Morphotectonic Units Research Articles

Dense collection areas and terrestrial alteration of meteorites in the Atacama Desert

AbstractIn the last 15 years, more than 2700 meteorites have been recovered and officially classified from the Atacama Desert. Although the number of meteorites collected in the Atacama has risen, the physical and climatic properties of the dense collection areas (DCAs) have not been fully characterized. In this article, we compiled the published data of all classified meteorites found in the Atacama Desert to (i) describe the distribution by meteorite groups, (ii) compare the weathering degree of chondrites among different Atacama DCAs and other hot and cold deserts, and (iii) determine the preservation conditions of chondrites in the main Atacama DCAs in relation with the local climatic conditions. The 35 DCAs so far identified in the Atacama Desert are located in three main morphotectonic units: The Coastal Range (CR), Central Depression (CD), and Pre‐Andean Range/Basement. A comparison with reported weathering data from other cold and hot deserts indicates that the mean terrestrial weathering of Atacama chondrites (W1–2), displays less alteration than other hot deserts (W2–3) and resembles the weathering distribution of the Antarctic meteorites (W1–2). The highest abundance of Atacama chondrites with low weathering (≤W2) is localized in the CD (78.8%, N = 1435), which is protected from the coastal fog influence and seasonal rainfalls and displays the oldest surfaces in the Atacama Desert. The morphogenetic classification based on present‐day temperatures and precipitations of the main Atacama DCAs reveals similar regional/subregional climatic conditions in the most productive areas and a truly productive surface for meteorite recovery between 5% and 58% of the quadrangles formally defined for each Atacama DCA. Our morphogenetic classification lacks consideration of some meteorological parameters such as the coastal fog, so it cannot fully explain the differences in weathering patterns among CR chondrites. Future studies of chondrite preservation in the Atacama DCAs should consider other meteorological variables such as relative humidity, specific humidity, or dew point, in combination with exposure ages of meteorites and its surfaces.

Straight to Low-Sinuosity Drainage Systems in a Variscan-Type Orogen—Constraints from Tectonics, Lithology and Climate

A holistic-modular approach has been taken to study the evolution of three straight to low-sinuosity drainage systems (=SSS) in an uplifted basement block of the Central European Variscides. The development of the SSS is described by means of a quadripartite model. (1) The geological framework of the SSS: Forming the lithological and structural features in the bedrock as a result of different temperature, pressure and dynamic-metamorphic processes. (2) Prestage of SSS: Forming the paleo-landscape with a stable fluvial regime as a starting point for the SSS. (3) Proto-SSS: Transition into the metastable fluvial regime of the SSS. (4) Modern SSS: Operation of the metastable fluvial regime Tectonics plays a dual role. Late Paleozoic fold tectonic creates the basis for the studied SSS and has a guiding effect on the development of morphotectonic units during the Neogene and Quaternary. Late Cenozoic fault tectonics triggered the SSS to incise into the Paleozoic basement. The change in the bedrock lithology has an impact on the fluvial and colluvial sediments as well as their landforms. The latter reflects a conspicuous modification: straight drainage system ⇒ higher sinuosity and paired terraces ⇒ hillwash plains. Climate change has an indirect effect controlling via the bedrock the intensity of mechanical and chemical weathering. The impact on the development of the SSS can be assessed as follows: Tectonics >> climate ≅ bedrock lithology. The three parameters cause a facies zonation: (1) wide-and-shallow valley (Miocene), (2) wide-angle V-shaped valley (Plio-Pleistocene), (3) acute-angle V-shaped valley (Pleistocene), (4) V-shaped to U-shaped valleys (Pleistocene-Holocene). Numerical data relevant for the hydrographic studies of the SSS are determined in each reference area: (1) Quantification of fluvial and colluvial deposits along the drainage system, (2) slope angles, (3) degree of sinuosity as a function of river facies, (4) grain size distribution, (5) grain morphological categorization, (6) grain orientation (“situmetry”), (7) channel density, (8) channel/floodplain ratios. Thermodynamic computations (Eh, pH, concentration of solubles) are made to constrain the paleoclimatic regime during formation of the SSS. The current model of the SSS is restricted in its application to the basement of the Variscan-Type orogens, to an intermediate crustal maturity state.

Crustal architecture and tectonic evolution of the southernmost Río de la Plata Craton and its Neoproterozoic–Paleozoic sedimentary cover: Insights from 3D litho-constrained stochastic inversion models

In the last decade, several models have been proposed to explain the location and geometry of the southern margin of the Archean–Paleoproterozoic Río de la Plata Craton. However, these topics and the regional distribution of the Neoproterozoic–Paleozoic sedimentary cover of the craton are still widely debated. This contribution presents a 3D litho-constrained gravity inversion model of the southern sector of the Río de la Plata Craton, based on the integration of geological, geophysical, and petrophysical data. The distribution of the Neoproterozoic–Paleozoic sedimentary cover of the region is reassessed considering a common and protracted geological history of the three morphotectonic units involved in the study area: the Tandilia System, the Claromecó Basin, and the Ventania System. Our results provide key information on the location and geometry of the southern margin of the Río de la Plata Craton that supports its relationship with the Neoproterozoic Brasiliano/Pan-African Orogeny and, subsequently, with the Paleozoic Terra Australis and Gondwanide orogenies. In this context, the Neoproterozoic basement of the Ventania System was dextrally transported from the Brasiliano/Pan-African Orogen during the late Ediacaran–early Cambrian and thrusted over the Río de la Plata Craton and its Neoproterozoic–early Paleozoic sedimentary cover during the Permian. Likewise, our 3D model also shed new insights into the orogenic mechanisms of deformation transfer from the North Patagonian Massif to the Ventania System. The deep crustal geometry determined for the latter suggests intraplate deformation, mainly due to the Permian reactivation of the boundary between the Río de la Plata Craton and the Brasiliano/Pan-African basement. This implies that the Ventania System was mechanically disconnected from the Permian orogenic front located further southwest in the North Patagonian Massif, thus challenging previous models of orogenic architecture for the region.

Morphotectonic Nature of the South Moesian Morphostructural Zone

The article represents the author’s contemporary mobility concept about the morphotectonic nature of the South Moesian Morphostructural Zone in North Bulgaria. The mentioned morphounit corresponds with the Moesian Continental Microplate South Margin between Timok River to the west and Kamchia River to the east. The north boundary of the zone coincides with fault bundle system along the Lower Danube River between Timok River Infuse to the west and the town of Cherna Voda to the east and between the towns of Cherna Voda and Constantsa in Nord Dobrudzha. The south boundary of the zone is following on the north slopes of the Fore Balkan and Stara Planina Mountain Ranges. The short west boundary near the Timok River separates the zone from the Carpathian Continental Microplate. The east zonal boundary limits it from the Black Sea Oceanic Microplate. The South Moesian Morphostructural Zone is representing one of the most contemporary fragments from the large post Early Pleistocene Orthoplain in the Balkan Peninsula North-East Part. It plane-lowland zonal relief contrasts with the relief of the neighbor first-rare morphotectonic units. The internal zonal pattern includes the Lower Danube Morphostructural Area (with Lom and Lovech Morphostructural Regions) and Ludogorie Morphostructural Area (with Isperih, Shumen and Dobrich Morphostructural Regions). The South Moesian Morphostructural Zone is a north part of the Maestrichtian-Early Neozoic Morphotectonic Suture between the Bulgarian and Moesian Continental Microplates during the New Europe Continental Massif Building. The till today continued Gondwana-New Europe Transcontinental Collision in the Mediterranean Region has bring very intensive Post Early Pleistocene Orthoplain Destruction and high mountain relief building (Rila, Pirin, Rhodope Mountain Massifs) in the Bulgarian Continental Microplate South-West Parts. The mentioned collision has causes the Fore Balkan and Stara Planina Syncinematic Uplifting in the suture zone between the Bulgarian and Moesian Continenta Microplates to. The South Moesian Morphostructural Zone has stay unaffected from those morphotectonic processes.

Common pattern of distribution for Mesoamerican Triatoma dimidiata suggest geological and ecological association

The phylogeny of the Triatoma dimidiata complex has been widely assessed with different genetic and morphological data, which has allowed to reach the consensus that the complex consists of at least three taxonomic units. However, these taxonomic units seem to have a distribution related to geography throughout Mesoamerica, with different groupings depending on the source of information used. In the present study, we aimed to determine if there is a common biogeographical, genetic and phenetic distribution pattern among the T. dimidiata species in Mesoamerica and if this pattern is related to ecological and geological variability of the region. We found that panbiogeographical analysis showed three generalized tracks that coincide with genetic/phenetic data which showed a general pattern of distribution in two big clusters to the north and south of Mesoamerica. We also found that these clusters were significantly related to geological tectonic plates and ecotypes. We conclude that the geological history may be a plausible explanation for the greater differentiation observed in the T. dimidiata complex, but that the current ecological characteristics of the morphotectonic units or ecotypes may be responsible for the additional variation observed and therefore differential control strategies for each cluster considering geological history and ecotype should be used. Further, more detailed biogeographical and landscape genetic analyses are necessary with the goal to elucidate T. dimidiata differentiation related with ecological and geological variables in the region and the possible epidemiological and evolutionary consequences.

Evolution of the Edea‐Eseka geomorphic units: A 'natural laboratory' of a prototype active rifting cross‐cutting the Southern Cameroon (West African) passive margin

The SW Cameroonian passive margin, a part of the Cameroon Low‐Plateau, presents several topographic levels cross‐cut by the Sanaga Fault (SF), Benue Triple Junction and Cameroon Volcanic Line (CVL), three pre‐ and syn‐rift tectonic features that are still active. This study carried out on the Edea‐Eseka Region (EER) a portion of this margin (3°30′–4°N, 10°–10°55′E) aims to constrain the relationships between these features and the development of the morphology. Geomorphic indices, combined with field observations and supported by literature data show that the interactive activity of these structures constitutes the main force that controls the EER morphology. From West to East, EER consists of three morphotectonic units: the Coastal, Intermediate and Upper units. The Coastal unit built on the Douala‐Kribi/Campo Basin (<65 Ma) and assigned to the Aptian South Atlantic rifting, exhibits low reliefs deeply incised. The Intermediate and Upper units are developed on the Nyong and Oubanguide crystallophyllian complexes during the Eburnean/Trans‐Amazonian (2,400–1,750 Ma) and Pan‐African (650–540 Ma) orogenies, respectively. The Intermediate unit with moderate reliefs registers a strong differential erosion, whilst the Upper unit records high‐reliefs. Geomorphic indices, tectonic and recent seismic data reveal that the EER has been rejuvenated, experienced uplifts and tiltings synchronously with the main active phases of these features. The timing and magnitude of these activities vary from one unit to another. The morphotectonic model is consistent to the crucial tectonic phases: emplacement of SF (Palaeozoic), the breakup of Gondwana and erection of CVL (Cretaceous).

What is the structure of the forearc region in the Central Andes of northern Chile? An approach from field data and 2-D reflection seismic data

The tectonic evolution of the Andean forearc in the Central Andes is understood by the superimposition of deformational events associated with different tectonic regimes, which control the main morpho-tectonic units of northern Chile. Varied interpretations have opened a great discussion about the deep structure of the Andean forearc and its implications in the evolution of the Central Andes. These ideas are commonly accompanied by the lack of regional tectonic models that explain the geometry and kinematics of first-order structures. The main limitations are due to the unknown origin of the structural styles in the substrate and their relationships with those exposed in the field. In order to solve this problem, we present a new structural model of the forearc region of northern Chile, specifically along the Central Depression (22°-23°S) supported by field observations and the structural interpretations of 2D seismic data. Four major tectono-sequences have been recognized related to (a) a Paleozoic-Triassic basement rocks, (b) a Jurassic-Lower Cretaceous synrift deposits, (c) Upper Cretaceous-Paleocene volcano synorogenic deposits and (d) a Late Cenozoic covered gravel. The first-order structural styles identified correspond to inverted half-graben basement structures related to the Jurassic Tarapacá Basin. The hanging wall blocks of the master faults are usually composed of large inversion anticlines along which, Jurassic and Lower Cretaceous siliciclastic deposits were expelled. Other basement contractional structures consist of short-cut and by-pass faults that modified the previous geometry of extensional systems. The second-order thin-skinned fold and thrust exposed in the region accommodated the shortening experienced by the Mesozoic synrift deposits during the basin inversion. The Upper Cretaceous-Paleocene deposits usually unconformably overlie the folded Mesozoic synrift deposits. This structural feature is first-order evidence of the positive reactivation of the Mesozoic rift basins and therefore is a regional marker of the onset of the Andean uplift in the region.

Estimation of the long-term slip, surface uplift and block rotation along the northern strand of the North Anatolian Fault Zone: Inferences from geomorphology of the Almacık Block

The Almacık Block is one of the key morphotectonic units in the eastern Marmara Region associated with the long-term slip partitioning within the North Anatolian Fault Zone (NAFZ). In this study, we provide new geomorphic reconstructions of offset drainage basins, morphometric analysis of topography, and longitudinal profiles of the rivers crossing different flanks of the Almacık Block. Our geomorphic reconstructions of offset drainage basins along the Hendek and Karadere faults imply mean offsets of 2.3±0.4km and 8.4±0.7km, respectively, during the Quaternary. Our dataset also imply that slip partitioning occurs in a broader zone than previously proposed, and that the total 10.7±0.6km offset along the Hendek and Karadere faults of the northern strand must be taken into account for long-term slip partitioning in the Eastern Marmara Region. Together with previously suggested 10km offset along the southern strand (Yaltırak, 2002), 16±1.0km offset along the middle strand (Özalp et al., 2013) and the 52±1.0km offset along the Mudurnu Segment of the northern strand (Akbayram et al., 2016) our newly proposed geomorphic markers raise the cumulative offset in the eastern Marmara region associated with the NAF to 89±1.0km since the Latest Pliocene – Quaternary. In addition to these lateral displacements, our morphometric analysis and longitudinal profiles of the rivers imply up to 1130±130m surface uplift of the Almacık Block as a combined result of vertical displacement within the deformation zone of the northern strand of the NAFZ. Finally, by assuming that river basins act as passive deformation markers, our basin azimuth analyses imply 20°±2° clockwise rotation of the Almacık Block associated with the NAFZ.

The Morphotectonic units of Ikaria island – Contribution in the natural hazards research

Present morphological and tectonic image of Ikaria island is the complex result of both the tem-poral evolution of the island, as part of the geodynamical evolution of the Hellenic Arc, especially that of the last stages (from the upper Miocene and after), and the exogenous factors. Also human impact functions as an additional parameter for the formation of Ikaria geoenvironment.According to field data and their analysis, computing and estimation which took part with the use of modern technologies (use of GIS, analysis of geographical and descriptive databases) the mor-photectonic units of Ikaria Island were defined. The definition of the morphotectonic units was based on their special features and more precisely on the lithological differentiation (granite, metamorphic rocks and post alpine formations) as well as the complex ductile and brittle structures (large scale ductile shear-zones and brittle detachment faults, normal faults, strike-slip transfer faults and join sets) and the morphological features (slope distribution, asymmetry of the drainage system, planation surfaces, morphological discontinuities etc).The synthesis of the special features of each morphotectonic unit in combination with the human impact (fires, overgrazing etc), defines the kind, the intensity and the geographical localization of the natural hazards which occur in various sites of the island, such as landslides, erosion, floods, seismic activity, relief changes, coastline changes etc.

Uplift sequence of the Andes at 30°S: Insights from sedimentology and U/Pb dating of synorogenic deposits

The South Central Andes at 30°S represent a key area to understand the Andes geodynamics as it is in the middle of the flat slab segment and all the morphotectonic units of the Central Andes are well developed. This work is focused in the proximal synorogenic deposits of the Western Precordillera, in the La Tranca valley, in order to unravel the uplift sequence of this belt. Nine facies associations were recognized; most of them represent piedmont facies with local provenance from Precordillera and were deposited in the wedge-top depozone, as is expected for proximal sinorogenic deposits. However there are intercalations of transference fluvial systems, which show mixed provenance indicating that Permo-Triassic igneous rocks were already exposed to the west (Frontal Cordillera). There are also lacustrine deposits which are interpreted as the result of damming by fault activity at east of the studied basin.Finally, two maximum depositional ages at ca. 11 Ma and 8 Ma of these deposits indicate that the onset of uplift of the Precordillera at 30°S is little older than 11 Ma. These data change two previous ideas about the evolution of the Precordillera: its uplift at 30° S is younger than proposed by previous works and it is nearly synchronous along strike.

Quaternary tectonics along oblique deformation zones in the Central Andean retro-wedge between 31°30′S and 35°S

Abstract The distribution of the Quaternary deformation in the outer retro-wedge of the Andes (31°30′–35°S) is controlled by the subduction geometry, the position of the structural front, and the location of oblique pre-Cenozoic mechanical anisotropies. In the Southern Precordillera, Quaternary structures tend to group along the Barreal–Las Peñas deformation zone with a NW to NNW trend. This Cenozoic belt (31°30′–32°40′S) developed on the northern segment of the Triassic Cuyo Basin and broadened laterally during the Quaternary. New radiocarbon ages on dam deposits confirm Holocene tectonic activity on the northwestern edge. The oldest ages of dam deposits are 5810±90 a BP (Cabeceras Creek) and 810±50 a BP (Dolores Creek). Palaeoseismological and seismic data suggest active tectonic growth on the NW and SE extremes. Quaternary tectonics has contributed to modifying the relief along this oblique belt. This contribution is evident from the tectonic uplift of blocks (minimum 90–120 m in the Barreal block), the initial development of intermontane basins (Pampa de los Burros Basin), the Quaternary rejuvenation of tectonic depressions (at least 32–37 m of tectonic subsidence in the Vizcacheras half-graben) and the incipient development of low-relief morphotectonic units by soft-linkage of Quaternary structures.

Late Cenozoic Tectonic Activity of the Śnieżnik Massif Area (Sudetes, Sw Poland)in the Light of Lidar Dem Morphometric Analysis

AbstractŚnieżnik Massif represents a prominent morphological feature in the East Sudetes, which is bounded by a system of faults controlling its differential uplift. Vertical movements originated at least during the Oligocene times, with culmination phase in Pliocene times, whereas estimated total uplift was in the range of 500-1000 meters. This study presents a qualitative (geomorphometric) and quantitative (morphotectonic) approach that combines Late Cenozoic tectonic uplift model with landscape evolution theories. Application of basin asymmetry factor (AF) and hypsometric integral (Hi) analyses allowed recognizing a NW trending tilted fault blocks. They originated as a result of Palaeogene planation surface braking and differential uplift. Uplift and later fault-block tilting in the Śnieżnik Massif morphotectonic unit, were generally realized along NE-SW striking Wilkanow fault to the west and WNW-ESE striking southern fault zone, as expressed here e.g. by Potoczek-Branna, Herˇmranice and Pisary faults.

Electrical resistivity tomography applied to the study of neotectonic structures, northwestern Precordillera Sur, Central Andes of Argentina

Abstract The Precordillera, which is one of the main morphotectonic units along the Pampean flat-slab subduction segment of the Central Andes of Argentina, is characterized by its high neotectonic activity. Thus, the study of the Late-Cenozoic to Recent deformation along this zone directly contributes to the seismic hazard characterization of the region. The Paleozoic and Mesozoic geological history of the southern sector of the Precordillera (Precordillera Sur) resulted in an inhomogeneous basement whose mechanical anisotropies seem to control the Andean structural features. As the northwestern edge of the Precordillera Sur and its piedmont sector shows no Cenozoic rocks, it is not possible to use them as a tool to reconstruct the tectonic deformation of this age. However, the presence of a regional Pre-Cenozoic tilted erosion surface can be use as a structural marker. The Andean tectonic deformation is here represented by some scattered Cenozoic to Recent structural highs carved in Paleozoic rocks and Quaternary sediments and by drainage modifications within the Quaternary alluvial fans. The aim of this contribution is to present a geophysical study of two piedmont neotectonic structural features: the Yalguaraz structural high and a subtle drainage incision anomaly. We studied the shallow subsurface character of these structural features by means of electrical resistivity tomographies in order to evaluate the subsurface presence of the erosion surface, its structural fabric and its relationship with Late-Cenozoic to Recent tectonic structures. This methodology showed to be effective and useful in the study of such features. We interpreted the Yalguaraz fault as a subvertical NE-dipping reverse fault, related to a fault scarp retreat of about 50–70 m. Furthermore, its NW-trending could be associated with mechanical anisotropies, likely Paleozoic in age. According to analyses of aerial photographs, the oldest aggradation level of the study zone (Early–Middle Pleistocene) could be affected by the activity of the Yalguaraz fault. The youngest Quaternary deposits (Holocene) do not show surface as well as subsurface evidence of deformation. In the case of the studied Quaternary drainage incision anomaly, the performed electrical resistivity tomography corroborates the relationship between these elements and incipient tectonic deformation.

Los temblores sentidos en Costa Rica durante: 1973-1983, y su relación con la sismicidad del país

Earthquakes in che metropolitan arca of San José, felt with intensity equal or higher than III (MM) for che period 1973-1983, mere localized by means of a local network of stations and portable seismographs, combined with information talen from international bulletins (ISC, PDE, EDR). The distribution of seismi-city and its relation with morphotectonic units allowed a geografic zonification of the country, and mas found that the main seismic sources were associated with subduction and local faults. The last eme proved lo be the most dangerous seismic source and the borders of the internal basins the ones more potentially risky, as evidenced by the Tilarán (1973) and the Pérez Zelechán (1983) earthquakes. The central pacific coast represents a seismic gap and aleo has a high seismic poten-tial. Seismic sequences of the "swarm" type or precursors, main quake and after-shocks hace been observed in the Central Valley, mainly oriented toman d the volca nic area. The type of seismicity observed for the strong earthquakes in the subI duction zone has been, majo quake and aftershocks. The mean value of the felt earthquakes (I= III) in the metropolitan aren of San José mas 14.7 , Per Yeat, that is, about a monthly earthquake. Pee highest seismic activity (VI - VII) mas felt during April 1983. d.le td violent activity around Golfito (Ms = 7.3). The year 1983 has been the most ac,we of tha wbole period as measured by the energy release and material damages, mainly che arcas of Golfito-Osa ami Pérez Zele-dón. However, landslides due o Tilarán's earthquake (1973) yie1ded the largest number of casualties (23), during the whole period.

Deformación y esfuerzos neotectónicos en Costa Rica

Seismological, vulcanological, geomorphological and structural data and criterion are used (...) to define stress trayectories and the neotectonic deformation that occur in the morphotectonic units of Costa Rica. The neotectonic deformation data show that the trench-forearc-arc-backarc region has been subjected to maximum horizontal compressive stresses (ECHM) that correspond to the maximum principal stress. These stresses trend N30°E between the Middle American Trench and the forearc area. The predominant faulting is thrust or reverse faulting. In the arc, the predominant orientation of is NO°E, and the principal faulting is strike-slip. In the backarc area also trends NO°E. The 20°-30° counterclock-wisy ECHM rotation between the interplate margin and the internal arc is aparent and is explained by oblique convergence between the Cocos-Caribbeean plates.

Morphotectonic Features and Fault Propagation Folding of Bhuban Hills, NE India Using Satellite Image and DEM

Present topography of Bhuban Hills, lying in the Indo-Burman frontal fold belt of Northeastern part of India, is an aberration from a normal anticlinal morphology and exhibits several transverse and longitudinal fault affected segments resulting into distinct morphotectonic units. Six different morphotectonic units could be delineated along N-S stretch of the hill ridge. The western side of the northern most part of the hill ridge forms steep escarpment as this portion has been affected by the longitudinal faulting representing a case of fault propagation folding. The northernmost segment comprising three morphotectonic units (MU1 to MU3) is unique in the sense that this part exhibits effect of both the longitudinal and transverse faulting, uplifted narrow ridge with downthrown eastern side (MU2). Northern part of the Bhuban Hills has become curved westward due to the right lateral movement along the transverse fault TF1. The fifth morphotectonic unit (MU5) has undergone subsidence whereas, the sixth unit (MU6) exhibit bulging effect as this part experienced differential fault movements. Stream profiles, longitudinal and transverse topographic profiles extracted from contour map and Digital Elevation Model corroborated with the topographical anomalies developed over the Bhuban Hills.

Morphotectonics of the Area Around Renukoot, District Sonbhadra, U.P. Using Remote Sensing and GIS Techniques

A part of Precambrian rocks of central India around Renukoot, district Sonbhadra, U.P., exhibits noteworthy differences in morphometric characteristics such as drainage density, mean stream length, bifurcation ratio and stream frequency across Son Narmada South Fault of the Son Narmada Lineament Zone. The Remote Sensing and GIS based present study explains the tectonic evolution of the terrain by dividing the area into two morphotectonic units namely Dudhi Morphotectonic Unit (DMU) and Mahakoshal Morphotectonic Unit (MMU) with the help of a proposed model. The study reveals that the landform features of the rocks of DMU and MMU of the study area are strongly controlled by underlying lithology and structures. The study also reveals different tectonic histories for the units until the last or the fourth phase of deformation dominated by shearing movement.

Tectonic evolution of the Satpura Mountain Belt: A critical evaluation and implication on supercontinent assembly

The Satpura Mountain Belt (also referred as Central Indian Tectonic Zone in recent literature) forms an important morphotectonic unit in the central part of India. Some of the recent workers have reported an orogenic event at ∼1000–900 Ma (termed “Sausar orogeny”) which led to amalgamation of the North Indian Block and the South Indian Block and formation of the Satpura Mountain Belt. In this model the stratigraphic relations of two important lithostratigraphic units on either side of the Satpura Mountain Belt (the Sausar Group in the south and the Vindhyan Supergroup on the north) are suggested to be revised from previously held ideas. Critical analyses of available published work in the region to assess the status of the Sausar Group vis a vis the Vindhyan Supergroup was carried out. It is found that the ideas proposed by the recent workers stem from an earlier interpretation that the Sausar Group has monocyclic evolution and the earliest fabric in the Sausar Group is marked by a schistosity with EW strike. Re-mapping of the gneissic rocks and adjacent matasedimentary rocks of Khawasa, Deolapar, and Kandri–Mansar areas revealed presence of gneissic rocks and granulites of two generations, and of four phases of superposed deformations in the metasediments and gneisses. The older gneisses and granulites constitute the basement over which the rocks of the Sausar Group were deposited; and the younger gneisses developed by metamorphism and migmatisation of the rocks of the Sausar Group. The latter types are found in the Khawasa–Ramakona areas. Contrary to the belief of the recent workers that no volcanic activity is present in the Sausar Group, volcanic rocks marked by amygdular basic flows and tuffs have been mapped from different parts of the Sausar Group. Migmatisation and metamorphism of these volcanic rocks (of the Sausar Group) have given rise to amphibolites and granulites in Khawasa and Ramakona areas. Therefore, the use of fabric patterns in these areas to suggest that the granulite facies metamorphism in the Ramakona–Katangi granulite domain was pre-Sausar in age is debatable. Available geochronological data of the Satpura Mountain Belt and its eastward continuation into the Chhotanagpur Gneiss terrain indicate that the basement and cover rocks of these areas were subjected to multiple deformation and metamorphic episodes of similar style and nature. The earliest deformation and metamorphism of the rocks of the Sausar Group and its equivalent rocks to the east took place at ∼2100–1900 Ma. The regional EW trend of the belt developed during the second deformation at ∼1800–1700 Ma and again at ∼1600–1500 Ma. This deformation was accompanied by migmatisation and granulite facies metamorphism in the northern domain of the Sausar Belt and in the Chhotanagpur Gneiss region. Late phase low intensity deformations in the region were associated with thermal events at ∼1100–1000 Ma and ∼900–800 Ma. The ∼EW trending fabric, referred as “Satpura orogenic trend” in Indian literature marks a major compressional tectonic event, developed during the second deformation of the Sausar Group. This has its counter part in Western Australia as the Capricorn orogeny (∼1780–1830 Ma). The development of the Satpura Mountain Belt during the Grenvillian orogeny is ruled out from the synthesis of event stratigraphic data of the region and from its comparison with the Western Australian Craton.

A Constrained 3D Density Model of the Upper Crust from Gravity Data Interpretation for Central Costa Rica

The map of complete Bouguer anomaly of Costa Rica shows an elongated NW-SE trending gravity low in the central region. This gravity low coincides with the geographical region known as the Cordillera Volcánica Central. It is built by geologic and morpho-tectonic units which consist of Quaternary volcanic edifices. For quantitative interpretation of the sources of the anomaly and the characterization of fluid pathways and reservoirs of arc magmatism, a constrained 3D density model of the upper crust was designed by means of forward modeling. The density model is constrained by simplified surface geology, previously published seismic tomography and P-wave velocity models, which stem from wide-angle refraction seismic, as well as results from methods of direct interpretation of the gravity field obtained for this work. The model takes into account the effects and influence of subduction-related Neogene through Quaternary arc magmatism on the upper crust.

Morphotectonic characteristics of Lefkas Island during the Quaternary (Ionian Sea, Greece)

This paper focuses on the study of the Quaternary morphotectonic evolution of the Lefkas Island using morphological and tectonic data. Based on our mainly morphological studies, two principal tectonic structures have been distinguished: (i) the Nydri-Vasiliki Fault Zone (NVF) and (ii) the Ionian Zone overthrust onto the Paxos Zone, which both divide the island into three morphotectonic units of Karya (KMTU), Maradochori (MMTU) and Athani (AMTU). Paleogeographically, it has been suggested that the broader Lefkas area was dominated by a NE–SW to ENE–WSW compressional regime since the early Pliocene that continuous in our days, resulting in the uplift of the southwestern part of the island and the submergence of the northeastern part of the island. This deformation is characterized by principal fault structures of a N110°–130° strike. These structures, combined with a fault system of N40°–60° strike representing an older Miocene fault zone, control the main morphological characteristics such as watersheds and streams and are responsible for the KMTU formation producing a northeastward plunging monoclinal en-echelon structure. During the Early Pleistocene, a shift of the compressional regime towards the east was responsible for the formation of a N70°–90° strike fault system. These faults had a morphotectonic effect throughout the island, controlling the watersheds and stream evolution. The continuous compressional regime recorded in our days results in the formation of fault structures, striking N20°–40° and N170°–190° that bound almost exclusively the coastal area of the island.