ENE-WSW Direction Research Articles

Rifting and Lifting Neogene Age in Biak-Yapen Basin Based on Structural Trajectory Analogy in Biak and Supiori Island

The aim of this study is to calculate the rifting and lifting phase of Neogene age in the Biak - Yapen Basin region, related to the prediction of an oil and gas trap zone based on the analogy of the surface measurement trajectory. The methodology used is the measurement of geological structures on the surface and in the data analysis using Delvaux, 1997 and Zoback, 2007 concept. Based on the structure measurement in outcrop, there are 78 stations along Biak Island and Supiori Island, which will be used and projected as an analogy to the offshore basin. Statistically in the archipelago shows that there are three times rifting phase domination candidates categorized as maximum intensity and a lifting phase candidates are also categorized as maximum intensity. There are three times rifting phase with movement direction, σ-3 is relatively horizontal, consisting of NE-SW direction with an intensity of 15.60% rifting aged Middle to Late Miocene, ENE-WSW direction with intensity 13.30% rifting aged Late Miocene to Pliocene and finally from the W-E direction with an intensity of 17.80% rifting aged Pleistocene. The three rifting phases are followed by sedimentation of carbonate rock from the Middle Miocene to the Pleistocene aged which consists of Napisendi Fm, Korem Fm, Wardo Fm, and Mokmer Fm. The lifting phase once occurred with the compressional direction, σ-1 is relatively horizontal, directed at W-E with an intensity of 21.20% lifting aged Pleistocene to Resen. This phase has elevated formations from the age of the Late Oligocene to the Pleistocene in the archipelago.

Characterization, origin, and evolution of one of the most eroded mafic monogenetic fields within the central Andes: The case of El País lava flow field, northern Chile

El País is a monogenetic lava flow field located 16 km southeast of Peine town in the Altiplano-Puna area, Antofagasta region, Chile. El País is a monogenetic lava flow field located 16 km southeast of Peine town in the Altiplano-Puna area, Antofagasta region, Chile. El País is composed by lava flows of small-to-moderate volumes, which are fed from individual point sources unassociated with a central volcano of large-volume (stratovolcano) typical of the Andean arc. This lava flow field was emplaced in an area dominated by thin-skinned deformation under a compressive tectonic regime, where multiple volcanic centers (monogenetic and polygenetic volcanoes) have been developed. The volumetric and chemical evolutions were determined by fieldwork, stratigraphic, morphometric, textural (density and vesicularity), petrographic, and geochemical analyses. El País can be divided into three principal mafic lava flows such as Northern-, Main-, and Western-lava flows, which display an E-W orientation. Besides, at least eight ephemeral vents were identified as small erosion remnants of lava emitting point-sources. The identified vents are principally aligned in an ENE-WSW direction, east of the Main lava flow. It is inferred that El País was emplaced near-simultaneously above two ignimbrite sheets: Tucúcaro Ignimbrite (3.2 Ma) and Patao Ignimbrite (3.1 Ma). Stratigraphically, the Main lava flow has a surface texture with strong similarities to an ʻaʻā lava flow, composed of three unique layers well distinguishable in the field such as i) Basal, ii) Top auto-breccia, composed of sub-angular scoriaceous and dense clasts in an oxidized matrix, and iii) A single core between both auto-breccias, composed of dense lavas, exhibiting multiple cooling jointing, such as vertical to platy jointing. The advanced stage of erosion since the formation of El País is evidenced by the poorly preserved lava flows (flat morphology), upper auto-breccia layer, and the presence of large sub-angular blocks of lava (vesicular and dense) along the axis of the lava flows. The eruptive products are geochemically basaltic andesite (Main lava flow and ephemeral vents) and andesite (specifically in the Northern lava flow), making the lava flow field one of the most mafic in the broader region. The lava presents a glomeroporphyric texture, showing at least three different glomerocrysts: i) Plagioclase + clinopyroxene having reabsorption boundaries, ii) Clinopyroxene with reabsorption boundaries, and iii) Plagioclase with sieve-texture. The groundmass is principally composed of glass, plagioclase microlites with a low orientation preference, and opaque minerals (magnetite). This study helps understand the development of dispersed-monogenetic-volcanism (e.g., Tilocálar complex and Cerro Tujle maar), and its relationship with neighboring polygenetic volcanism (e.g., Toloncha stratovolcano) in the Central Volcanic Zone of the Andes, northern Chile.

LITOGEOQUIMICA E QUÍMICA MINERAL DAS ROCHAS DO MACIÇO CORREAS

O Maciço Correas está localizado na região sul do estado de São Paulo, relacionado à evolução da granitogênese neoproterozoica na parte norte do Terreno Apiaí e encontra-se intrusivo nas rochas encaixantes da sequência metavulcanossedimentar da Formação Água Clara, do Supergrupo Açungui e em rochas do Complexo Granítico Três Córregos. Constitui um stock granítico alongado de 5 km2 na direção ENE-WSW e apresenta mineralizações associadas de cassiterita e a volframita. É caracterizado pelas fácies biotita monzogranito porfirítico, biotita-muscovita sienogranito porfirítico, muscovita-zinnwaldita-albita granito porfirítico com topázio e pegmatito. Análises de química mineral revelam a presença de biotita e muscovita nas fácies graníticas mais antigas e comprovam o caráter sódico dos plagioclásios (albita) e variação na composição das micas, de muscovita a predominantemente na zinnwaldita na fácies muscovita-zinnwaldita-albita granito porfirítico com topázio. São rochas peraluminosas pertencentes às séries cálcio-alcalina monzogranítica de alto potássio a shoshonítica a alcalina sódica. O magmatismo é compatível com granito do tipo A, rapakivi, pós-colisional a anorogênico associado a um ambiente intraplaca a um ambiente sin- a pós-colisional de arco magmático, com colocação em estruturas transtensivas correlacionadas à Zona de Cisalhamento Itapirapuã, em ambiente extensional no final do evento colisional da Orogênese Ribeira.

Relocation, Focal Mechanisms and Stress Field Characteristics of Earthquake Swarms in the Songyuan Area of Jilin Province, China

Two earthquake swarms, the Qianguo swarm and Ningjiang swarm, have been observed since 2013 in the Songyuan area, Jilin Province, China. Using the seismic data of broadband permanent and temporal stations that recorded a larger number of earthquakes in the two swarms, we analyze the distribution of aftershocks and the focal mechanisms of these earthquakes and investigate the stress field and faulting properties of the Songyuan area. The relocated hypocenters of the Qianguo earthquakes are distributed along a NNW direction at focal depths of 4–13 km, while the dominant distribution of relocated Ningjiang earthquakes is along a NE direction at depths of 8–16 km. The focal mechanism solutions of 36 earthquakes with ML ≥ 3.6 demonstrate a combined strike-slip and thrust faulting mechanism with centroid depth concentrated at 3–7 km for the Qianguo swarm and a strike-slip mechanism with centroid depth at 5–7 km for the Ningjiang swarm. The full moment tensors of seven moderate–strong earthquakes show that these earthquakes contain a high percentage of non-double-couple components. The regional stress field is inverted using the focal mechanism parameters of the 36 earthquakes. In the Qianguo area, the horizontal maximum principal compressive stress ( $$\sigma_{1}$$ ) is in the E–W direction with a dip angle of 14.1°. In the Ningjiang area, the $$\sigma_{1}$$ is in the ENE–WSW direction with a dip angle of 9.2°. The $$\sigma_{1}$$ directions of the two areas are slightly different, but both approximately along an E–W direction. The comprehensive results of this study show that the Qianguo swarm is likely caused by the movement of a buried fault in the NNW direction oblique to the Changling–Dashanzi fault, whereas the Fuyu–Zhaodong fault in the NE direction is responsible for the Ningjiang swarm. Both the Qianguo and Ningjiang swarms are probably closely related to the thrusting effect of the subduction of the Pacific Plate into the Northeast Asian continental margin and the complex geological conditions in the Songyuan area.

Structural and hydrothermal alteration mapping related to orogenic gold mineralization in part of Kushaka schist belt, North-central Nigeria, using airborne magnetic and gamma-ray spectrometry data

This paper presents an interpretation of airborne magnetic and gamma-ray spectrometry data over a part of the Kushaka schist belt of Nigeria with a view to assess the sub-surface structural framework and hydrothermal alteration haloes that are related to orogenic gold mineralization in the study area. The geophysical analyses performed to improve the quality of the aeromagnetic data for better understanding of the subsurface geology were reduction to the equator, upward continuation, total horizontal derivative, analytical signal, source edge detection, tilt-angle derivative of total horizontal derivative. The analyses performed on the airborne gamma-ray spectrometry data were made on K/eTh, F parameter and deviation of ideal K values (Kd). Deep-seated, brittle–ductile shear/fracture zones with characteristic depth of 428.0–607.6 m and area extent of 15.5 km by 6.5 km that were delineated in the area coincide with beehive of artisanal miners exploiting gold deposits. In this study, subsurface geologic structures, specifically dykes/faults, that trend in the ENE–WSW direction constitute a first-order control on orogenic gold mineralization in the study area. The hydrothermally altered zones mapped in the area indicated they are structurally controlled and closely associated with orogenic gold mineralization. Apart from geologic structural evidences that are controlling orogenic gold mineralization, this study has indicated that hydrothermal alteration mapping is equally important for a promising orogenic gold mineralization mapping.

Magnetite compositions from the Baba Ali iron deposit in the Sanandaj-Sirjan zone, western Iran: Implications for ore genesis

The economically significant Baba Ali iron ore deposit, is located in the Sanandaj-Sirjan zone, western Iran, is associated with diorite. The mineralization trends in a ENE-WSW direction with thickness that varies from 30 m up to 50 m and a length of about 250 m. The main mineral assemblages are massive magnetite, epidote, actinolite, tourmaline, quartz, calcite, and pyrite. Using different magnetite compositional discrimination diagrams, the low concentrations of Ti (0.11 wt%), Al (0.06 wt%), Cr (19.62 ppm), and Co (20.26) and high Ni/Cr ratios (6.34) are consistent with a hydrothermal origin, similar to typical skarn mineralization. The different elemental compositions of various magnetite generations might be due to an ore-forming fluid that initially a high-T magmatic hydrothermal character, then evolved to a lower temperture meteoric water dominated system. It seems that Fe-bearing saline fluids infiltrated the carbonate host rocks, causing high temperature, acid metalliferous fluids to become neutralized during reaction with carbonates, causing a decrease in iron solubility and saturating as a magnetite with increasing pH and decreasing the temperature. The close spatial and temporal association of the mineralization with the fracture systems suggests that a pressure decrease also had a significant impact on the iron solubility, triggering ore precipitation and replacement at relatively low temperatures (~300 °C), under reducing conditions.

Mapping of subsurface structural features in some parts of Anambra Basin, Nigeria, using aeromagnetic data

Aeromagnetic data of some parts of Anambra Basin, Nigeria, covering Illushi, Nsukka, Igumale, Onitsha, Udi and Nkalagu areas were digitally processed, analyzed and interpreted qualitatively and quantitatively. The study was carried out to delineate the subsurface structural lineaments/trends that provide the locales for mineral deposit and hydrocarbon resources and to estimate the depth to magnetic sources/sedimentary thickness of the area. The data were qualitatively interpreted using reduction to equator-inverted (RTE_INV), vertical derivatives (VD), tilt derivative (TDR) filter, lineament density filter and Rose plot. Quantitative interpretation was done using source parameter imaging and Euler deconvolution methods. The results depicted that the study area has enormous structural lineaments especially in the northeast and northwest that showed a high cluster of these lineaments. The results showed that the trends of the structural lineaments have a dominance of NE–SW direction, with ancillary trends in E–W, NW–SE, N–S, NNE–SSW and ENE–WSW directions. The SPI depth result ranges from 318.45 m for shallow magnetic sources to − 11,253 m for sedimentary thickness. The 3D Euler deconvolution depth estimate revealed depths to magnetic sources ranging from − 400 to − 4300 m. The results show good evidence of the presence of the essential factors for the exploration of both mineral deposits and hydrocarbon resources in the study area.

GEOLOGIA DO MACIÇO CORREAS, SUL DO ESTADO DE SÃO PAULO

O Maciço Correas localiza-se na região sul do estado de São Paulo, no distrito de Itaboa, município de Ribeirão Branco e encontra-se relacionado à evolução da granitogênese neoproterozoica da Província Mantiqueira Central, inserido na porção centro-sul do Cinturão Ribeira e na parte norte do Terreno Apiaí. Destaca-se na literatura geológica devido a sua correlação com a ocorrência de greisens mineralizados em cassiterita e volframita, que constituem o depósito polimetálico do Bairro dos Correas. O corpo abrange uma área de um stock granítico de aproximadamente 5 km², de forma elipsoidal alongada na direção ENE-WSW e intrusivo em rochas metavulcanossedimentares da Formação Água Clara, pertencente ao Supergrupo Açungui e em rochas do Complexo Granítico Três Córregos. As rochas graníticas estão representadas por variedades de coloração cinza a rósea, isotrópicas e porfiríticas e distintas em três fácies denominadas de biotita monzogranito porfirítico, biotita-muscovita sienogranito porfirítico, mica-albita granito porfirítico com topázio e a fase pegmatítica.

Upper Mantle Anisotropy beneath the Western Segment, NW Indian Himalaya, Using Shear Wave Splitting

Abstract This study investigates the upper mantle deformation pattern beneath the Indo-Eurasia collision zone utilizing the core-refracted (S(K)KS) phases from 167 earthquakes recorded by 20 broadband seismic stations deployed in the Western Himalaya. The 76 new shear wave splitting measurements reveal that the fast polarization azimuths (FPAs) are mainly oriented in the ENE-WSW direction, with the delay times varying between 0.2 and 1.7 s. The FPAs at most of the stations tend to be orthogonal to the major geological boundaries in the Western Himalaya. The average trend of the FPAs at each station indicates that the seismic anisotropy is primarily caused due to strain-induced deformation in the top ~200 km of the upper mantle as a result of the ongoing Indo-Eurasian collision. A contribution from the mantle flow in the direction of the Indian plate motion is possible. The mantle strain revealed in the present study may be due to a combination of basal shear resulting from plate motion and ductile flow along the collision front due to compression.

Contribution of bedding to the petrophysical characterization of naturally fractured reservoirs: Example of the Matachines fields, Upper Magdalena Valley (Valle Superior del Magdalena – VSM) Colombia

The Matachines field, located in the Girardot subbasin, Upper Magdalena Valley (Valle Superior del Magdalena – VSM) basin, has a morphology characterized by antiforms arranged along a N–S axis. These antiforms involve multiphase tectono-sedimentary sequences with half-graben geometries associated with Mesozoic sequences reactivated by at least three Andean phases. Bedding surfaces are mechanically active planes that contribute to the flexural slip that is generated by the folding of multilithologic sequences. In the Matachines field, the bedding planes help to improve the petrophysical characteristics of the reservoirs by incorporating a significant number of discontinuities, which complement the fluid connectivity. Thus, the subhorizontal planes are linked to subvertical fractures preferentially arranged in the ENE–WSW direction, generated by horizontal compressive stress. In particular, these effects are magnified on the western flank and hinge zone of the anticline structure, where they contribute greatly to the connectivity of the production wells. In naturally fractured reservoirs, the correct 4D technical and economic evaluation of the quality and arrangement of discontinuities is essential to determine their actual contribution to improving the petrophysical properties of such reservoirs. Accordingly, many methods often used to study wells from core samples or images identify, along with different types of fractures, the presence of bedding surfaces, although they evaluate them separately, so they overlook petrophysical factors that affect the porosity and permeability of the wells. The present study discusses the genetic and morphological aspects of bedding surfaces that enhance the petrophysical potential of reservoirs, which usually have limited primary values of permeability and porosity, to meet the economic expectations of specific resources in hydrocarbon exploration and/or production activities.

Curvature interpretation of gravity data for delineating structural features across the transition zone of Narmada–Son lineament in central India

Potential-field anomalies can be converted to a common function which describes the ridge, peaks over an isolated source. In this study, attempt has been made to interpret curvature attributes of equipotential surface using gravity gradients for delineating thrust–fault locations in one of the seismically active transition zones of Narmada–Son Lineament (NSL) in central India. The NSL is oriented in the ENE–WSW direction, divides the area into two geological provinces. The northern part of this NSL comprises Vindhyan formations and southern part covers Gondwana formations. It has been observed that, the northern part (around Jukehi) of the area has higher elevation with lower gravity anomaly and the southern part (around Khamaria and Kataria) has lower elevation with higher gravity anomaly. The tectonic activities like intrusions, volcanisms and earthquake occurrences were the sources of crustal resettlement during the past in this area. Various researchers commented about the structural configuration; however, the present study helps to understand the structural features using various curvature analysis like maximum, minimum, most-positive, most-negative, mean, dip (profile), strike (tangential), contour (plan), curvedness, shape index and Gaussian curvatures. Out of these curvatures most positive, maximum, mean, dip and curvedness show more effective results compared to other curvatures. However, shape index states domes, ridge, flat, valley, bowl shape type structures. The results are also correlated with the conventional horizontal gravity gradient, analytic signal and tilt derivative analysis. The colour contrast variation of these differential curvatures make in-depth understanding with extensive multiplicities of integrity for delineating subsurface structures.

Chapter 12 Dolerites (1.27–1.25 Ga) and alkaline ultrabasic dykes ( c. 1.14 Ga) related to intracratonic rifting

Abstract Doleritic sills, lopoliths and dykes were emplaced into the Paleoproterozoic craton in central Sweden at 1271–1264, 1259–1256 and c. 1247 Ma, a complex temporal zonation occurring in a WSW–ENE direction. The dolerites are subalkaline to alkaline and show predominantly gabbroic, with a trend towards monzogabbroic and quartz monzodioritic, compositions. Positive ɛ Nd and ɛ Hf values suggest a significant depleted mantle component in the source volume of the parental magmas. Dyke orientations indicate extension, at least locally, in a northwesterly direction, consistent with a magma flow direction determined using the anisotropy of magnetic susceptibility values. Intracratonic rifting linked to the break-up of the supercontinent Columbia, back-arc extension above a subduction boundary in a westwards-retreating mode or a mantle plume tail above a continental hotspot have all been proposed for the tectonic setting. Renewed intracratonic rifting at c. 1.14 Ga in the coastal area in northeasternmost Sweden resulted in the emplacement of alkaline ultrabasic dykes, including carbonatites (beforsites), silico-carbonatites and lamprophyres, in a north–south direction along an older shear belt. The broader tectonic setting of this extensional event is not known.

The uplift of the Adriatic flank of the Apennines since the Middle Pleistocene: New insights from the Tronto River basin and the Acquasanta Terme Travertine (central Italy)

The Apennines chain is an active Neogene fold-and-thrust belt resulting from the westward subduction of the Adriatic microplate. Starting from the end of the Early Pleistocene, the chain was affected by an increase in regional uplift. Recent GPS data resolved uplift rates of 1–2 mm/yr for the whole Apennines, whereas, in the Adriatic flank, several studies estimated rates between 0.3 and 0.5 mm/yr over the last 1 Myr. A number of works investigated the evolution of the drainage systems along the Periadriatic margin of the Apennines providing long-term incision rates. Studies from the northern part of this sector reported uplift rates varying from 0.2 to 1.1 mm/yr, whereas only few studies concentrated on the central sector of the Adriatic flank of the Apennines, focusing mainly on the evolution of the lower reach of major rivers. This work aims to quantify the long-term rock uplift and incision rates of the eastern portion of the central Apennines through the analysis of the Tronto River basin. Because of its geologic and geomorphological configurations, this basin is an ideal test site to investigate the influence of tectonics and climate on the recent topographic evolution of the central Apennines. The basin extends, with a roughly WSW-ENE direction, from the inner sector of the chain to the Adriatic coast, crossing several tectonic structures such as the Amatrice extensional basin and the Acquasanta and Montagna dei Fiori anticlines. In particular, in the Acquasanta Terme area, the right flank of the Tronto River valley is characterized by fluvial and travertine deposits organized and exposed in several levels. In this work, we investigated the hydrography (river longitudinal profiles) and topography (swath profile, slope, and local relief) of the Tronto River basin coupling these data with field observations and geochronological analysis on the continental sediments (fluvial deposits and travertines) outcropping in the Acquasanta Terme area. To better characterize the nature of travertines, we performed geochemical characterization of three travertine-forming thermal springs obtaining their physico-chemical parameters, the percentage of dissolved gases, and the isotopes content. Finally, we applied a knickpoint celerity model to chronologically constrain the geomorphological evolution of the whole drainage system. The results show the occurrence of a continuous tectonic uplift (~0.5 mm/yr) across the study area since Middle Pleistocene. The uplift, together with climate fluctuations, drove the incision (~0.6 mm/yr) of the landscape and the delineation of the present drainage network. These data are consistent with previous estimates of uplift and incision rates in adjacent areas and provide new constraints on the Quaternary evolution of the central Apennines. This study highlights how the coupling of field surveys with morphometric and topographic analyses of a drainage system is crucial to understand and quantify the influence of tectonic and climate changes in shaping the landscape.

Aeromagnetic Mapping of Iwo Region of Southwestern Nigeria for Lithostructural Delineation

Abstract The IGRF filtered Aeromagnetic data over Iwo, southwestern part of Nigeria within the basement complex was subjected to reduction to magnetic equator filtering, residual filtering, upward and downward continuation filtering, automatic gain control filtering, tilt angle derivative, second vertical derivative, analytical signal and Euler deconvolution. This reveals the geologic information such as structural trend. Based on the result of the total magnetic intensity map, reduction to equator map, analytical signal map and residual magnetic intensity map, it can be concluded that; The rocks in the study area have a trend of approximately northeast-southwest direction as seen on the upward continuation map. Most of the delineated lineaments found within the study area strike mostly in NNE-SSW, NE-SW and NW-SE with minor trend of E-W and ENE-WSW direction. Structural lineament orientation suggested that they were products of Pan-African orogeny (NE-SW, NW-SE and NNE-SSW trends) and pre-Pan-African orogeny (NNW-SSE and E-W trend). The interpretation of the aeromagnetic dataset gave an insight into the regional geology and structural trends of the area.

Disparate behaviour of deformation patterns beneath northeast Indian lithosphere inferred from shear wave splitting analysis

New shear wave splitting measurements are obtained from the North East Indian region utilizing the core refracted PKS/SKS/SKKS phases, suggesting the region as more complex and anisotropic in nature. The splitting parameters namely time delays (δt) and fast polarization directions (ϕ) are computed at nine stations and the results are found to be more consistent with the geologic/tectonic structures and present mantle deformation patterns under this particular region. The result streamlines the deformation patterns strictly into three categories. Significant anisotropy in the western fringe of Shillong plateau and surrounding regions implies an asthenospheric flow related strain dominating the splitting direction inline the direction of absolute plate motion (APM) of the Indian plate in a no net reference frame and discards the effects from lithospheric strain. The stations in Himalayan collision zone redefines an actual deformation pattern in ENE-WSW direction in line with the maximum shear plane construing the Himalayan arc at the northeast corner as a consequence of N-S Indo-Eurasian collisional derived lithospheric strain. The anisotropic effect at the Himalayan foredeep section signifies the lithospheric strain induced E-W deformation from N-S continental collision. Mapping the anisotropic layer depth under these stations also strengthens our anisotropic observations and geodynamics understanding of this region with a similar thought of ideas where the deformation patterns are supposed to be dominated by huge forces like APM and lithospheric strains with negligible effects from the local geological structures.

14C and 40Ar/39Ar radiometric dating and geologic setting of young lavas of Rancho Seco and Mazcuta volcanoes hosting archaeological sites at the margins of the Pátzcuaro and Zacapu lake basins (central Michoacán, Mexico)

Geologic mapping of two neighbouring areas (totalling ∼770km2) centred around the Rancho Seco and Mazcuta monogenetic scoria cones and situated between the Pátzcuaro and Zacapu lake basins in the Michoacán-Guanajuato Volcanic Field (central portion of the Trans-Mexican Volcanic Belt), allowed the recognition of 62 Quaternary monogenetic volcanic structures, which include cinder cones with associated lava flows, domes, and small-to-medium sized shields. 40Ar/39Ar and 14C radiometric dating, petrography, and whole-rock chemical analyses of volcanic products provide a stratigraphic framework and insight into different eruptive styles, and erupted volumes (∼45km3 of calc-alkaline magma). Pliocene to Holocene monogenetic activity has been frequent in this region, forming structures, which are generally aligned along an ENE-WSW direction associated to the Morelia-Cuitzeo-Acambay normal fault system.The young Rancho Seco and Mazcuta volcanoes are of particular interest because their distal lava flows host the pre-Hispanic archaeological urban centres of Angamuco and Cortijo Viejo, respectively. The Rancho Seco scoria cone was radiocarbon-dated at 27,845+445/−425yr BP and emitted at least six andesitic lava flows which were emplaced toward the SW (Lake Pátzcuaro) covering an area of 21.3km2 with a volume of ∼0.64km3. The Mazcuta scoria cone dated at 7970±135yr BP produced five basaltic andesite-andesite lava flows toward the NW (Lake Zacapu), where they cover an area of 28.85km2 with a volume of ∼0.57km3. The recently studied archaeological site of Angamuco became an important urban centre during the rise of the Tarascan Empire in the Post-Classic period (AD 900–1521), while the Cortijo Viejo site remains largely unexplored, but its occupation might fall within the same period. Although the young lava flows on which these sites are built seem inhospitable and barren with a rugged topography and rocky substrate unfit for agriculture, early inhabitants adapted and modified its surface according to their needs. Hence, these archaeological sites exemplify how a seemingly hostile landscape was ingeniously modified to establish population centres with patterns similar to those observed on lava flows elsewhere.

Fault relay zones within the eastern sector of the Jiloca Basin (Iberian Chain): geometry, kinematics and analogue modelling

The eastern sector of the Jiloca basin (Iberian Chain) developed due to the right-relay arrangement of three NW-SE striking normal faults: the Calamocha, Sierra Palomera and Concud faults. Together with the Teruel fault, they all bound three relay zones where evidence of recent fracturing has been found. Thanks to the analysis of brittle deformation, at both map and outcrop scales, and to its comparison with results from analogue modelling, we are able to infer its geometrical, kinematical and dynamical relationship with the macrostructures, within the framework of the near-multidirectional extension regime active in the studied area. During analogue modelling it was important to analyse possible variations in the resulting fractures, controlled by different extension velocities in two orthogonal directions and by the orientation of the main faults within both directions of extension. The fractures, both in the studied area and in analogue models, show a mostly parallel orientation to the macrostructures that bound the relay zones. They are controlled by the main fault strikes and, to a greater extent, by the dominant ENE-WSW direction of dominant extension within the regional stress field. All this has allowed us to define a new kind of interaction within extensional fault relay zones, called in this study relay with along-strike distributed fractures.

Structural style and evolution of inversion structures of Horus field, Alamein Basin, northern Western Desert of Egypt

Abstract High-quality three-dimensional (3D) seismic reflection and borehole data are used to characterize in detail the structural style and evolution of inversion structures in Horus oil field. This field lies in the central part of Alamein Basin, northern Western Desert of Egypt, in the hanging-wall of a major Jurassic-Early Cretaceous normal fault. This fault delineates the northwestern margin of the basin and extends in an ENE-WSW direction, bounding a half-graben trough in its hanging-wall. This trough had continued subsidence during Early Cretaceous time with depositional thickening of the Lower Cretaceous Alam el Bueib Formation. Fault displacement had ceased near the top of Barremian level. Aptian-Lower Senonian seismically traced levels show a major NE-plunging asymmetrical anticline overlying the Jurassic-Barremian half-graben. This anticline is sub-parallel to the inherited Jurassic rifting fault. At shallower Cretaceous levels, this fault is replaced by a set of WNW-ESE-trending en echelon faults of considerable displacements, which probably indicates a strike-slip component of deformation. These faults display normal separation on all displaced stratigraphic levels and tip upwards in the upper part of the Upper Cretaceous succession. This marks a considerable change in the tectonic mode of the area. NW-SE extensional faults were developed perpendicular to the fold axis, dissecting the anticline into several blocks entrapping hydrocarbons. Detailed seismic structural analysis of growth strata indicates that the fold initiated in Early Senonian time was associated with the inversion of the earlier Jurassic-Barremian half-graben. This basin inversion is attributed to the Syrian-Arc event that dominated North Africa during the Late Cretaceous time and continued through to the Early Miocene. Low fold amplitude coupled with normal displacements on the deep-seated ENE-WSW-trending Jurassic-Barremian fault indicate a mild phase of positive inversion. The Upper Senonian-Eocene stratigraphic sequences increased in thickness in the back-troughs that were associated with basin inversion.

The Campo de Calatrava Volcanic Field (central Spain): Fluid geochemistry in a CO2-rich area

The Campo de Calatrava Volcanic Field (CCVF) located in central-southern Spain (along with Selva-Emporda in Catalonia, NE Spain) is regarded as one of the most important CO2 emitting zones in Peninsular Spain. Here, we report and evaluate new molecular and isotopic geochemistry of thermal waters and CO2-rich gas discharges from the CCVF. Locally, these CO2-rich fluid emissions represent the remnants of the past volcanic activity that affected this area from the late Miocene through the Quaternary, with the most recent events occurring in the Holocene. The locations of discharging fluids and previous volcanic centers appear to be aligned along well-defined NW-SE and NNW-SSE lineaments, with subordinate trends in the ENE-WSW direction. The chemical and isotopic composition of the thermal waters suggests a meteoric origin, dominated by three distinct geochemical facies: 1) HCO3-Mg(Ca) type waters, associated with a relatively shallow aquifer and related to the interaction of meteoric waters with CO2-rich gases, alkaline volcanic products, and sedimentary formations, 2) SO4(Cl)-Ca(Mg) type waters, which stems from the two rivers (Guadiana and Jabalón) that drain Triassic evaporitic rocks before entering the study area, and 3) HCO3-Na type waters, hosted in deep geopressurized CO2-rich reservoirs within the Ordovician basement rocks.The 87Sr/86Sr isotopic compositions (ranging between 0.70415 and 0.71623) and δ34S-SO4 values (+10.7 to +18.3‰ vs. CDT) of CO2-rich fluids are consistent with interactions between water and either the Paleozoic basement, Triassic evaporites, Quaternary volcanic rocks, or a combination thereof. Dissolution of a CO2-rich gas phase into the aquifer produces low pH values (down to 5.4) and enhances water-rock interactions causing relatively high salinity (Total Ionic Salinity: up to ∼185 meq/L). Carbon dioxide is by far the most abundant gas constituent (up to 992 mmol/mol) and is dominated by mantle-derived sources as indicated by the combination of relatively high helium isotopic ratios (up to 2.7 R/Ra), high isotopic ratios of carbon in CO2 (ranging between −6.8 and −3.2‰ V-PDB), and the carbon isotopic signature of TDIC (from −6.8 to +2.2‰ vs. VPDB).In the last two decades, numerous (CO2-rich) gas blowouts have occurred in the area during well drillings, suggesting the presence of a geopressurized gas reservoir at relatively shallow depth.

Facies architecture of the Cambrian succession at the western margin of Baltica in the Podlasie region (E Poland)

Sedimentary features of the Cambrian-age succession transected in seven borehole cores sited in the Podlasie region document vertical and lateral variations of shallow-marine sedimentary facies, deposited at the rifted western margin of the Baltica Palaeocontinent. The boreholes are distributed along two lines of cross-section (E–W and NE–SW) running roughly perpendicular to the margin of the palaeocontinent. The easternmost borehole represents a proximal setting located on a relatively stable, shallow basement in the east; the remaining boreholes document conditions of deposition in the subsiding shallow-marine basin, extending towards the SW. Fourteen sedimentary facies defined on the basis of their lithological and sedimentary features are interpreted in terms of the sedimentary environments they represent. Strata deposited upon the stable craton in the east document a stratigraphically condensed succession of proximal facies, 240 m thick, whereas a sequence three times thicker is positioned distally, 170 km to the west. Facies associations in the proximal section represent the lower to upper shoreface in the lower part of the section and evolve upwards to the intermediate shoreface. Facies complexes in the remaining, intermediate and distal areas form a symmetrical megasequence, composed of a positive (i.e., fining-upwards – FU) transgressive sequence, overlain by a negative (coarsening-upwards – CU) regressive sequence. The vertical arrangement of the sedimentary subenvironments during the transgression indicates a tidally influenced shoreline followed by oscillations between the swash zone, the upper, intermediate and lower shoreface, and the offshore. The symmetry of the megasequences and the rhythmic pattern of the component facies complexes indicate that the intensity of supply in the terrigenous material and the efficiency of its reworking and redistribution within the basin were similar during the transgression and the regression. The facies types and variations within the basal part of the succession reflect syndepositional movements of tectonic blocks parallel to the rifted basin margin. Differences in total thickness and facies associations between the two lines of cross-section approximately perpendicular to the basin margin indicate that sedimentation was also influenced by a synsedimentary hinge fault, extending in a WSW–ENE direction.