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In the Gasht-Masuleh area in the Alborz Mountains, gabbroic magma intruded Palaeozoic metasediments and Mesozoic sediments and crystallised as isotropic and cumulate gabbros. LREE enrichment points to relatively low degrees of mantle melting and depletion of Ti, Nb and Ta relative to primitive mantle points to an arc related component in the magma. Clinopyroxene compositions indicate MORB to arc signatures. U–Pb zircon crystallisation ages of 99.5 ± 0.6 Ma and 99.4 ± 0.6 Ma and phlogopite 40Ar/39Ar ages of 97.1 ± 0.4 Ma, 97.5 ± 0.4 Ma, 97.1 ± 0.1 Ma, within 2σ error, indicate that gabbro intrusion occurred in the (Albian-)Cenomanian (mid-Cretaceous). As active subduction did not take place in the Cretaceous in North Iran, the small volume mafic magmatism in the Gasht-Masuleh area must be due to local, extension-related mantle melting. Melting was most likely caused by far field effects triggered by roll-back of the Neo-Tethys subducting slab. As subduction took place at a distance of ~ 400 km (present distance) from the Alborz Mountains, the observed arc geochemical signatures must be inherited from a previous subduction event and concomitant mantle metasomatism, possibly in combination with contamination of the magma by crustal material. Highlights: Gasht-Masuleh gabbros calc-alkaline, extensional setting, inherited arc signature (Albian-) Cenomanian, 99 Ma zircon ages 97–98 Ma 40Ar/39Ar phlogopite ages Mantle upwelling and formation of gabbros triggered by Neo-Tethys slab roll-back causing extension [ABSTRACT FROM AUTHOR]

The paper presents the first study of heavy-mineral sand beaches from the Mediterranean coast of Annaba/Algeria. The studied beaches run along the basement outcrops of the Edough massif, which are mainly composed by micaschists, tourmaline-rich quartzo-feldspathic veins, gneisses, skarns and marbles. Sand samples were taken from three localities (Ain Achir, Plage-Militaire and El Nasr). The heavy-mineral fraction comprises between 74 and 91 vol%. The garnets of the beaches are almandine rich and tourmalines vary with respect to their location from schorl to dravite. Tourmaline at Ain Achir and the Plage-Militaire is schorlits, while at El Nasr beach dravite is ubiquitous. The World Shale Average normalised REE of the sands and the basement outcrops reveal: (i) Ain Achir beach: REE pattern of sand and the coastal rocks from the studied beaches reflects a multiple sources; (ii) Plage-Militaire: the sand and the coastal outcrops show similar LREE and a strong enrichment in HREE, suggesting the presence HREE-rich phases found as inclusions in staurolite; (iii) El Nasr: two types of sand patterns are found: one with flat REE pattern similar to the proximal rocks and other one enriched in HREE suggesting a mixed source. [ABSTRACT FROM AUTHOR]

The study presents the first evidence of metamorphosed submarine ashes in the Edough Massif, in northeastern Algeria. It occurs below the greenschist-facies Tellian units that represent the thrusted Mesozoic to Eocene passive paleomargin of northern Africa deposited on thinned continental crust. The metamorphic complex consists of tectonically superposed units composed of gneisses (lower unit) and micaschists (upper unit). At the Cap de Garde, these units enclose an “intermediate unit” composed of micaschists and meter-thick layers of marbles, which are sometimes intercalated with amphibolites. The latter occur as discontinuous small lenses and layers. The amphibolites are parallel to the primary bedding of the marbles and the main foliation. Chemical markers and field observations indicate that they are metamorphic equivalents of basic igneous rocks. The lenticular character, low thickness and multiple intercalations with marine sediments and the unusual high lithium concentrations suggest subaqueous near-source basaltic ash-fall deposits in a marine environment. [ABSTRACT FROM AUTHOR]

The Cumbres Calchaquíes Range forms part of the Famatinian metamorphic basement of the Eastern Sierras Pampeanas. The sedimentary protoliths of the metamorphic sequence were deposited in a marine basin alongside the western margin of Gondwana during the Neoproterozoic. New petrologic, geochemical and thermobarometric data give insight into the evolution of the sedimentary basin, its sediment source area, its later metamorphic overprint and its regional relationship to other parts of the Famatinian basement. The metamorphic series studied here consists of banded schists and gneisses and rare calcsilcate-rocks and migmatites that have been reworked by mid-to deep-crustal metamorphic and tectonic processes. The bulk rock compositions indicate shale, wacke, marl and litharenitic protoliths. The metamorphosed clastic sediments have major and trace element compositions indicating a continental granitoid-dominated source area with low sediment recycling. Low SiO 2 /Al 2 O 3 ratios suggest a relatively low maturity of the sedimentary protoliths. Therefore, the Cumbres Calchaquíes section represents a sequence of turbidity currents with progressive shallowing of the depositional environment, as indicated by quartz- and carbonate-rich sediments. The overall data are consistent with the geodynamic environment of a basin adjacent to a continental magmatic arc as the most probable scenario. Whereas the sedimentary protoliths of the metamorphic basement in the Sierra de Ancasti and Sierra de Aconquija, located ca 100–300 km south of the study area are interpreted as originating in an evolving back-arc basin, our results from the Cumbres Calchaquíes region indicate a sedimentary source in a felsic continental arc with no significant influx of basic rocks. The Famatinian metamorphic evolution of the Cumbres Calchaquíes rocks is of typical Barrow-type, culminating in partial melting of the metasediments. Conventional thermobarometry combined with thermodynamic models (pseudosections) reveal a prograde evolution reaching peak conditions of ca 665 °C/6.1 Kbar. This implies a geothermal gradient of ca 35 °C/km, which is slightly higher than the average for continental crust and suggests a period of crustal thinning, as known from back-arc basins, or additional heat supply by voluminous intrusions. • The metamorphic series studied here consists of banded schists and gneisses. • The bulk rock compositions indicate shale, wacke, marl and litharenitic protoliths. • Thermobarometry reveals peak conditions of ca 665 °C/6.1 Kbar. • This implies a geothermal gradient of ca 35 °C/km. [ABSTRACT FROM AUTHOR]

In order to evaluate depositional environment, provenance and tectonic setting, 19 samples of the metasedimentary rocks of the late Cambrian – early Tremadocian from the north of the Sierra de Narváez, developed at the upper-crustal section of the Famatinian Orogen, together with units of the same ages present at the central portion of the Famatina System (s.l.), the Volcancito and Bordo Atravesado Formations, were petrographic and geochemical analyzed. Although the analyzed metasedimentary rocks were affected by a low grade metamorphic event and locally by thermal metamorphism, the relatively uniform pattern of the REE and trace-element concentrations for the different samples attest nearly isochemical processes related to the metamorphic events, without significant remobilization. The metasandstone from the Sierra de Narváez, with abundance of quartz, feldspar and mainly volcanic fragments, are comparable with those related to a signature of magmatic arc influence. The plagioclase and the typical volcanic quartz point to the dominated volcanic inputs. Taking into account geochemical data, the metasedimentary successions (metapsammite and metapelite) display similar characteristics to those from recent deep-sea turbidite developed in continental arc margins. The presence of black shales facies in the succession, record deepening of the depositional environment due to an overall sea-level rise, denoting an oxygen depletion characteristic of them. The remarkable involvement of volcanic components in the north of the Sierra de Narváez deposits, interbedded as riodacitic to basaltic effusions and as lithic clastic components with the same nature in the metasandstone, allow to indicate that they represent the beginning of the volcanic activity along the Famatina System (s.l.), under the tectonic regime of a continental island arc. • Metasedimentary late Cambrian – Tremadocian successions cropping out at the Famatina System, Sierras Pampeanas. • Chemical composition of metasandstone, metapelite and black metashale. • The sediments underwent simple recycling in an active continental margin. • The sediments were transported and deposited by turbidity currents related to a continental island arc source. • Sedimentation was contemporaneous with volcanic activity. [ABSTRACT FROM AUTHOR]