Geologica Acta
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Read more: www.revistes.ub.edu/index.php/GEOACTA/index
Phone: +34 93 403 19 89
Address: Library of Geology (UB-CSIC) | Faculty of Earth Sciences | University of Barcelona
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Vol 21 by Geologica Acta
The Daralu porphyry shows adakites affinity, that is, high Sr/Y and La/Yb ratios and positive Eu anomalies. The REEs patterns indicate a strong fractionation ([La/Yb]n= 28.73). High La/Sm and Dy/Yb ratios suggest enrichment of amphibole and garnet as residual phases in melt source, whereas partial melting of plagioclase increases Eu and Sr in the parent magma. The presence of garnet implies a pressure equivalent to the thickness of more than 40km of crust.
To elucidate the evolutionary history of fluids and the origin of the Daralu deposit, we focused on the origin and composition of the fluid through petrography, Raman spectroscopy, and microthermometry studies of fluid inclusions. The fluid inclusions have been divided into four types: vapor (type I), aqueous-vapor (type II), CO2- bearing (type III), and multiphase (type IV). The Raman shifts included 1284 and 1388 cm−1 for CO2 and 2750–3900 cm−1 for H2O. The events such as NaCl supersaturation, exhausting of CO2-rich components, high oxygen fugacity and temperature decreasing through mineralization stages were critical in controlling the fertility of the Daralu PCD. The obtained δ34S data for sulfides yielded an average of +5.5‰. Based on the observed features, it was concluded that Daralu porphyry shares formation conditions with other productive porphyries of the KCMA.
Despite the serpentinization of the studied mantle rocks, few relicts of primary chromite, olivine and pyroxene are preserved. Chromite is partly altered having unaltered Al-rich chromite cores surrounded by Fe-rich chromite and Cr-rich magnetite rims. The unaltered Al-rich chromite cores show compositions equilibrated at temperatures mostly below ~500-600°C, which is a temperature comparable to that estimated for primary chromite in greenschist up to lower amphibolite facies rocks. The high Cr# [100×Cr/(Cr+Al)= 47-76] of the unaltered chromite cores and the Mg-rich nature of the olivine relicts (Fo91–94) indicate that the studied mantle rocks were produced from a highly depleted mantle that experienced high degrees of melt extraction (mostly ~30-40%). This range of melt extraction resembles that estimated for supra-subduction zone peridotites, but higher than that in abyssal and passive margin peridotites. Furthermore, the clinopyroxene relicts show compositions comparable to those from the Mariana forearc peridotites. Bulk-rock geochemistry also reflects derivation from an extremely depleted and a highly refractory mantle source. Modeling of rare-earth elements suggests that the studied mantle rocks were possibly formed by the interaction of their highly depleted harzburgitic mantle precursors with subduction-related melts/fluids during their evolution in a fore-arc basin of the supra-subduction zone.
The proposed geodynamic model suggests that the oceanic lithosphere generated during the seafloor spreading of the Mozambique Ocean was emplaced in the upper plate of the intra-oceanic subduction zone, in which the formely depleted Neoproterozoic mantle of the Arabian-Nubian Shield experienced mature phases of hydrous melting, extreme depletion and enrichment.
Vol 20 by Geologica Acta
In accordance with compiled zircon data and taking into account the evidence of North African peri-cratonic inliers, Ediacaran (~610Ma) zircons incorporated in Paleozoic magmas provide indirect evidence of Pan-African magmatism, suggesting that these magmas and synorogenic sediments are likely to constitute the cryptic stratigraphic infrastructure of most of the Iberian Massif. The main source of ~610Ma inherited zircons may be the lateral chrono-equivalents of the Saghro and Bou Salda-M`Gouna Groups (Anti-Atlas, Morocco) and/or coeval igneous rocks from West African Craton or Trans-Sahara Belt, emplaced at a stratigraphic level below the late- Ediacaran sediments of the Ossa Morena Zone and the Central Iberian Zone.
Assuming that the Iberian crust is a fragment of the Pan-African orogen, a relative paleoposition situated between the West African Craton and the Trans-Saharan Belt during the Late Neoproterozoic is proposed. The closed- system behaviour of Stenian-Tonian detrital zircon ages in the Trans-Sahara Belt suggests that this mega-cordillera acted as a barrier, in paleogeographic terms, separating the Sahara Metacraton from Iberia. In Iberia, the opening of the system to Stenian-Tonian detrital zircons during the Ordovician indicates that, at that time, the Trans-Saharan Belt had already become a vast peneplain, which favoured a large drainage system with a long-distance transport mechanism that fed the passive continental margins.
have been described from the Frasnian through the Famennian in eastern Laurussia. However, those previous specimens were retrieved through palynological preparations and more closely resemble sheath structures rather than the full forms found herein, which were retrieved through complete maceration with ammonium surfactants.
The Daralu porphyry shows adakites affinity, that is, high Sr/Y and La/Yb ratios and positive Eu anomalies. The REEs patterns indicate a strong fractionation ([La/Yb]n= 28.73). High La/Sm and Dy/Yb ratios suggest enrichment of amphibole and garnet as residual phases in melt source, whereas partial melting of plagioclase increases Eu and Sr in the parent magma. The presence of garnet implies a pressure equivalent to the thickness of more than 40km of crust.
To elucidate the evolutionary history of fluids and the origin of the Daralu deposit, we focused on the origin and composition of the fluid through petrography, Raman spectroscopy, and microthermometry studies of fluid inclusions. The fluid inclusions have been divided into four types: vapor (type I), aqueous-vapor (type II), CO2- bearing (type III), and multiphase (type IV). The Raman shifts included 1284 and 1388 cm−1 for CO2 and 2750–3900 cm−1 for H2O. The events such as NaCl supersaturation, exhausting of CO2-rich components, high oxygen fugacity and temperature decreasing through mineralization stages were critical in controlling the fertility of the Daralu PCD. The obtained δ34S data for sulfides yielded an average of +5.5‰. Based on the observed features, it was concluded that Daralu porphyry shares formation conditions with other productive porphyries of the KCMA.
Despite the serpentinization of the studied mantle rocks, few relicts of primary chromite, olivine and pyroxene are preserved. Chromite is partly altered having unaltered Al-rich chromite cores surrounded by Fe-rich chromite and Cr-rich magnetite rims. The unaltered Al-rich chromite cores show compositions equilibrated at temperatures mostly below ~500-600°C, which is a temperature comparable to that estimated for primary chromite in greenschist up to lower amphibolite facies rocks. The high Cr# [100×Cr/(Cr+Al)= 47-76] of the unaltered chromite cores and the Mg-rich nature of the olivine relicts (Fo91–94) indicate that the studied mantle rocks were produced from a highly depleted mantle that experienced high degrees of melt extraction (mostly ~30-40%). This range of melt extraction resembles that estimated for supra-subduction zone peridotites, but higher than that in abyssal and passive margin peridotites. Furthermore, the clinopyroxene relicts show compositions comparable to those from the Mariana forearc peridotites. Bulk-rock geochemistry also reflects derivation from an extremely depleted and a highly refractory mantle source. Modeling of rare-earth elements suggests that the studied mantle rocks were possibly formed by the interaction of their highly depleted harzburgitic mantle precursors with subduction-related melts/fluids during their evolution in a fore-arc basin of the supra-subduction zone.
The proposed geodynamic model suggests that the oceanic lithosphere generated during the seafloor spreading of the Mozambique Ocean was emplaced in the upper plate of the intra-oceanic subduction zone, in which the formely depleted Neoproterozoic mantle of the Arabian-Nubian Shield experienced mature phases of hydrous melting, extreme depletion and enrichment.
In accordance with compiled zircon data and taking into account the evidence of North African peri-cratonic inliers, Ediacaran (~610Ma) zircons incorporated in Paleozoic magmas provide indirect evidence of Pan-African magmatism, suggesting that these magmas and synorogenic sediments are likely to constitute the cryptic stratigraphic infrastructure of most of the Iberian Massif. The main source of ~610Ma inherited zircons may be the lateral chrono-equivalents of the Saghro and Bou Salda-M`Gouna Groups (Anti-Atlas, Morocco) and/or coeval igneous rocks from West African Craton or Trans-Sahara Belt, emplaced at a stratigraphic level below the late- Ediacaran sediments of the Ossa Morena Zone and the Central Iberian Zone.
Assuming that the Iberian crust is a fragment of the Pan-African orogen, a relative paleoposition situated between the West African Craton and the Trans-Saharan Belt during the Late Neoproterozoic is proposed. The closed- system behaviour of Stenian-Tonian detrital zircon ages in the Trans-Sahara Belt suggests that this mega-cordillera acted as a barrier, in paleogeographic terms, separating the Sahara Metacraton from Iberia. In Iberia, the opening of the system to Stenian-Tonian detrital zircons during the Ordovician indicates that, at that time, the Trans-Saharan Belt had already become a vast peneplain, which favoured a large drainage system with a long-distance transport mechanism that fed the passive continental margins.
have been described from the Frasnian through the Famennian in eastern Laurussia. However, those previous specimens were retrieved through palynological preparations and more closely resemble sheath structures rather than the full forms found herein, which were retrieved through complete maceration with ammonium surfactants.
essentially of clinopyroxene, olivine, and plagioclase. These basalts display alkaline affinity and negative Ta, Zr, Rb anomaly, but slightly negative Nb anomaly, relative to elements with similar compatibility, and positive Ba, K,
Sr anomaly, suggesting their magma source related to subduction-accretion with implication of subducted slab derived components to the source. In the primitive mantle and chondrite normalized diagrams, these rocks show trace elements (except depletion in Nb, Ta) and Rare Earth Element (REE) patterns similar to the Ocean Island Basalts (OIB) and share trace and major element characteristics similar to High-Nb Basalts (HNBs). Geochemical analyses for major and trace elements suggest that the Shahr-e-Babak HNBs have undergone insignificant crustal contamination and minor olivine + Fe-Ti oxide ±clinopyroxene fractional crystallization. These HNBs derived from a partial melting (~5%) of garnet-peridotite mantle wedge, which have already metasomatized by overlying sediments, fluids, and adakitic (slab-derived) melts as major metasomatic agents in post-collision setting in the KCMA. We conclude that asthenospheric upwelling arising from slab break-off followed by the roll-back of subducting Neotethys slab also triggered metasomatized peridotite mantle wedge and caused its partial melting in the subduction zone.
biostratigraphy is presented herein. This work was performed in shallow marine siliciclastics rich in larger
foraminifera, around the Ypresian/Lutetian boundary in the Ésera valley (South-Central Pyrenees). Although the
calcareous nannofossil content in the studied interval is low, not allowing a precise Y/L boundary to be recognised,
the taxa found are enough to support the chronostratigraphic attribution.
Data obtained in the Ésera valley section has improved the knowledge of larger benthic foraminifera (Nummulites
and Assilina) distribution through chron C21. SBZ 11 to SBZ 12 transition took place at the lowermost C21r, as
shown in previous works. SBZ 12 assemblages extend into C21n, where the SBZ 12 to SBZ 13 boundary occurs.
These data, obtained in shallow marine siliciclastic facies, with in situ fauna, results in a shift of the SBZ 12/SBZ
13 boundary to the Lower Lutetian, younger than previously believed. Accordingly, the Ypresian/Lutetian boundary
occurs in SBZ 12.
Discrepancies on formation temperature for chlorites located at different positions within the veins are discussed, concluding that veins grew in a low fluid/rock ratio regime. V1 veins can be related to the Late Ordovician
synsedimentary faulting episode as revealed by their distribution patterns, formation mechanisms, and fluid-rock interactions. We propose an Alpine age for the V2 veins, based on their structure and the emplacement conditions of 318±12°C and 2.4±0.2kbar, with an estimated geothermal gradient of 34°C∙km-1 and a burial depth of ca. 9km. Results obtained here are compared with other quartz veins spread throughout the Palaeozoic basement of the Eastern Pyrenees.
Formation, which has not yet been investigated in detail. A total of 166 core and cutting samples were selected
from four wells in the Dezful Embayment to investigate the organic geochemical and mineralogical compositions,
as well as the shale oil potential of the BSU. X-Ray Diffraction (XRD) results show that it is mainly comprised
of calcite (53wt.%), clay minerals (25wt.%) and quartz (14wt.%). Total Organic Content (TOC) values generally
range from 1 to 9wt.% (avg. 4.2, 2.9, 5.2 and 3.3wt.%, for GS, KR, RR and RS wells, respectively) with Hydrogen
Index (HI) values ranging between 400 and 650mg HC/g TOC. Based on average values of Tmax and vitrinite
reflectance, as well as saturate biomarker ratios, the BSU is immature at wells RR and RS (ranging from 0.3 to
0.53%) and its maturity increases northward at wells KR and GS (ranging from 0.5% to 0.67%). The organic
matter is dominated by Type ΙΙ kerogen and is generally composed of liptinite and amorphous material with minor
terrestrial input. Based on various biomarker parameters, the organic matter was most likely deposited under
anoxic marine conditions. The favorable mineralogical composition (i.e. presence of brittle minerals) and organic
geochemical properties (i.e. TOC>2wt% and Type II kerogen) support the conclusion that the Pabdeh BSU displays
a considerable shale oil potential where it attains appropriate thermal maturity.
All genera and some species are known to have extant representatives. Aetobatus cappettai antunes and balbino, 2006, is described now from Langhian material which suggests it is older than previously supposed. The biogeographic ranges, environmental constraints and behaviour of the species described in this study point out to an infralittoral environment characterized by the dominance of warm water conditions, where episodic upwelling contributed to the occurrence of different types of batoids coexisting in the same habitat.
zone between Arabia and Anatolia. The Adıyaman fault is a major splay from the East Anatolian Fault (EAF),
one of the most important tectonic structures in the Eastern Mediterranean region. These faults are consequence
of the collision between the Arabian and Anatolian plates and the resulting westward tectonic escape of Anatolia.
Although the EAF has been intensively studied since its discovery in the late 1960s, little is known about the
Adıyaman fault and its tectonic activity. In this study, we extract geomorphic indices including mountain-front
sinuosity (Smf), valley floor width-to-height ratio (Vf), stream length-gradient (SL), catchment Asymmetry Factor
(AF) and hypsometric integrals and curves (HI and HC) to evaluate the relative tectonic activity of the Adıyaman
fault. These three geomorphic indices (AF, HI, and HC) are averaged to define an index for Relative Tectonic
Activity (RTA) that allows the Adıyaman fault to be divided into categories of low, moderate and high RTA.
The results confirm that the Adıyaman fault is an active fault with high to moderate Quaternary tectonic activity.
However, this fault is of minor importance on accommodating plate boundary deformation, as evidenced by the
recent crustal motions determined by GPS studies. Nevertheless, it is worthwhile to note that the Adıyaman fault
still poses a significant seismic hazard for the region despite its relatively moderate tectonic activity.
This work presents a phase equilibria study in a high-K2O granodioritic system. A series of experiments were conducted with a granodioritic composition (GEMbiot) to study the crystallization sequence at the emplacement conditions in the Gredos massif, i.e. 4 H2O wt.% and 0.4GPa. Experimental results show that orthopiroxene is the liquidus phase at 1010ºC, which reacts with the H2O-rich melt to stabilize biotite between 980 and 940ºC. Plagioclase crystallizes at around 910ºC, and K-feldspar crystallizes in the matrix between 750 and 700ºC when the crystal fraction is around 0.5. However, at 850ºC, a pelite-doped experiment shows euhedral K-feldspar (≈5vol%) in both the reactive xenolith domain together with cordierite and the granodioritic domain, where the K2O wt.% rose from 4.5 in the normal experiment to 5.9 in the doped experiment. These results suggest that the bulk-assimilation process promotes the bulk and heterogeneous K2O enrichment in a huge granodioritic magma volume, which triggers an early crystallization of K-feldspar megacrysts. Because of this early crystallization of the megacrysts, the magmatic foliations defined by K-feldspar megacrysts are formed during and after the emplacement processes and are highly influenced by tectonic kinematics.
New whole rock geochemical analysis performed in seven samples of metatonalites and fourteen samples of metagranodiorites are characterized by: i) slight enrichment in incompatible elements (Rb, Ba, Th, U), ii) negative anomalies in Nb, Ta, P, and Ti, and iii) negative anomalies in Eu. These chemical features are in agreement with a subduction-related setting for the genesis of both types of magma, which is also supported by chemical discrimination using tectonic setting diagrams. Positive anomalies of Pb suggest a crustal component. The new geochemical data reveal that the convergent orogen that ruled the paleogeography of the Gondwana periphery during the Neoproterozoic (Cadomian orogen) remained active beyond the Neoproterozoic-Cambrian transition, up to at least late Cambrian times.
Large-scale folds and boudins cause dome-like undulations in the detachments, which are inferred to overlap in time with the deformation in the shear zones. One shear zone in the eastern part of the orogen is top-N; the other, in the western part, is top-E. The change in the shear direction may represent a temporal evolution in the direction of shear, possibly related to a change in the subduction direction in space and time.
pressure solution with a predominant NE to ENE trend. Observed relationships and structural analysis suggest an obliquity between the here inferred direction of the Late Jurassic-Early Cretaceous stretching (i.e. about N015E) and the onshore boundary faults, whereas the contractional structures are broadly parallel to the NE-striking Conejera Fault and suggest a roughly SSE- to SE-oriented Alpine convergence.
The geochemical characteristics of the study rocks, particularly their high Sr/Y ( 51.6-136.8) at low Y ( 4.43–16.2ppm) and high La/Yb ( 28.4–118.4ppm) at low Yb ( 0.2–1.3ppm), are coherent with a high silica adakitic signature. The whole-rock positive Eu/Eu* anomaly and zircon Ce/Ce* anomaly reflect the effects of an oxidized magmatic signature where the rocks of the study area originated from a mantle source. The high silica adakite geochemical characteristics of the Chenar volcanic cone support formation by partial melting of the modified mantle under the influence of metasomatized subducted oceanic slab in a post-collisional environment.