Chapter 15: Goldstrike Gold System, North Carlin Trend, Nevada, USA

2020 ◽  
pp. 313-334
Author(s):  
Paul J. Dobak ◽  
François Robert ◽  
Shaun L.L. Barker ◽  
Jeremy R. Vaughan ◽  
Douglas Eck
Keyword(s):  
Gold Mineralization ◽  
Normal Fault ◽  
Thermal Anomaly ◽  
Fault System ◽  
Normal Faults ◽  
Main Stage ◽  
Arsenian Pyrite ◽  
Carlin Trend ◽  
Structural Architecture ◽  
Clastic Sedimentary

Abstract The Eocene Goldstrike system on the Carlin Trend in Nevada is the largest known Carlin-type gold system, with an endowment of 58 million ounces (Moz) distributed among several coalesced deposits in a structural window of gently dipping carbonate rocks below the regional Roberts Mountains thrust. The 3.5- × 2.5-km Goldstrike system is bounded to the east by the Post normal fault system and to the south by the Jurassic Goldstrike diorite stock and is partly hosted in the favorable slope-facies apron of the Bootstrap reef margin that passes through the system. The carbonate and clastic sedimentary sequence is openly folded, cut by sets of reverse and normal faults, and intruded by the Jurassic Goldstrike stock and swarms of Jurassic and Eocene dikes, establishing the structural architecture that controlled fluid flow and distribution of Eocene mineralization. A proximal zone of permeability-enhancing decarbonatization with anomalous gold (>0.1 ppm) extends a few hundreds of meters beyond the ore footprint and lies within a carbonate δ18O depletion anomaly extending ~1.4 km farther outboard. The full extent of the larger hydrothermal system hosting Goldstrike and adjacent deposits on the northern Carlin Trend is outlined by a 20- × 40-km thermal anomaly defined by apatite fission-track analyses. The bulk of the mineralization is hosted in decarbonatized sedimentary units with elevated iron contents and abundant diagenetic pyrite relative to background. Gold is associated with elevated concentrations of As, Tl, Hg, and Sb, and occurs in micron-sized arsenian pyrite grains or in arsenian pyrite overgrowths on older, principally diagenetic pyrite, with sulfidation of available iron as the main gold precipitation mechanism. The intersection of a swarm of Jurassic lamprophyre dikes with the edge of the limestone reef provided a favorable deeply penetrating structural conduit within which a Jurassic stock acted as a structural buttress, whereas the reef’s slope-facies apron of carbonate units, with high available iron content, provided a fertile setting for Carlin-type mineralization. The onset of Eocene extension coupled with a southwestward-sweeping Cenozoic magmatic front acted as the trigger for main-stage gold mineralization at 40 to 39 Ma. All these factors contributed to the exceptional size and grade of Goldstrike.

Rifting in SW China: structural and sedimentary investigation of the initial crustal response to emplacement of the Permian Emeishan LIP

2018 ◽  
Vol 156 (4) ◽  
pp. 745-758 ◽  
Author(s):  
YU WANG ◽  
INGRID UKSTINS PEATE ◽  
ZHAOHUA LUO ◽  
SHUZHI WANG ◽  
LILU CHENG ◽  
...  
Keyword(s):  
Near Field ◽  
Flood Basalt ◽  
Large Igneous Province ◽  
Normal Faults ◽  
Rift System ◽  
Main Stage ◽  
Plate Motions ◽  
Sedimentary Deposits ◽  
Icp Ms ◽  
Clastic Sedimentary

AbstractDetailed structural, volcanic, and sedimentary investigations of the crustal response to the emplacement of the Middle–Late Permian Emeishan large igneous province show that a rifting system developed prior to the main stage of flood basalt eruptions, in the form of sedimentary breccias, clastic sedimentary deposits and mafic hydromagmatic units. Detrital zircon grains from sandstones yield ~750–800 Ma LA-ICP-MS 206Pb/238U age clusters, showing that material was sourced from the Yangtze crystalline basement. Gabbros and pegmatites intruded along the normal faults of the rift system yield zircon ages of 264–260 Ma, and thus constrain the timing of rifting. N–S-trending rift zones developed along the western flank of the Pan-Xi palaeo-uplift, with NE–SW- and NNE–SSW-trending rifts on the eastern side and along the western and eastern margins of the Yangtze Block. The rifting progressed in pulses, with an initial phase of normal faulting followed by rapid deposition of breccias. Later there was lower-energy deposition of sandstone, with accompanying rhyolitic eruptions. This was followed by low-energy sedimentation of mudstones and dolomites, with accompanying hydromagmatic deposits. Rift system formation was constrained by a combination of far- and near-field tectonic stresses due to plate motions and lithospheric interaction with initial Emeishan volcanism.

scholarly journals Segmentation of the Wassuk Range normal fault system, Nevada (USA): Implications for earthquake rupture and Walker Lane dynamics

2021 ◽  
Author(s):  
Ben Surpless ◽  
Sarah Thorne
Keyword(s):  
Seismic Hazard Assessment ◽  
Normal Fault ◽  
Relative Strength ◽  
Fault System ◽  
Normal Faults ◽  
Slip Rates ◽  
Future Evolution ◽  
Walker Lane ◽  
Differential Uplift ◽  
Wassuk Range

Normal faults are commonly segmented along strike, with segments that localize strain and influence propagation of slip during earthquakes. Although the geometry of segments can be constrained by fault mapping, it is challenging to determine seismically relevant segments along a fault zone. Because slip histories, geometries, and strengths of linkages between normal fault segments fundamentally control the propagation of rupture during earthquakes, and differences in segment slip rates result in differential uplift of adjacent footwalls, we used along-strike changes in footwall morphology to detect fault segments and the relative strength of the mechanical links between them. We applied a new geomorphic analysis protocol to the Wassuk Range fault, Nevada, within the actively deforming Walker Lane. The protocol examines characteristics of footwall morphology, including range-crest continuity, bedrock-channel long profiles, catchment area variability, and footwall relief, to detect changes in strike-parallel footwall characteristics. Results revealed six domains with significant differences in morphology that we used to identify seismically relevant fault segments and segment boundaries. We integrated our results with previous studies to determine relative strength of links between the six segments, informing seismic hazard assessment. When combined with recent geodetic studies, our results have implications for the future evolution of the Walker Lane, suggesting changes in the accommodation of strain across the region. Our analysis demonstrates the power of this method to efficiently detect along-strike changes in footwall morphology related to fault behavior, permitting future researchers to perform reconnaissance assessment of normal fault segmentation worldwide.

Role of Basement Structural Inheritance and Strike-Slip Fault Dynamics in the Formation of the Pataz Gold Vein System, Eastern Andean Cordillera, Northern Peru

2021 ◽  
Author(s):  
Daniel Wiemer ◽  
Steffen G. Hagemann ◽  
Nicolas Thébaud ◽  
Carlos Villanes
Keyword(s):  
Structural Control ◽  
Structural Model ◽  
Gold Mineralization ◽  
Strike Slip ◽  
Fault System ◽  
Normal Faults ◽  
Vein System ◽  
Structural Inheritance ◽  
Andean Cordillera ◽  
Northern Peru

Abstract New regional- to vein-scale geologic mapping and structural analysis of the Carboniferous Pataz gold vein system (~10 Moz Au) reveal critical insights into the structural control on gold mineralization along the Eastern Andean Cordillera of northern Peru. The Pataz basement comprises continental volcanic arc and marginal to marine sedimentary rocks, which experienced intensive D2 deformation associated with Late Famatinian northeast to southwest compressive fold-and-thrust belt development. The D2 event produced an E-NE–dipping structural grain, including (1) tilted and F2 folded S1 foliations, (2) local F2 axial planar S2 foliations, and (3) subparallel D2 thrust faults. Intrusions, constituting the ca. 342 to 332 Ma (Mississippian) Pataz batholith, were emplaced along strike of the prominent Río Marañón fault and inherited the D2 basement structures, as evident in the orientation of suprasolidus magmatic flow zones and intrusive contacts within the batholith. Progressive horst-and-graben development affecting the volcanic carapace of the Pataz batholith records late syn- to postmagmatic uplift and transition into a NW-SE–extensional regime. We show that the E-NE–dipping, batholith-hosted gold vein system formed through synchronous activation of two geometric fault-fill vein types, following (1) the moderately E-NE–dipping D2 basement-inherited competency contrasts within the batholith and (2) shallow NE-dipping Andersonian footwall thrusts, during NE-directed shortening (D3a). Both geometric vein types display an early paragenetic stage (I) of quartz-pyrite, progressing texturally from hydraulic breccia into crack-seal laminated shear veins. A second (II), undeformed quartz-pyrite-sphalerite-galena paragenetic stage is observed to fill previously established dilational sites adjacent to newly formed D3b normal faults, which likely formed during regional NW-SE–extensional horst-graben development. Kinematics and relative timing indicate that, upon batholith solidification, D3a transpressional dextral strike-slip ruptures along the Río Marañón fault superimposed a lower-order Riedel-type fault system. Fluid-assisted fault activation preferentially impinged on the D2 basement-inherited competency contrasts within the batholith. Subsequent transition into a transtensional regime led to the D3b normal faulting, providing a feeder system for stage II fluid influx. The tectonic switch may be explained either by increasing tensile strain accommodation upon progressive strike-slip movement within a regional dilational jog or by larger-scale crustal relaxation of the late Gondwana margin upon final Pangea assembly. Our new structural model for the Pataz vein system evolution highlights the importance of basement structural inheritance in controlling the localization of gold mineralization along polycyclic supercontinent margins. We provide valuable insights for exploration targeting of complex vein arrays within rheologically heterogeneous host rocks.

scholarly journals Structural characterization of fault damage zones in carbonates (Central Apennines, Italy)

2021 ◽  
Author(s):  
Miriana Chinello ◽  
Michele Fondriest ◽  
Giulio Di Toro
Keyword(s):  
Fault Zone ◽  
Hanging Wall ◽  
Damage Zone ◽  
Normal Fault ◽  
Vertical Displacement ◽  
Fault System ◽  
Normal Faults ◽  
Central Apennines ◽  
Fault Surface ◽  
Fracture Intensity

<p>The Italian Central Apennines are one of the most seismically active areas in the Mediterranean (e.g., L’Aquila 2009, Mw 6.3 earthquake). The mainshocks and the aftershocks of these earthquake sequences propagate and often nucleate in fault zones cutting km-thick limestones and dolostones formations. An impressive feature of these faults is the presence, at their footwall, of few meters to hundreds of meters thick damage zones. However, the mechanism of formation of these damage zones and their role during (1) individual seismic ruptures (e.g., rupture arrest), (2) seismic sequences (e.g., aftershock evolution) and (3) seismic cycle (e.g., long term fault zone healing) are unknown. This limitation is also due to the lack of knowledge regarding the distribution, along strike and with depth, of damage with wall rock lithology, geometrical characteristics (fault length, inherited structures, etc.) and kinematic properties (cumulative displacement, strain rate, etc.) of the associated main faults.</p><p>Previous high-resolution field structural surveys were performed on the Vado di Corno Fault Zone, a segment of the ca. 20 km long Campo Imperatore normal fault system, which accommodated ~ 1500 m of vertical displacement (Fondriest et al., 2020). The damage zone was up to 400 m thick and dominated by intensely fractured (1-2 cm spaced joints) dolomitized limestones with the thickest volumes at fault oversteps and where the fault cuts through an older thrust zone. Here we describe two minor faults located in the same area (Central Apennines), but with shorter length along strike. They both strike NNW-SSE and accommodated a vertical displacement of ~300 m.</p><p>The Subequana Valley Fault is about 9 km long and consists of multiple segments disposed in an en-echelon array. The fault juxtaposes pelagic limestones at the footwall and quaternary deposits at the hanging wall. The damage zone is < 25 m  thick  and comprises fractured (1-2 cm spaced joints) limestones beds with decreasing fracture intensity moving away from the master fault. However, the damage zone thickness increases up to ∼100 m in proximity of subsidiary faults striking NNE-SSW. The latter could be reactivated inherited structures.</p><p>The Monte Capo di Serre Fault is about 8 km long and characterized by a sharp ultra-polished master fault surface which cuts locally dolomitized Jurassic platform limestones. The damage zone is up to 120 m thick and cut by 10-20 cm spaced joints, but it reaches an higher fracture intensity where is cut by subsidiary, possibly inherited, faults striking NNE-SSW.</p><p>Based on these preliminary observations, faults with similar displacement show comparable damage zone thicknesses. The most relevant damage zone thickness variations are related to geometrical complexities rather than changes in lithology (platform vs pelagic carbonates).  In particular, the largest values of damage zone thickness and fracture intensity occur at fault overstep or are associated to inherited structures. The latter, by acting as strong or weak barriers (sensu Das and Aki, 1977) during the propagation of seismic ruptures, have a key role in the formation of damage zones and the growth of normal faults.</p>

scholarly journals Recent Activity and Kinematics of the Bounding Faults of the Catanzaro Trough (Central Calabria, Italy): New Morphotectonic, Geodetic and Seismological Data

Geosciences ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 405
Author(s):  
Claudia Pirrotta ◽  
Graziella Barberi ◽  
Giovanni Barreca ◽  
Fabio Brighenti ◽  
Francesco Carnemolla ◽  
...  
Keyword(s):  
Scaling Laws ◽  
Normal Fault ◽  
Historical Earthquakes ◽  
Fault System ◽  
Normal Faults ◽  
The North ◽  
Seismological Data ◽  
Geomorphic Features ◽  
Half Graben ◽  
Fault Scarps

A multidisciplinary work integrating structural, geodetic and seismological data was performed in the Catanzaro Trough (central Calabria, Italy) to define the seismotectonic setting of this area. The Catanzaro Trough is a structural depression transversal to the Calabrian Arc, lying in-between two longitudinal grabens: the Crati Basin to the north and the Mesima Basin to the south. The investigated area experienced some of the strongest historical earthquakes of Italy, whose seismogenic sources are still not well defined. We investigated and mapped the major WSW–ENE to WNW–ESE trending normal-oblique Lamezia-Catanzaro Fault System, bounding to the north the Catanzaro Trough. Morphotectonic data reveal that some fault segments have recently been reactivated since they have displaced upper Pleistocene deposits showing typical geomorphic features associated with active normal fault scarps such as triangular and trapezoidal facets, and displaced alluvial fans. The analysis of instrumental seismicity indicates that some clusters of earthquakes have nucleated on the Lamezia-Catanzaro Fault System. In addition, focal mechanisms indicate the prevalence of left-lateral kinematics on E–W roughly oriented fault plains. GPS data confirm that slow left-lateral motion occurs along this fault system. Minor north-dipping normal faults were also mapped in the southern side of the Catanzaro Trough. They show eroded fault scarps along which weak seismic activity and negligible geodetic motion occur. Our study highlights that the Catanzaro Trough is a poliphased Plio-Quaternary extensional basin developed early as a half-graben in the frame of the tear-faulting occurring at the northern edge of the subducting Ionian slab. In this context, the strike-slip motion contributes to the longitudinal segmentation of the Calabrian Arc. In addition, the high number of seismic events evidenced by the instrumental seismicity, the macroseismic intensity distribution of the historical earthquakes and the scaling laws relating to earthquakes and seismogenic faults support the hypothesis that the Lamezia-Catanzaro Fault System may have been responsible for the historical earthquakes since it is capable of triggering earthquakes with magnitude up to 6.9.

Field and petrographic reconnaissance of Franciscan complex rocks of Mount Diablo, California: Imbricated ocean floor stratigraphy with a roof exhumation fault system

2021 ◽  
Author(s):  
John Wakabayashi
Keyword(s):  
Fault System ◽  
Normal Faults ◽  
Coast Range ◽  
Franciscan Complex ◽  
The North ◽  
Tectonic Window ◽  
Coast Range Ophiolite ◽  
Great Valley Group ◽  
Clastic Sedimentary ◽  
Great Valley

ABSTRACT Franciscan subduction complex rocks of Mount Diablo form an 8.5 by 4.5 km tectonic window, elongated E-W and fault-bounded to the north and south by rocks of the Coast Range ophiolite and Great Valley Group, respectively, which lack the burial metamorphism and deformation displayed by the Franciscan complex. Most of the Franciscan complex consists of a stack of lawsonite-albite–facies pillow basalt overlain successively by chert and clastic sedimentary rocks, repeated by faults at hundreds of meters to <1 m spacing. Widely distributed mélange zones from 0.5 to 300 m thick containing high-grade (including amphibolite and eclogite) assemblages and other exotic blocks, up to 120 m size, form a small fraction of exposures. Nearly all clastic rocks have a foliation, parallel to faults that repeat the various lithologies, whereas chert and basalt lack foliation. Lawsonite grew parallel to foliation and as later grains across foliation. The Franciscan-bounding faults, collectively called the Coast Range fault, strike ENE to WNW and dip northward at low to moderate average angles and collectively form a south-vergent overturned anticline. Splays of the Coast Range fault also cut into the Franciscan strata and Coast Range ophiolite and locally form the Coast Range ophiolite–Great Valley Group boundary. Dip discordance between the Coast Range fault and overlying Great Valley Group strata indicates that the northern and southern Coast Range fault segments were normal faults with opposite dip directions, forming a structural dome. These relationships suggest accretion and fault stacking of the Franciscan complex, followed by exhumation along the Coast Range fault and then folding of the Coast Range fault.

scholarly journals Evolution of a Normal Fault System, northern Graben, Taranaki Basin, New Zealand

2021 ◽  
Author(s):  
◽  
Hamish Cameron
Keyword(s):  
New Zealand ◽  
Seismic Reflection ◽  
Normal Fault ◽  
Growth Patterns ◽  
Fault System ◽  
Normal Faults ◽  
3D Seismic ◽  
Fault Evolution ◽  
Migration Pathways ◽  
Insight Into

<p>This study investigates the evolution (from initiation to inactivity) of a normal fault system in proximity to active petroleum systems within the Taranaki Basin, New Zealand. The aim of this research is to understand the evolution, interaction, and in some cases, death of normal faults in a region undergoing progressive regional extension. This research provides insight into the geometry, development, and displacement history of new and reactivated normal fault evolution through interpretation of industry standard seismic reflection data at high spatial and temporal resolution. Insight into normal fault evolution provides information on subsidence rates and potential hydrocarbon migration pathways.  Twelve time horizons between 1.2 and 35 Ma have been mapped throughout 1670 square kilometres of the Parihaka and Toro 3D seismic reflection surveys. Fault displacement analysis and backstripping have been used to determine the main phases of fault activity, fault growth patterns, and maximum Displacement/Length ratios. The timing, geometry, and displacement patterns for 110 normal faults with displacements >20 m have been interpreted and analysed using Paradigm SeisEarth and TrapTester 6 seismic interpretation and fault analysis software platforms.  Normal faults within the Parihaka and Toro 3D seismic surveys began developing at ˜11 Ma, with the largest faults accruing up to 1500 m of displacement in <10 Myr (mean throw displacement rate of 0.15mm/yr). Approximately 50% of the 110 mapped faults are associated with pre-existing normal faults and have typical cumulative displacements of ˜20 – 1000 m, with strike parallel lengths of <1 – 23 km. In contrast, new faults have typically greater displacements of 20 – 1400 m, and are generally longer with, with strike parallel lengths of ˜1 – 33 km.   New faults were the first faults within the system to become inactive when strain rates decreased from 0.06 – 0.03 between 3.6 and 3.0 Ma. Eight of the largest faults with > 1000 m cumulative displacement reach the seafloor and are potentially active at present day. An earthquake on one of these faults could be expected to produce MW 2.2 based on the maximum strike-parallel length of the fault plane.</p>

scholarly journals Joint Interpretation of Geophysical Results and Geological Observations for Detecting Buried Active Faults: The Case of the “Il Lago” Plain (Pettoranello del Molise, Italy)

2021 ◽  
Vol 13 (8) ◽  
pp. 1555
Author(s):  
Rosa Nappi ◽  
Valeria Paoletti ◽  
Donato D’Antonio ◽  
Francesco Soldovieri ◽  
Luigi Capozzoli ◽  
...  
Keyword(s):  
Seismic Tomography ◽  
Active Faults ◽  
Low Frequency ◽  
Normal Fault ◽  
Seismic Source ◽  
Fault System ◽  
Normal Faults ◽  
Macroseismic Data ◽  
Epicentral Area ◽  
Seismogenic Source

We report a geophysical study across an active normal fault in the Southern Apennines. The surveyed area is the “Il Lago” Plain (Pettoranello del Molise), at the foot of Mt. Patalecchia (Molise Apennines, Southern Italy), a small tectonic basin filled by Holocene deposits located at the NW termination of the major Quaternary Bojano basin structure. This basin, on the NE flank of the Matese Massif, was the epicentral area of the very strong 26 July, 1805, Sant’Anna earthquake (I0 = X MCS, Mw = 6.7). The “Il Lago” Plain is bordered by a portion of the right-stepping normal fault system bounding the whole Bojano Quaternary basin (28 km long). The seismic source responsible for the 1805 earthquake is regarded as one of the most hazardous structures of the Apennines; however, the position of its NW boundary of this seismic source is debated. Geological, geomorphological and macroseismic data show that some coseismic surface faulting also occurred in correspondence with the border fault of the “Il Lago” Plain. The study of the “Il Lago” Plain subsurface might help to constrain the NW segment boundary of the 1805 seismogenic source, suggesting that it is possibly a capable fault, source for moderate (Mw < 5.5) to strong earthquakes (Mw ≥ 5.5). Therefore, we constrained the geometry of the fault beneath the plain using low-frequency Ground Penetrating Radar (GPR) data supported by seismic tomography. Seismic tomography yielded preliminary information on the subsurface structures and the dielectric permittivity of the subsoil. A set of GPR parallel profiles allowed a quick and high-resolution characterization of the lateral extension of the fault, and of its geometry at depth. The result of our study demonstrates the optimal potential of combined seismic and deep GPR surveys for investigating the geometry of buried active normal faults. Moreover, our study could be used for identifying suitable sites for paleoseismic analyses, where record of earthquake surface faulting might be preserved in Holocene lacustrine sedimentary deposits. The present case demonstrates the possibility to detect with high accuracy the complexity of a fault-zone within a basin, inferred by GPR data, not only in its shallower part, but also down to about 100 m depth.

scholarly journals Observations and dynamical implications of active normal faulting in South Peru

2020 ◽  
Vol 222 (1) ◽  
pp. 27-53 ◽  
Author(s):  
Sam Wimpenny ◽  
Carlos Benavente ◽  
Alex Copley ◽  
Briant Garcia ◽  
Lorena Rosell ◽  
...  
Keyword(s):  
Late Quaternary ◽  
Normal Fault ◽  
Temporal Variations ◽  
Alluvial Fan ◽  
Force Balance ◽  
Fault System ◽  
Normal Faults ◽  
Shear Stresses ◽  
Total Force ◽  
The Andes

SUMMARY Orogenic plateaus can exist in a delicate balance in which the buoyancy forces due to gravity acting on the high topography and thick crust of the plateau interior are balanced by the compressional forces acting across their forelands. Any shortening or extension within a plateau can indicate a perturbation to this force balance. In this study, we present new observations of the kinematics, morphology and slip rates of active normal faults in the South Peruvian Altiplano obtained from field studies, high-resolution DEMs, Quaternary dating and remote sensing. We then investigate the implications of this faulting for the forces acting on the Andes. We find that the mountains are extending ∼NNE–SSW to ∼NE–SW along a normal fault system that cuts obliquely across the Altiplano plateau, which in many places reactivates Miocene-age reverse faults. Radiocarbon dating of offset late Quaternary moraines and alluvial fan surfaces indicates horizontal extension rates across the fault system of between 1 and 4 mm yr–1—equivalent to an extensional strain rate in the range of 0.5–2 × 10−8 1 yr–1 averaged across the plateau. We suggest the rate and pattern of extension implies there has been a change in the forces exerted between the foreland and the Andes mountains. A reduction in the average shear stresses on the sub-Andean foreland detachment of ≲4 MPa (20–25 per cent of the total force) can account for the rate of extension. These results show that, within a mountain belt, the pattern of faulting is sensitive to small spatial and temporal variations in the strength of faults along their margins.

scholarly journals Tectonic structure and evolution of the upper plate of Vlahokerasia Metaporphic core (Central Peloponnesus)

2001 ◽  
Vol 34 (1) ◽  
pp. 217 ◽  
Author(s):  
Ε. ΣΚΟΥΡΤΣΟΣ ◽  
Α. ΑΛΕΞΟΠΟΥΛΟΣ ◽  
Σ. ΛΕΚΚΑΣ
Keyword(s):  
Cross Section ◽  
Normal Fault ◽  
Opposite Polarity ◽  
Early Miocene ◽  
Fault System ◽  
Lower Plate ◽  
Normal Faults ◽  
Fault Plane Solutions ◽  
Extensional Deformation ◽  
Metamorphic Core

The geological structure of Vlahokerasia metamorphic core is consisted by a series of imbricated tectonic units, the occurrence of which, from the bottom to the top is as follows: Marbles, Phylites-Quartzites, Tripolitza and Pindos unit. Nevertheless, it has often been observed that some units are juxtaposed, not on the immediate tectonically underlying unit but on even lower units (i.e. Pindos unit lies directly on the Phyllites-Quartzites unit). The first two units, which have undergone Late Oligocene - Early Miocene HP/LT metamorphism, represents the lower plate of the metamorphic core, whereas the latter two (Pindos and Tripolitza units) correspond to the upper plate. The rocks of the upper plate are mainly characterized by a relatively small thickness (<300m) and they are strongly tectonized by two sets of normal faults. The main fault system trends in a ΝW orientation whereas the second one, which is younger, intersects the first set in a NNE orientation. Fault plane solutions performed on the previous-mentioned fault scarps showed a NE-SW oriented extensional stress distribution. In order to study the extensional tectonics, which has obviously influenced the fabric of the whole upper plate, a cross-section parallel to the main extensional axis and very close to the detachment surface has been constructed. The restoration of the cross-section showed that the extension of the upper plate was a result of the function of two sets of 'domino faults' of, relatively, opposite polarity. The gradual activation of these two sets of faults caused a severe thinning of the upper plate, expressed by a horizontal extensional deformation in the order of 302-422 %. Based on the existing radiochronological data, derived from the lower plate and on the age of the postalpine formations, which cover uncomformably the older structures, we assume that the extensional deformation of the upper plate took place during Early Miocene-Lower Pliocene. Regarding the post-alpine sediments, they have been deposited into basins created during the activity of a NW-oriented normal fault system, which cut through the older extensional features.

Sign in / Sign up

Export Citation Format

Share Document