Volcano-sedimentary Sequence Research Articles

The early Paleozoic Huangtupo VMS Cu—Zn deposit in Kalatag, Eastern Tianshan: Implications from geochemistry and zircon U—Pb geochronology of volcanic host rocks

The Tianshan in China forms the southern part of the Central Asian Orogenic Belt (CAOB) and also hosts important polymetallic resources. Here we investigate the Huangtupo medium–size copper–zinc deposit, located in the central part of the Kalatag copper Polymetallic Belt with a view to evaluate the nature and genesis of the early Paleozoic volcanogenic massive sulfide (VMS) Cu—Zn deposits. This deposit is correlated to intermediate–felsic volcano–sedimentary sequences of the early Paleozoic Daliugou Formation which are mainly composed of andesite, dacite, and rhyolite with minor basalt, as well as their pyroclastic equivalents. The ore bodies are hosted in the contact zone between andesitic volcanic breccia and tuff representing an eruptive hiatus between the two volcanic cycles with massive sulphide lens at the top and stockwork zone at lower part of the Daliugou Formation. We report new zircon U—Pb data, major and trace element geochemistry and Sr—Nd isotopes from the andesite, dacite and andesitic tuff in the Huangtupo deposit. Zircon from the dacite and the andesite occurring above the ore bodies yield and age of 440.1 ± 1.2 Ma and 439.7 ± 0.95 Ma, and that from the andesitic tuff in footwall shows and age of 442.0 ± 1.1 Ma. All samples show typical geochemical signatures of subduction–related calc–alkaline magmas with slight enrichment in LILE and LREE but depletion in Nb and Ti content relative to primitive mantle. The andesites are characterized by high MgO (7.6–10.8 wt%) contents and Mg# values (64–72) with low Sr/Y and La/Yb ratios, belonging to sanukite. Both dacite and tuff have low MgO (<2.5 wt%) and Al2O3 content (15–16.4 and 11.3–15.3 wt%) with Eu negative anomalies (Eu/Eu* = 0.71–0.75 and 0.44–0.6), showing their low–MgO affinity. All the volcanic rocks display similar Nd and Sr isotopic signature, with εNd(t) of 6.5 to 7.3 and moderately high (87Sr/86Sr)i ratios of 0.705274 to 0.706977. The geochemical characteristics and regional geology indicate that these volcanic rocks were formed in an intra–oceanic arc during southward subduction of the oceanic lithosphere in the northern part of the Eastern Tianshan. They were most likely derived from the partial melting of the mantle wedge with input and interaction with subducted–related melts and/or fluids. We also propose that the Huangtupo VMS deposit is analogous to Kuroko type VMS deposits developed within intra–oceanic rift.

Details Geological Mapping and Petrological Characteristics of EL Shereik Study Area, River Nile State, North Sudan

The present study focused on details geology of the lithostratigraphy, phenomena and petrogenesis, with full classification of rock units and correlate by the regional geology in the study area. The previous studies, focused on regional geology, which can be divided in Bayuda Terrane, represented by Dem El Tor Shear Zone (DTSZ), its Precambrian to Tertiary ages (isotopic signatures of later cooling 590 to 550 Ma), with dominated by metamorphic and intrusive rocks belonging to the Pre-Nubian basement complex. The study area lies at El Shereik, River Nile State, Sudan. It is characterized by low-lying bed plains, covered with superficial deposits, with an arid climate. The techniques of this work, represented in an official, field works and laboratory test, with used Land Sat Images ETM. And Nubian Arabian Shield, represented by the Keraf Shear Zone (KSZ), its Precambrian to Phanerozoic ages (Neoproterozoic, Pb isotope ages dating, of forms is -730 -710Ma and ended in -565Ma), with dominated by metamorphic, ophiolitic mélange, volcano-sedimentary sequences, and Phanerozoic sediments. But through this detailed surveyed, we discovered different types of rock units; they were found as accumulated and highly deformed, affected by various thrusting faults. collected more than 40 samples, through six traverses, for classification and petrographic studies and classified more than 9 types of rooks units didn’t mentioned before in previous study, all of them well exposed as following: metamorphic rocks, included, migmatites, calc-silicates, wollastonite, talc-schist, carbonaceous (dolomitic marble), amphibolites, graphitic schist, mica schist, quartzo-feldspathic schist, and grey gneiss, While the Igneous rocks, consisted of dykes, as dolerite, trachy-basaltic, Rhyolite porphyry, pegmatites, diorite, and quartz veins, whereas the superficial deposits, included, of aeolian, fluvial, and collovial. These rocks extend and spread to the outside of the limits of the study area and most of them oriented parallel with KSZ SE - NW region and a few of them are oriented E-W, This is maybe due to the collusion of the contact boundary between KSZ and DTSZ Bayuda Tehran. Talc-schist, Wollastonite and graphitic schist, represent a strategic stockpile besides gold mining. Studies conducted with DTSZ, its old age, occurred before Neoproterozoic compared to KSZ. Because it has the first deformation of the folding of pre- KSZ proportion to the presence of folding in the west and east of the Nile zone, according to the border between Bayuda Terrane and Nubian Arabian Shield, as the suggest result. And the previous studies of the ages dating confirm it.

From arc evolution to arc-continent collision: Late Cretaceous–middle Eocene geology of the Eastern Pontides, northeastern Turkey

AbstractThe Eastern Pontide Arc, a major fossil submarine arc of the world, was formed by northward subduction of the northern Neo-Tethys lithosphere under the Eurasian margin. The arc’s volcano-sedimentary sequence and its cover contain abundant fossils. Our new systematical paleontological and structural data suggest the Late Cretaceous arc volcanism was initiated at early-middle Turonian and continued uninterruptedly until the end of the early Maastrichtian, in the northern part of the Eastern Pontides. We measured ∼5500-m-thick arc deposits, suggesting a deposition rate of ∼220 m Ma–1 in ∼25 m.y. We have also defined four different chemical volcanic episodes: (1) an early-middle Turonian–Santonian mafic-intermediate episode, (2) a Santonian acidic episode; when the main volcanic centers were formed as huge acidic domes-calderas comprising the volcanogenic massive sulfide ores, (3) a late Santonian–late Campanian mafic-intermediate episode, and (4) a late Campanian–early Maastrichtian acidic episode. The volcaniclastic rocks were deposited in a deepwater extensional basin until the late Campanian. Between late Campanian and early Maastrichtian, intra-arc extension resulted in opening of back-arc in the north, while the southern part of the arc remained active and uplifted. The back-arc basin was most probably connected to the Eastern Black Sea Basin. In the back-arc basin, early Maastrichtian volcano-sedimentary arc sequence was transitionally overlain by pelagic sediments until late Danian suggesting continuous deep-marine conditions. However, the subsidence of the uplifted-arc-region did not occur until late Maastrichtian. We have documented a Selandian–early Thanetian (57–60 Ma) regional hiatus defining the closure age of the İzmir-Ankara-Erzincan Ocean along the Eastern Pontides. Between late Thanetian and late Lutetian synorogenic turbidites and postcollisional volcanics were deposited. The Eastern Pontide fold-and-thrust belt started to form at early Eocene (ca. 55 Ma) and thrusting continued in the post-Lutetian times.

Geochemical constraints on the origin of Neoarchean magmatic rocks in the Lüliang Complex, North China Craton: Tectonic implications

The North China Craton suffered a strong tectonothermal event in the late Neoarchean, with its crystalline basement dominantly composed of ca. 2.6–2.5 Ga granitoid gneisses and metamorphosed volcano-sedimentary sequences. However, controversial issues have long existed on the geodynamic setting of this event. We present new in-situ LA-(MC-) ICP-MS zircon U-Pb and Lu-Hf isotope data, and whole-rock geochemical data for Neoarchean magmatic rocks from the Lüliang Complex. Zircon U-Pb dating reveal that the basalts, andesites and felsic volcanics yield crystallization ages of 2535–2486 Ma, followed by crustal anatexis and metamorphism at ∼2489 Ma. The basalts and andesites yield positive εHf(t) values of 5.1–11.6 and 2.2–6.5 for zircons, corresponding to average Hf model ages of 2547 Ma and 2660 Ma, respectively. The felsic volcanic rock yields positive zircon εHf(t) values of 1.4–6.3, with Hf model ages averaging 2775 Ma. Such ages are consistent with 207Pb/206Pb ages of 2.8–2.7 Ga for relict zircons, indicating reworking of crustal rocks. The basalts and andesites have geochemical compositions of island arc tholeiite (IAT) and calc-alkaline basalt (CAB), suggesting that they were both derived from partial melting of subarc mantle sources that were generated by metasomatic reaction of the mantle wedge peridotite with subducting crust-derived fluids. Compared with the basalts, the andesites were also originated from a subarc mantle source with incorporation of more subducting sediment-derived melts. Thus, both the basalts and andesites would most likely form in a continental arc setting. In this regard, plate subduction and arc magmatism in the North China Craton can be traced back to at least 2.65 Ga in the Lüliang area. The 2.6–2.5 Ga tectonothermal event manifested as widespread accretionary orogeny in the North China Craton, resulting in significant growth of the juvenile mafic crust as well as extensive reworking of the old basement dominated by 2.8–2.7 Ga crustal rocks.

The Alamos Metamorphic Complex, evidence of late Paleozoic collision between Laurentia and Gondwanan blocks in northwestern Mexico

The Alamos Complex is a metamorphosed volcano-sedimentary sequence exposed south of the late Paleozoic Ouachita–Marathon–Sonora orogen in northwestern Mexico, which in turn, is regarded as a continuation of the Alleghenian–Variscan mountain chain. Mineral assemblages in metavolcanic rocks indicate greenschist facies metamorphism. Thermobarometric studies yield an average metamorphic temperature of 380 °C, whereas andalusite in metapelites indicates pressure less than 0.4 ± 0.05 GPa. The main deformation phase generated pervasive foliation, which in turn was isoclinal to close folded and a second axial planar cleavage was developed. Metavolcanic rocks of the Alamos Complex can be separated in two suites: (1) an anorogenic suite, similar to enriched middle ocean basalts (E-MORB) in the Tesia region, and (2) an orogenic suite, characteristic of volcanic-arc setting in the Mocuzari region. U–Pb detrital zircon geochronology of one sample from Tesia yielded a maximum depositional age averaging 395 ± 28 Ma. One sample from the Mocuzari region yielded a maximum depositional age averaging 1104 ± 24 Ma, with the largest peak at 1428. A clastic sequence correlated with the Middle Triassic–Lower Jurassic Barranca Group, nonconformably cover the Alamos Complex. The basal conglomerate of that group yields a maximum depositional age averaging 372 ± 23 Ma. Accordingly, the Alamos Complex must be in part deposited after the early Devonian time and before the Middle Triassic. The main sources of detritus for the complex are the Meso- and Paleoproterozoic rocks of southwestern Laurentia, whereas the main source of detritus for the Barranca Group is the Rio Fuerte Formation exposed ~ 100 km south of the study area. The metamorphic event is ascribed to the late Paleozoic collision of Gondwanan blocks against the southern margin of Laurentia.

Haida Gwaii (British Columbia, Canada): a Phanerozoic analogue of a subduction-unrelated Archean greenstone belt

Understanding the formation and evolution of Precambrian greenstone belts is hampered by gaps in the rock record and the uncertainty of the tectonic regime that was operating at the time. Thus identifying a modern analogue of a Precambrian greenstone belt can be problematic. In this paper we present geological, geochemical and petrological evidence outlining the case for Haida Gwaii (British Columbia, Canada) as a modern example of a greenstone belt. Haida Gwaii is comprised of two rift-related volcano-sedimentary sequences. The older (Early Triassic) Karmutsen volcanic sequence consists of subaqueous ultramafic-mafic volcanic rocks that are capped by marine carbonate and siliciclastic rocks. The younger (Paleogene) Masset bimodal volcanic sequence consists of tholeiitic and calc-alkaline basalt along with calc-alkaline silicic volcanic and intrusive rocks that are capped by epiclastic sandstones. The Karmutsen and Masset volcanic rocks have indistinguishable Sr-Nd-Pb isotopes demonstrating they were derived from a similar mantle source. Some of the Masset calc-alkaline rocks are compositionally similar to magnesian andesites (SiO2 = 56–64 wt%; Mg# = 0.50–0.64) that are typical of subduction-related Archean greenstone belts. We show that the calc-alkaline signature observed in the bimodal sequence of the Masset Formation is likely due to fractional crystallization of a tholeiitic parental magma under relatively oxidizing (ΔFMQ + 0.7) conditions indicating that a calc-alkaline signature is not prima facie evidence of a subduction setting. Given the geological and geochemical evidence, Haida Gwaii represents one of the best analogues of a modern subduction-unrelated Archean greenstone belt.

Evaluating petrophysical properties of volcano-sedimentary sequences: A case study in the Paraná-Etendeka Large Igneous Province

Abstract The Parana-Etendeka represents a major magmatic province associated with the rifting of West Gondwana and the formation of the South Atlantic Ocean. The area represents a direct analogue for similar aged volcanic rocks buried within hydrocarbon-rich basins offshore the South Atlantic margin. We present here a detailed integration of outcrop data with laboratory measurements of porosity, permeability, and ultrasonic acoustic velocities (P and S-waves) for volcanic and interbedded sedimentary rocks of the Parana-Etendeka Province in southern Brazil. The lava pile is formed of compound pahoehoe basaltic lavas at the base (Torres Formation) followed by thick tabular rubbly pahoehoe basaltic andesites (Vale do Sol Formation) and the upper stratigraphy is characterized by locally fed domes and extensive tabular acidic units. Sedimentary interbeds occur throughout the entire lava pile. For the volcanic rocks petrophysical properties have a cyclic variation controlled by the lava internal structure. Lava upper and lower crusts have relatively high porosity (>10%) and low acoustic velocities, whilst lava flow cores are characterized by porosities of less than 5% and velocities typically 0.5–1.0 kms−1 higher than lava crust facies. The highest porosities are found in the upper crust of both rubbly pahoehoe (c. 28.3%) and pahoehoe lavas (c. 26.6%) where vesicles account for most of the pore space. Permeability is relatively low in the volcanic rocks ( 15%) and permeability (avg. 450 mD) and represent the best reservoir rocks within the Parana-Etendeka Province. Nevertheless, where diagenesis is intense porosity and permeability are significantly diminished. The petrophysical properties of volcanic rocks are controlled primarily by lava emplacement mechanisms (e.g. inflation, degassing and flow fragmentation), and secondarily by bulk mineral composition. Petrophysical properties can be further modified by diagenetic and hydrothermal alteration processes. Understanding the interplay between primary and secondary processes on the final petrophysical characteristics of the rocks is key for defining reservoir properties in offshore areas, such as the North and South Atlantic margins, where volcanic rocks are intrinsically associated with prolific hydrocarbon-bearing sedimentary basins.

Petrography and detrital zircon U-Pb geochronology of sedimentary rocks of the Campo Alegre Basin, Southern Brazil: implications for Gondwana assembly

Abstract The Campo Alegre Basin is a volcano-sedimentary sequence covering an area of about 500 km2 , located at the northeast portion of Santa Catarina state (Brazil), and formed during the late stages of the Neoproterozoic era. Three main stratigraphic units compose this basin, the lowermost of which is the Bateias Formation, corresponding to the pre-volcanic stage. It is characterized by the fanglomeratic sediments at the basin’s northern boundary, which were deposited in a fluvial environment and progressively replaced by fluvial sandstones towards the south. Poorly sorted conglomerates and breccias compound the fanglomeratic facies, which comprises angular to subrounded fragments in a matrix ranging from sand fractions to fragments larger than gravel. The ubiquitous presence of volcanogenic and metamorphic fragments in the fanglomeratic facies strongly suggests that the Pien Magmatic Arc and a volcanic manifestation coeval with the earlier stages of the basin formation were important source areas, as well as the basin basement (the Luis Alves Terrane). In this sense, geological, petrographic, and detrital zircon geochronology data are combined in order to interpret the mechanisms that had acted during the deposition of these sedimentary rocks and to constraint the maximum depositional ages of Bateias Formation at ca. ~606 Ma.

Uranium ore mineralization at the Western Carpathians / Slovakia (conditions and social aspects)

Uranium ore mineralisation occurrences at the Western Carpathians/Slovakia are deposited within Permian volcano-sedimentary sequences. The mineralisation principally consists of two genetic types, the stratiform one and U-Mo vein mineralization linked to andesite volcanites. Geological exploration of uranium mineralization in Slovakia is subject to rigorous assessment of Ministry of Environment and municipalities. The limited energy sources and dependence to foreigner, open space for prospection of new energy sources (reneweable, uranium or traditional from coal, oil, gas).

Geological, geochemical and Rb–Sr isotopic studies on tungsten mineralised Sewariya–Govindgarh granites of Delhi Fold Belt, Rajasthan, NW India

Neoproterozoic granites are widespread in the Delhi Fold Belt of the Aravalli craton, some of which are associated with tungsten mineralisation. In one such instance, the volcano-sedimentary sequence of Barotiya Group in the South Delhi Fold Belt is intruded by a pluton of biotite granite gneiss known as Sewariya Granite (SG) and later by stocks and dyke swarm of tourmaline leucogranite known as Govindgarh Granite (GG). GG magmatism was associated with wolframite mineralisation in hydrothermal quartz veins occurring along the sheared contact between SG pluton and Barotiya mica schist. SG pluton shows the evidence of ductile and brittle deformations, whereas GG is by and large undeformed. Apart from quartz and feldspars, SG contains biotite and muscovite, and GG contains muscovite, tourmaline and garnet. Although both SG and GG are peraluminous, SG has a wide range of \(\hbox {SiO}_{2}\) and narrow range of alkalis, and GG has a narrow range of \(\hbox {SiO}_{2}\) and a wide range of alkalis. REE (rare Earth elements) modelling shows that the parent magma of SG and GG was derived from partial melting at different crustal levels. Rb–Sr isotope data of GG yield a mineral isochron age of \(860\pm 7.4\,\hbox {Ma}\) which represent the time of igneous crystallisation and cooling of the granite to less than 400\({^{\circ }}\)C.

Faunal elements from the Deccan volcano‐sedimentary sequences of India: A reappraisal of biostratigraphic, palaeoecologic, and palaeobiogeographic aspects

The sedimentary sequences associated with the Deccan Flood Basalts, i.e., infratrappean and intertrappean deposits, are known to yield a diverse assemblage of fauna that includes foraminiferans, ostracods, molluscs, fishes, frogs, turtles, lizards, snakes, crocodiles, dinosaurs, and mammals. The existing literature debates the exact nature of origin, age, and duration of the Deccan volcanic activity; however, there is a general accord within the geosciences community that the Deccan Flood Basalts bestrode the Cretaceous–Palaeogene Boundary. Within the past few decades, the record of the biotic component (particularly faunal elements) reported from the Deccan‐volcano sedimentary sequences have grown both numerically and taxonomically. Constraining the age of the Deccan‐volcano sedimentary sequences has a direct bearing on the studies that discuss the origin, evolution of the biota in a palaeobiogeographic framework, and also in the context of changes in the palaeoenvironment and palaeoecology. Thus, it becomes important to reinforce the age, environment of the Deccan‐volcano sedimentary sequences, and the origin/affinity of the faunal elements recovered from within these sedimentary deposits. We here reappraise the biotic (with an emphasis on the fauna) evidence in a biostratigraphic, palaeoecologic, and palaeobiogeographic aspect.

Synneusis: does its preservation imply magma mixing?

Abstract The Ghansura Felsic Dome (GFD) occurring in the Bathani volcano-sedimentary sequence was intruded by mafic magma during its evolution leading to magma mixing. In addition to the mafic and felsic rocks, a porphyritic intermediate rock occurs in the GFD. The study of this rock may significantly contribute toward understanding the magmatic evolution of the Ghansura dome. The porphyritic rock preserves several textures indicating its hybrid nature, i.e. that it is a product of mafic-felsic magma mixing. Here, we aim to explain the origin of the intermediate rock with the help of textural features and mineral compositions. Monomineralic aggregates or glomerocrysts of plagioclase give the rock its characteristic porphyritic appearance. The fact that the plagioclase crystals constituting the glomerocrysts are joined along prominent euhedral crystal faces suggests the role of synneusis in the formation of the glomerocrysts. The compositions of the glomerocryst plagioclases are similar to those of plagioclases in the mafic rocks. The results from this study indicate that the porphyritic intermediate rock formed by the mixing of a crystal-rich mafic magma and a crystal-poor felsic melt.

Heliborne Time Domain Electromagnetic Data Aiding Delineation of Carbonaceous Shale in Southwestern Part of Bijawar Basin and its Implication on Basinal Stratigraphy

Geophysical methods are tools to unravel concealed geological features that enhance knowledge. Heliborne time domain electromagnetic (TDEM) survey carried out over volcano-sedimentary sequence of Palaeoproterozoic Bijawar basin indicated presence of conductor in the western part of the basin. Subsequently boreholes drilled intercepted rhythmites made up of carbonaceous shale and dolomite within Bajno dolomite Formation. Measurement of conductivity on core samples established the high conductive carbonaceous shale as the contributor for TDEM response. TDEM signature indicate widespread presence of rhythmites in the western part of Bijawar basin reflecting different hydrodynamic condition from other parts of Bajno dolomite. Thus, Bajno dolomite Formation is classified into two members viz. Tigoda member and Sarwa member.

Mass balance and origin of fluids associated to smectite and chlorite/smectite alteration in Seival Mine Cu–Mineralization – Camaquã Basin – Brazil (Part II)

The Seival Mine, located in the Camaquã Basin, hosts several small Cu and Ag ore deposits in volcano–sedimentary sequence surrounding the Lavras do Sul Intrusive Complex. Alteration minerals consist of calcite, sulfate, smectite and chlorite/smectite associated with Cu–rich sulfides. The mass balance calculations from less altered to altered volcanic rocks show large chemical changes with the mobility of mettallic elements in major or trace amounts. Mass balance calculations for similar volcanic protoliths, with different degrees of alteration or textural variations, indicate that increasing proportions of clay minerals reflects higher degrees of alteration. This alteration did not mobilize Si, Al, Fe, and Mg and had a small effect on other metallic elements such as Cu, Zn, Ni, and Au. Consequently, fluids associated with propylitic to argillic alteration with chlorite–smectite precipitation did not participate in the transport of base metals and ore deposition. Interpretations of oxygen stable–isotopes for magmatic, late magmatic and hydrothermal minerals show decreasing proportion magmatic fluid (δ18Ofluid of andesine labradorite ca. 5 to 7‰), toward a predominance of meteoric fluid (δ18Ofluid of quartz and calcite) between −12 and 0‰ for the low–temperature alteration (250 to 80 °C). Carbon stable isotopes result suggest a mixture of inorganic carbon ca. −7 to −5‰ from volcanic CO2 with late carbonate precipitation with atmospheric signatures ca. −4 to −1‰. These mass balance and stable isotopes interpretations suggest that high–temperature late–magmatic fluid/rock interaction (650 to 350 °C) has promoted the base metal enrichment.

Tectonic evolution of the western Jiangnan Orogen: Constraints from the Neoproterozoic igneous rocks in the Fanjingshan region, South China

The Jiangnan Orogen in South China formed through collision between the Yangtze and Cathaysia blocks during the Neoproterozoic. The Fanjingshan Group, located in the western part of the Jiangnan Orogen, consists of the deformed volcano-sedimentary sequences intruded by the ca. 830 Ma S-type granites. The volcanic rocks are mainly composed of rhyolitic tuffs associated with minor basalts. The basalts are rich in LILEs (e.g. Th and U) and LREEs and depleted in HFSEs (e.g. Nb and Ta), and have high La/Nb (1.69–2.86) and Th/Yb ratios (0.92–3.34), as well as negative whole rock εNd values (−4.2 to −0.4), suggesting that they were derived from a subduction-modified lithospheric mantle. The rhyolitic tuffs show variable SiO2 (63.43–79.60 wt%), MgO (0.22–4.44 wt%) and Ni (17–41 ppm), and have negative εNd (−7.7 to −6.1) and large variable εHf values (−6.3 to +10.4). Modeling calculations reveal that the rhyolitic tuffs were likely produced by mixing between basaltic and felsic melts. The S-type monzogranites show high FeO/MgO (1.33–95.4) and (K2O + Na2O)/CaO (7–64), and low Zr/Hf (11–18) and Nb/Ta ratios (1.6–3.9) that are indicative of strong fractionation and significant hydrothermal alteration. Their negative εNd (−13.0 to −7.3) and εHf values (−2.7 to +0.7) and Paleoproterozoic two-stage Hf-isotope ages (1.69–1.87 Ga) suggest that the granites were partial melts of the ancient crustal rocks. The Fanjingshan Group is proposed to have been deposited in a forearc basin, and its volcano-sedimentary rocks were deformed and metamorphosed due to the collision between the Yangtze and Cathaysia blocks at ca. 830 Ma. The subsequent peraluminous granites were partial melts of the ancient crustal basement during or post the collision event.

Geochronology of Mexican mineral deposits. VII: the Peña Colorada magmatic-hydrothermal iron oxide deposits (IOCG ‘clan’), Colima

Geochronology of Mexican mineral deposits. VII: the Peña Colorada magmatic-hydrothermal iron oxide deposits (IOCG ‘clan’), Colima

The Sukari Neoproterozoic granitoids, Eastern Desert, Egypt: Petrological and structural implications

The Sukari granitoid pluton is situated in the southern central Eastern Desert of Egypt and is considered as one of the best examples of the gold–bearing granites in the Arabian Nubian Shield (ANS). It consists of coarse– to medium–grained alkali–feldspar granite, syenogranite and monzogranite intruded the volcano–sedimentary sequences and metagabbro–diorite complex. Geochemically, these granitoids are metaluminous to peraluminous in character. They are characterized by positive Rb, K, Zr and Pb and negative Ba, Sr, P, Nb and Ti anomalies and exhibit similar trace element patterns. Moreover, they show pronounced LREE–enriched patterns and negative Eu anomalies that indicate plagioclase fractionation. The studied rocks are typical of within plate granites generated in tensional environment. They belong to ferroan/A–type granites, particularly A2–type suggesting post-collisional setting. Their high SiO2, Al2O3 and low MgO contents along with the low Ce/Pb ratios reflect derivation from melting crustal source.The major structures of the Sukari area encompass Akbar Wahid, Golden Boy, Buthinae and Kaolinitic Faults. The area is characterized by NNE-NE trending shear zone and WNW-EW stress orientation. The mineralized structures contain quartz veins trending mostly EW, NS and NNW; joints with NS, EW, NNE and NNW trends; faults with NNW, NNE, NS and EW trends; and breccia with NNW trend. The kinematic indicators are represented by mylonites, quartz fish and augen structures. Mineralization in Sukari area found as quartz veins, stockworks and brecciated veins.

The multistage tectonic evolution of the northeastern Carajás Province, Amazonian Craton, Brazil: Revealing complex structural patterns

Structural data collected in the Carajás Province region led to a new interpretation of the southeastern Amazonian Craton geotectonic evolution. The purpose of this article is to present a new evolutionary proposal for the region. A detailed analysis of the several extensional-compressional cycles that overprinted each other from the Archean to the Neoproterozoic-Cambrian is presented. At about 2.87–2.83 Ga, collisional processes led to the formation of a stable crustal substrate that supported the installation of an extensional basin at 2.76–2.70 Ga and the deposition of the Itacaiúnas Supergroup shallow marine volcanosedimentary sequences, together with contemporary bimodal plutonism. Paleoproterozoic arc magmatism in the Bacajá Domain was followed by collision with the Carajás Province between 2.09 and 2.06 Ga, resulting in expressive tectonic thickening and low to high grade regional metamorphism, and in the deposition of the Águas Claras Formation. A second Paleoproterozoic orogenic event affected the Carajás Province, which resulted in oblique tectonism and regional counterclockwise rotation of previous associations, followed by late to post-orogenic sedimentation and 1.88 Ga anorogenic alkaline A-type magmatism. The eastern Carajás Province margin was extensionally reactivated during the Neoproterozoic, in a rifting event, followed by tectonic inversion during the Ediacaran/Cambrian.

Early Cambrian alkaline volcanism on the southern margin of Laurentia: evidence in the volcaniclastic units from the Puerto Blanco Formation in the Caborca block, NW Mexico

ABSTRACTVolcaniclastic units are exposed at the base of the Puerto Blanco Formation in the Caborca region, northwestern Mexico. The lower unit reveals the presence of Early Cambrian mafic volcanism in this region. It consists of a volcano-sedimentary sequence represented by tuffaceous conglomerates, agglomerates, lapillistones, tuffs, and altered mafic volcanic flows. Petrographic analysis classified the volcanic clasts as albite-sphene-calcite-actinolite granofels, with a moderate to intense hydrothermal alteration, precisely characterized by EPMA analysis. Albite-actinolite geothermometry indicates temperatures from 400 to 500°C, suggesting metamorphic conditions in the upper temperature greenschist facies. Geochemistry analysis shows a high TiO2 basic–ultrabasic volcanism that originated the volcanic clasts. Rock protoliths were studied using immobile trace elements, which classified them as OIB-type alkaline basalts with the characteristic spider hump-shaped pattern, situated in an anorogenic intracontinental tectonic setting with enriched mantle signatures. 40Ar/39Ar geochronology shows metamorphic ages of 52.58 ± 2.0 and 91.67 ± 0.55 Ma, consistent with the emplacement of Laramidic granitoids identified in the region. Possible correlations of this alkaline volcanism include the Southern Oklahoma Aulacogen and the late stages of the rifting of north western Laurentia represented in western United States.

Features of magmatim-related metallogeny of Gorny Altai and Rudny Altai (Russia)

The Rudny Altai and Gorny Altai regions had different geologic histories and differ in metallogenic patterns. The Vendian-Early Cambrian to Permian-Triassic multistage evolution of Gorny Altai included subduction, accretion-collision, and rifting events accompanied by magmatism and related mineralization. Metallogeny evolved in discrete pulses, with especially abundant Late Paleozoic-earliest Mesozoic mineralization. The Devonian-Carboniferous pulse produced diverse mineral deposits (iron, mercury, gold, silver, molybdenum, tungsten, cobalt, polymetallic ores, and rare earths), some of considerable economic value. The territory of Gorny Altai includes several large ore districts that belong to different zones. They are the Beloretsk-Kholzun iron district in the west, the Kayancha-Sinyukha fluorine-gold district in the northeast, the Kurai gold-mercury and Yustyd rare-metal-silver districts in the southeast, and the Kalguty rare-metal-tungsten and Ulandryk U-REE-Cu districts in the south. The largest mineral deposits are Kholzun (Fe, P2O5), Karakul (Co, Bi), Sinyukha (Au), Aktash and Chagan-Uzun (Hg), Ozernoe and Pogranichnoe (Ag), Kalguty (Mo, W), Alakha (Li, Ta), Rudnyi Log (Y,Fe-specularite), and Urzarsai (W-scheelite). Mineralization in Rudny Altai is mainly pyritic: copper-pyrite, pyrite-polymelallic ore, and barite-polymelallic ore. It resides in suprasubduction basalts and rhyolites and in Emsian to Frasnian island-arc volcanics at different stratigraphic levels of Devonian volcanosedimentary sequences in six ore districts. The Kurchum high-grade metamorphic block hosts copper-pyrite and gold-quartz mineralization related to Hercynian volcanism.