Compressional Tectonic Event Research Articles

Relations between Fault and Fracture Network Affecting the Lastoni di Formin Carbonate Platform (Italian Dolomites) and Its Deformation History

In this study, we analyze the fault and fracture network of the Middle Triassic carbonate platform of the Lastoni di Formin (Italian Dolomites, Italy). The reconstruction of the deformation history is of primary importance for a full comprehension of the present structural setting of this carbonate platform. The huge dimensions of the carbonate body and superb exposure of its vertical cliffs and gently dipping top plateau make the Lastoni di Formin platform an ideal outcrop to integrate traditional fieldwork with Digital Outcrop Modelling analysis. The results of the structural studies partially confirm that the present-day fracture pattern is the result of differential compaction-induced deformation that generated WNW-ESE-trending extensional fractures and normal faults, perpendicular to the direction of progradation of the platform. Successively, extensional tectonics, likely related to the Jurassic rifting phase, led to the formation of NNW-SSE striking fractures and westward-dipping normal faults. A Neogene compressional tectonic event, characterized by N-S to NW-SE crustal shortening, deformed the platform, essentially with strike-slip structures.

Tectonic evolution of the northern Verkhoyansk Fold-and-Thrust Belt: insights from palaeostress analysis and U–Pb calcite dating

AbstractA combined structural and geochronological study was carried out to identify the tectonic evolution of the northern Verkhoyansk Fold-and-Thrust Belt, formed on the east margin of the Siberian Craton during late Mesozoic collision. Fault and fold geometries and kinematics were used for palaeostress reconstruction along the Danil and Neleger rivers cross-cutting the central and western parts of the Kharaulakh segment of the northern Verkhoyansk. Three different stress fields (thrust, normal and strike-slip faulting) were identified after separation from heterogeneous fault-slip data. Thrust and normal faulting stress fields were found in both areas, whereas a strike-slip faulting stress field was only found in Neoproterozoic rocks of the Neleger River area. U–Pb laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) dating of calcite slickenside samples reveals the following succession of major deformation events across the northern Verkhoyansk: (i) The oldest tectonic event corresponding to the strike-slip faulting stress field with NE–SW-trending compression axis is Early Permian (Cisuralian, 284 ± 7 Ma) and likely represents a far-field response to the late Palaeozoic collision of the Kara terrane with the northern margin of the Siberian Craton. (ii) A slickenfibrous calcite age of 125 ± 4 Ma is attributed to the Early Cretaceous compression event, when the fold-and-thrust structure was formed. (iii) U–Pb slickenfibre calcite ages of 76–60 Ma estimate the age of a Late Cretaceous – Palaeocene compression event, when thrusts were reactivated. Slickensides related to both (ii) and (iii) compressional tectonic events formed by similar stress fields with W–E-trending compression axes. (iv) From the Palaeocene onwards, extensional tectonics with approximately W–E extension predominated.

Implication of Dynamic Recrystallization Mechanism for the Exhumation of Lower Crustal Rocks: A Case Study in the Shear Zones of the Ambaji Granulite, NW India

Abstract Shear zones are important channels for the exhumation of lower crustal rocks. The Ambaji granulite of the Aravalli-Delhi mobile belt (ADMB) has been exhumed along several shear zones, and earlier studies have shown a two-stage exhumation process during a continuous compressional tectonic event, consisting of an initial phase of vertical flow that brought the granulites to the brittle-ductile transition zone and a successive phase during which the granulite underwent a lateral flow. In this contribution, we studied the microtectonics of granulites by analyzing the dynamic recrystallization behaviour of quartz, while the granulite was passing through the vertical flow regime to the horizontal flow regime. We show that the dynamic recrystallization process assists the flow pattern at different levels of exhumation. The vertical flow is dominated by grain boundary migration (GBM), registering high temperatures for recrystallization between 490 and 600°C and low flow stresses of 12-15 MPa. The horizontal flow at the brittle-ductile transition (BDT) is characterized by bulging (BLG) and subgrain rotation (SGR), which occurred at low temperatures of 390-490°C and high flow stresses of 18-26 MPa. Strain rates are between 1.20×10−12 and 7.26×10−14/s. For the ductile exhumation of the granulite, we suggest that at depths of ~22 km, the granulite exhumed in a vertical direction facilitated by GBM. Once the granulite reached the BDT, at ~16 km depth, the material flowed laterally assisted by BLG and SGR. Once an exhuming body reaches the BDT, the deformation mechanism changes to BLG-SGR, and the only direction in which the material can move further is in the horizontal plane.

Dawn and dusk of Late Cretaceous basin inversion in central Europe

Abstract. Central and western Europe were affected by a compressional tectonic event in the Late Cretaceous, caused by the convergence of Iberia and Europe. Basement uplifts, inverted graben structures, and newly formed marginal troughs are the main expressions of crustal shortening. Although the maximum activity occurred during a short period of time between 90 and 75 Ma, the exact timing of this event is still unclear. Dating of the start and end of Late Cretaceous basin inversion gives very different results depending on the method applied. On the basis of borehole data, facies, and thickness maps, the timing of basin reorganization was reconstructed for several basins in central Europe. The obtained data point to a synchronous start of basin inversion at 95 Ma (Cenomanian), 5 Myr earlier than commonly assumed. The end of the Late Cretaceous compressional event is difficult to pinpoint in central Europe, because regional uplift and salt migration disturb the signal of shifting marginal troughs. Late Campanian to Paleogene strata deposited unconformably on inverted structures indicate slowly declining uplift rates during the latest Cretaceous. The differentiation of separate Paleogene inversion phases in central Europe does not appear possible at present.

Mesozoic compressional to extensional tectonics in the Central East Iranian Microcontinent: evidence from the Boneh Shurow metamorphic core complex

The Boneh Shurow metamorphic core complex (BSMCC) in the Central East Iranian Microcontinent (CEIM) provides a good example of the Mesozoic succession of nonsynchronous compressional and extensional deformation events attributed to the transitional Cimmerian events. The D1 compression developed subvertical dextral ductile shear zones and corresponds to continental accretion and crustal thickening, producing kyanite- and sillimanite-grade rocks and migmatites in the Early Cimmerian Orogeny in the CEIM. The D2 deformation event is marked by extension during the mid-Cimmerian Orogeny. It is characterized by top-to-the-NE normal sense of shear along a low-angle detachment surface. Field evidence for cross-cutting relationships of D1- by D2-related structures reveals that the occurrence of Barrovian facies metamorphism and associated partial melting in the core of the BSMCC formed during compressional tectonic events. These structures formed before the initiation of extension and the formation of the low-angle detachment shear zone. Finally, during the Late Cimmerian D3 event, the east and west Boneh Shurow reverse faults ruptured on both sides of the MCC. Recognition of the complicated origin and exhumation mechanisms of the BSMCC provides crucial constraints on the prolonged evolution of Palaeo- and Neotethys ocean basins and collisional and post-collisional events in this region.

The use of gravity and aeromagnetic data to define the structural configuration of the Western Desert, Iraq

A gravity and magnetic analysis was performed over the Western Desert (WD) of Iraq to determine the structural makeup of the Phanerozoic sediments that overlie Precambrian lithologies. The WD contains a series of basins that were formed during a series of Precambrian to Paleozoic compressional tectonic events. Regional and residual gravity and magnetic anomaly maps created by a variety of methods, and a CET lineament analyzes of these maps indicate that the basins were formed mainly by strike-slip and transverse faults. These faults may have been the reactivation of faults formed during Precambrian compressional tectonic events. The prominent Nukhaib graben was found to be a series of smaller grabens and horsts whose origin is probably related to reactivation of Precambrian faults.

Effects of paleoweathering and supergene activity on volcanogenic massive sulfide (VMS) mineralization in the Penokean Volcanic Belt, northern Wisconsin, Michigan and east-central Minnesota, USA: Implications for future exploration

Three cycles of paleoweathering and supergene activity have been identified within the Penokean Volcanic Belt (PVB) of northern Wisconsin, Michigan and east-central Minnesota, USA. These cycles are responsible for significant subaerial weathering, erosion, oxidation and most importantly local supergene Au, Ag and Cu enrichment that has a major economic impact upon volcanogenic massive sulfide (VMS)-style mineralization within the PVB. The paleoweathering profile (regolith-saprolite) that developed on the exposed PVB surface now marks an angular unconformity with stratigraphically overlying, late Paleoproterozoic Baraboo Interval quartzites and late Cambrian sandstones.Differential uplift of the PVB surface is a direct result of the ∼1850 Ma compressional tectonic event that occurred during the Penokean orogeny. The uplifted PVB paleosurface experienced its first weathering cycle in the mid to late Paleoproterozoic. VMS mineralization near the paleosurface was exhumed and affected during this protracted cycle which ceased upon deposition of Baraboo Interval quartzites (1788–1714 Ma). Further uplift and subsequent unroofing of the quartzites during the Mazatzal orogeny (∼1650–1630 Ma) initiated a second paleoweathering cycle that culminated within the Neoproterozoic – Cambrian transition. During this cycle of accelerated and uninterrupted paleoweathering, new and surviving supergene Au-Ag-Cu-enriched profiles geochemically matured over exhumed mineralized sections in terrains with favorable fault block movements. Supergene systems that developed during both cycles were highly acidic environments. Low protolith reactivity and high hypogene pyrite concentrations promoted acidity of supergene fluids thus facilitating enhanced Cu, Au and Ag mobility. In those systems that lacked sufficient carbonate, Zn and Pb were lost to surrounding aqueous regimes.The second paleoweathering cycle ended with the deposition of overlying late Cambrian sandstone (497–485.4 Ma). Erosional retreat of the overlying Paleozoic sequence exposed many of these supergene deposits to a third, possibly brief paleoweathering cycle before the onset of Quaternary continental glaciation. VMS profiles not protected by sandstone outliers or within down-dropped fault blocks were glacially eroded.Of the 14 or more known VMS deposits and occurrences in the belt, four have preserved or partially preserved paleoweathering profiles. The most significant are at the Flambeau and Back Forty deposits where Au-Ag-enriched indigenous gossans with extensive or local underlying supergene-enriched Cu sulfide zones have developed over hypogene massive sulfide horizons. These profiles demonstrate efficient cumulative or multicyclic Au, Ag and Cu-enrichment to ore grades.Although commonly small (≤2 million tonnes), such supergene-enriched deposits are generally shallow, allowing for development by low cost open pit methods and production of exceptionally high-grade, direct shipping copper and/or gold ores. As such, the buried PVB unconformity is considered a prime exploration target that is highly prospective for new discoveries of commercially viable, supergene-enriched VMS resources.

The thickness of cover sequences in the Western Desert of Iraq from a power spectrum analysis of gravity and magnetic data

The Western Desert of Iraq is part of the stable shelf region on the Arabian Plate where the subsurface structural makeup is relatively unknown due to the lack of cropping out rocks, deep drill holes and deep seismic refraction and reflection profiles. To remedy this situation, magnetic and gravity data were analyzed to determine the thickness of the Phanerozoic cover sequences. The 2-D power spectrum method was used to estimate the depth to density and magnetic susceptibility interfaces by using 0.5° square windows. Additionally, the gravity data were analyzed using isostatic residual and decompensative methods to isolate gravity anomalies due to upper crustal density sources. The decompensative gravity anomaly and the differentially reduced to the pole magnetic map indicate a series of mainly north-south and northwest-southeast trending maxima and minima anomalies related to Proterozoic basement lithologies and the varying thickness of cover sequences. The magnetic and gravity derived thickness of cover sequences maps indicate that these thicknesses range from 4.5 to 11.5km. Both maps in general are in agreement but more detail in the cover thicknesses was determined by the gravity analysis. The gravity-based cover thickness maps indicates regions with shallower depths than the magnetic-based cover thickness t map which may be due to density differences between limestone and shale units within the Paleozoic sediments. The final thickness maps indicate that the Western Desert is a complicated region of basins and uplifts that are more complex than have been shown on previous structural maps of the Western Desert. These basins and uplifts may be related to Paleozoic compressional tectonic events and possibly to the opening of the Tethys Ocean. In addition, petroleum exploration could be extended to three basins outlined by our analysis within the relatively unexplored western portions of the Western Desert.

New insight on the recent tectonic evolution and uplift of the southern Ecuadorian Andes from gravity and structural analysis of the Neogene-Quaternary intramontane basins

The sedimentary basins of Loja, Malacatos-Vilcabamba and Catamayo belong to the Neogene-Quaternary synorogenic intramontane basins of South Ecuador. They were formed during uplift of the Andes since Middle-Late Miocene as a result of the Nazca plate subduction beneath the South American continental margin. This E-W compressional tectonic event allowed for the development of NNE-SSW oriented folds and faults, determining the pattern and thickness of sedimentary infill. New gravity measurements in the sedimentary basins indicate negative Bouguer anomalies reaching up to −292 mGal related to thick continental crust and sedimentary infill. 2D gravity models along profiles orthogonal to N-S elongated basins determine their deep structure. Loja Basin is asymmetrical, with a thickness of sedimentary infill reaching more than 1200 m in the eastern part, which coincides with a zone of most intense compressive deformation. The tectonic structures include N-S, NW-SE and NE-SW oriented folds and associated east-facing reverse faults. The presence of liquefaction structures strongly suggests the occurrence of large earthquakes just after the sedimentation. The basin of Malacatos-Vilcabamba has some folds with N-S orientation. However, both Catamayo and Malacatos-Vilcabamba basins are essentially dominated by N-S to NW-SE normal faults, producing a strong asymmetry in the Catamayo Basin area. The initial stages of compression developed folds, reverse faults and the relief uplift determining the high altitude of the Loja Basin. As a consequence of the crustal thickening and in association with the dismantling of the top of the Andes Cordillera, extensional events favored the development of normal faults that mainly affect the basins of Catamayo and Malacatos-Vilcabamba. Gravity research helps to constrain the geometry of the Neogene-Quaternary sedimentary infill, shedding some light on its relationship with tectonic events and geodynamic processes during intramontane basin development.

The Jabal Akhdar dome in the Oman Mountains: Evolution of a dynamic fracture system

The Mesozoic succession of the Jabal Akhdar dome in the Oman Mountains hosts complex networks of fractures and veins in carbonates, which are a clear example of dynamic fracture opening and sealing in a highly overpressured system. The area underwent several tectonic events during the Late Cretaceous and Cenozoic, including the obduction of the Samail ophiolite and Hawasina nappes, followed by uplift and compression due to the Arabia-Eurasia convergence. This study presents the results of an extensive tectonic survey, and correlates subseismic-scale structures in Jabal Akhdar (faults, fractures, veins and stylolites) with the main tectonic events in the Northeastern Arabian plate. As some of the studied formations host large oil reserves in neighboring areas, determining the relative timing of these events in the exhumed rocks is important to understand hydrocarbon distribution and fracture patterns in these reservoirs. The formation of early veins and stylolites in the Oman Mountains is followed by top-to-the- South layer-parallel shearing that may be associated with the obduction of the Samail and Hawasina nappes. This compressional tectonic event is followed by normal (dip-slip) to oblique-slip faults and veins. Top-to-the-Northeast layer-parallel shearing, which corresponds to the first stage of exhumation of the autochthonous rocks offsets these structures. Our new data indicate that this first phase of events is overprinted by complex strike-slip networks of veins and fractures, as well as by the reactivation and onset of seismic-scale faults. Strike slip structures belong to three distinct events. The first one (NW-SE-oriented compression) is probably associated with the oblique collision of the Indian plate against the Arabian platform during the Late Campanian to the Mid Eocene. The second event (E-W-oriented compression) is likely to have been formed during the Late Oligocene-Middle Miocene during uplift. The last event (NE-SW-oriented compression) probably took place during the Miocene-Pliocene. Structures of the first two strike-slip events have the same orientation as seismic-scale faults observed in the subsurface of Oman and Abu Dhabi. In addition, increasing vein intensity towards the top of the autochthonous formations in the Oman mountains, as well as the small angle between conjugate vein sets, indicate that high fluid pressures that are thought to be present during strike-slip deformation.

Zircon fission-track dating of granites from the Vepor-Gemer Belt (Western Carpathians): constraints for the Early Alpine exhumation history

*Corresponding author We present new zircon fission-track (ZFT) data from Variscan granitoid bodies in the Veporic (footwall unit) and Gemeric (hangingwall unit) thick-skinned nappe sheets of the Central Western Carpathians. All samples show Late Cretaceous to earliest Paleogene cooling ZFT ages, which contribute to constraining the low-temperature exhumation history of the Vepor–Gemer Belt. Four granite samples from the western part of the Gemericum near the contact with the underlying Veporicum provided central ZFT ages between 70.4 ± 5.4 and 74.7 ± 5.6 Ma. One sample from this area shows an older age of 87.7 ± 5.9 Ma, possibly owing to its higher structural position. One remoter sample from the SE part of the Gemeric Unit has 61.7 ± 3.4 Ma central ZFT age, which probably reflects exhumation associated with a younger compressional tectonic event in that area. One sample from the centre of the Veporic metamorphic core complex yielded a cooling age 64.9 ± 4.8 Ma. However, most of these samples exhibit an internal age scatter pointing to complex cooling and exhumation history influenced by a slow passage through the zircon partial annealing zone and/or reheating brought about by the Cretaceous Rochovce granite intrusion. In spite of this, the acquired ages generally match the exhumation trend of the Veporic metamorphic core complex.

U‐Pb Dating of Volcanic Rocks and Granites along the Wuyishan Belt: Constraints on Tuning of Late Mesozoic Tectonic Events in Southeast China

Abstract:Five volcanic rock samples and two granite samples taken from the volcanic basins in western Fujian and southern Jiangxi were dated by using the zircon laser albation‐inductively coupled plasma mass spectrometry U‐Pb method. Together with previously dated ages, the dates obtained provide important constraints on the timing of late Mesozoic tectonic events in SE China. The volcanic rock samples yield ages of 183.1±3.5 Ma, ca. 141 Ma to 135.8±1.1 Ma, 100.4±1.5 to 97.6±1.1 Ma, confirming three episodes of late Mesozoic volcanic activities, which peaked at 180±5 Ma, 140±5 Ma and 100±5 Ma, respectively, along the Wuyishan belt. Moreover, based on field investigations of these volcano‐sedimentary basins, we have recognized two compressional tectonic events along this belt The early one was characterized by Upper Triassic to Middle Jurassic NNE‐trending folds that were intruded by late Jurassic granites; and the late one caused the Lower Cretaceous volcano‐sedimentary layer to be tilted. The dated age 152.9±1.4 Ma of the granitic samples from the Hetian granitic pluton in the Changting Basin and that from the Baishiding granitic pluton, 100.2±1.8 Ma, in the Jianning Basin, give the upper boundaries of these two tectonic events respectively. Hence, the late Mesozoic tectonic evolution of SE China was alternated between extension and compression.

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

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

Mongolian coal-bearing basins: Geological settings, coal characteristics, distribution, and resources

Abstract This paper presents geological settings, stratigraphy, coal quality, petrography, reserves and the tectonic history of the Mongolian coal-bearing basins. This is based on a synthesis of the data from nearly 50 coal deposits. The results of ultimate and proximate analyses, and calorific value, maceral composition and vitrinite reflectance data is given. The coal deposits of Mongolia tend to become younger from west to east and can be subdivided into two provinces, twelve basins, and three areas. Main controlling factor of coal rank is the age of the coal bearing sequences. Western Mongolian coal-bearing province contains mostly high rank bituminous coal in strata from Late Carboniferous. The basins in southern Mongolia and the western part of central Mongolia have low rank bituminous coal in strata from the Permian. The northern and central Mongolian basins contain mainly Jurassic subbituminous coal, whereas the Eastern Mongolian province has Lower Cretaceous lignite. The Carboniferous, Permian and Jurassic coal-bearing sequences were mainly deposited in foreland basins by compressional tectonic event, whereas Cretaceous coal measures were deposited in rift valleys caused by extensional tectonic event. Petrographically, Mongolian coals are classified as humic type. Vitrinite/huminite groups of Carboniferous, Permian, and Cretaceous coal range from 44.9% to 82.9%. Inertinite group varies between 15.0% and 53.3%, but liptinite group does not exceed more than 7%. Jurassic coals are characterized by high percentages of vitrinite (87.3% to 96.6%) and liptinite groups (up to 11.7%). This might be explained by paleoclimatic conditions. Mongolian coal reserves have been estimated to be 10.2 billion tons, of which a predominant portion is lignite in the Eastern Mongolian province and coking coal in the South Gobi basin.

Successive Paleocene and Eocene infillings of polyphase paleokarsts within the Cretaceous limestones of the Empordà thrust sheets (Catalan Pyrenees, Spain) : relationships between tectonics and karstification

Abstract The Mesozoic series of the southern units of the Pyrenean Empordà thrust sheets (Montgrí and Figueres nappes, Catalonia, Spain) were finally emplaced over the autochthonous basement and its Cenozoic cover during Eocene times. However, they have originally been folded by the “Laramian” compressional event (Late Cretaceous/Early Paleocene), while they were still in their root zone more than 50 km to the N-NE. Postdating the Santonian, the emersion of the Cretaceous tectorogen induced karst formation at the expense of Berriasian to Santonian limestone sequences. Karst cavities of this paleokarst 1 (lapiaz and canyons) were subsequently coated with a fine, red or black, Microcodium-bearing, continental silt, and infilled with marine chaotic breccias. Following a new episode of emersion then erosion, the original paleokarst 1 was cross-cut by newly formed cavities of the paleokarst 2, filled with Lutetian-Bartonian marine breccias. Both types of marine breccias (Paleocene then Eocene in age) are now relatively well dated by means of planktonic foraminifera (Globigerinacea) occurring within the argillaceous-sandy matrix, and for the older ones, within the argillaceous-sandy or carbonate, finely laminated, interbedded hemipelagites, that mark the top of marine sequences tens of centimetres thick. The relationships of the “Laramian” and “Pyrenean” compressional tectonic events, occurring from latest Cretaceous to Bartonian, with the development of paleokarsts 1 and 2 are analysed in the perspective of the progressive southwards emplacement of the Montgrí thrust sheet, during Eocene time.

Mesozoic extensional tectonics: its impact on oil accumulations in Campeche Sound, Gulf of Mexico

Compressional tectonics of the Tertiary age created large structures in the easternmost part of the Akal horst, in the Campeche Sound, offshore Campeche, Mexico (Figure 1). Prolific fields such as Cantarell, Sihil, Ku, Abakatun, Taratunich, and Bacab are on those structures. The tremendous magnitude of these structural events left very little evidence (have masked the presence) of the Mesozoic extensional system. For these reasons, much effort has been dedicated to explaining the compressional tectonic events and associated structural styles while the importance of the Mesozoic extensional system has been underestimated or minimized. Our current work suggests that some of these large structures are more closely related to the Mesozoic extensional tectonics than previously thought.

Structural geology of the Penobsquis salt structure: late Bashkirian inversion tectonics in the Moncton Basin, New Brunswick, eastern Canada

This study uses new information acquired from field mapping, mineral exploration boreholes, and seismic reflection profiles to constrain the structural geology, deformation mechanisms, and timing of the Penobsquis salt structure. This information is used to place the development of the salt structure into the context of the tectonic evolution of the Moncton Basin. The Penobsquis salt structure is an elongate salt wall separated from underlying rocks by a mylonitic detachment horizon. It may be divided into two segments: a southwestern asymmetric, southeast-verging structure and a northeastern strongly asymmetric to overturned, southeast-verging structure associated with the Penobsquis fault. An initial low-amplitude salt anticline formed during deposition of the Mabou Group (Serpukhovian time). The salt anticline was modified into a high-amplitude salt wall after deposition of Cumberland Group sediments (early Bashkirian or later). The sense of asymmetry of the Penobsquis salt structure, the presence of thrust faults within the structure, the spatial association of the structure with a major reverse fault in the salt cover, and the temporal association of salt movement and compressional tectonic events suggest that the salt structure developed in response to tectonic contraction during inversion of the Moncton Basin.

Tectonic Controls on the Formation of the Liwu Cu‐rich Sulfide Deposit in the Jianglang Dome, S W China

Abstract. The Liwu Cu‐rich sulfide deposit occurs within the Jianglang dome in the eastern margin of the Tibetan plateau. The dome consists of a core, a middle slab and a cover sequence. The main deposit is hosted in the core with minor ore bodies in the middle slab. The protolith of the core consists of clastic sedimentary rocks with inter‐layered volcanic rocks.All of the ore bodies are substantially controlled by an extensional detachment fault system. The ore bodies within the core are distributed along the S2 foliation in the hinge of recumbent fold (D2), whereas ore bodies with en echelon arrangement are controlled by the mylonitic foliation of the lower detachment fault. Ore bodies within the middle slab are oriented with their axes parallel to the mylonitic foliation. Pyrite and pyrrhotite from the ores contain Co ranging from 37 to 1985 ppm, Ni from 2.5 to 28.1 ppm, and Co/Ni ratios from 5 to 71. These sulfides have δ34S values ranging from 1.5 to 7.5 % whereas quartz separates have δ18O values of 11.9 and 14.3 % and inclusion fluid in quartz has δD value of‐88.1 %. These features suggest that the deposit was of hydrothermal origin.Two ore‐forming stages are recognized in the evolution of the Jianglang dome. (1) A low‐temperature ore‐forming process, during the tectonic transport of the upper plate above the lower detachment, and the initial phase of the footwall updom‐ing at 192–177 Ma. (2) A medium‐temperature ore‐forming stage, related to the final structural development of the initial detachment at 131–81Ma. Within the core, the ore bodies of the first stage were uplifted to, or near, the brittle/ductile horizon where the ore‐forming metals were re‐concentrated and enriched. A denudation stage in which a compressional tectonic event produced eastward thrusting overprinted the previous structures, and finally denuded the deposit. The Liwu Cu‐rich sulfide deposit was formed during a regional extensional tectonic event and is defined as a tectono‐strata‐bound hydrothermal ore deposit.

Geological setting of the Argentine Frontal Cordillera in the flat-slab segment (30°00′–31°30′S latitude)

The Argentine Frontal Cordillera, between latitudes 30°20′ and 31°20′S, presents an eastward-verging polycyclic structure. Two large groups of rocks with markedly different structural nature can be distinguished: a Paleozoic basement with characteristic thin-skinned structure and the Andean cover showing remarkable extensional Mesozoic structures inverted by Tertiary compressional tectonic events. These groups are divided by a large tectonic unconformity separating not only rocks with different style and degree of deformation but also different paleogeographic settings. The Cenozoic tectonic inversion is linked with the subhorizontal subduction of the Nazca Plate in the Pampean flat-slab segment and subsequent uplift of the Andean Cordillera. The Paleozoic basement is composed of Devonian and Permo-Carboniferous marine sedimentary rocks, separated by an angular unconformity. These rocks were deposited in siliciclastic and mixed sedimentary platforms, respectively, and intruded by Permo-Triassic granitoid rocks. The Devonian rocks were deformed by the Famatinian orogeny in Late Devonian times. The most important Paleozoic structures are related to the Gondwanic orogeny, of Permian age. These include east-vergent thrusts and related folds that record a large shortening component. The Andean cover, lying unconformably over the Paleozoic basement, is primarily volcanic and volcanoclastic, with some interbedded continental sedimentary rocks. Two main stratigraphic groups can also be defined here: an older sequence linked to an extensional tectonic event and a synorogenic sequence connected to a compressional tectonic event that produced an inversion of previous extensional features. The lower unit (Choiyoi Group: Permian and Triassic) is affected by normal faults with downthrown western blocks and intruded by Jurassic granodioritic rocks. The faults in this unit involve the Gondwanic basement in a typical thick-skinned tectonic style and are grouped in bands with N–S strike. The uppermost units (Vizcachas, Melchor, and Olivares groups: Tertiary and Plio-Quaternary) also lie unconformably over the latter. The normal faults were inverted in the upper Miocene by the uplift of the western block, deforming the lower and upper units in a compressional context during the Andean orogenic cycle. Displacement on reverse faults, measured in the Tertiary synorogenic rocks, is usually less than 1 km. The Tertiary crustal shortening calculated from cross-sections is about 10%, in contrast with the estimated 50% shortening of the Precordillera unit. All this shows that most of the crustal shortening of the Andean Cordillera during the compressional stage has been transferred to the Precordillera unit through the lower detachment fault. These facts also show that the Cordillera Frontal unit is an uplifted block in which the extensional structures have been preserved, and that the Rodeo–Upsallata basin is a piggy-back type.

The occurrence of the Internal Hellenides on Parnon mountain range, Centraleastern Peloponnesus

Detailed mapping of the Parnon mountain range (centraleastern Peloponnesus) showed that over the already well-identified alpine units, which consist the principal mass of Peloponnesus, lies a clastic flysch-type formation, named by the authors as Glypia unit (nappe). This unit encounters in the broader area of Paleochori-Ag. Vasilios, west to the town of Leonidio. The northern margin of the exposure overlies tectonically the Upper Cretaceous limestones of Pindos unit whereas at the eastern, southern and western margins it overlies the Upper Cretaceous - Eocene limestones and the transitional to flysch formation of Tripolis unit through an normal fault. The principal flysch mass is consisted of reddish to brownish and greenish alterations of pelitic horizons, yellowish marly limestones and greenish coarse-grained sandstones. The grains of the latter have been derived from the erosion of a metamorphic exposure, most probably corresponding to 'Pelagonian' zone. After fossil determination, which took place on some of the horizons of the marly limestones, they turn out to be of Danian age. The occurrence of exotic blocks within the flysch matrix of the Glypia unit is quite often. They have derived from carbonate formations of Upper Cretaceous age with either pelagic or neritic character, carbonate formations of Permian age with a neritic character, dolomitic breccias, radiolarites, basaltic lavas along with reddish or greenish pelites and microbrecciated limestones of Upper Creataceous age and, coming to the end, serpentinites along with greenish pelites, sandstones and microbrecciated limestones of unknown age. The study of the tectonic fabric of the Glypia unit reveals an early compressional tectonic event, which has been overprinted by an intense extensional episode of NE-SW orientation. The latter has caused a significant thinning of the unit. The combination of the above mentioned data provides strong evidence, which integrates to the conclusion that the Glypia unit represents a similar unit either to the Ermioni complex in Argolis or to the nappe of Arvi and Miamou in Crete.