Transpressional Tectonic Regime Research Articles

Structural analysis, tectonic fracturing modeling, and kinematic evolution along the South Atlas Fault at the northern border of the Tinghir-Errachidia-Boudenib basin (Pre-African Trough, Morocco)

The structural evolution of the High Atlas orogenic belt is characterized by the formation of the thrust propagation folds. The exploration and understanding of the southern central-eastern High Atlas orogenic wedge system are still in their infancy. The significance of the growth of the Tinghir-Errachidia-Boudenib foreland basin (TEB) is underestimated due to limited constraints on surface structural styles and kinematics analysis, as well as insufficient surface data. This question is addressed by using several multi-sources and multi-scale data including a geological map constrained from fieldwork and kinematic analysis, combined with subsurface magnetic data. The integration and analysis of these data provided a comprehensive understanding tectonic fracturing model and reconstruct the kinematic evolution of the northern border of the TEB basin. Analysis of surface and subsurface data identify E−, ENE-to WNW- trending Jbel Tisdar and Jbel Rhouir anticlines interpreted as a fault-propagation fold. Magnetic investigations show a positive anomaly superposed on the hinge of the Jbel Tisdar and the Jbel Rhouir anticlines indicating a Triassic and/or Paleozoic uplifted magnetic materials. Along the southern Atlas margin, brittle tectonic is represented by E−to ENE-reverse faults with a small dextral strike-slip component and NNE-to NE-trending strike-slip faults with a reverse component and associated with NW- trending ones. Fracturing mechanism fault-propagation fold highlights three fracture sets: (i) syn-folding E−trending axial fractures; (ii) syn-folding NW- trending transverse fractures and (iii) late-folding NE-trending fractures. Fault kinematics analyses provide a transpressional tectonic regime, responsible for the structuring (folding, faulting, fracturing) of the Jbel Tisdar and the Jbel Rhouir fault-propagation fold, developed in response to Alpine compressional inversion of the central-eastern High Atlas belt.

Geodynamics and tectonic stress model for the Zagros fold–thrust belt and classification of tectonic stress regimes

Stress measurement in rocks is an essential parameter in Earth and petroleum sciences. In hydrocarbon exploration and production from oilfields, a lack of sufficient knowledge on the initial stress field for the fracturing of formations limits proper simulation of the production process.To date, only a limited number of studies have investigated the state of stress in the Zagros Mountains. In this paper, well-established analytical techniques were used to determine the stress state in the Zagros Mountains. First, the Angelier method was used to invert earthquake data in different structural domains. Second, the pattern of crustal stresses was analyzed, and four classes of stress regimes were identified. The stress patterns were reconstructed for five distinct structural domains (zones 1–5). In all five zones, the compressive stress was normal to the main structures (fold axis and fault trace with NW‒SE strike). It can be inferred that the structural pattern in the sedimentary cover of the Zagros fold-and-thrust belt (ZFTB) is controlled by R1 (Regime 1) and R4 for zones 1 and 2; R3 for zone 3; R1 and R2 for zone 4; and zone 5. The reconstructed stress patterns are consistent with the observed strike-slip faulting and compressional tectonic deformation regimes. The patterns indicate that deformation in the ZFTB can be explained by a dextral transpressional tectonic model. First-order NE–SW compression stress controls the main convergence tectonics within the Zagros Mountains. Two subordinate compression directions were also identified: one oriented in a dextral main compression direction (N 241°–243°) and another in a sinistral (N135°–177°) and minor extension (N201°–229°). Classification and modeling of the stress regimes identified both thrusting and strike-slip systems; the former controls the Main Zagros Reverse Fault (hereinafter MZRF), and the latter results in a transpressional tectonic regime.

A-type granites in space and time: Relationship to the supercontinent cycle and mantle events

Field, petrologic and geochemical data indicate that post-Archean A-type granites were emplaced in extensional, compressional or transpressional tectonic regimes, mostly in accretionary orogen (>75%) and continental rift settings (10-20%), with only minor examples in hotspot (≤ 8%) and collisional orogen (≤ 5%) settings. Only hotspot/rift-related A-type granites should be considered characteristic of within-plate or intracratonic settings since most A-type granites are orogen-related. The greatest proportion of post-Archean A-type granites was produced in orogens of two ages: 1.7-1.0 Ga in the Great Proterozoic Accretionary Orogen in Laurentia and Baltica, and at 300-100 Ma in East Asian orogens. The widespread production of A-type granite magma in orogens between 1700 and 1100 Ma is not consistent with a single-lid tectonic regime during the Mesoproterozoic. Age-frequency peaks in A-type granites occur at 2.7, 1.85, 1.45, 1.1, 0.6, 0.3 and 0.1 Ga. The geographic age distribution of these peaks is heterogeneous as recorded in Eastern Asia (300 and 100 Ma), Arabian-Nubian orogen (600 Ma), the Laurentian Grenville orogen (1100 Ma), Central/Southwest Laurentian orogens (1450 Ma), and in Brazilian orogens (1850 and 2700 Ma). Thus, none of these age peaks should be considered global based on our current database. During supercontinent assembly, orogen A-type granites dominate (chiefly in back-arc settings), and during breakup, hotspot/rift types increase in abundance but do not dominate until the breakup of Pangea in the last 200 Myr. A-type granite frequency peaks at 1.85, 1.1, 0.6 and 0.3 Ga comprise mostly orogenic back-arc types and correspond to a high frequency of orogens at these times and those at 1.85, 1.45, 1.1 and 0.6 Ga also coincide with peaks in plate speed. A remarkable correlation of six orogen A-type granite frequency peaks at 2.7, 1.85, 1.1, 0.6, 0.3 and 0.1 Ga with zircon and LIP age peaks suggests that back arc A-type granite frequency is related to secular mantle events such as global plume events or mantle overturn.

Geology and Structural Evolution of the La Huifa Ore Deposit, Central Chile: A Newly Discovered Porphyry Cu-Mo System in the El Teniente District

Abstract La Huifa is a breccia-related Cu-Mo porphyry deposit located in the Andes of central Chile, 3 km northeast of the giant El Teniente porphyry Cu-Mo orebody. It was discovered as part of CODELCO’s (Corporación Nacional del Cobre de Chile) brownfield exploration activities in the El Teniente district. It is the first major discovery in the area, and this work presents its first detailed geologic description. The La Huifa orebody is related to a complex of late Miocene diorite and granodiorite intrusions and hydrothermal breccias, the latter characterized by abundant tourmaline-anhydrite cement, emplaced in middle to late Miocene volcanic and subvolcanic rocks. The structural architecture of La Huifa is dominated by WNW-and NE-striking high angle faults. Usually, slip on the WNW-striking faults involves a sinistral component, whereas slip on the NE-striking faults is predominantly dextral. The main hydrothermal breccia body at La Huifa is located at the intersection of WNW- and NE-striking faults. Four stages are proposed for the tectono-magmatic-hydrothermal evolution of La Huifa:Premineralization, involving tourmaline-albite veins and sodic calcic alteration emplaced under a transpressive tectonic regime with a subhorizontal, ~E-W–trending σ1 (~N-S–trending σ3);Early mineralization, involving a polydirectional vein system associated with poorly developed potassic and transitional alteration zones with a scarce presence of Cu and Mo sulfides;Main mineralization, involving Cu- and Mo-rich anhydrite-tourmaline hydrothermal breccias and polydirectional veins associated with strong chlorite-sericite alteration with a 270° to 290°C emplacement temperature, obtained from chlorite geothermometry. The regional stress field during this period was exceeded by the local fluid pressure. These breccias and veins are followed by the emplacement of NE-striking C and D type veins associated with gray and white sericite alteration, respectively, which show a similar temperature range.Late mineralization, involving a NE-striking, carbonate-rich vein system containing polymetallic sulfides. It is associated with argillic alteration, whose temperature was 200° to 260°C. This stage occurred under a compressive tectonic regime with NE-trending σ1. The relatively low temperature at which mineralization was introduced in this deposit (~270°–290°C) and the predominantly vertical fluid flow pattern typical of hydrothermal breccia systems allow us to infer the presence of more mineralized rock at depth, below the recognized portion of the system. The association of Cu and Mo enrichment with chlorite-sericite alteration, instead of higher-temperature potassic or gray sericite alteration events, makes La Huifa a unique case among the porphyry deposits of central Chile and broadens the scope of mineralization styles that could be targeted in this belt. Finally, the intersection of arc-oblique, high-angle faults and, in particular, the presence of fault systems orthogonal to the main compression direction, favorable for magma storage and differentiation and metal concentration, constitute a valuable tool for exploring porphyry Cu deposits in similar geologic contexts.

Structural control and tectono-sedimentary evolution of the Gulf of Cadiz, SW Iberia since the late Miocene: Implications for contourite depositional system

The Gulf of Cadiz Contourite Depositional System (GCCS) developed due to the interaction of the Mediterranean Outflow Water (MOW) with the middle continental slope of the SW Iberian continental margin. The GCCS evolved in a complex tectonic setting within the foreland of the Betic Orogeny and near the Nubia-Eurasia plate boundary. This study used tectonostratigraphic analysis of an extensive 2D multichannel seismic reflection dataset to investigate how inherited basin configuration and tectonic activity controlled sedimentary stacking pattern and evolution of the GCCS. Three regional tectonostratigraphic units (U1-U3) were recognised in the margin. The younger seismic unit U3 corresponds to the Miocene-Quaternary foreland basin system where the contourite system is generated. Seismic analysis also detected the dextral strike-slip Gil Eanes Fault Zone (described herein for the first time), the Cadiz Fault, the Albufeira-Guadalquivir-Doñana Basement High and several diapiric structures. Integrated analysis of seismic profiles showing these tectonic structures with thickness and earthquake distribution maps suggest four tectono-sedimentary domains. The distinct characteristics shown by contourite features in the different domains, depends at broad-scale on the tectonic-control of the accommodation space (i.e., subsidence or uplift) and at local-scale on the presence of structural highs and fault-related depressions. Both influence bottom-current circulation and thus the evolution of the contourite deposits through the late Miocene and Quaternary. Three main stages have been recognised in the Gulf of Cadiz evolution: 1) the region was the western continuation of the Betic Corridor until the final re-opening of the Strait of Gibraltar (8–5.3 Ma). In this stage there is a predominance of turbidites or hemipelagic deposits, dependant on tectonic activity; 2) with the final re-opening of the Mediterranean-Atlantic connection there is the onset of the Pliocene- Quaternary contourite depositional system (5.3–2.0 Ma). Short-term changes in sedimentation during this stage, from contourite to turbidite deposits, indicate periods of increased tectonic activity; and 3) after the onset of the transpressive tectonic regime in the area (from 2.0 Ma), sedimentation became more homogeneous suggesting stable conditions (decrease of tectonic activity) with dominant contourite deposition. This work highlights the remarkable influence of structural features and tectonic events in controlling the seafloor relief and in turn in influenced the local oceanic circulation processes that controlling the morphology and sedimentary evolution of contourite systems.

Rees and other critical raw materials in Cretaceous Mediterranean-type bauxite: The case of the Sardinian ore (Italy)

Mediterranean-type bauxite deposits in Sardinia formed during the Upper Cretaceous (Cenomanian–Turonian) due to the emergence of the south European margin of the Alpine Tethys in an area affected by monsoonal climate. The deposits were controlled by the structural frame formed in a transpressive tectonic regime and unconformably overlie carbonate rocks of different age and composition, which led to the formation of different bauxite types. In general, in the Sardinian bauxite deposits, boehmite is the main Al-phase, kaolinite is the main Si-rich mineral, and hematite as well as goethite are the Fe-rich phases. Secondary authigenic anatase and detrital rutile control the Ti contents. Eu/Eu* anomalies show that the bauxite types were derived from the Variscan basement. However, there are differences in Al2O3 and SiO2 contents, which suggest there was localised variability in the extent of epigenetic replacement of kaolinite by boehmite. R-mode factor analysis suggests that most critical raw materials (as defined by the devoted European Union working group), such as Sc, Ga, Nb, Hf, Ta, and W, covary with Al2O3 contents. In the Si-poor bauxite, these metals of economic interest are likely controlled by boehmite, whereas in the Si-rich bauxite they are mostly controlled by weathering-resistant minerals. Rare earth element (REE)-rich minerals, including fluorocarbonates and cerianite, are concentrated in the basal, illuvial horizon, especially in the silica-rich bauxite (ΣREE = 1006–2034 ppm). Cerianite formation required Ce oxidation, whereas fluorocarbonate formation involved mobilisation of trivalent REEs and further fluoride complexation. Both REE-rich mineral phases precipitated under alkaline pH conditions near to the carbonate bedrock. Our evaluation of the critical raw materials distribution in the Sardinian bauxite, coupled with the “economic importance” and “supply risk” parameters, indicate the ore contains large amounts of metals characterised by a “supply risk”, such as light and heavy REEs, and metals of “economic importance”, such as V and W. In this way, the Sardinian bauxite deposits could be reconsidered as a potential source of critical raw materials.

Geometry and kinematics of right‐lateral transpressional faults and growth folds, the western side of the Gulf of Suez, Egypt

Elaborated geological mapping and structural analysis of the Gulf of Suez's western side revealed two superimposed tectonic regimes; Late Cretaceous‐Early Eocene dextral transpression along ENE‐oriented deep‐seated faults and NE Oligo‐Miocene extension. Pre‐rift structures are represented by four ENE‐oriented right‐lateral strike‐slip deformation zones (DZ). Each DZ is defined by the ENE‐oriented right‐lateral strike‐slip faults, NE to ENE growth folds, and NW‐oriented normal faults. The orthogonal relation between the growth folds and NW‐oriented faults indicates their association to a strike‐slip tectonic regime. The tight overturned folds and the small angles between the growth fold axis and the principal deformation zone implies transpression rather than simple shearing. A transpressional tectonic regime with NW‐SE maximum principal stress (σ1) and NE‐SW minimum principal stress (σ3) were dominantly active during Late Cretaceous‐Early Eocene. The occurrence of three angular unconformities at different stratigraphic levels within the Upper Cretaceous‐Lower Eocene sedimentary sequences infer the deformation age. ENE anticlines have grown above the propagating deep‐seated transpressional faults, associated with continuous exhumation along their hinge zones and syntectonic deposition in the sub‐basins beyond their steep limbs.

Tectonic geomorphology assessment of neotectonics in the north of Damghan Region, Alborz Mountain Belt, Northern Iran

In mountain ranges, recent and active tectonics can be viewed as the main factor contributing to rock uplift, their present-day topography being the result of the competition between tectonic and erosional processes. The region coincides with three faults which show signs of activity during the late Quaternary period: The Astaneh, North Damghan, and Damghan faults, which collectively make up the SW section of the left‐lateral Shahrud fault system. In this study we have analyzed morphotectonic and neotectonic indices to evaluate tectonic activity of the study area.Tectonic geomorphological indices that are used in this study are drainage basin based (drainage basin asymmetry factor (Af), Hypsometric integral (Hi)) and mountain front based (mountain-front sinuosity (Smf), valley floor width – valley height ratio (Vf)) which can be useful tools for studying active tectonics. The study area includes pop-up structures that are formed during inverse tectonic activities of Alborz mountain belt. Strike-slip faults and flower structures suggest transpressional tectonic regime at eastern part of Alborz.

A new model for the optimal structural context for giant porphyry copper deposit formation

AbstractPorphyry-type deposits are the main global source of copper and molybdenum. An improved understanding of the most favorable structural settings for the emplacement of these deposits is necessary for successful exploration, particularly considering that most future discoveries will be made under cover based on conceptual target generation. A common view is that porphyry deposits are preferentially emplaced in pull-apart basins within strike-slip fault systems that favor local extension within a regional compressive to transpressive tectonic regime. However, the role of such a structural context in magma storage and evolution in the upper crust remains unclear. In this work, we propose a new model based on the integration of structural data and the geometry of magmatic-hydrothermal systems from the main Andean porphyry Cu-Mo metallogenic belts and from the active volcanic arc of southern Chile. We suggest that the magma differentiation and volatile accumulation required for the formation of a porphyry deposit is best achieved when the fault system controlling magma ascent is strongly misoriented for reactivation with respect to the prevailing stress field. When magmas and fluids are channeled by faults favorably oriented for extension (approximately normal to σ3), they form sets of parallel, subvertical dikes and veins, which are common both during the late stages of the evolution of porphyry systems and in the epithermal environment. This new model has direct implications for conceptual mineral exploration.

Structural styles of the Aras fault zone with implications for a transpressive fault system in NW Iran

• NE-striking Aras Fault Zone (AFZ) bounds the Talesh and Lesser Caucasus blocks. • The AFZ is characterized by well-developed geological and geomorphological features. • Paleostress results along the AFZ indicate a similar tectonic regime since Pliocene. • The transpressive tectonic regime controls the structural evolution of the AFZ. • Transpressive tectonic regime leads to strain partitioning along the AFZ. Aras Fault Zone (AFZ) is one of the most important intra-plate fault zones within the Turkish-Iranian Plateau. The AFZ is divided into five fault branches based on geometrical and structural properties called the Aras Main, Horadiz, Khodafarin, Asadkandi, and Aslanduz fault branches. Our geometric and kinematic analysis indicates that these faults exhibit compressional left-lateral strike-slip fault characteristics with general directions of NE-SW and dipping to SE. Structural mapping has revealed that the NE section of the AFZ shows typical horsetail fault geometry. Few meters to approximately 17 km of left-lateral displacements were observed along the AFZ, indicating the occurrence of numerous historical earthquake events. Paleostress analysis of fault slip data reveals that the AFZ has developed in the dominant NNE-SSW and NE-SW oriented compressional stress regime. Evaluating the Ratio of Principal Stress Differences (R), Stress Regime Index (R'), and principal stress directions show that the zone is under the transpressional tectonic regime. Paleostress orientations are consistent with orientations of the GPS velocity vectors, which indicates that the region, including the AFZ, is under the effect of the same tectonic regime, at least since Pliocene. The amounts of strike-slip partitioning on discrete strike-slip faults are determined as 33–41%, which means at least 41% of total wrench components in the region have been accommodated by discrete strike-slip faulting along the AFZ. Results indicate that the simple shear component of total stress applied to the area is consistent with the GPS slip velocities.

Geophysical implications for the exploration of concealed orogenic gold deposits: A case study in the Sandy Lake and Favourable Lake Archean greenstone belts, Superior Province, Ontario, Canada

Since 2000, gold discovery rates have not reflected the record levels of exploration expenditure, with those discoveries that are made being predominantly in areas of post-mineral cover. Hence, gold exploration has been increasingly focused on concealed exploration targets where geophysics takes on an increasingly important role in the exploration process.Archean orogenic gold deposits are attractive exploration targets that represent a major proportion of global gold resources. Orogenic gold deposits consistently form late during the tectonic and structural evolution of their host terranes, normally during a transition from compressional to transpressional tectonic stress regimes. Thus, for target generation, the late timing of gold mineralization within the structural history of a prospective orogenic belt is crucial, as it means that current geological maps and sections reflect the geometry of the gold deposits at the time of formation unless there has been subsequent orogeny. Lithological contacts between granitic intrusions and volcano-sedimentary greenstone sequences, as well as between volcanic and sedimentary sequences, are important rheological and geochemical trap sites. Lithosphere-scale faults and dilational jogs in second-order faults act as ore-fluid conduits with anticlinal folds as structural traps for ore-fluid infiltration and gold deposition given suitable host rocks and fluid seals.Geophysical exploration for concealed orogenic gold deposits is challenging due to normally subtle petrophysical contrasts between the gold lodes and their host rocks. Most greenstone-hosted lode-gold deposits do not contain strong conductors as they normally contain <5 vol% of disseminated arsenopyrite and pyrite, which are poor conductors, and rarely contain significant quantities of strong conductors such as pyrrhotite. However, pyrrhotite may be a component of rock sequences such as sulfidic shales or cherts adjacent to the orogenic gold lodes. It is proposed that the combination of HTEM and magnetic surveys be used to explore for concealed orogenic gold deposits, using the Favourable Lake and Sandy Lake greenstone belts in the Superior Province, Canada, as a case study. AIP Cole-Cole time-constants, combined with magnetic and EM data, can efficiently detect disseminated pyrite/magnetite at shallow depths, indicating their potential use as vectoring tools for concealed Archean orogenic gold deposits.

Kharvana‒Zonouz Active Fault System: An Evidence of Transpressional Tectonic Regime, North-West of Iran

The Kharvana‒Zonouz Fault system with general NW‒SE trending right-lateral folds and strike-slip and reverse faults is located in NW Iran. This fault system could be considered as the southeastern continuation of the Nakhichevan‒Sardarapat Fault system in Azerbaijan toward NW Iran. Toward SE, the Kharvana‒Zonouz Fault system reaches to the active Qoshadagh Fault. The major faults in the Kharvana‒Zonouz Fault system from north to south are Kharvana Fault with dextral strike-slip movement, Estarkhan‒Komar Fault with reverse movement, Nahand Fault with dextral strike-slip and reverse movements and Zonouz Fault with dextral strike-slip movement. Dextral displacement in drainage pattern and occurrence of earthquakes show the activity of the Kharvana‒Zonouz fault system. Strike-slip faults almost parallel to the folds and reverse faults at the same rock formations could be evidence of transpressional tectonic regime within the Kharvana‒Zonouz Fault system.

Polyphasic tectonic history of the N70° DASA Graben (northern, Niger)

Located in northern Niger, the N70° DASA graben is a trough discovered recently in the Tim Mersoï basin. In this study, a tectonic history of the DASA graben was presented based on the combined use of satellite imagery, field observations and measures, available literature and borehole data. These data were used to analyse the sedimentary facies and the tectonic deformations in the DASA graben, and derive their relative chronology. For this purpose, uplift and rift deformations and their interactions with sedimentation were characterized. Overall, the analyses suggest that the DASA graben was affected from the Carboniferous to the Cretaceous by three major tectonic phases: the first phase was an uplifting stage with extension during the Carboniferous to Permian; the second phase was a rifting stage. The mean extension was ~ N160° and dominantly produced ENE-WSW trending normal faults; and the third phase was a postrift stage. It was characterized by a ~ N130° compression. The structural and sedimentological features defined the DASA graben as a particular type of syn-sedimentary basin evolving from a transpressive tectonic regime during the period ranging from Carboniferous to Permian to an extensive tectonic regime during the period ranging from Triassic to Lower Cretaceous. Thus, the second period marked by an extensional regime would probably be related to the initial stage of the opening of the Atlantic Ocean. After this rifting period, the DASA graben was affected by a compressional phase related to the collision between Africa and Europe.

Kinematics and Timing Constraints in a Transpressive Tectonic Regime: The Example of the Posada-Asinara Shear Zone (NE Sardinia, Italy)

Detailed geological field mapping, integrated with meso- and microstructural investigations, kinematic of the flow and finite strain analyses, combined with geochronology, are fundamental tools to obtain information on the temperature–deformation–timing path of crystalline rocks and shear zone. The Posada-Asinara shear zone (PASZ) in northern Sardinia (Italy) is a steeply dipping km-thick transpressive shear zone. In the study area, located in the Baronie region (NE Sardinia), the presence of mylonites within the PASZ, affecting high- and medium-grade metamorphic rocks, provides an opportunity to quantify finite strain and kinematic vorticity. The main structures of the study area are controlled by a D2 deformation phase, linked to the PASZ activity, in which the strain is partitioned into folds and shear zone domains. Applying two independent vorticity methods, we detected an important variation in the percentage of pure shear and simple shear along the deformation gradient, that increases from south to north. We constrained, for the first time in this sector, the timing of the transpressive deformation by U–(Th)–Pb analysis on monazite. Results indicate that the shear zone has been active at ~325–300 Ma in a transpressive setting, in agreement with the ages of the other dextral transpressive shear zones in the southern Variscan belt.

Basin inversion and structural architecture as constraints on fluid flow and Pb–Zn mineralization in the Paleo–Mesoproterozoic sedimentary sequences of northern Australia

Abstract. As host to several world-class sediment-hosted Pb–Zn deposits and unknown quantities of conventional and unconventional gas, the variably inverted 1730–1640 Ma Calvert and 1640–1575 Ma Isa superbasins of northern Australia have been the subject of numerous seismic reflection studies with a view to better understanding basin architecture and fluid migration pathways. These studies reveal a structural architecture common to inverted sedimentary basins the world over, including much younger examples known to be prospective for oil and gas in the North Sea and elsewhere, with which they might be usefully compared. Such comparisons lend themselves to suggestions that the mineral and petroleum systems in Paleo–Mesoproterozoic northern Australia may have spatially, if not temporally overlapped and shared a common tectonic driver, consistent with the observation that basinal sequences hosting Pb–Zn mineralization in northern Australia are bituminous or abnormally enriched in hydrocarbons. Sediment-hosted Pb–Zn mineralization coeval with basin inversion first occurred during the 1650–1640 Ma Riversleigh Tectonic Event towards the close of the Calvert Superbasin with further pulses taking place during and subsequent to the onset of the 1620–1580 Ma Isa Orogeny and final closure of the Isa Superbasin. Mineralization is typically hosted by the post-rift or syn-inversion fraction of basin fill, contrary to existing interpretations of Pb–Zn ore genesis where the ore-forming fluids are introduced during the rifting or syn-extensional phase of basin development. Mineralizing fluids were instead expelled upwards during times of crustal shortening into structural and/or chemical traps developing in the hangingwalls of inverted normal faults. Inverted normal faults predominantly strike NNW and ENE, giving rise to a complex architecture of compartmentalized sub-basins whose individual uplifted basement blocks and doubly plunging periclinal folds exerted a strong control not only on the distribution and preservation of potential trap rocks but the direction of fluid flow, culminating in the co-location and trapping of mineralizing and hydrocarbon fluids in the same carbonaceous rocks. An important case study is the 1575 Ma Century Pb–Zn deposit where the carbonaceous host rocks served as both a reductant and basin seal during the influx of more oxidized mineralizing fluids, forcing the latter to give up their Pb and Zn metal. A transpressive tectonic regime in which basin inversion and mineralization were paired to folding, uplift, and erosion during arc–continent or continent–continent collision, and accompanied by orogen-parallel extensional collapse and strike-slip faulting best accounts for the observed relationships.

Geodynamical evolution of the Misis structural high, Ceyhan (Adana)/Turkey

An elongate mountain range known as the “Misis Structural High” located ca. 40 km southeast of Adana city in Turkey, evidences vast tectonic processes in Neogene time. This lineation represents the former border of the Tauride and Eastern Mediterranean basins and extends from Northern Cyprus to the Engizek Mountains by passing through the Misis (Yakapınar) and northerly Andırın regions. Located about 80 km west of the triple junction of the Arabian, Anatolian and African plates, this region is one of the key tectonic lineaments studied for understanding the geologic development of southeast Anatolia. To reveal the geodynamical evolution of the Misis Structural High, we analysed measurements of fault planes including movement vectors (striae), obtained mainly from the highly deformed Misis Complex. The complex is thought to have formed in a basin by the destabilisation of the northerly Tauride margin related to slab pull-back in the Paleogene. Following generation of the Misis Complex by continental collision in the region, units were compressed, thrust over each other and began to rise as an elongate mountain range. Detailed geological fieldwork, mapping and structural analysis of fault planes in the region indicate that the Misis Structural High was uplifted by the effects of a regional transpressional tectonic regime from the NNE-SSE direction which is forming a positive flower structure.

Dual-Driven Fault Failure in the Lower Seismogenic Zone

ABSTRACTFrictional instability leading to fault rupture may be driven by increasing differential stress or by increases in pore-fluid pressure within the rock mass. Geological evidence (from hydrothermal vein systems in exhumed faults) together with geophysical information around active faults support the localized invasion of near lithostatically overpressured hydrothermal fluids, derived from prograde metamorphism at greater depths, into lower portions of the crustal seismogenic zone at depths of about 10–15 km (250°C&amp;lt;T&amp;lt;350°C). This is especially true of compressional–transpressional tectonic regimes that lead to crustal thickening and dewatering and are better at containing overpressure. Extreme examples are associated with areas undergoing active compressional inversion where existing faults, originally formed as normal faults during crustal extension, undergo reverse-slip reactivation during subsequent shortening though poorly oriented for reactivation. Extreme fault-valve action is likely widespread in such settings with failure driven by a combination of rising fluid pressure in the lower seismogenic zone lowering fault frictional strength, as well as by rising tectonic shear stress—dual-driven fault failure. Localized overpressure affects rupture nucleation sites, but dynamic rupturing may extend well beyond the regions of intense overpressuring. Postfailure, enhanced fracture permeability along fault rupture zones promotes fault-valve discharge throughout the aftershock period, increasing fault frictional strength before hydrothermal sealing occurs and overpressures begin to reaccumulate. The association of rupture nucleation sites with concentrated fluid overpressure is consistent with selective invasion of overpressured fluid into the roots of major fault zones and with nonuniform spacing of major vein systems along exhumed brittle–ductile shear zones.

The evolution of the Dominga Fe-Cu deposit (northern Chile): Insights from mineral textures and micro-CT analysis

The Fe-Cu Dominga deposit (2082 Mt at 23% Fe, 0.07% Cu), located in the Coastal Cordillera of northern Chile, is hosted by volcanic rocks of the Punta del Cobre Formation (131.5 ± 1.5 Ma zircon U-Pb) and into subvolcanic units (Dioritic Complex, 131.6 ± 1.0 Ma zircon U-Pb). The Fe-Cu mineralization is controlled by three structural systems which developed from a transtensional to a transpressional tectonic regime and can be divided into three groups: Early iron, Late iron and Early copper ores. Early iron ores are comprised of magnetite + pyrite + biotite breccia (1A ore), veins (1B ores), layers (1C ores) and disseminated ores (1D ores). Late iron ores are characterized by two groups of magnetite-apatite-actinolite hydrothermal breccias (2A, 2C ores) and syntaxial/antitaxial veins (2B, 2D, 2E ores). Early copper ores occur as syntaxial K-feldspar and quartz + epidote + chalcopyrite veins (3A ores), and as anhydrite + chalcopyrite-rich matrix breccia and veins (3B ores). This work presents a detailed mineral texture study of veins, hydrothermal breccias and disseminated iron-rich layers of the Dominga deposit which aims to determine fluid flow mechanisms associated with both iron and copper ores. The description of vein and breccia textural and internal structures was conducted in thin/polished sections perpendicular and parallel to the wall using optical and Scanning Electron Microscope techniques. In addition, two oriented surface samples were analyzed by computerized X-ray microtomography and numerical fluid flow simulations through the Lattice-Boltzmann method to obtain (3D) permeability anisotropy associated with early iron ores. Microtextures associated with Dominga iron and copper ores suggest that the main mass transfer fluid flow mechanism corresponds to advection (channelized and pervasive fluid flow), regardless of the tectonic regime. However, early copper ores have more complex mineral textures and internal structure due to the recurrence of crack-seal episodes. We propose that the various mineral textures and structures indicate changes in fluid flow direction over time, controlled by the permeability anisotropy of each tectonic regime. Results from numerical fluid flow simulations of early iron ore (1B) veins show a higher value of structural permeability in the vertical direction (kVz), which is consistent with a transtensional tectonic regime and the formation of vertical veins. Moreover, permeability related to 1C layered ore is higher in horizontal directions (kHx, kHy) rather than vertical (kVz) because of the natural permeability anisotropy of volcaniclastic rocks parallel to bedding. However, the kVz value suggests that the development of such layered ores also exhibits a degree of structural control at several length scales consistent with a transtensional regime. These results indicate that the occurrence of early iron ores as veins and layers may be controlled by both primary permeability anisotropy related to each lithology present at the Dominga Fe-Cu deposit and to the tectonic regime at the time. Finally, the Dominga Fe-Cu deposit attests to long lived hydrothermal activity with a transition from early fluids capable of precipitating iron ores under a transtensional system to later-stage fluids which precipitated copper ores under a transpressional regime that generated multiple crack and seal episodes.

Crustal anatexis and mantle-derived magmas forming Neoarchean A-type granitoids in Carajás Province, northern Brazil: Petrological evidence and tectonic control

Neoarchean hybrid granitoids from the Vila União suite are located in the central portion of the Canaã dos Carajás domain, Carajás Province (Amazonian craton, Brazil), and suggest that magma mixing events played an important role in their origin. According to complete evidence, including field observations, petrography, geochemical modeling, zircon SHRIMP and LA-MC-ICP-MS U-Pb ages, and Nd-Hf isotope data, we propose a geodynamic model based on initial mafic underplating promoted by lower crustal delamination, which generated mantle-derived mafic melts that were injected into the lower/middle crust (composed of Mesoarchean felsic granulite) and caused partial melting, producing leucogranitic melts. The interaction between these contrasting felsic and mafic magmas occurred by both mixing and mingling processes. The hybrid magma ascent and emplacement occurred in a N–S pure shear-dominated transpressional tectonic regime, with an E–W sinistral sense of tectonic movement, in which the hybrid melt was channeled into pre-existing shear zones trending E–W (Itacaiúnas shear zone). This tectonic regime (transpressional) proceeded coevally with the hybrid magma cooling, producing 2.75–2.73 Ga Neoarchean deformed A-type granitoids with a syntectonic nature in the Vila União suite, in addition to the Pium diopside-norite, which represents the mafic endmember generated by underplating.

The Archean granulite-enderbite complex of the northern Carajás province, Amazonian craton (Brazil): Origin and implications for crustal growth and cratonization

The central portion of the Canaã dos Carajás domain (Ouro Verde area) exhibits a peculiar scenario involving two units of orthopyroxene-bearing sodic rocks: (i) the Mesoarchean Ouro Verde felsic granulite with protolith crystallization and metamorphism ages of 3.05–2.93 Ga and 2.89–2.84 Ga, respectively, and (ii) the Neoarchean Café enderbite, composed of tonalites, trondhjemites and scarce quartz diorites that crystallized at 2.75–2.73 Ga and show syntectonic character. While the orthopyroxene in the felsic granulites was formed by breakdown of primary biotite during metamorphism, in the enderbitic rocks, this mineral was formed by crystallization of a hot water-poor magma at deep crustal levels. This terrane evolved in three important geodynamic stages: (1) at 3.05–2.93 Ga, TTG crust was generated by partial melting of LILE-enriched basalts in a N–S subduction setting; (2) from 2.89 to 2.84 Ga, in a collisional setting, large volumes of anatectic granites formed and contributed to crustal thickening, which triggered granulite-facies ultrahigh-temperature metamorphism in the TTG crust, forming the Ouro Verde felsic granulite; and (3) in the Neoarchean, at 2.75–2.73 Ga, the lowermost mafic crust was delaminated during crustal thickening, causing crustal underplating followed by partial melting of Mesoarchean mafic granulites, which was responsible for the origin of the enderbitic magma. This area was subjected to a transpressional tectonic regime, leading to the development of plutons (E–W-trending) amalgamated linearly and emplaced along ancient suture zones (ductile-brittle transition). Lu-Hf isotope data of magmatic zircon cores from the Mesoarchean felsic granulite show Hf-TDM2 values of 3.44–3.15 Ga and εHf(t) values between −1.7 and 3.0, which suggest juvenile sources. The Neoarchean enderbites present Hf-TDM2 ages of 3.46–3.29 Ga and lower εHf(t) values (between −4.8 and −1.9), which indicate a longer crustal residence time for these rocks. All these findings lead us to consider the central portion of the Canaã dos Carajás domain as exhumed lower crust, and the tectonic juxtaposition of anatectic granites, enderbites and high-grade metamorphic rocks suggests that the Ouro Verde area represents middle and deep exposure levels of the same crust.