Volcano-sedimentary Complex Research Articles

Late Variscan, Permo-Carboniferous, Al-K plutonism in the South Portuguese Zone: El Crispinejo cordierite-bearing granite.

The El Crispinejo granite forms part of a small, but distinctive late intrusive suite of cordierite-bearing peraluminous granites in the South Portuguese Zone (SPZ). This granite has the best outcrop relationships of the suite. It cross-cuts different members of the Sierra Norte Batholith of the SPZ and the Carboniferous Volcano-Sedimentary Complex of the Iberian Pyrite Belt, producing contact metamorphism. This late pluton has a high K content which results in a contrasting geophysical response (K-Th-U) with respect to the surrounding trondhjemitic granitoids of the TTG suite of the Sierra Norte Batholith. A concordant monazite-zircon U-Pb ID-TIMS age of 300.5 +0.5/-1.5Ma demonstrates Permo-Carboniferous age for this late Variscan magmatic event. The granite is associated with a series of ore showings (F-Pb-Zn and Sn-W) which are completely different from the nearby, massive sulphide and manganese ore deposits of the Iberian Pyrite Belt, indicating the unique character of this intrusion.

THE TECTONOSTRATIGRAPHY OF CYCLADIC BLUESCHIST UNIT ON SIKINOS AND SIFNOS: IMPLICATION FOR THE MESOZOIC TECTONIC SETTING

This study presents new results for the tectonostratigraphic configuration of the Cycladic Blueschist unit (CBU) in the islands of Sikinos and Sifnos. These results show that the observed tectonostratigraphy in CBU results from tectonic repetitions of a thinner sequence. Tectonic repetitions have been achieved by a series of largescale ductile thrusts that operated during burial and exhumation of CBU. Restoration of the tectonostratigraphy in both islands implies an original, pre-metamorphic sequence, which was made up by a volcano sedimentary complex at the base and an overlying carbonate-rich sedimentary succession. This Mesozoic protolithic sequence was possibly formed in a continental terrane or in a transitional domain between a continental terrane and an oceanic basin. We suggest that the Mesozoic protolith of the CBU was formed in an incipient oceanic basin rather than a mature ocean like Pindos Ocean. This incipient oceanic basin was developed either along south part or along the north margin of Pelagonian microcontinent.

Geochemical constraints on the oldest arc rocks of the Arabian-Nubian Shield: The late Mesoproterozoic to late Neoproterozoic (?) Sa'al volcano-sedimentary complex, Sinai, Egypt

The Wadi Sa'al metamorphosed volcano-sedimentary complex represents the deepest exposed stratigraphic levels of the Arabian-Nubian Shield (ANS). Recent isotopic ages (1.12–0.95Ga, Be'eri-Shlevin et al., 2012) assigned the Sa'al complex as the oldest arc rocks of the ANS (pre-Pan-African?). It encompasses a wide variety of non-consanguineous, late Mesoproterozoic to late Neoproterozoic (?) rock units that preserve a complicated and protracted record of orogenic and tectonic assembly. They experienced regional low-pressure greenschist up to amphibolite facies metamorphism. The tectono-stratigraphic rock units of the Wadi Sa'al complex can be distinguished into two superimposed metavolcanic formations (Agramiya and post-Ra'ayan), separated by the metasedimentary Ra'ayan Formation. Both the Agramiya and post-Ra'ayan metavolcanics comprise basalts, basaltic andesite and rhyolite. The Ra'ayan metasediments encompass metagreywacke, semi-metapelite and metapelite. Geochemical consanguinity, tectonic setting and petrogenesis of the different rock units of the Sa'al complex are addressed. The metavolcanics of the Sa'al complex imply calc-alkaline affinities with subordinate tholeiitic signature and probable island-arc setting. The Ra'ayan metasedimentary rocks were accumulated as fluvial sediments in basins adjacent to their uplifted volcanic protoliths (Agramiya Formation). The detritus was deposited in fresh-water environment. New geological mapping was undertaken for the area using remote sensing and GIS techniques. Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) band rationing-based images (b6/b4, b6/b7, and b4/b2) effectively discriminate the different basement rock units of the Wadi Sa'al area from each other.

A remote sensing-based discrimination of high- and low-potential mineralization for porphyry copper deposits; a case study from Dehaj–Sarduiyeh​ copper belt, SE Iran

ABSTRACTThis work seeks to implement surface indicators of porphyry copper deposits (PCDs) at known source regions and to apply these indicators to recognize high- and low-potential mineralization through remote sensing in other areas. Thirty copper deposits in central Iranian volcano-sedimentary complex, Kerman province, Southeast of Iran, which are different in grade and size, were selected as test sites. The abundances of alteration minerals at these deposits were discriminated using a partial sub-pixel unmixing algorithm, mixture tuned matched filtering (MTMF), on Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data to find​ an indicator whether the abundances of alteration minerals correspond to the grade and size of each deposit. In general, comparison of sub-pixel abundances with known mineral occurrences showed a reasonable correspondence such that areas with high abundances of alterations corresponded well with important mineralized districts. It is concluded that suggested sub-pixel analysis of ASTER data leads to identifying alteration zones with high-potential mineralization in PCDs.

ANALÝZA LABORATORNÍCH HODNOT RADIOAKTIVITY HORNIN NA MAPOVÉM LISTU 15-11 ZLATÉ HORY

Natural radioactive elements (potassium, uranium and thorium) abundances were measured in 769 samples of metamorphic and igneous rocks and pre-Cenozoic sedimentary rocks from all geological units on the map sheet 15-11 Zlaté Hory, using a laboratory gamma-ray spectrometer. Metamorphic rocks belong to two geological units of the Silesicum: to the Vrbno Group (a volcanosedimentary complex composed mainly of phyllites, quartzites, amphibolites, greenschists, acid to intermediate metavolcanites and their metatuff s) and the Desná Group (metagranites and blastomylonites). Unmetamorphosed pre-Cenozoic sedimentary rocks are represented by three Variscan flysch formations – the Andělská Hora, Horní Benešov, and Moravice Fms. (rocks of the first formation are unmetamorphosed to anchimetamorphosed), only in small areas by Cretaceous sandstones of the Peruc-Korycany Formation and Devonian limestones of the Líšeň Formation. Unmetamorphosed magmatites are represented by granitoids, lamprophyres andmicrogabbro. From calculated values of mass activity of 226Ra equivalent it is evident that natural radioactivity of most of the studied rocks is low. Slightly increased mass activity values were found in feldspar-rich quartzites (186 Bq.kg-1 on average), metakeratophyres (200 Bq.kg-1) and felsic metatuff s (229 Bq.kg-1) of the Vrbno Group.

The leading role of geophysical methods in the discovery of the La Magdalena VMS deposit in the Pyrite Belt, Huelva

The La Magdalena deposit is located in the central, northern part of the IPB (Figure 1) in an area where the three main regional lithostratigraphic units of the Belt are well represented. The stratigraphic package is complicated by deformation from the different tectonic events resulting in a degree of ‘disorder’ in the units on the geological map as a result of this tectonic complexity. As a result of the tectonic deformation the oldest rocks corresponding to the PQ Group (phyllites and quartzites) appear thrusted over the VS (Volcano-sedimentary complex) in the northern limits of the prospect, but also appear as a thin band in the western half of the study area. To the south and away from the area of La Magdalena there are extensive areas of Lower Carboniferous Culm rocks, which are the youngest stratigraphic units and comprised of phyllites and greywackes. Between the Lower Carboniferous Culm in the south and the Devonian PQ in the north, the VS Complex outcrops and is well developed in the prospect area. The VS Complex comprises of mainly volcanic rocks (lavas and pyroclastics) with the rare appearance of sediments and it is in this VS sequence where many of the sulphide deposits are hosted including Aguas Tenidas, Esperanza and La Magdalena. The local geological map around La Magdalena deposit is shown in Figure 2.

Mineralogy of low grade metamorphosed manganese sediments of the Urals: Petrological and geological applications

The paper describes mineralogy of the low grade metamorphosed manganese sediments, which occur in sedimentary complexes of the Pai Khoi Ridge and the Polar Urals and volcanosedimentary complexes of the Central and South Urals. The degree of metamorphism of the rocks studied corresponds to PT conditions of the prehnite–pumpellyite (deposits of Pai Khoi and Polar and South Urals) and green schist (deposits of the Central Urals) facies. One hundred and nine minerals were identified in the manganese-bearing rocks on the basis of optical and electron microscopy, X-ray diffraction, and microprobe analysis. According to the variations in the amount of major minerals of the manganese rocks of the Urals, they are subdivided on carbonate (I), oxide–carbonate–silicate (II), and oxide–silicate (III) types. Carbonates, various Mn2+-bearing silicates associated with oxides and carbonates, and braunite (Mn3+-bearing silicate) are the major Mn hosts in types I, II, and III, respectively. Because of the different oxidation state of Mn, the rocks of types I and II are termed as “reduced” and the rocks of type III, as “oxidized”. The formation of a certain mineralogical type of metamorphic assemblage is controlled by the content of organic matter in the primary sediments. The sequence type I→type II→type III reflects the decrease in the amount of organic matter in metalliferous sediments. Mineralogical data indicate that manganese in the primary sediments accumulated in a silicate form (MnSi gel, glass, etc). During diagenesis, the Mn–Si phase was transformed to neotokite with subsequent formation of caryopilite and further crystallization of pyroxmangite, rhodonite, tephroite, and other silicates due to reactions involving caryopilite. The hydrated Mn-silicates (caryopilite and/or friedelite) and the spatially associated parsettensite, stilpnomelane, and other minerals are the index minerals of the low grade metamorphism. Under PT conditions of prehnite–pumpellyite facies, nearly 70% of silicate minerals are hydrous. The metamorphosed Mn-bearing sediments are characterized by the low-temperature caryopilite (or tephroite-caryopilite-pyroxmangite±rhodonite) and the high-temperature caryopilite-free (or tephroite-pyroxmangite±rhodonite) facies. Their PT conditions correspond to zeolite and prehnite-pumpellyite (the low-temperature) and green schist and higher grade (the high-temperature) facies.

Flora from the Induan stage (Lower Triassic) of Middle Siberia

The first data on the taxonomic composition of the Induan flora of Siberia are presented. The investigation of Triassic reference sections in northern Siberia (eastern Taimyr, Lena–Anabar Trough, Verkhoyansk region) and correlation with volcano-sedimentary complexes of the Tungus and Kuznetsk basins made it possible to establish for the first time the taxonomic composition of the flora from the Induan Stage of Siberia. Its composition is heterogeneous, forming two large plant formations, which occupied different ecological niches. On the eastern coastal-marine margins of Siberia (eastern Taimyr, Olenek coast, Verkhoyansk region), the Induan flora was largely characterized by lepidophytic (Tomiostrobus) plants, while in the intracontinental areas (Tungus and Kuznetsk basins, partly Verkhoyansk region), it was characterized by Equisetales–Filicales communities.

Superimposed thermal histories in the southern limit of the Ossa Morena Zone – Portugal

AbstractThe Mississippian volcano-sedimentary complex in the Toca da Moura – Cabrela areas represents remnants of intra-volcanic marine sedimentary basins, formed during the collision between the Ossa Morena Zone with the South Portuguese Zone. These rock units are unconformably overlain by the Pennsylvanian intramontane coal-bearing Santa Susana Basin. Vitrinite reflectance determinations from rocks of these two basins indicate two episodes of thermal maturation. During the first episode, the Toca da Moura – Cabrela volcano-sedimentary complexes attained high maturation levels, equivalent to anthracite coal rank (3.0–3.5% Roran), which pre-dates the middle Moscovian Santa Susana Basin. The Santa Susana Basin attained moderate maturation levels equivalent to bituminous coal rank (1.35–1.5% Roran) recording a second episode of thermal maturation. Here, peak thermal conditions did not overprint the first maturation episode. The observed effects of magmatic intrusion on the thermal maturity and the lack of any increase in vitrinite reflectance with depth through c. 400 m of section in borehole SDJ-1 indicate high geothermal gradients during the first maturation episode. A contemporaneous magmatic event associated with the c. 335–320 Ma Cuba-Alvito Gabbros/Diorites of the Beja Massif was the possible cause for the high geothermal gradients postulated for the first maturation episode. Burial under a post-upper Moscovian sedimentary cover was the most likely process to account for the maturation levels determined for the Santa Susana Basin and for the second episode of thermal maturation.

Early Paleozoic monzodiorite–granodiorite association in the northeastern flank of the South Mongolia–Khingan orogenic belt (Nora–Sukhotinsky Terrane): Age and tectonic setting

The paper presents the results of U–Pb geochronological and geochemical studies of the rocks of the monzodiorite–granodiorite association in the northeastern flank of the South Mongolia–Khingan orogenic belt, which composes a tectonic block among the provisionally Lower Paleozoic volcanosedimentary complexes of the Nora–Sukhotinsky Terrane. It is shown that the studied rocks have similar petrographic features (with the presence of transitional varieties) and form common trends in the petrographic diagrams. This suggests that they are members of a single magmatic association. The geochemical features of the monzodiorites, quartz monzodiorites, and granodiorites, in particular their enrichment in large ion lithophile elements (LILE) and depletion in some HFSE, indicate their similarity with island-arc magmatic rocks. The presence of monzonites and quartz monzonites in the studied monzodiorite–granodiorite association along with high K, Rb, Th, and Pb concentrations gives reasons to believe that it formed in active continental margin or ensialic island-arc environments. The granodiorites of the monzodiorite–granodiorite associations of the Nora–Sukhotinsky Terrane are dated at 440 ± 10 Ma and may be considered as a fragment of the early Silurian active continental margin or ensialic mature island arc in the structure of the South Mongolia–Khingan orogenic belt.

The Mesozoic successions of western Sierra de Zacatecas, Central Mexico: provenance and tectonic implications

AbstractCentral Mexico was subject to active tectonics related to subduction processes while it occupied a position in western equatorial Pangea during early Mesozoic time. The subduction of the palaeo-Pacific plate along the western North American and South American active continental margins produced volcanic arc successions which were subsequently rifted and re-incorporated to the continental margin. In this context, the fringing arcs are important in unravelling the continental accretionary record. Using petrographic analysis, detrital zircon geochronology and structural geology, this paper demonstrates that the Guerrero Arc (Guerrero Terrane) formed on top of a felsic volcaniclastic unit (Middle Jurassic La Pimienta Formation) and siliciclastic strata (Upper Triassic Zacatecas Formation and Arteaga Complex) of continental Mexican provenance, deposited across the continental margin and oceanic substrate. This assemblage was rifted away from continental Mexico to form an intervening oceanic assemblage (Upper Jurassic – Lower Cretaceous Las Pilas Volcanosedimentary Complex of the Arperos Basin), then accreted back more or less at the same place, all above the same east-dipping subduction zone. The accretion of the Guerrero Arc to the Mexican continental mainland (Sierra Madre Terrane) caused the deposition of a siliciclastic unit (La Escondida Phyllite), which recycled detritus from the volcaniclastic and siliciclastic underlying strata.

Geology of the volcano-sedimentary complex of the Kaminnyi Potik Unit on Chyvchyn Mountain (Ukrainian Carpathians): preliminary results

The Kamyanyi (Kaminnyi) Potik Unit (Nappe) is the most internal and structurally-highest unit of the Fore-Marmarosh units, and in many places is directly covered by the Marmarosh Nappes of the Marmarosh Crystalline Massif. Chyvchyn Mount is built of this unit and forms a separate tectonic cap (Chyvchyn Mt. Klippe). It consists of the Upper Jurassic/lowermost Cretaceous Chyvchyn Formation, composed mainly of basic volcanic rocks, and the Tithonian-Early Cretaceous Kamyanyi Potik Formation, represented by calcareous and/or turbiditic deposits containing volcanic material. Geological mapping showed that this complex forms a tectonic klippe, which consists of four small tectonic thrust slices. Structurally, the lowermost one is represented by thin-bedded micritic limestones with cherts, and is interbedded with coarse/fine-grained calcareous pyroclastic turbidites (flysch). The second thrust slice is composed of calcareous-pyroclastic breccia with blocks of limestone, basalt, and chert (radiolarite?), which occur within a pyroclastic matrix and of coral limestones with basalt fragments and pyroclastic intercalations. The third thrust slice is constructed of breccia with a pyroclastic and volcanic matrix and clasts of effusive rocks and limestone. The fourth thrust slice – the highest – is represented by massive basaltic pillow lavas. Sedimentologically, the volcano-sedimentary complex represents a whole spectrum of marine mass-movement deposits, from debris flows through proximal turbidites to distal ones, which were formed during latest Jurassic/earliest Cretaceous time in the Outer Dacide-Severinide part of the Carpathian basins.

Study of Calc-Silicate Rocks of Hammer-Head Syncline from Southern Sandmata Complex, Northwestern India: Implications on Existence of an Archaean Protolith

Abstract Existence of an Archaean protolith is suggested in present study from an ensemble of rocks named as Sandmata Complex from northwestern India which have a debatable stratigraphic status of Archaean vs. Proterozoic. Rocks of the Sandmata Complex are represented by a highly metamorphosed volcano-sedimentary complex with multiple cycles of deformation. The manifold tectono-thermal events have obscured the pristine character of the protoliths. In this work we present geochemical features of calc-silicate protolith that show consistent Archaean affinity in the Hammer-Head Syncline (HHS) from southern part of the Sandmata Complex. Notable geochemical characteristics of calc-silicate metasediments in the HHS include high Th/U, high Cr concentrations, high La/Th, moderate La/Yb, and weak positive Eu anomaly. Carbon and oxygen stable isotope compositions of these carbonate metasediments vary between −3.0 and −0.3‰ (δ13Ccarb),-11.6 and −35.0 (δ13Corg) and −19.1 and −13.4‰, (δ18O) respectively. These geochemical observations are in conjunction with the recently published Neoarchaean ages from the HHS and the proximal Hooke syncline.

Petrology and geochemistry of the Cretaceous granitoid magmatism of Central Kamchatka, exemplified by the Krutogorova and Kol’ intrusive complexes

The problem of the geochemical classification of granitoid magmatism in the zone of interaction of oceanic and continental plates is considered in this paper by the example of Mesozoic granitoids of the Krutogorova and Kol’ intrusive complexes of the Sredinny Range, Kamchatka. Based on new geological, petrological, and geochemical data (including the Sr, Nd, and Pb isotope systematics of rocks), it was shown that the protoliths of the granitoids were volcanic-terrigenous sequences accumulated within a Cretaceous marginal basin in the eastern Asian continent. The granitoids crystallized at ∼80 Ma (SHRIMP U-Pb age) under the conditions of the andalusite-sillimanite depth facies corresponding to a pressure of approximately 2 kbar and induced contact metamorphism in the host sequences, which are made up of sediments with sheetlike bodies of mafic and ultramafic volcanics (Kikhchik Group and its metamorphic analogues of the Kolpakova, Kamchatka, and Malki groups). The lower age boundary of sedimentation of the host sequences and the time of basic volcanism coincide with the beginning of the formation of the Okhotsk-Chukotka volcanic belt. Such a correlation is not accidental and reflects a genetic connection between the processes of magmatic activation in the continental-margin sedimentary basin and the formation of the continental margin volcanic belt in eastern Asia. The development of basic volcanism in the sedimentary basin accompanied by the ascent of deep fluids resulted in the entrainment of crustal materials into magmatic processes and the formation of crustal magma chambers, the activity of which was manifested by the eruption of intermediate and silicic lavas and emplacement of shallow granitoid intrusions of considerable areal extent. These intrusions induced contact metamorphism in the enclosing volcanosedimentary complexes. The subsequent Eocene (60-50 Ma) collision processes related to the obduction of the oceanic segment of the crust of the transitional zone onto the Asian continental margin resulted in the tectonic piling of the rocks of Central Kamchatka and strong crustal thickening, which was favorable for its metamorphic alteration reaching the kyanite-sillimanite depth level of the amphibolite facies under the influence of a thermal front and deep fluids affecting lower crustal zones. The Eocene regional metamorphism caused not only metamorphic transformations, migmatization, and granitization in the sequences of the Sredinny Range, which underwent only contact hornfels formation during the first stage, but also metamorphism, migmatization, and extensive foliation in the igneous rocks of the Kol’ and Krutogorova complexes, which were transformed into gneissic metagranites.

Alkaline rocks of Meso-Cenozoic volcanosedimentary complex of the West Siberian Plate: petrologic composition

This paper is concerned with study of tephriphonolites, rare rocks that have been first found in the pre-Jurassic basement of West Siberia. Based on geological observations of the bedding of different types of volcanics and their geochemical peculiarities, the conclusion about the synchronous occurrence of subalkaline and alkaline volcanism is drawn. This is confirmed by the coexistence of compositionally contrasting volcanics in the borehole section. The hypothesis is put forward that these rocks alternate in the section, as is the case in the Tunguska syneclise of the Siberian Platform. The new data on Sr and Nd isotopy suggest the participation of crustal material in the formation of alkaline rocks. The rift nature of the regional intraplate volcanism is confirmed.

Copper, Zn and Pb soil geochemistry data from the NE domain of the Iberian Pyrite Belt in Portugal: implications for mineral exploration

The area-concentration multifractal modelling of a soil geochemical survey performed in the Alfarrobeira–Chança region (covering the Pulo do Lobo Terrane, PLT, and the Iberian Pyrite Belt, IPB) shows that the upper limit of Cu, Zn and Pb background concentrations in soils over PLT metasediments are c . 20, 55 and 20–30 ppm, respectively. In soils derived from the Volcano-Sedimentary Complex of IPB, the Cu, Zn and Pb regional threshold values are within the 25–45, 40–60 and 20–90 ppm intervals, respectively. The lower limit of Cu, Zn and Pb soil anomalies overlying metasediments are within the 30–50, 90–115 and 45–60 ppm intervals, respectively; over soils with abundant volcanic-derived components those lower limits are scattered in the 30–70, 70–90 and 33–100 ppm intervals. Proximity to mineralized rocks is indicated by Cu, Pb and Zn soil contents above c . 100, 120–150 and 250 ppm, respectively. Most of the anomalies display strong anisotropy. Separation of Cu, Zn and Pb soil anomalies reflects mostly the existence of distinct metal sources related to original compositional differences or to chemical changes developed during Variscan times. Metavolcanics represent the prevailing sources of Cu and, to a lesser extent, Pb; the prevalent sources of Zn are metasediments of the Phyllite-Quartzite (IPB) and Chança (PLT) Groups.

Neoproterozoic–Cambrian stratigraphic framework of the Anti-Atlas and Ouzellagh promontory (High Atlas), Morocco

In the last two decades, great progress has been made in the geochronological, chrono- and chemostratigraphic control of the Neoproterozoic and Cambrian from the Anti-Atlas Ranges and the Ouzellagh promontory (High Atlas). As a result, the Neoproterozoic is lithostratigraphically subdivided into: (i) the Lkest-Taghdout Group (broadly interpreted at c. 800–690Ma) representative of rift-to-passive margin conditions on the northern West African craton; (ii) the Iriri (c. 760–740Ma), Bou Azzer (c. 762–697Ma) and Saghro (c. 760?–610Ma) groups, the overlying Anezi, Bou Salda, Dadès and Tiddiline formations localized in fault-grabens, and the Ouarzazate Supergroup (c. 615–548Ma), which form a succession of volcanosedimentary complexes recording the onset of the Pan-African orogeny and its aftermath; and (iii) the Taroudant (the Ediacaran–Cambrian boundary lying in the Tifnout Member of the Adoudou Formation), Tata, Feijas Internes and Tabanite groups that have recorded development of the late Ediacaran–Cambrian Atlas Rift. Recent discussions of Moroccan strata to select new global GSSPs by the International Subcommissions on Ediacaran and Cambrian Stratigraphy have raised the stratigraphic interest in this region. A revised and updated stratigraphic framework is proposed here to assist the tasks of both subcommissions and to fuel future discussions focused on different geological aspects of the Neoproterozoic–Cambrian time span.

Volcanic-sedimentary complex of Otrozhnaya sheet in the Ust-Belaya Terrane, western Koryakia

New data on the structure and composition of the rock complexes making up the Otrozhnaya sheet of the UstBelaya Terrane are discussed. This sheet is curre ntly regarded as a complete section of the Early Devonian oceanic crust. The U-Pb age of zircon (547 ± 17 Ma) from plagiogranite porphyry that cuts through the ultrama� fic-gabbroic complex indicates that the country rocks are much older. Basalts of volcanic complex are similar to MORBtype rocks. The contact between volcanic and volc anosedimentary complexes is tectonic. No volcanic- cherty association of rocks typical of ophiolites has been established at the base of the sedimentary sequence. The U-Pb age of detrital zircons from the base of this section is 571 Ma. As follows from the composition of terrigenous rocks and the suprasubduction origin of andesitic lavas and tuffs, the rocks of the lower part of volcanosedimentary complex were deposited at the marginal part of the basin near convergent boundary. The remains of conodont ele� ments make it possible to estimate the age of the upper part of the volcanosedimentary complex as Late Devonian. The composition of terrigenous rocks shows that the provenance has abruptly changed. Sporadic rock fragments evidence the erosion of ophiolitic sections. Silurian rocks became the main source of clastic material. This is cor� roborated by redeposited microfauna species and U-Pb age of detrital zircons (~432 Ma). The geochemistry of dacite pebbles from conglomerate indicates that this volcanic rock was formed in a suprasuduction setting. The Ordovician-Silurian island arc could have been a source.

Spectral angle mapping, spectral information divergence, and principal component analysis of the ASTER SWIR data for exploration of porphyry copper mineralization in the Sarduiyeh area, Kerman province, Iran

The study area is located in the southern part of the central Iranian volcano-sedimentary complex (Uromiyeh-Dokhtar belt), southeast of Kerman province. The advanced space-born thermal emission and reflection radiometer (ASTER) shortwave infrared (SWIR) bands enabled the generation of maps designed to represent the presence of minerals such as kaolinite, muscovite, and chlorite which are important in the identification of hydrothermal alteration related to porphyry copper mineralization. The purpose of this paper is to enhance alteration in the Sarduiyeh area, using spectral angle mapper (SAM), spectral information divergence (SID), and principal component analysis (PCA) methods. The individual principal component images generated by directed principal component analysis (DPCA). This investigation resulted in the identification of three groups of alteration minerals, namely: (1) sericite-illite, (2) kaolinite-montmorillonite, and (3) chlorite-calcite-epidote. Results of these methods were validated by field sampling and further laboratory studies. The findings showed that SAM and SID are suitable methods as compared with DPCA for mapping alteration minerals. The altered zones were sampled and subjected to X-ray diffraction (XRD) analysis. The spectra of few samples representing the hydrothermally altered rocks were also measured. Microscopic studies of the thin sections were conducted. Field observations revealed that all of the known copper mineralized localities occur within the interpreted alteration areas.

Stratigraphic review of the Cambrian-Lower Ordovician volcanosedimentary complexes from the northern Montagne Noire, France

The northern Montagne Noire possesses one of the most complete Cambrian-Lower Ordovician successions of West Gondwana. The strata are poorly fossiliferous, metamorphized and disturbed by Variscan tectonism, and their stratigraphic nomenclature dramatically multiplied by the designation of numerous informal units exclusively identifiable in their ownVariscan thrust slices and nappes. This paper presents an updated revision of lithostratigraphic units and volcanic complexes. Special attention is given to crosscutting relationships of the latter and the setting and age of fossiliferous phosphorites, such as the Watsonella crosbyi-bearing phosphatic limestones of the Marcou Formation. This mollusc is key to defining in the next future the Global Standard Cambrian (Terreneuvian) Stage1/Stage2 boundary. The absence of Cadomian tectono-thermal events is documented by meso- and microstructural and metamorphic analyses.