of voluminous mylonitized granites and minor basaltic rocks generally along the ARSZ. The latest episode (<17 Ma) magmatic rocks are sporadically exposed with dominant OIB-type basaltic rocks and minor A-type granites. From the earliest to the latest episodes, the mafic rocks exhibit progressive depletion in Sr Nd isotopic compositions, with initial Sr isotopic ratios and ε Nd (t) values from 0.70509 to 0.71151 and − 12.5 ~ −0.3 to 0.70313–0.70734 and − 3.9 ~ +8.1, respectively. These data, together with the covariations in the (Nb/La) PM and Zr/Nb ratios, signify a dramatic mantle-source shift from enriched to depleted through time for these Cenozoic mafic rocks. Mafic rocks from the earliest episode were generated from an enriched lithospheric mantle through convective thinning. In contrast, the OIB-type basalts from the latest episode were pure asthenospheric magma from decompression melting. Therefore, we propose an interdependent evolution between the shift of mantle sources and the development of synchronous deformation in and around the ARSZ. Our discovery of 32–17 Ma mafic rocks stands as the first direct evidence for the key role of the synchronous development of the lithospheric-scale ARSZ in the shift of mantle sources, asthenospheric melt transportation, and heating-induced crustal magma generation. • First discovery of 32–17 Ma mafic rocks in the Ailaoshan-Red River shear zone. • The mantle sources of regional mafic rocks have changed dramatically since 40 Ma. • Post-collisional deformation and lithospheric shifts drove changes in magmatism. [ABSTRACT FROM AUTHOR]

• 50 years post-discovery the Isua supracrustal belt remains the best Eoarchean archive. • Rare relicts of volcanic and sedimentary structures are unique for the Eoarchean. • The belt provides the most robust and diverse evidence for early life (3800–3700 Ma) • The belt and adjacent orthogneisses are tectonically-complex with multiple events. • The Isua area's geology is inconsistent with stagnant-lid/heat-pipe models. In the early 1970s, Vic McGregor and Stephen Moorbath demonstrated that the Isua supracrustal belt (Greenland) and its surrounding orthogneisses formed in the Eoarchean (Moorbath et al., 1972 , 1973). Fifty years later, these rocks are a key resource globally for understanding the Eoarchean Earth. This is because there is an extensive area (∼200 km2) of abundant outcrops where superimposed Neoarchean strain is modest, and Neoarchean metamorphism was only at lowest amphibolite facies; these are low tectonothermal conditions compared with other Eoarchean crustal remnants globally. Therefore, this region can provide the clearest window onto early Earth geodynamics. Within the Isua supracrustal belt there are rare areas where Eoarchean strain is also low, and these areas provide unambiguous recognition of diverse lithologies including sedimentary carbonates with the oldest proposed but contested stromatolites, pillow lavas, volcano-sedimentary lithologies and ultramafic rocks derived from layered intrusions (accepted) and slivers of mantle-derived meta-serpentinite that underwent Eoarchean ultra-high-pressure metamorphism (contested). As explored in previous papers (e.g., Polat et al., 2002), the geochemical signatures of the mafic igneous rocks, which include a boninite-like suite, indicate their magmas were derived by fluid fluxing of peridotites. Radiogenic isotopic signatures define discrete pulses of Eoarchean juvenile crustal growth, until a tectonic event at ∼3660 Ma with high pressure metamorphism that was followed by a switch to crustal recycling with the production of granites sensu stricto. Our appraisal of the integrated evidence points to complex superimposed Eoarchean events (∼3820–3600 Ma) driven by lateral lithosphere movements in convergent boundary settings, rather than a single crustal overturn such as within a model heat-pipe scenario. [ABSTRACT FROM AUTHOR]

The rift-related magmatism that generated the Roraima Alkaline Province (RAP) took place along main faults and shear zones that stretch out for circa 200 km in the central Guyana Shield, northern Amazonian Craton. As such, RAP is the first alkaline province proposed to the Guyana Shield. It encompasses felsic and mafic rock types – the former constituting foid-syenites and phonolites, while the latter including lamprophyre, tephrite and tephriphonolite dikes. In this paper, we examine whether these rocks are cogenetic and construct a genetic model for RAP with coupled petrography, geochemistry, and U-Pb zircon geochronology. Our data show that the RAP rocks are nepheline-normative, metaluminous to peralkaline, and miaskitic to agpaitic. The geochemical signatures indicate that fractional crystallization was the primary mechanism that produced the compositional variability between mafic and felsic magmas. Increasing peralkalinity is attributed to extensive alkali feldspar fractionation. Elemental, isotopic, geochronological and petrographic features show that crustal assimilation also played a role in magma genesis. Both ages obtained in this study and compiled from previous works range from 100 to 116 Ma, indicating that the Cretaceous alkaline magmatism in the Guyana Shield was short-lived. The Sr-Nd isotopic signatures of the least-contaminated samples require mixing of depleted and enriched mantles. Depleted-mantle model ages obtained from the least-contaminated samples fall in relatively short intervals, between 548 and 657 Ma, which coincide with the model ages of the Central Atlantic Magmatic Province (CAMP) tholeiites, suggesting that the same metasomatic event affected both Mesozoic alkaline and tholeiite magmatic occurrences of the Guyana Shield. It is concluded that the lithospheric mantle metasomatism took place shortly before magmatism, triggered by an extensional tectonic event involving the Tacutu rifting and the opening of the Atlantic. [Display omitted] • The Roraima Alkaline Province - RAP is the first Cretaceous alkaline province proposed for the Guyana Shield. • RAP ages range from 100 to 116 Ma and indicate a short-lived event. • Fractional crystallization was the primary mechanism of evolution of the RAP rocks. • Isotopic signatures of less-contaminated rocks indicate mixing of depleted and enriched mantle components. [ABSTRACT FROM AUTHOR]

The history of crustal thickening is critical for comprehending the evolution process of the Tibetan plateau. The genetic relationship and spatiotemporal distribution of adakitic rocks with high Sr/Y, (La/Yb) N ratios may impose fundamental constraints on specific geodynamic and crustal thickening processes. The Songka intrusive suite consists of adakitic rocks with high-Mg adakite (monzonites), low-Mg adakitic rocks (quartz monzonites), and gabbroic-diorites. Their geochemical characteristics, petrogenesis, and geodynamic implication is discussed in this paper. Songka high-Mg adakites formed when subducting Neo-Tethyan oceanic slab melts were assimilated by mantle peridotite at elevated temperatures (average Ti-in-zircon temperatures of sample SK1319 are 830 °C). Low-Mg adakitic rocks exhibit markedly different geochemical characteristics than those formed in the juvenile thickened lower crust. The least-squares mass balance and trace element simulations indicate that Songka low-Mg adakitic samples were formed at a degree of 60–65% fractional crystallization of melts resembling Songka high-Mg adakites. Songka gabbroic diorites are formed in the metasomatic mantle wedge. The genetic relationship between these rocks indicates that the crust of the southern Tibet did not appear to thicken obviously during the early stage of late Cretaceous (100–90 Ma). The intensive emplacement of late Cretaceous high-Mg adakites (Mg# > 50) and mafic rocks (SiO 2 < 52%) in the southern Lhasa terrane around 95–90 Ma, together with the slow convergence velocity of the Indian-Asian continent, can be explained by the response of rapid crustal thickening and Neo-Tethyan slab rollback at 95–90 Ma. • High-Mg adakitic rocks were formed from partial melting of Neo-Tethyan slab. • Coeval low-Mg adakitic rocks were produced by fractional crystallization. • Rapid crustal growth and Neo-Tethyan slab rollback occurred at 95–90 Ma. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Luanjiajie rock assemblage was formed at ca. 3.1 Ga. • They were formed by plume-induced underplating and crustal melting. • The NCC underwent episodic crust growth and recycling during the Eo- to Mesoarchean. The North China Craton (NCC) is one of the oldest cratons on Earth and preserves abundant Mesoarchean igneous rocks. However, the petrogenesis of the Mesoarchean magmatism and the associated geodynamic regime in the NCC remain controversial. In this paper, we conducted a systematic study to constrain the petrogenesis of the recently discovered Mesoarchean Luanjiajie rock assemblage (LRA) and infer the regional Mesoarchean tectonic setting. The LRA is composed mainly of tonalite–trondhjemite–granodiorite (TTG) gneiss with minor dioritic gneiss and amphibolite. The amphibolite shows intrusive contact with the surrounding TTG gneiss, whereas the dioritic gneiss displays transitional boundary with the TTG gneiss. Zircon U-Pb dating revealed that these three lithologies were roughly contemporaneous, with crystallization and metamorphic ages of ca. 3.1 and ca. 2.5 Ga, respectively. Geochemical characteristics (e.g., high Sr/Y and La N /Yb N ratios and weak positive Eu anomalies), zircon Hf isotopic features (T DM2 ages of 3822 to 3531 Ma with ε Hf (t) values of −2.44 to +0.97), and slightly elevated δ18O values (+5.48‰ to +7.24‰) indicate that the ca. 3.1 Ga TTG was derived from the partial melting of ancient hydrated low-K mafic rocks. The Luanjiajie TTG gneiss and other reported Mesoarchean TTGs in the NCC are classified mainly as medium- to low-pressure types. The linear trends between SiO 2 content and Fe 2 O 3 T, MgO, Y, Yb, Sm, and Gd contents of the ca. 3.1 Ga dioritic gneiss reflect that the dioritic gneiss might be a product related to amphibole fractionation of the coeval TTG magma. The ca. 3.1 Ga amphibolite displays OIB-affinity geochemistry and positive ε Hf (t) (up to +4.65) and ε Nd (t) (+0.2 to +7.7) values. The amphibolite was most likely formed through the partial melting of a depleted garnet-peridotite mantle and underwent minor crustal contamination during magma ascent. Hence, the LRA was most likely formed under a plume-related tectonic setting involving basaltic magma underplating and recycling of ancient crust. Combining our new results with existing zircon Hf data, we suggest that the NCC experienced initial continental nuclei formation during the Eo- to Paleoarchean, and followed by episodic crustal growth and recycling during the Meso- to Neoarchean. [ABSTRACT FROM AUTHOR]

Mafic igneous rocks are volumetrically limited in collisional orogens but are significant for revealing specific geological processes. The mafic intrusive rocks in the eastern Lhasa batholiths along the Parlung fault (the easternmost branch of the Jiali fault zone), southern Tibet, are commonly regarded as the easternmost mafic components of an inferred Shiquanhe–Nam Tso–Jiali–Parlung suture zone, which is assumed to mark a back-arc oceanic basin related to the southward subduction of the Bangong-Nujiang Meso-Tethyan Ocean. However, the petrogenesis and tectonic setting of the mafic intrusive rocks have been poorly constrained. In this paper, we present petrological, geochemical and geochronological data for this mafic suite and evaluate the tectonic implications. The mafic intrusive rocks can be approximately divided into pyroxene-amphibole cumulate and medium-grained and pegmatitic hornblende gabbros that are characterized by the occurrence of very calcic plagioclase (An = 80–92) and abundant amphibole crystals, indicating an H 2 O-enriched magmatic signature. Their whole-rock compositions, which include negative Nb and Ta anomalies, also suggest a subduction-modified setting. Zircon Lu Hf isotope data show that their magmas were formed by magmatic mixing between melts derived from enriched subcontinental lithospheric mantle and liquids derived from upwelling asthenosphere. Zircon U Pb dating results reveal crystallization ages of ~114–110 Ma for this mafic suite, corresponding to the late stage of regional granitic magmatism (~135–110 Ma) that was related to the Lhasa-Qiangtang collision after the closure of the Bangong-Nujiang Meso-Tethyan Ocean. Given that coeval mafic and felsic rocks are distinctly controlled by the Parlung fault, we suggest that asthenospheric upwelling due to the break-off of the subducted Bangong-Nujiang oceanic slab not only induced partial melting of the enriched subcontinental lithospheric mantle but also resulted in regional rifting/extension and the initial development of the eastern Jiali (Parlung) fault. • Early Cretaceous mafic magmatism along the eastern Jiali fault is demonstrated. • The mafic suite marks the initial development of the eastern Jiali fault. • The active Jiali fault zone might exploit and connect the pre-existing faults. [ABSTRACT FROM AUTHOR]

The role of the Meso-Tethyan oceanic plateau in the growth of the Tibetan Plateau is debated. In this paper, we report coexistence of large-scale mid-ocean ridge basalt (MORB)-like and enormous ocean island basalt (OIB)-type mafic rocks from the Dongco ophiolitic rocks of the Bangong–Nujiang Suture Zone. The MORB-like rocks host tholeiitic geochemical characterizes, and have supra-subduction zone affinity such as enrichments in large ion lithophile elements (LILEs), depletions in high field strength elements, high ε Nd (t) values (+6.5 to +9.5) and low initial 87Sr/86Sr ratios (0.7033–0.7050). The OIB-type rocks have an alkaline affinity and are characterized by enrichments in LILEs and light rare earth elements, strongly negative Sr anomalies, variable ε Nd (t) values of −3.7 to +7.3, and low initial 87Sr/86Sr ratios ranging from 0.7034 to 0.7050. Metamorphic zircons from amphibolites in the sole of the ophiolitic rocks yielded U Pb ages of 104–100 Ma. Detrital zircons from the upper Cretaceous sandstone of the Abushan Formation (K 2 ab) yielded young U Pb ages of 100–86 Ma. Considering the regional geology, we suggest that the Dongco MORB-like rocks were derived from a depleted mantle source and formed from an intra-oceanic subduction-related setting, representing remnants of normal oceanic crust, whereas the OIB-type rocks were derived from an enriched mantle source representing remnants of a Meso-Tethyan oceanic plateau. Our preferred hypothesis is that the Meso-Tethyan oceanic plateau experienced a phase of accretion at 104–100 Ma, which probably increased local subduction erosion of the upper plate and providing provenance for the deposition of the K 2 ab sandstone. The maximum depositional ages of K 2 ab sandstone constraint the minimum ages for closure of the Bangong–Nujiang Tethys Ocean most likely at 100–86 Ma. • Identified a new 104 Ma metamorphic event in the western Bangong–Nujiang Suture • Closure of the Bangong–Nujiang Tethys Ocean most likely occurred during 100–86 Ma • Dongco ophiolitic rocks contain remnants of normal oceanic crust and oceanic plateau [ABSTRACT FROM AUTHOR]

• The emplacement ages of Zhangbaling Uplift mafic igneous rocks are 808–787 Ma. • Their mantle source was formed by interaction between slab-derived fluids and mantle. • Their enriched isotopic composition inherit from Paleoproterozoic metasomatic mantle. • These mafic igneous rocks record two assembly events of Precambrian supercontinent. The Yangtze Block bears witness to a prolonged Precambrian evolutionary history and records the assembly of Precambrian supercontinents. Significantly, compared with the widely recognized ancient continental crustal growth and reconstruction, subduction-related mafic magmatism contains detailed possess of crust-mantle interaction in convergent plate boundaries. This paper reports Neoproterozoic mafic igneous rocks, represented by the 808–787 Ma amphibolites, from the Zhangbaling Uplift, northeastern sector of the Yangtze Block. Their prominent arc-affinity trace-element geochemical compositions with high concentration of LILE, the trough of Th, U, Zr and Hf in the spider diagram as well as natural δ18O values (5.3–6.5‰), indicate an interaction between the lithospheric mantle wedge peridotite and slab-derived fluids during early Neoproterozoic subduction event, and deficient in the involvement of felsic melts from crustal materials and sediments. Analyses of radioisotopes for amphibolites yield extremely low zircon ε Hf (t) (−25.3 to −3.6) and whole-rock ε Nd (t) (−17.1 to −10.4) values respectively, corresponding to an enriched mantle source. However, in consideration of the fact that the recycled slab-derived fluids is difficult to alter the isotopic composition (especially hafnium) of lithospheric mantle compared with its geochemical characteristics. Meanwhile, on the compilation of all Precambrian subduction-related magmatism in the Yangtze Block, it appears that the enriched isotopic signature in amphibolites is mainly inherited from the Paleoproterozoic (ca. 2.0 Ga) lithospheric mantle beneath the Yangtze Block, and extremely negative ε Hf (t) values (–25.3 to –18.4) further reflect prominent crust-mantle interaction correspond to the assembly of Columbia supercontinents. Therefore, the Zhangbaling mafic rocks witness the modification of lithospheric mantle by two episodic subduction events during Paleoproterozoic and Neoproterozoic respectively, which provide new evidence for the Yangtze Block to get involved in the reconstruction of Columbia and Rodinia supercontinents. [ABSTRACT FROM AUTHOR]

[Display omitted] • The igneous rocks in the Meratus Complex mainly formed at ∼115–140 Ma. • The Cretaceous Meratus mafic rocks originated from the slab-related wedge mantle. • The Cretaceous granitoids represent the product of wedge-originated juvenile crust. • Meratus Complex has a NW-Australian affinity and formed in an fore-arc setting. • The Meratus Neotethyan Ocean subducted beneath the Argo fragment until ∼100 Ma. SE Borneo lies at the junction of the Pacific and Tethyan realms. The Mesozoic geological record of the region is dominated by convergent plate margin activity, although the geological details and its broader role in the SE Asia evolution are poorly documented. This paper presents geochronological, whole-rock elemental and Sr-Nd-Pb isotopic data on the igneous rocks from the Meratus Complex in SE Borneo. The Meratus ophiolite might form at the Late Jurassic-Early Cretaceous (∼150–115 Ma), and the spatially-associated Haruyan Volcanics, Belawayan granitoids and their equivalents generated in the Early Cretaceous (∼140–107 Ma). The Haruyan and Pitap formations and their equivalents are dominated by Early Cretaceous (∼140–115 Ma) volcanic rocks and late Early Cretaceous (∼115–100 Ma) siliciclastic rocks, respectively. The mafic-intermediate igneous rocks in the Meratus Complex are characterized by MgO = 2.04–13.20 wt%, TiO 2 = 0.48–1.51 wt%, Nb/La = 0.09–0.42, ε Nd (t) = +4.6–+7.7, (206Pb/204Pb) i = 18.15–18.61, (207Pb/204Pb) i = 15.41–15.63 and (208Pb/204Pb) i = 38.03–38.63, and originated from the slab-related mantle wedge. The granitoids share similar elemental ratios and Sr-Nd-Pb isotopic compositions with the coeval mafic rocks, with Nb/La = 0.20–0.30, ε Nd (t) = +4.8–+6.0, Δ8/4 = 26.2–38.8 and Δ 7/4 = 5.0–7.7, representing the products of the wedge-originated juvenile crust. Synthesis of all data reveals a NW-Australian affinity for SE Borneo. The Early Cretaceous fore-arc tectonic setting extends southerly into the Bantimala (SW Sulawesi) and Luk Ulo (Central Java), constituting a united Early Cretaceous Central Indonesian accretionary zone. The Meratus Ocean subducted beneath the Argo fragment since ∼140 Ma and likely assembled with the Sundaland margin at ∼100 Ma in response to the Neotethyan consumption. [ABSTRACT FROM AUTHOR]

Tectonics, climate, and lithology are the three main factors controlling the generation and transfer of sediments as well as their textural and compositional signatures. In this paper, we investigate the generation of sands from volcanic rocks in nine drainages with mixed lithological assemblage in a high-relief – subtropical climate setting (Sierra Nevada de Santa Marta, NE Colombia). The integration of geomorphological analysis with sand petrography, and bulk-rock and clay geochemistry allows us to constrain the dynamics regulating the generation of sediments derived from felsic and mafic-intermediate volcanic basement rocks in relation to plutonic and metamorphic lithologies. The petrographic composition of modern fluvial sands from the area is extremely variable (litho-feldspatho-quartzose, feldspatho-quartzose, and quartzose-feldspatho-lithic), but it reveals a strong dilution of (especially mafic) volcanic compositional signals, and a consequent overrepresentation of plutonic and metamorphic lithologies. Traditional chemical weathering indices fail to represent the extent of chemical alteration, but instead seem to favour preservation of provenance signals. Chemical weathering primarily affects feldspars and the ferromagnesian groundmass of mafic volcanic rock fragments. Enrichment of ferromagnesian elements in the clay fraction supports the notion that mafic volcanic rock fragments are unstable relative to plutonic and metamorphic rocks. Drainage features (particularly river network and relief) control the abundance of volcanic lithic fragments and the rates and extent of chemical weathering. A linear log-ratio model permits us to quantify sediment generation from volcanic rocks in this mixed-lithology setting. The results indicate that even in the case where volcanic grains are practically absent in the sand fraction, there could still be up to 20% of volcanic rocks in the drainage basin, and in the case that 50% of the sand grains are volcanic, around 75% of drained lithologies are expected to be volcanic. Our results demonstrate that the contribution of volcanic detritus to modern sands systematically underrepresents the areal proportion of volcanics rocks in mixed source areas. Post-depositional diagenetic modifications are likely to alter and/or dissolve volcanic lithic fragments, making accurate reconstruction of sediment provenance even more difficult. Sediment-generation models based on a range of mixed lithologies in various tectonic and climatic settings will be needed to improve estimates of the abundance of volcanic rocks in drainage basins of ancient sediment routing systems. [ABSTRACT FROM AUTHOR]

Exposed within the reworked basement of the Araçuaí orogen, eastern Brazil, the Pedro Pereira metavolcanosedimentary sequence (PPMS) comprises a lower unit dominated by metaultramafic/mafic rocks, an intermediate unit dominated by metarhyolites and a predominant upper unit of acid metavolcanites associated with chemical and clastic metasedimentary rocks. This sequence has been defined and investigated in the '80s when it was considered as a Mesoarchean greenstone belt. Since then, few studies have addressed these rocks, and due to the lack of reliable geochronological data, a Paleoproterozoic age has also been suggested for the sequence. To reevaluate the age and evolution of the unit, new whole-rock geochemical and zircon U–Pb (LA-ICPMS) geochronologic data were obtained for the iron formation and acid metavolcanic rocks, respectively. When normalized to post-Archean Australian Shale standard, BIF samples can be divided into three groups. Group 1 BIF samples are marked by significant enrichment of the LREE, very high ∑REE + Y, positive La anomaly, extreme negative Ce anomaly, negative Eu anomaly, and subchondritic Y/Ho ratio. In contrast, Group 2 BIFs are marked by the enrichment of HREE, low ∑REE + Y, positive La anomaly, negative Eu anomaly, slight negative Ce anomaly, and predominantly super- and subchondritic Y/Ho ratios. The massive iron formation (MIF) group shows very high middle-to-heavy REE + Y enrichment, strong negative Ce anomaly, negative Eu anomaly, very high ∑REE + Y, and variable Y/Ho ratios. The modification of the iron formation by post-depositional hydrothermal alteration might have disturbed the original basin water signature. However, Group 2 is more compatible with pure chemical precipitates and its slight negative anomalies suggest an oxic environment. A PPMS metarhyolite from the upper portion of the sequence interlayered with the BIFs yielded the Concordia Age of 2771 ± 8.4 Ma. This age rules out a Paleoproterozoic origin for the PPMS, as suggested/considered by recent papers. The results imply that PPMS possibly represents one of the oldest records of oxygenation previous to the GOE in the geologic archives and could provide information to understand the early evolution of localized pockets of oxygen before the Great Oxidation Event. • First robust U-Pb zircon age (2.77 Ga) for Pedro Pereira metavolcanosedimentary sequence (PPMS). • PPMS unaltered BIFs possibly represent one of the oldest records of oxygenation previous to the GOE. • PPMS BIFs are partially altered by hydrothermalism. [ABSTRACT FROM AUTHOR]

[Display omitted] • The South Siberian post-collisional magmatic belt contains 1.88–1.86 Ga igneous rocks. • The belt records the final event of the Siberian craton assembly. • The belt consists mainly of granitoids and coeval felsic volcanics. • Mafic rocks and carbonatites are less abundant in the belt. • The igneous rocks have dissimilar chemical and isotopic signatures. The paper presents an overview of geological, geochronological, geochemical, and isotopic data on 1.88–1.84 Ga igneous rocks from the South Siberian post-collisional magmatic belt that records the final event of craton assembly. The belt consists mainly of granitoids and coeval felsic volcanics, less abundant mafic rocks, and sporadic carbonatites. In spite of the chronological and geodynamic proximity, the igneous rocks from different parts of the belt have dissimilar chemical and isotopic signatures, which are well consistent with the events that preceded the final assembly of the craton. Samples from the southwestern part of the belt show the greatest diversity, with an affinity of granitoids and felsic volcanics to different granite types (I-, S-, and A), and large ε Nd (T) ranges from positive to strongly negative for both felsic and mafic rocks. The compositional diversity of post-collisional igneous rocks here may be due to their origin shortly after the collisional events (1.90–1.87 Ga) during the orogen collapse. The diversity can have different explanations for felsic and mafic rocks: melting of heterogeneous sources assembled in the thickened orogen, as well as lithospheric delamination and asthenospheric upwelling, respectively. In the latter case, a source for mafic melts can be both asthenospheric material and subcontinental lithospheric mantle. The rocks of the southeastern belt segment are less diverse. Almost all granitoids and felsic volcanics have ferroan compositions, A -type granite affinity, and variable negative ε Nd (T) values similar to those in mafic rocks and in the Aldan shield carbonatites. The granitoids and volcanics here have compositions that commonly form in within-plate extension settings, which correlate with the 2.00–1.90 Ga age of collisional events in the area prior to the belt formation. The cessation of collisional movements in the southwestern craton part led to extension throughout its southern (and southeastern) areas. The ensuing melting of continental crust and subcontinental lithospheric mantle produced, respectively, felsic and mafic melts. The igneous rocks of the easternmost part of the South Siberian belt include also alkaline carbonatites and host diverse mineral deposits indicates that this part of the craton may have been exposed to the effect of a hot spot. [ABSTRACT FROM AUTHOR]

The Kuching zone, the most important tectonic boundary in Borneo, separates the Sibu zone in Central Sarawak from the Schwaner Mountains granitoids in SW Borneo. It potentially provides a key window for probing the paleo-Pacific subduction process. This paper presents new geochronological, elemental and Sr Nd isotopic data for the Pakong-Serabang and Serian mafic rocks, along with detrital zircon U Pb age-data for the associated greywacke in the Sarawak Kuching zone. These mafic rocks are dated at ~77–98 Ma and show distinctive geochemical signatures. The Pakong- Serabang mafic rocks are subalkaline basalt with SiO 2 = 46.22–51.75 wt%, TiO 2 = 0.49–2.42 wt% and MgO = 6.30–10.54 wt%. They exhibit MORB-like PM-normalized patterns with depletion in LILEs and HFSEs. Their 87Sr/86Sr(t) and ε Nd (t) range from 0.70285 to 0.70728 and + 7.4 to +9.4, respectively, originating from a slab-derived fluid-modified MORB-like source. The late Cretaceous Serian Volcanics are marked by SiO 2 of 51.52–57.90 wt%, MgO of 3.50–5.06 wt% with mg-number = 36–46 and show arc-like geochemical signatures with (Nb/La) n = 0.37–0.47. They have 87Sr/86Sr(t) = 0.71188–0.71417 and ε Nd (t) = −11.1 ~ −7.3, and were derived from a mantle wedge with the input of recycled sedimentary components. The detrital zircon grains from the associated sandstones give similar age-spectra to those in East Peninsular Malaysia and SE Vietnam. Our data revealed a Cretaceous Kuching trench-arc system. In combination with other geological observations, it is concluded that NW Borneo to the southwest of the Sarawak Kuching zone was a part of the Indochina/East Peninsular Malaysia fragment in SE Asia prior to the Jurassic and re-activated as an active continental margin in the Cretaceous. Widespread accretionary orogenesis along the Kuching zone likely initiated at or before the early Cretaceous and ended no earlier than the latest Cretaceous in response to the westward subduction of the paleo-Pacific slab. • The mafic rocks in the Kuching zone of Sarawak Malaysia were dated at 77–98 Ma. • The Pakong-Serabang basalts originated from the slab fluid-modified MORB-like source. • The Serian Volcanics were derived from the recycled sediment-modified wedge source. • The Kuching Cretaceous accretionary orogenesis results from paleo-Pacific subduction. [ABSTRACT FROM AUTHOR]

Potassic alkaline rocks are instrumental in unveiling the composition and geodynamic evolution of mantle lithosphere. The Zhuopan alkaline complex, located in the western Simao block, SW China, exhibits features of high potassium, enrichment in LILEs, and depletion in HFSEs. These same elemental features and Sr Nd isotopic compositions are also evident in the coeval clinopyroxenitic and syenitic rocks, indicating a comagmatic origin. In this paper, we present new data and discuss the petrogenesis of these rocks. We show that magmas parental to the Zhuopan alkaline complex are derived from highly enriched clinopyroxene-rich lithospheric mantle. These alkaline magmas emplaced in shallow crustal level and experienced crustal assimilation during ascent and through magma chamber processes. Pyroxenite is of cumulitic origin dominated by clinopyroxene and apatite. It formed at an early stage and received more effective crustal contamination. Pyroxene syenite, syenite and nepheline syenite are compositional mixture of variably evolved melt with incompletely segregated liquidus phases (e.g., clinopyroxene, biotite, alkali-feldspar, apatite, nepheline). An important observation is that the Dy/Yb ratio, LILE and LREE abundances of the Zhuopan complex are significantly higher than those of the contemporaneous mafic volcanic rocks in the western Yangtze block, reflecting different sources and source histories. The lithospheric mantle beneath Simao and western Yangtze blocks must have been heterogeneously metasomatized by oceanic subduction-related fluids and melts. Particularly, the mantle source for the Zhuopan alkaline rocks exhibits feature of carbonatite metasomatism. This is further supported by our modeling where melts derived from marine carbonate play a crucial role. • Parental magmas of the Zhuopan complex are derived from extremely enriched mantle. • Different lithologies are mixtures of evolved melt and accumulation of liquidus phases. • A heterogeneous SCLM is recognized beneath the Simao and western Yangtze blocks. • The mantle source of the Zhuopan complex exhibit feature of carbonatite metasomatism. [ABSTRACT FROM AUTHOR]