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Dilip Saha - One of the best experts on this subject based on the ideXlab platform.
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inversion of calcite twin data Paleostress reconstruction and multiphase weak deformation in cratonic interior evidence from the proterozoic cuddapah basin india
Journal of Structural Geology, 2015Co-Authors: Vikash Tripathy, Dilip SahaAbstract:Abstract Paleostress orientations from mechanically twinned calcite in carbonate rocks and veins in the neighborhood of large faults were investigated to comment on the nature of weak upper crustal stresses affecting sedimentary successions within the Proterozoic Cuddapah basin, India. Application of Turner's P–B–T method and Spang's Numerical dynamic analysis on Cuddapah samples provided Paleostress orientations comparable to those derived from fault-slip inversion. Results from the neighborhood of E–W faults cutting through the Paleoproterozoic Papaghni and Chitravati groups and the Neoproterozoic Kurnool Group in the western Cuddapah basin, reveal existence of multiple deformation events − (1) NE–SW σ3 in strike-slip to extensional regime along with an additional event having NW–SE σ3, for lower Cuddapah samples; (2) compressional/transpressional event with ESE–WNW or NNE–SSW σ1 mainly from younger Kurnool samples. Integrating results from calcite twin data inversion, fault-slip analysis and regional geology we propose that late Mesoproterozoic crustal extension led to initial opening of the Kurnool sub-basin, subsequently influenced by weak compressional deformation. The dynamic analysis of calcite twins thus constrains the stress regimes influencing basin initiation in the southern Indian cratonic interior and subsequent basin inversion in relation to craton margin mobile belts and plausible global tectonic events in the Proterozoic.
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plate margin Paleostress variations and intracontinental deformations in the evolution of the cuddapah basin through proterozoic
Precambrian Research, 2013Co-Authors: Vikash Tripathy, Dilip SahaAbstract:Abstract The sedimentary basins are often influenced by adjoining mobile belts as is the case of the Proterozoic Cuddapah basin in southern India, lying in proximity of the Eastern Ghats granulite belt (EGB) and the Southern granulite terrain (SGT). Two major faults – Gani–Kalva and Kona faults – in the western part of the Cuddapah basin have been examined in this work to comment on the changes in Paleostress conditions affecting the basin evolution punctuated by several stages of extensional and compressional regimes in the time interval 1.9–0.5 Ga. The tensor solutions were obtained for the mesoscale faults and fault striae using the improved Right Dihedron method followed by the Rotational Optimization method (TENSOR, Delvaux and Sperner, 2003 ). Combining the Paleostress field reconstruction and other structural/stratigraphic attributes we propose a possible scenario of punctuated evolution of the Cuddapah basin and its inversion. The stress regimes are tentatively correlated with multiple stages of basin opening and deformation of basin in-fill, representing the pre-Grenvillian through the Pan-African orogeny. The Paleostress conditions derived from various stratigraphic horizons provide an opportunity to comment on the changes in tectonic stresses including several stages of extensional and compressive regimes in the Cuddapah basin. The tensor solutions were obtained for the mesoscale faults and fault striae in the neighborhood of above two fault lines using the improved Right Dihedron method followed by the Rotational Optimization method (TENSOR, Delvaux and Sperner, 2003 ). The most prominent stress states recorded around the two fault lines can be classified into those affecting (1) the Paleoproterozoic lower Cuddapah successions, (2) the younger Kurnool Group and (3) both the groups. Integrating the stress states of the fault-slip analysis obtained from different unconformity bounded rock groups of lower Cuddapah and other geologic data, we suggest extensional to transtensive/pure strike-slip regime to be active during the first phase of basin opening and c. 1.89 Ga mafic igneous activity. Late compressional to transpressive/pure strike-slip regimes are well recorded from the younger Kurnool Group, representing late Neoproterozoic deformations. The tensor solutions from different unconformity bound stratigraphic horizons constrain different states of deformation. We relate the extensional to transtensive/pure strike-slip regimes from lower Cuddapah successions to the ongoing basin opening events and the associated Palaeoproterozoic igneous activities. The late Neoproterozoic to early Paleozoic compressional to transpressive/strike-slip regime present the possible effects of compressional activities happening around the cratonic margin. The present analysis lends further support to the idea that estimation of Paleostress states from fault-slip data even in regions of relatively weak deformation in continental interior are important while assessing influence of plate margin stresses on the continental interior.
Jacques Angelier - One of the best experts on this subject based on the ideXlab platform.
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Structure and activity of the geothermal field of Hvalfjörour (Iceland) from brittle tectonic, geothermal and Paleostress analysis
Bulletin de la Société Géologique de France, 2013Co-Authors: Françoise Bergerat, Kristjan Saemundsson, Loïc Fourel, Jacques AngelierAbstract:This paper presents the results of brittle tectonic, palaeostress inversion, and hydrothermal mineralisation studies of the Hvalfjörður low-temperature geothermal field in Southwest Iceland. This geothermal field (including two pronounced thermal anomalies) is located in the highly altered core area of an extinct and deeply eroded Tertiary central volcano. Most of the geothermal water appears to be conducted by vertical extension fractures. Palaeostress analysis indicates a rather complex stress history, with four major trends of extension involving normal and strike-slip faulting modes as well as dyke injection. Analysis of the data on the relative chronology indicates that these four regimes were closely intricate in time and space. The most important regime is a NW-SE, rift-perpendicular extension related to the oceanic rifting in Iceland. This trend partly controls the past (Pliocene-Early Pleistocene) hydrothermal activity in the Hvalfjörður area; however, an E-W rift-oblique extension also occurred with a N-S trending fracture system including normal faults, dykes and veins that show higher levels of hydrothermal mineralisation. Currently, there is strong hot-water convection, producing a thermal anomaly, in this N-S-trending fracture system. Our study highlights the Paleostress evolution and the development of fracture systems in Hvalfjörður, including the past geothermal history; nevertheless the most efficient tool in geothermal prospection in such complex area remains the shallow geothermal survey. It has proved successful in many localities in Early Pleistocene to Miocene rocks where no surface indication of geothermal activity exists.
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evolution of Paleostress fields and brittle deformation of the tornquist zone in scania sweden during permo mesozoic and cenozoic times
Tectonophysics, 2007Co-Authors: Françoise Bergerat, Jacques Angelier, Pergunnar AndreassonAbstract:Abstract The NW-SE oriented Sorgenfrei–Tornquist Zone (STZ) has been thoroughly studied during the last 25 years, especially by means of well data and seismic profiles. We present the results of a first brittle tectonic analysis based on about 850 dykes, veins and minor fault-slip data measured in the field in Scania, including Paleostress reconstruction. We discuss the relationships between normal and strike-slip faulting in Scania since the Permian extension to the Late Cretaceous–Tertiary structural inversions. Our Paleostress determinations reveal six successive or coeval main stress states in the evolution of Scania since the Permian. Two stress states correspond to normal faulting with NE-SW and NW-SE extensions, one stress state is mainly of reverse type with NE-SW compression, and three stress states are strike-slip in type with NNW-SSE, WNW-ESE and NNE-SSW directions of compression. The NE-SW extension partly corresponds to the Late Carboniferous–Permian important extensional period, dated by dykes and fault mineralisations. However extension existed along a similar direction during the Mesozoic. It has been locally observed until within the Danian. A perpendicular NW-SE extension reveals the occurrence of stress permutations. The NNW-SSE strike-slip episode is also expected to belong to the Late Carboniferous–Permian episode and is interpreted in terms of right-lateral wrench faulting along STZ-oriented faults. The inversion process has been characterised by reverse and strike-slip faulting related to the NE-SW compressional stress state. This study highlights the importance of extensional tectonics in northwest Europe since the end of the Palaeozoic until the end of the Cretaceous. The importance and role of wrench faulting in the tectonic evolution of the Sorgenfrei–Tornquist Zone are discussed.
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Paleostress analysis of atlantic crustal extension in the quebec appalachians
The Journal of Geology, 2006Co-Authors: Stephane Faure, Alain Tremblay, Michel Malo, Jacques AngelierAbstract:Abstract A Paleostress analysis using normal fault slip data and Jurassic dike trends has been conducted in the Quebec and New England Appalachians. Stress tensor analysis of fault slip by a numerical inversion method has distinguished homogeneous and directionally consistent E‐W‐ and NW‐SE‐oriented extensional stress regimes in the Quebec Appalachians and St. Lawrence Lowlands. The directions of extension compare well with the mean direction of extensional stress inferred from the Jurassic dolerite dike trend in New England. Both extensions are interpreted as the result of rift‐related stress associated with the separation of North America and Africa, early in the Late Triassic–Early Jurassic fragmentation of Pangea. The Paleostress field configuration is assumed to be related to the direction of divergent plate motion. The N‐S and NE‐SW Late Proterozoic faults that bordered the Quebec Reentrant and Taconian‐Acadian structures of the Quebec Appalachians appear to have played a significant role in the dis...
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the silidor deposit rouyn noranda district abitibi belt geology structural evolution and Paleostress modeling of an au quartz vein type deposit in an archean trondhjemite
Economic Geology, 2000Co-Authors: Alain Carrier, M. Jébrak, Jacques Angelier, Peter HolylandAbstract:Late orogenic gold-bearing quartz vein deposits within the Rouyn-Noranda mining district occur mainly within Archean tonalitic plutons of the Blake River Group (southern Abitibi belt). The Silidor deposit is a representative example of a pluton-hosted lode gold deposit. The Silidor mine contained 2.95 million tons (Mt; mined and estimated reserves), grading 5.1 g/t Au (~15 t Au). The mineralized zone is 900 m in length and has a vertical extent of 900 m, an average thickness of 3.5 m, and trends northwest-southeast with a dip of 50° to 70° NE. Its alteration envelope consists of a red hematite-altered trondhjemite. Measured δ 18 O values for quartz veins (7.7–10.9‰) and δ 34 S values for pyrite (–6.1 to –9.4‰) imply oxidizing conditions during gold deposition. The mineralized zone comprises: vein quartz (white, gray, and smoky varieties), beige mineralized trondhjemite, and green carbonate-sericite-fuchsite breccia, which resulted from shearing and metasomatism of an early northwest-southeast dioritic dike. A quantitative microtectonic study (>400 measurements) was carried out on the Powell tonalitic sill in the Silidor mine area to reconstruct the deformation before, during, and after the mineralizing events. The reduced stress tensors display large variations in σ 1 orientation, trending successively northwest-southeast, northeast-southwest, and finally north-south. The Silidor deposit is the result of several vein-filling events, which occurred during evolution from strike-slip faulting to reverse faulting regimes, with σ 1 remaining northeast-southwest but with exchange of orientation of σ 2 and σ 3. Such variations may reflect an oblique collision and processes of stress permutation. Paleostress mapping of Archean terranes can be used as a targeting tool for mesothermal lode gold deposits. Reduced stress tensors were used for the computation of Paleostress maps, using a distinct element model. The Silidor Au quartz mineralization appears on these Paleostress maps in an area characterized by low mean stress throughout the deformation history of the area near the Horne Creek fault. This study emphasizes the role of second-order faulting in the location of low- and high-pressure zones in the Archean crust and the possible role of a tectonic indentor in the location of Au mineralization.
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Paleostress trajectory maps based on the results of local determinations the lissage program
Computers & Geosciences, 1994Co-Authors: Jiancheng Lee, Jacques AngelierAbstract:Abstract This paper presents a program to reconstruct maps of Paleostress trajectories for a given tectonic event, based on the results of multiple local stress determinations. The compiling process from local field data to regional Paleostress database, is summarized. Two methods allow transformation of the local scattered directional data into a 2-D regional distribution of trajectories of principal Paleostress axes, including a smoothing process: (1) a linear model uses a bivariate polynomial function to express the distribution of regional stress vectors; (2) a distance-weighting method uses an inverse distance weighting function to determine the Paleostress direction for any given point within the calculated area. The smoothness degree of trajectories is controlled by the degree of the polynomial function for the linear model, and by the power value and threshold distance for the distance weighting method. The second method generally provides better results. The effects of local stress deviations (resulting from determination uncertainties or local stress perturbations) also are considered through weighting of local data; such individual weights are quantified with confidence intervals according to the quality of the data. The detailed description of the algorithm enables the users to understand the running routine of the program. The graphic output of the program consists of (1) the gridded map, and (2) the trajectories map corresponding to the smoothed stress/Paleostress field. A case study shows how the program works.
Aline Saintot - One of the best experts on this subject based on the ideXlab platform.
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comparison of methods to reconstruct Paleostress regimes in the nw greater caucasus fold and thrust belt
Comptes Rendus Geoscience, 2012Co-Authors: Anton V Marinin, Aline SaintotAbstract:Abstract Two groups of researchers have used the same datasets in order to determine Paleostress regimes and the corresponding tectonic phases in the northwestern-Greater Caucasus fold-and-thrust belt. The kinematic indicators were inverted by both groups to determine the magnitude and orientation of the tectonic stresses. The Russian group's method is based on the “structural pattern” that developed under a single stress-strain state in a given rock volume. The French group used a fault slip data inversion. Stress fields reconstructed by both groups show similarities. Because the methods are independent, the Paleostress fields may reflect natural processes. The best-expressed Paleostress field is a NE-SW compression related to the Late Eocene folding and thrusting event. A stress field that may correspond to the latest tectonic phase of the northwestern-Greater Caucasus is characterized by a NNW-SSE striking pressure axis. Other Paleostress fields that span from Late Cretaceous to present-day are also reconstructed by both groups.
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brittle tectonic evolution and Paleostress field reconstruction in the southwestern part of the fennoscandian shield forsmark sweden
Tectonics, 2011Co-Authors: Aline Saintot, M B Stephens, Giulio Viola, O NordgulenAbstract:[1] Six hundred fault slip data have provided robust Paleostress fields within an approximately 35 km3 volume of Paleoproterozoic (1.9 Ga) rocks in the southwestern Fennoscandian Shield, Forsmark, Sweden. These rocks were affected by penetrative ductile strain from 1.87 to 1.86 Ga, folding, ductile strain along discrete zones around 1.8 Ga, and semibrittle or brittle deformation around and after 1.8 Ga. Compatible Paleostress fields have been identified using site-by-site and merged data sets from outcrops and oriented drill cores. Transpressive deformation with a regional NNW-SSE σ1 axis, associated with clockwise stress deviation inside a tectonic lens, resulted in dextral slip along regionally significant, steep WNW-ESE and NW-SE deformation zones. The semibrittle and most of the brittle structures, including specifically the epidote-bearing fractures, were established during this oldest regime around 1.8 Ga (latest Svecokarelian). A younger Paleostress field with a NE-SW σ1 axis, which was also transpressive in character, is inferred to have been active at 1.7–1.6 Ga. The best defined Paleostress field is transpressive in character with a WNW-ESE σ1 axis that resulted in sinistral reactivation along the WNW-ESE and NW-SE zones. The main set of laumontite-stepped faults developed at this stage at 1.1–0.9 Ga (Sveconorwegian). It is impossible to exclude fully the influence of reactivation during even younger Phanerozoic tectonic events. Subordinate extensional Paleostress fields were related either to the latest Svecokarelian and Sveconorwegian transpressive regimes, due to σ1 and σ2 stress permutations, or to regional extensional tectonic regimes during the Meso- or Neoproterozoic or later during the Permo-Carboniferous and/or Mesozoic.
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Paleostress field reconstruction and revised tectonic history of the donbas fold and thrust belt ukraine and russia
Tectonics, 2003Co-Authors: Aline Saintot, Randell Stephenson, Arjan Brem, S M Stovba, V A PrivalovAbstract:[1] In the WNW-ESE Donbas fold belt (DF), inversion of 3500 microtectonic data collected at 135 sites, in Proterozoic, Devonian, Carboniferous, and Cretaceous competent rocks allowed reconstruction of 123 local stress states. Accordingly, four successive Paleostress fields reveal the tectonic evolution of the DF. At the numerous sites that have been affected by polyphase tectonics, the chronology between local Paleostress states (also Paleostress fields) was established using classical criteria (crosscutting striae, pre- or post-folding stress states, stratigraphic control). The oldest event is an extensional stress field with NNE-SSW σ3. It corresponds to the rifting phases that generated the basin in Devonian times and its early Visean reactivation. Later, the DF was affected by a transtension, with NW-SE σ3 characterizing Early Permian tectonism, including the development of the “Main Anticline” of the DF and the pronounced uplift of its southern margin and Ukrainian Shield. Two Paleostress fields characterize the Cretaceous/Paleocene inversion of the DF, which was accompanied by folding and thrusting. Both are compressional in type but differ by the trend of σ1, which was first NW-SE and subsequently N-S. The discrete Paleostress history of the DF allows a revised interpretation of its tectonic evolution with significant implications for understanding the geodynamic evolution of the southern margin of the East European Craton.
O Nordgulen - One of the best experts on this subject based on the ideXlab platform.
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brittle tectonic evolution and Paleostress field reconstruction in the southwestern part of the fennoscandian shield forsmark sweden
Tectonics, 2011Co-Authors: Aline Saintot, M B Stephens, Giulio Viola, O NordgulenAbstract:[1] Six hundred fault slip data have provided robust Paleostress fields within an approximately 35 km3 volume of Paleoproterozoic (1.9 Ga) rocks in the southwestern Fennoscandian Shield, Forsmark, Sweden. These rocks were affected by penetrative ductile strain from 1.87 to 1.86 Ga, folding, ductile strain along discrete zones around 1.8 Ga, and semibrittle or brittle deformation around and after 1.8 Ga. Compatible Paleostress fields have been identified using site-by-site and merged data sets from outcrops and oriented drill cores. Transpressive deformation with a regional NNW-SSE σ1 axis, associated with clockwise stress deviation inside a tectonic lens, resulted in dextral slip along regionally significant, steep WNW-ESE and NW-SE deformation zones. The semibrittle and most of the brittle structures, including specifically the epidote-bearing fractures, were established during this oldest regime around 1.8 Ga (latest Svecokarelian). A younger Paleostress field with a NE-SW σ1 axis, which was also transpressive in character, is inferred to have been active at 1.7–1.6 Ga. The best defined Paleostress field is transpressive in character with a WNW-ESE σ1 axis that resulted in sinistral reactivation along the WNW-ESE and NW-SE zones. The main set of laumontite-stepped faults developed at this stage at 1.1–0.9 Ga (Sveconorwegian). It is impossible to exclude fully the influence of reactivation during even younger Phanerozoic tectonic events. Subordinate extensional Paleostress fields were related either to the latest Svecokarelian and Sveconorwegian transpressive regimes, due to σ1 and σ2 stress permutations, or to regional extensional tectonic regimes during the Meso- or Neoproterozoic or later during the Permo-Carboniferous and/or Mesozoic.
Gloria Arancibia - One of the best experts on this subject based on the ideXlab platform.
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fracture network fluid pathways and Paleostress at the tolhuaca geothermal field
Journal of Structural Geology, 2017Co-Authors: Pamela Perezflores, Eugenio E Veloso, Jose Cembrano, Pablo Sanchezalfaro, Martin Lizama, Gloria ArancibiaAbstract:Abstract In this study, we examine the fracture network of the Tolhuaca geothermal system located in the Southern Andean volcanic zone that may have acted as a pathway for migration and ascent of deep-seated fluids under the far/local stress field conditions of the area. We collected the orientation, slip-data and mineralogical content of faults and veins recovered on a ca. 1000 m deep borehole (Tol-1) located in the NW-flank of the Tolhuaca volcano. Tol-1 is a non-oriented, vertical borehole that recovered relatively young ( 1 axis (083/74) and a subhorizontal, NS-trending σ 3 axis (184/03). Within the topmost 400 m of the borehole, faults and veins are randomly oriented, whereas below 400 m depth, faults and veins show preferential NE-to EW-strikes and steep (>50°) dips. The EW-striking veins are compatible with the calculated local stress field whereas NE-striking veins are compatible with the regional stress field, the morphological elongation of volcanic centers, alignments of flank vents and dikes orientation. Our results demonstrate that the paleomagnetic methodology proved to be reliable and it is useful to re-orient vertical boreholes such as Tol-1. Furthermore, our data show that the bulk transpressional regional stress field has local variations to a tensional stress field within the NE-striking fault zone belonging to the Liquine-Ofqui Fault System, favoring the activation of both NW- and NE-striking pre-existent discontinuities, especially the latter which are favorably oriented to open under the prevailing stress field. The vertical σ 1 and NS-trending subhorizontal σ 3 calculated in the TGS promote the activation of EW-striking extensional veins and both NE and NW-striking hybrid faults, constituting a complex fluid pathway geometry of at least one kilometer depth.
