Felsic Research Articles

The bimodal Fii-A2-type and calc-alkaline volcanic sequence of the Aljustrel brownfield region, Iberian Pyrite Belt, SW Iberian Massif

The Iberian Pyrite Belt (IPB) is a late Devonian – Early Carboniferous world-class polymetallic VMS province that includes significant Cu-(Sn)-Pb-Zn-(Ag) deposits of massive sulphides and feeder zones. The Aljustrel brownfield region contains one of the highest concentrations of ore in the IPB in 6 known deposits (Gavião, São João, Moinho, Algares, Estação and Feitais). To delve into the petrogenesis of the Aljustrel early Carboniferous (∼355 Ma) felsic-dominated bimodal volcanism, new whole-rock trace elements and SmNd isotopes, and UPb in zircon were obtained.Based on Ga/Al and Y/Nb ratios, it is shown that Aljustrel felsic magmatism has the geochemical features of A2-type melts, typical of post-collisional and back-arc settings. UPb in zircon for a juvenile felsic volcanic rock point to antecrysts ages spanning from 387.9 to 366.6 Ma and a maximum emplacement age of 354.3 ± 2.6 Ma. These long-lasting melting events, present in both juvenile (ƐNdi = +1.79) and evolved felsic rocks (ƐNdi = −5.07), imply heterogeneous sources dominated by zircon-bearing igneous rocks. The SmNd model ages are in accordance with previous LuHf model ages in zircon, reinforcing that the isotopic variability is related to the same petrogenetic process.Subordinated Aljustrel mafic rocks, coeval with the abundant felsic volcanism, show orogenic signatures, namely Nb-Ta-Ti negative anomalies and calc-alkaline affinities, whereas SmNd isotopic data (ƐNdi = +1.54 to +5.48) points to variable to no contamination with crustal material. These geochemical results suggest derivation from an enriched mantle source modified by subduction metasomatism. In addition, the mafic rocks did not provide zircons for geochronological analysis, with the exception of one sample, in which a Concordia age of 402.1 ± 15.5 Ma was obtained from a single grain.The combined geochemical signatures of mafic and felsic volcanic rocks suggest asthenospheric rise, but this solely does not explain the abundance of zircon antecrysts in the felsic rocks. Therefore, a geodynamic model that includes a continuous evolution from Devonian to Carboniferous times is inferred. This more complex and broader geodynamic model for the Iberian Pyrite Belt in which successive metal remobilization occurred after successive melting events, fits the present geochemical data and is more likely to explain why the Iberian Pyrite Belt is a unique metallogenetic province.

The search for plausible economic mineral deposits in the central parts of Tanzania; insight from stream sediment geochemistry, multivariate statistics and geostatistics

Exploration success relies heavily on the data obtained, but, significantly on the type of analytical methods deployed and the interpretation reached. A poorly analyzed data may obscure the true reflectivity of the data, and thus, compromised the decision made. A combined data processing approach of descriptive statistics, enrichment-depletion data normalization, geospatial elemental distribution, and stacked overlayed comparison of elements have been used in this study. The prime purpose was to demonstrate potential elemental anomalies, and predict areas of higher degree of confidence for subsequent exploration and mineral resource evaluation. One-hundred and sixty-six stream sediment samples from the Dodoma Region of the Tanzania Craton have been examined; to reveal potential elements or mineral commodity that warrant further exploration. Forty-three elements of target were examined, as this craton is globally known for its rich earth mineral commodity. Our result indicates an enrichment of transition metals (TMs) (Cu, Ni, Co, Cr, Mn and Zn), High Field Strength Elements (Y, Th, U, Zr, Nb, Hf, Ta and Pb), Large Ion Lithophile Elements (Ba and Rb) and Rare-Earth Elements (La and Ce), Platinum Group Element (Pd and Pt) and other metals (Au, As, Bi, W, Mo and Li).Obtained results point to a likely poly-metallic sources and processes; as the underlain geology is marked largely by pegmatite and migmatites, and moderate proportion of fine clastic sedimentary rocks, and minor volcanic rocks mostly to the northern domain. Theoretically, the Large Ion Lithophile Elements (LILEs), Rare-Earth Elements (REEs) and Platinum Group Elements (PGEs) are associated with felsic rocks or variable stages of plutonic granitization. Although, the TMs are often associated with mafic-ultramafic rocks, the linkage of such metals with organic-rich shales been reported elsewhere. These rocks may equally contribute to the occurrence of other metals as stated in this paper. Its intriguing to note a strong positive correlation of Li with TMs, possibility of Li control by mafic minerals in pegmatite bodies. This work proposes a polymetallic enrichment controlled by the area geology. To suggest an alluvial mining potential of the above elements in the area, resource evaluation is a requirement. The geospatial maps reveal areas worth focusing for subsequent exploration. The adopted geostatistical methods and other approach utilized in this research are effective, indicative of handling bulk exploration data for decision and subsequent exploration.

Maastrichtian – Paleocene environmental and climatic conditions in Koum Basin (northern benue trough, Cameroon) inferred using a multiproxy approach including sedimentology, mineralogy, and geochemistry

The Koum Basin is one of major intracontinental basins in northern Cameroon. It is part of the Upper Benue Trough and has genetic ties to the West and Central African Rift System. The main purpose of studying the Koum Basin sedimentary deposits was to re-examine the time of the deposition and constrain the palaeoenvironmental and paleoclimatic conditions during deposition. To accomplish this, we used a combination of sedimentologic, palynologic, mineralogic, and geochemical data. Claystone units interbedded with calcareous siltstones dominate sedimentary sequence, including few clay beds, fine to medium-grained sandstone, and rare marl layers. The palynomorph assemblage suggests a previously unknown Maastrichtian – Paleocene age in this basin. The sediments originated from intermediate igneous parent rocks with a relative contribution of felsic rocks. These rocks underwent low detritism (Si/Al: 2.51–4.43; K/Al: 0.11–0.36; Ti/Al: 0.05–0.10) and chemical weathering (CIA: 55–64; PIA: 56–68) in the source region. Consequently, deposits are immature (ICV values > 1) and weakly recycled (Si2O3/Al2O3 ratios ≤5). The organic matter analysis and the palynoflora assemblage, reveal Type III kerogen with significant contributions of Type II-III and type II kerogens, as well as a continental paleo-depositional environment with open rainforest to savannah vegetation. The clay minerals distribution suggests moderate illitization and chloritization processes and thus moderate burial diagenesis at temperatures ranging from 70 to 90 °C, also attested by immature to mature Tmax values (≤436 °C) marginally. The low CIA values and very low kaolinite contents, indicate dry climatic conditions. In addition, two major-element-based discrimination diagrams show that the parent rocks of clastic sediments formed primarily in a continental arc system, with a moderate contribution from the rift system and a low contribution from the oceanic island arc, implying compressional conditions, which is consistent with previous studies on the tectonic background of the region during the late Maastrichtian to Paleocene period.

Early Permian Post-Collision Extensional Setting in the Southern Beishan Orogenic Belt: Evidence from the Zhangfangshan Granodiorite and the Baishantang Bimodal Volcanic Rocks

Outcrops of late Paleozoic magmatic rocks are common in the Southern Beishan Orogenic Belt (SBOB), Southern Central Asian Orogenic Belt (CAOB), which is a key object for the understanding of regional tectonism and defining the final closure time of the Paleo-Asian Ocean (PAO). We present zircon U-Pb chronology and whole-rock geochemistry data for late Paleozoic granodiorites and bimodal volcanic rocks from the Shuangyingshan-Huaniushan unit in the north Huitongshan-Zhangfangshan ophiolitic belt in the SBOB. The Zhangfangshan granodiorites (LA-ICP-MS, Ca. 288 Ma) are A2-type granite enriched in Rb, Th, Pb and LREEs and depleted in Nb, Ta, Ti, Sr, Ba and HREEs. They have varying MgO and TFe2O3 contents with high Mg# (38.56~48.97) values; the Lu/Yb ratios (0.14~0.15) of these granodiorites are similar to mantle-derived magma. A clear plagioclase zoning structure and acicular apatite occur in mineral assemblages derived from magma mixing between mafic and felsic magmas. The Baishantang bimodal volcanic rocks (272 Ma) consist of rhyolite and basaltic andesite. Baishantang rhyolites are A2-type felsic rock enriched in Rb, Th, Pb and LREEs and depleted in Nb, Ta, Ti, Sr, Ba and HREEs, with negative εNd(t) and εHf(t) (−5.2~−4.8 and −2.2~−1.9, respectively). Rhyolites originated from the partial melting of the crust, influenced by mantle material. Basaltic andesites belong to calc-alkaline series and have an enrichment of Rb, Ba, Th, U, Pb and LREEs, are weakly enriched in Zr-Hf, and are depleted in Nb, Ta, Ti and HREEs. The Nd-Hf isotopes of these basaltic andesites are not coupled with negative εNd(t) (−2.8~−0.4) and positive εHf(t) (1.8~5.5) values. These characteristics indicate that they originated from the partial melting of the mantle mixed with sediment-derived melts. In combination with previous studies, our findings show that the early Permian Zhangfangshan granodiorites and Baishantang bimodal volcanic rocks formed in a post-collision extensional setting, and the Huitongshan-Zhangfangshan ocean had been closed before early Permian.

Neoarchean to Paleoproterozoic crustal evolution of the central Aravalli-Banded Gneissic Complex (NW India): Evidence from zircon U-Pb-Hf isotope systematics and whole-rock composition of Neoarchean sanukitoids, Paleoproterozoic granitoids and metasedimentary rocks

The central Aravalli-Banded Gneissic Complex in NW India is an Archean nucleus that was extensively reworked during the late Paleo- to Neoproterozoic. New results of combined zircon U-Pb-Hf isotopes and whole-rock geochemical data reveal that the basement was affected by felsic magmatism during the Neoarchean and Paleoproterozoic, followed by a passive margin stage. The results provide evidence for coeval emplacement of sanukitoids and TTGs at ca. 2540 Ma, and for granitoid magmatism at ca. 1875 Ma. Similar REE patterns of the synchronous sanukitoids and TTGs, coupled with high SiO2 contents (59.2–70.9 wt%), subchondritic εHf2.55 Ga values (−5.0 to −2.6) and Hf-model ages (3246–3123 Ma) of the Masuda sanukitoids indicate that the sanukitoid magmas were formed mainly by interaction of TTG magmas (generated by the melting of subducted Paleo- to Mesoarchean oceanic crust) with the overlying enriched peridotite. The calc-alkalic and magnesian compositions, enrichment in LREE and LILE along with pronounced depletion in HFSE (Nb, P and Ti) in ca. 1875 Ma granitoid gneisses imply subduction-related magmatism during Paleoproterozoic. The predominance of subchondritic εHf1.87 Ga values, ranging from −4.4 to +1.7, suggests that the parental magmas mainly resulted from the reworking of heterogeneous Meso- to Neoarchean felsic crust. Age-Hf isotope data of detrital zircon grains provide evidence that clastic sedimentary rocks covering the central Aravalli basement were deposited in a passive margin setting at < 1730 Ma, and the detritus was mainly sourced from adjoining Neoarchean and Paleoproterozoic granitoids. Comparison of our new data with other Indian and worldwide cratons indicate that the Aravalli orogen represents a unique terrane, where the Neoarchean TTGs and sanukitoids with subchondritic Hf isotopic signatures were emplaced nearly coeval in a close spatial relationship. The Aravalli Archean basement was subsequently reconfigured by voluminous felsic magmatism during Paleoproterozoic at 1875–1810 Ma. Furthermore, the compiled zircon U-Pb age and Hf-Nd isotope data for the late Paleoproterozoic subduction-related magmatic rocks provide evidence for substantial crustal reworking during assembly of the Columbia supercontinent.

In situ probing of the present-day zircon-bearing magma chamber at Krafla, Northeastern Iceland

Active felsic magmatism has been rarely probed in situ by drilling but one recent exception is quenched rhyolite sampled during the 2009 Iceland Deep Drilling Project (IDDP). We report finding of rare zircons of up to ∼100 µm in size in rhyolite glasses from the IDDP-1 well products and the host 1724 AD Viti granophyres. The applied SHRIMP U-Th dating for both the IDDP and the Viti granophyre zircons gives zero-age (±2 kyr), and therefore suggests that the IDDP-1 zircons have crystallized from an active magma intrusion rather than due to the 20–80 ka post-caldera magmatic episodes recorded by nearby domes and ridges. Ti-in-zircon geothermometer for Viti granophyre reveals zircon crystallization temperatures ∼800°C–900°C, whereas IDDP-1 rhyolite zircon cores show Ti content higher than 100 ppm, corresponding to temperatures up to ∼1,100°C according to the Ti-in-zircon thermometer. According to our thermochemical model at such elevated temperatures as 1,100°C, rhyolitic magma cannot be saturated with zircon and zircon crystallization is not possible. We explain this controversy by either kinetic effects or non-ideal Ti incorporation into growing zircons at low pressures that start to grow from nucleus at temperatures ∼930°C. High temperatures recorded by IDDP-1 zircon together with an occurrence of baddeleyite require that the rhyolite magma formed by partial melting of the host granophyre due to basaltic magma intrusion. Zr concentration profiles in glass around zircons are flat, suggesting residence in rhyolitic melt for &amp;gt;4 years. In our thermochemical modeling, three scenarios are considered. The host felsite rocks are intruded by: 1) a basaltic sill, 2) rhyolite magma 3) rhyolite sill connected to a deeper magmatic system. Based on the solution of the heat conduction equation accounting for the release of latent heat and effective thermal conductivity, these data confirm that the rhyolite magma could be produced by felsic crust melting as a result of injection of a basaltic or rhyolite sill during the Krafla Fires eruption (1975 AD).

A Long-Lived Accretionary Process during the Amalgamation of the North China Craton: Insights from Neoarchean–Paleoproterozoic Polyphase Magmatism in the Lüliang Complex

Abstract There has been a long debate regarding the timing of the final amalgamation of the North China Craton, which is considered to have occurred either during the Neoarchean or Paleoproterozoic era. One major point of contention is whether there existed a long-lived subduction lasting through the Neoarchean to Paleoproterozoic. The Lüliang Complex contains multiphases of magmatism and thus represents the most viable region to address this controversy. In this study, we carried geochronological and geochemical analysis on the representative granitoids. Secondary ion mass spectrometry U–Pb dating revealed four distinct granitoid groups emplaced at 2531 ± 4, 2189–2173, 2027 ± 25, and 1852 ± 41 Ma, respectively. Notably, the 2531 Ma granitic gneiss was identified for the first time in this region. Based on the geochemical characteristics, the granitoids can be divided into two types. The 2531 and 2027 Ma groups display I-type features, while the 2189–2173 and 1852 Ma groups exhibit A-type geochemical affinities. Both I-type groups exhibit enrichment in Rb, depletion in Nb, Ta, and Ti, moderate fractionated REE patterns, substantial negative Eu anomalies, low Sr/Y ratios, and positive εHf(t) (+3.51 to +5.53 and +5.59 to +7.32, respectively), indicating that they were generated from partial melting of the juvenile mafic crust. In contrast, the 2189–2173 Ma granitoids belong to A2-type and were most likely generated by the partial melting of felsic rocks in the back-arc region, while the 1852 Ma granitoids belong to A1-type and were most possibly the result of partial melting of mafic-intermediate rocks during the post-collisional stage. Based on the records of A-type granitic magmatism and the ~1950 Ma peak metamorphism throughout the Trans-North China Orogen, we propose that a long-lived subduction process (2531–1950 Ma) can mostly explain the existing geological phenomena. It is likely that the subduction between the Eastern and Western Blocks should have commenced at ~2531 Ma, followed by a long-lived subduction. The two blocks ultimately collided with each other to form the North China Craton at ~1950 Ma, which triggered post-collisional exhumation and partial melting at ~1852 Ma.

Unravelling the genetic relationship between pegmatites and granites in the Jiajika Li-Be polymetallic district, Songpan-Ganze Orogenic Belt, Southwestern China: Insights from monazite U-Pb geochronology and trace element geochemistry

The Jiajika Li-Be Polymetallic District is located in the Songpan-Ganze Orogenic Belt, Southwestern China. The Li-Be mineralization is genetically, temporally, and spatially, related to pegmatites in the Jiajika District. Hundreds of pegmatite dikes were emplaced surrounding the adjacent Majingzi granite pluton. Drill core samples from the 3,200 m deep Jiajika Scientific Drilling project (JSD-1) were acquired to determine the vertical extent and the petrogenesis and metallogeny of the granites, and the pegmatites, respectively, and to obtain a better understanding of their genetic relationship. The vertical zonation of the pegmatites from shallow to deep is as follows: shallow albite pegmatites; albite-microcline pegmatites; microcline pegmatites; and deeper more albite pegmatite. Spodumene occurs mainly in the shallow albite pegmatites (55–105 m depth), and disseminated beryl, columbite-tantalite, and cassiterite, mainly occur in pegmatites at depths less than 700 m. Eight samples were selected for monazite U-Pb geochronology and trace element geochemistry analyses from pegmatites and granites at different depths. LA-ICPMS monazite U-Pb geochronology for the pegmatites indicates two episodes of magmatic activity; one at 211–205 Ma (2σ, 523–2,494 m depth) and another at 193–192 Ma (2σ, 3,170–3,211 m depth). The crystallization age of the older pegmatites is in good agreement with the monazite U-Pb geochronology of the adjacent Majingzi granite (208–205 Ma, 2σ, 1,265–2,568 m depth) within analytical uncertainty, indicating their close temporal relationship. The younger albite pegmatite (193–192 Ma) is associated with the columbite-tantalite Nb-Ta rare-metal mineralization. Compared to those in the deep pegmatites (excluding the younger albite pegmatite in 3,170–3,211 m depth), and the adjacent granites, monazites in the shallow pegmatites and the adjacent granites are relatively enriched in Li, Th, and U, indicating the continuous evolution of a felsic magmatic system; with the residual melt more enriched in various incompatible rare-metal elements. Hence, the monazite U-Pb geochronology and trace element geochemistry indicate that a highly evolved felsic magma plays an important role in the petrogenesis of the Jiajika Li-Be pegmatites.

Mafic and felsic magmatism in the Wadi Kalalat area, South Eastern Desert, Egypt: mineralogy, geochemistry and geodynamic evolution during the Neoproterozoic in the Nubian Shield

Mafic and felsic magmatism in the Wadi Kalalat area, South Eastern Desert, Egypt: mineralogy, geochemistry and geodynamic evolution during the Neoproterozoic in the Nubian Shield

Zircon U–Pb ages and O–Hf isotopes of Quaternary trachytes from the East Sea: Implications for the genesis of low-δ18O magmas

Quaternary intraplate magmatism formed several volcanic islands and seamounts, including Dokdo (DD), Ulleungdo (UD), Simheungtack (ST), Anyongbok, and Isabu in the southwest of the East Sea back-arc basin. In this study, we present whole-rock geochemical, zircon U–Pb age, and in situ O–Hf isotope data for the submerged volcanic rocks from DD, UD, and ST to provide new insights into the eruption timing of these volcanoes and constrain the magma evolution processes. All samples used in this study were trachytes and exhibited ferroan, alkalic, and metaluminous to weakly peraluminous characteristics. They showed light rare earth element (REE)-enriched patterns with (La/Yb)N ratios of 25.3–31.7 and mostly negative Eu anomalies in a chondrite-normalized REE plot. In addition, they were enriched in large-ion lithophile elements and high field strength elements; they exhibited positive Pb anomalies and strongly negative Ba, Sr, P, and Ti anomalies. The zircons yielded a weighted-mean 206Pb/238U age of 2.61, 0.348–0.704, and 2.76–2.94 Ma for the DD, UD, and ST trachytes, respectively. All zircons exhibited lower δ18O values than normal depleted mantle values, regardless of the crystallization age and spatial distribution of volcanoes. The δ18O values showed no correlation with U contents or Th/U ratios, indicating that the low δ18O signatures were of primary magmatic origin. The Hf isotopic compositions of the zircons were relatively heterogeneous but predominately characterized by positive εHf values. Binary O–Hf mixing modeling revealed that low-δ18O rocks with positive εHf values from the UD and ST volcanoes were derived from a hybrid source of recycled juvenile crustal materials with low-δ18O and positive εHf signatures and an enriched mantle source with normal δ18O and negative εHf values. The juvenile oceanic crust in the source was likely metasomatized by seawater at high temperatures prior to melting. In contrast, the felsic magma that formed the DD volcanoes may have assimilated with regional basement rocks (Triassic–Jurassic granitoids), resulting in increased δ18O values and decreased εHf values relative to those of the UD and ST volcanoes. Our study highlights the significant contribution of recycled oceanic crust materials to the generation of the Quaternary magmas.

Sulfur speciation in dacitic melts using X-ray absorption near-edge structure spectroscopy of the S K-edge (S-XANES): Consideration of radiation-induced changes and the implications for sulfur in natural arc systems

Abstract The synchrotron technique of micro X-ray absorption near-edge structure spectroscopy at the sulfur K-edge (S-XANES) provides a unique opportunity to measure the proportion of different oxidation states of sulfur (S) in silicate glasses. Although applied extensively in the analysis of basaltic silicate glasses, few S-XANES studies have investigated variations in S oxidation states with fO2 in felsic silicate glasses. In addition, no study has systematically compared the S-XANES results obtained from the same samples at different photon flux densities to quantify the relationship between exposure time and changes in S speciation in silicate glass, as has been done for Fe and V. This study evaluates observed differences in S speciation measured in experimentally produced H2O-saturated dacitic glasses over a range of reducing to oxidizing conditions (from log fO2 = ΔFMQ-0.7 to ΔFMQ+3.3; FMQ is the fayalite-magnetite-quartz mineral redox buffer) and equilibrated at 1000°C and 300 MPa. S-XANES spectra were collected at three different photon flux densities using three microspectroscopy beamlines. As is observed in S-XANES analyses of basaltic silicate glasses, beam-induced changes to the S6+/ΣS are observed as a function of photon flux density and beam exposure time. Our results demonstrate that silicate glasses of dacitic composition undergo beam-induced photo-reduction in samples equilibrated at ΔFMQ &amp;gt; +1.75 and photo-oxidation if equilibrated at ΔFMQ &amp;lt; +1. The time required to observe beam-induced changes in the spectra varies as a function of flux density, and our study establishes an upper photon density limit at ~1.0 × 1012 photons/μm2. The S6+/ΣS calculated from spectra collected below this absorbed photon limit at intermediate flux densities (~1−4 × 109 photons/sec per μm2) are affected by beam damage, as no conditions were found to be completely free of beam-induced changes. However, the S6+/ΣS ratios calculated below the limit at intermediate flux densities are consistent with thermodynamic constraints, demonstrating that S6+/ΣS ratios calculated from S-XANES spectra can be considered reliable for estimating the oxygen fugacity. Our results carry important implications for the S budget of felsic magmas and dissolution mechanisms in evolved melts. While our results from all three flux densities show the presence of S4+ dissolved in relatively oxidized (ΔFMQ &amp;gt; +1.75) dacitic glass, even in the spectra exposed to the lowest photon densities, we are unable to rule out the possibility that the S4+ signal is the result of instantaneous X-ray irradiation induced beam damage using S-XANES alone. When our spectra are compared to S-XANES spectra from basaltic silicate glasses, important differences exist in the solubility of S2- and S6+ between dacitic silicate melts, pointing to differences in solubility mechanisms as melt composition changes. This study highlights the need for further investigation into beam damage systematics, presence of S4+, and the solubility mechanisms of different oxidation states of S as silicate melt composition changes.

THE FIRST FIND OF CAMBRIAN VOLCANITES AND PLAGIOGRANITES IN TEKTURMAS OPHIOLITE ZONE (CENTRAL KAZAKHSTAN): AGE AND COMPOSITION

The complex of felsic rocks, intruded by plagiogranitic bodies are first revealed in the west of the Tekturmas ophiolite zone of Central Kazakhstan. The U–Pb (SIMS) geochronological study of one of the plagiogranitic bodies was carried out and the Early Cambrian age (537 ± 5 Ma) was first obtained. The peculiarities of effusives and plagiogranites composition indicate their formation in the supra-subduction setting within primitive volcanic island arc. Formation of this arc was not related to the evolution of the oceanic structures, which complexes participate in the structure of the Tekturmas zone.

Bulk-rock and mineral-scale geochemical evidence of open-system magmatic processes in the felsic rocks of the northern part of the Ditrău Alkaline Massif (Eastern Carpathians, Romania)

Bulk-rock and mineral-scale geochemical evidence of open-system magmatic processes in the felsic rocks of the northern part of the Ditrău Alkaline Massif (Eastern Carpathians, Romania)

Triassic felsic magmatism in SE Peninsular Malaysia: Petrogenesis and geodynamic implications for the Eastern Paleotethyan tectonic transition

Middle–Late Triassic volcanism and contemporary granitoids in East Malaya provide significant insights into the magmatic evolution and geodynamic processes of the Paleotethyan Ocean in SE Asia. This paper presents new zircon ages and whole-rock geochemical data including Sr-Nd-Pb-Hf isotopic analyses for newly identified felsic volcanic rocks and granites in SE Peninsular Malaysia. Zircon geochronological data constrain their formation time at 238–235 Ma. All samples have relatively high SiO2 contents with enrichment in light rare earth elements but have negative anomalies at Nb, Ta, Ti, and Eu on spidergrams. Calculated zircon saturation temperatures are between 840 °C and 957 °C. Samples have (87Sr/86Sr)i ratios between 0.70501 and 0.71014 and εNd (t) values ranging from −6.6 to −5.9, with (206Pb/204Pb)i = 18.45–18.77, (207Pb/204Pb)i = 15.68–15.71, and (208Pb/204Pb)i = 38.88–38.97. The zircon in-situ εHf (t) values and TDM2 ages range from −5.6 to +4.5 and 1.62 Ga to 0.98 Ga, respectively. The primary melting source which produced these felsic volcanic rocks and granites was Proterozoic crustal rocks with a juvenile middle-lower crustal component. Triassic volcanism in SE Peninsular Malaysia northerly correlates with synchronous volcanic rocks in the Lancangjiang and Chiang Khong-Lampang-Tak volcanic zones. Our data, along with regional observations, indicate that these volcanic rocks and granites formed in a localized extensional setting in response to the Paleotethyan slab breakoff. While the initial collision of Sibumasu with East Malaya may have occurred at ∼237 Ma.

Tectonic setting and provenance analysis of the Yaojia Formation in the northeastern Songliao Basin, NE China: constraints from sandstone geochemistry, Hf isotopes, and zircon U–Pb chronology

The Songliao Basin is rich in uranium ores, and the Yaojia Formation, which is dominated by gray fine-grained sandstones, contains the main ore-bearing stratum. Rocks in the formation contain high SiO2, Al2O3, and total alkali, with enrichment in Rb, Th, U, K, and light rare earth elements but are depleted in high field strength elements, similar to upper crustal rocks. U–Pb dating of zircon grains from sandstones in the formation yielded four groups of ages, including 99–182, 202–245, 284–365, and 1800–1900 Ma. These ages combined with the Hf isotope composition, geochemical characteristics, and regional history suggest that the Yaojia Formation rocks are associated with passive and active continental margin settings. These clastic rocks originate principally from felsic rocks in the Zhangguangcailing–Xiao Xing'anling area, and these were deposited in oxic freshwater environments.

Ore Genesis and the Magmatism of the Yuhaixi Mo(Cu) Deposit in Eastern Tianshan, NW China: Constraints from Geology, Geochemistry, Zircon U-Pb and Molybdenite Re-Os Dating

The Yuhaixi Mo(Cu) deposit is a new discovery in the eastern section of the Dananhu-Tousuquan island arc, Eastern Tianshan. However, the genesis of the Yuhaixi Mo(Cu) deposit is still not fully understood. The Yuhaixi intrusion is composed of monzonitic granites, diorites, granites, and gabbro dikes, among which disseminated or veinlet Mo and Cu mineralization is mainly hosted by the monzonitic granites. The LA-ICP-MS zircon U-Pb dating yields emplacement ages of 359.4 ± 1.6 Ma for the monzonitic granite, 298.8 ± 1.8 Ma for the diorite, and 307.0 ± 2.3 Ma for the granite. The Re-Os dating of molybdenite hosted by monzonitic granite yields a well-constrained 187Re-187Os isochron age of 354.1 ± 6.8 Ma (MSWD = 1.7) with a weighted average age of 344.5 ± 3.1 Ma. The Mo mineralization is closely associated with the Yuhaixi monzonitic granite. The Yuhaixi monzonitic granite rocks are characterized by high silica (SiO2 &gt; 70 wt.%), low MgO (0.23–0.36), Ni, Cr contents, and they are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs: e.g., K, Ba, Pb and Sr), and depleted in heavy rare earth elements (HREEs) and high field-strength elements (HFSEs: e.g., Nb, Ta and Ti). They are weak peraluminous and have high εHf(t) (11.37–17.59) and εNd(t) (1.36–7.75) values, and varied initial 87Sr/86Sr (0.7037–0.7128) values. The Yuhaixi post-ore granites exhibit similar geochemical and isotopic signatures to the Yuhaixi monzonitic granite. These characteristics suggest that the Yuhaixi felsic rocks are likely sourced from the partial melting of the juvenile lower crust. The Yuhaixi diorite has low SiO2, and K2O contents, relatively high Na2O, MgO (Mg# = 45–53) contents, and depletions in HFSE (e.g., Nb, Ta, and Ti). These geochemical features, coupled with isotopic data such as low initial 87Sr/86Sr (≤0.7043), high εNd(t) (2.5 to 3.0) and εHf(t) (≥11.6) values, and young Hf model ages, suggest that their parental magmas possibly originated from the partial melting of the depleted lithospheric mantle that was metasomatized by hydrous melts or fluids from the subducting oceanic plate. Integrating our new results with previous works on the Dananhu-Tousuquan island arc belt, we suggest that the Yuhaixi Mo(Cu)deposit is likely sourced from the juvenile lower crust, which was formed in an arc setting, where the bipolar subduction of the North Tianshan oceanic slab forms the Dananhu Tousuquan belt to the north and the Aqishan-Yamansu belt to the south. The eastern section of the Dananhu-Tousuquan island arc is a promising target for late Paleozoic porphyry Mo(Cu) deposits.

Mineralization of the In Ateï gold district (Central Hoggar, South Algeria)

The In Ateï gold district is located in the eastern part of the Laouni “LATEA” terrane (acronym of Laouni, Azrou-n-Fad, Tefedeset, Egéré-Aleksod) (central Hoggar, southern Algeria). In fact, during the post-collision period of the Pan-African orogeny (600 and 570 Ma), this microcontinent was partly destabilized until it corresponded to a meta-craton. The In Abeggui gold deposit is part of the In Ateï district and is located 210 km southeast of the town of Tamanrasset. It is located in a large gabbro-diorite massif of the Neoproterozoic volcano-sedimentary series. The In Abeggui deposit shows two morphological types of gold veins and a mineral paragenesis different from the rest of the Hoggar. In the In Abeggui deposit, a biotite granite pluton comprising contemporary gabbro-diorite bodies is intrusive in the Neoproterozoic volcano-sedimentary series. The mineralized veins are mainly hosted in one of these mafic bodies. Numerous dykes of mafic and felsic rocks cut both the biotite granite and the gabbro-diorite massif. Felsic dikes include granites, microgranites, pink aplo-pegmatites and aplites. The main objective of this work is to study the types of gold mineralization expressed in the Laouni terrane (central Hoggar) based more particularly on those of the In Atei region. Two generations of gold-bearing quartz from the In Abeggui deposit can be distinguished: Veins 1: Tourmaline quartz veins predominantly N30° embedded in the gabbro massif, and Veins 2: Stockwork and quartz veinlets, hosted in aplite dykes covering the vein system1

Identifying crustal contributions in the Patagonian Chon Aike Silicic Large Igneous Province

The volcanic rocks of the Chon Aike Silicic Large Igneous Province (CASP) are recognized as magmas dominantly produced by crustal anatexis. Investigating the zircon of the CASP provides an opportunity to gain further insight into geochemical and isotopic differences of the potential magmatic sources (i.e., crust versus mantle), to identify crustal reservoirs that contributed to the felsic magmas during anatexis, and to quantify the contributions of the respective sources. We present a combined zircon oxygen and hafnium isotope and trace element dataset for 16 volcanic units of the two youngest volcanic phases in Patagonia, dated here with LA-ICP-MS U–Pb geochronology at ca. 148–153 Ma (El Quemado Complex, EQC) and ca. 159 Ma (western Chon Aike Formation, WCA). The EQC zircon have 18O-enriched values (δ18O from 7 to 9.5‰) with correspondingly negative initial εHf values (− 2.0 to − 8.0). The WCA zircon have δ18O values between 6 and 7‰ and εHf values ranging between − 4.0 and + 1.5. Binary δ18O-εHf mixing models require an average of 70 and 60% melt derived from partial melting of isotopically distinct metasedimentary basements for the EQC and WCA, respectively. Zircon trace element compositions are consistent with anatexis of sedimentary protoliths derived from LIL-depleted upper continental crustal sources. The overlap between a high heat flux environment (i.e., widespread extension and lithospheric thinning) during supercontinental breakup and a fertile metasedimentary crust was key in producing voluminous felsic volcanism via anatexis following the injection and emplacement of basaltic magmas into the lower crust.

LA-ICP-MS U-Pb cassiterite age data of the Sadisdorf deposit link Sn-Li-(W-Cu) mineralization in the eastern Erzgebirge to the collapse of the Altenberg-Teplice Caldera

The Sadisdorf Sn-Li-(W-Cu) prospect in the eastern Erzgebirge (Germany) comprises two distinct styles of magmatic-hydrothermal mineralization, namely greisen-type mineralization at the Kupfergrube site, and stockwork-type mineralization at both the Kupfergrube and the Zinnklüfte sites. Previously, these two sites were regarded as expressions of two temporally distinct mineralization events. In this study, this temporal relation was tested by LA-ICP-MS U-Pb data obtained for 16 cassiterite samples, including samples from both sites and styles of mineralization. All 16 samples define a narrow range of ages between 315.1 ± 1.7 / 3.3 Ma and 311.0 ± 3.1 / 4.0 Ma. All ages overlap within uncertainty, suggesting that mineralization across the Sadisdorf prospect is likely related to the same magmatic-hydrothermal event.On the regional scale, the cassiterite ages suggest that Sn-Li mineralization is associated with late-stage felsic magmatism directly following the collapse (∼314–313 Ma) of the Altenberg-Teplice Caldera. The cassiterite ages also overlap with garnet U-Pb LA-ICP-MS ages of Sn-rich skarn occurrences in the western Erzgebirge (e.g., Breitenbrunn, Antonsthal and Hämmerlein). This observation provides direct evidence that greisen and skarn-hosted Sn mineralization are related to the same period of magmatism. The data indicate that the majority of Sn-mineralization in the Erzgebirge formed after 318 Ma (likely between 318 and 310 Ma), challenging previous models which invoked an older suite of granites (326–318 Ma) as causative source intrusions.

Provenance, diagenesis and reservoir quality of sandstone facies of the Maracangalha Formation, Recôncavo Basin – Northeastern Brazil

Sedimentary composition studies on siliciclastic reservoirs and their relationship with sedimentary provenance have proved to be useful in hydrocarbon exploration, enabling the prognosis of reservoir quality and diagenetic models. However, unconventional terrigenous reservoirs in the Maracangalha Formation, Upper Cretaceous from Recôncavo Basin, have not yet been evaluated regarding sedimentary provenance and its control over reservoir quality. This study aims to define the provenance of the Maracangalha Formation sandstones and its control on the diagenetic processes affecting the reservoir quality. Based on petrography analysis and X-Ray Fluorescence data, it was possible to identify a granite-gneissic terrain under wet climate as the primary source area for quartz-feldspathic sandstones. The granite-gneissic terrains with predominantly felsic minerals, within in the surrounding Precambrian Terrains, represent a major source area for the quartz-feldspathic sandstones found in the Maracangalha Formation. These sources are characterized by significant contributions from recycled sedimentary and metasedimentary rocks, leading to the occurrence of litho and quartzose petrofacies. The high chemical-textural sediment maturity and paleoweathering dispersion, under semi-umid to semi-arid climates, may be a result of paleoclimatic changes and the variable residence times of the sediments in the dispersion routes or temporary storage. The mineral composition and primary texture of sandstones show a clear influence on diagenetic evolution, particularly in terms of mechanical compaction inhibition, by early cementation, and the generation of secondary porosity due to the dissolution of framework grains and early cements. Therefore, understanding the sedimentary provenance, composition, and diagenesis is crucial for predicting the quality of the reservoir and the compartmentalization of the Maracangalha Formation and its analogues.