Magma emplacement in a thrust ramp anticline: The Gavorrano Granite (northern Apennines, Italy)
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Abstract:
Magma emplacement in the upper crust is often associated with crustal extension, whereby space for intrusions is made by dilation along transtensive and strike‐slip faults. The lenticular shape of several intrusions indicates that a further mechanism for magma intrusion is laccolith emplacement with roof uplift of the overburden. Additionally, melts exploit rheological discontinuities (e.g., sedimentary layering) during their ascent. We present an emplacement model for intrusion of the shallow level Gavorrano Granite (northern Apennine, Italy), which is located at the core of an open anticline. The shape of the intrusion and structural features of the host rocks are indicative of a synkinematic emplacement in a growing thrust anticline. Space was provided by the opening of dilatation zones at the core of anticline as a consequence of different amounts of translation between hanging wall and footwall units which were separated by evaporitic rocks. These evaporitic units acted as major décollement layers. Analog models provide results in good agreement with the structural setting of the anticline and emphasize the possibility that melts filled the dilatation zone, with the décollement layers further facilitating intrusion.Keywords:
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This paper reports on the integration of different modelling techniques to construct a unified conceptual model of structural evolution of the Pico del Aguila anticline (External Sierras, southern Pyrenees, Spain). The structure is a well-known example of a detachment fold, which exhibits a N-S structural trend, perpendicular to the general structural trend of the southern Pyrenees (mainly E-W). Based on field observations of an unevenly distributed Triassic decollement, analogue modelling shows how to generate orogen-perpendicular structures which may result in transverse anticlines. The models show how contrasts between high and low friction patches in the basal decollement led to the formation of structures at high angle, centered over the high friction areas. Numerical models investigate the effect of a complex mechanical stratigraphy, characterized by an interlayering of competent and incompetent layers, plus syn-kinematic sedimentation in the fold growth. Based on field data and seismic interpretations, a 3D reconstruction and sequential geomechanical restoration of the Pico del Aguila anticline suggests the coexistence of multiple folding mechanisms occurring simultaneously in different units and structural domains of the fold, leading to a complex strain pattern that can not be assessed by simplistic kinematic 2D approaches. By integrating the models with previous data in the region, the benefits and drawbacks of each modelling technique are discussed and an integrated model of structural evolution for the Pico del Aguila anticline is presented. This enables a better comprehension of the structure as well as of the processes that drove the evolution of the N-S detachment anticlines in the External Sierras of the southern Pyrenees.
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In the North Ucayali basin, HC reserves have been already found but the structural style is rather complex due to the variability of the sedimentary covers and the presence of inherited structures. The risk of undercharge of the prospects due to a timing problem exists. A calibration of the erosion at the top of the various structures published by Bertolotti and Moretti (2009) indicated that the tertiary structures have different ages. Although the importance of the Paleozoic depot centres and faults in localizing has been largely published, a major role of the early Mesozoic evaporitic pillows was only recently proposed although seismic data evidences these pillows that influence the thrust geometry. Such behaviour of the evaporites is similar with the one observed in other compressive fronts. However, in the classical example of compressive front above salt layer, the evaporite forms either the main decollement level (as in the Zagros). In the north Ucayali basin, the salt pillows are isolated rather flat bodies, there are also deeper decollement levels. We have designed analogue models to discuss the influence of the depth and continuity of the salt pillows on the structure style.
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Abstract Structural mapping from 3D seismic at southern Mexico confirm that there are NW-SE trend of discontinuous faulted-folds from a regional fold belt formed by Mesozoic carbonates and evaporates, and Cenozoic clastics. Tectonic folding is the main deformation developed in two phases progressively during late Eocene to early Miocene and middle Miocene to late Pliocene, based on age of syn-kinematic units. Lateral faulting possibly associated to deeper contraction through old-basement faults displaces fold axes between 1 and 8 km. Some folds related to lateral fault present salt out of the core emplaced along the plane. Halokinesis formed salt withdrawal structures as crestal graben at anticlines cores or transtensional grabens related to lateral faults and cannopies over the Dorado squeezed anticline. Heterogeneity and anisopachity of Jurassic evaporites that have 1–3 km of thickness approximately caused folding detachment surfaces. Salt cored folds have detachment within the evaporites but some folds are detached in the top of evaporites. An example of detailed map from seismic structural-attribute was integrated with normalized production from productive wells in a cretaceous reservoir anticline. Productive wells are close to major faulted zones which are outstanding undrilled areas with high probability to recover remnant hydrocarbons in associated fractures swarms to deformation corridors of faults.
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B038 MODELING THE EFFECT OF DECOLLEMENT LEVELS ON STYLE OF FOLDED STRUCTURES APPLICATION TO THE ZAGROS FOLDS 1 SHAHRAM SHERKATI 1 & JEAN LETOUZEY 2 1 National Iranian Oil Company Yaghma allay Jomhuri Ave. Tehran-Iran The geometry of the folds vary significantly in horizontal and vertical directions in Zagros orogenic belt despite having been subjected to a similar compressional regime. Structural style change from simple isopachly folded large anticlines to chevron type folds which cored by complex compressional structures and to small folds overlie widely spaced anticlines cut by major thrust faults. They show close relationship with different mechanical behavior
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The Broadtop synclinorium is a large regional synclinorium which extends from central Pennsylvania to western Virginia. Critical study of more than 125 mi of seismic reflection surveys, 22 wells, and surface maps shows that the synclinorium is broken into a series of folded and faulted structures which reflect a precise relation of basement movement to thin-skinned tectonics. This relation indicates that Taconic and older tension-induced features have a pronounced controlling effect on structures caused by later compression. Early tension faults localize features such as decollement ramping. This ramping in turn produces many large prominent first-order structural features in both the Valley and Ridge province and the Plateau province of the Appalachian basin, such as Wil s Mountain anticline and the Allegheny front. The decollement ramping in turn induces formation of smaller second-order features such as the Whip Cove anticlines, the Whip Cove syncline, and other faults and folds within the Broadtop synclinorium. End_of_Article - Last_Page 1893------------
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