Basement Reactivation Research Articles

Basement reactivation and structural inheritance in the Jurassic to Neogene evolution of the North Patagonian Andes (41° 08’ – 41° 11’ S), Argentina

Structural inheritance is a major control on the Andean structural architecture and magma emplacement, particularly in Patagonia, where the genesis of sedimentary basins and magmatic arcs has been largely influenced by basement fabrics. Based on new geologic, structural, microstructural and geochronologic data, the aim of this contribution is to evaluate the influence of pre-existing mechanical anisotropies of the Paleozoic basement on the Jurassic-Neogene tectonic evolution in the Paso de las Nubes area (North Patagonian Andes, Argentina). U-Pb zircon data of an orthogneiss yielded an age of 166 ± 2 Ma, which is consistent with the Jurassic batholith reported in the North Patagonian Andes, being thus coeval with retrograde metamorphism and deformation in the metasedimentary wallrock. Fault kinematic data indicate a Jurassic transtensional regime, strongly controlled by basement reactivation. On the other hand, a second kinematic population records a mainly strike-slip solution, associated with partitioned Neogene transpression.

Rift segmentation caused by reactivation of multiple basement structure systems: Evidence from the Hailar‐Tamtsag Rift, northeast Asia

AbstractSince the influence of structural inheritance on rift geometry has been widely documented, it is easy to assume that rift segmentation, a prominent feature of rift geometry, may have been also influenced by structural heterogeneity. However, limited studies using high‐quality seismic data have considered how basement reactivation is accommodated at individual fault scale and then how this results in rift segmentation at sub‐basin scale. Using extensive high‐quality 3D seismic data and 76 borehole data, we investigate the characteristics of rift architecture, rift‐related fault systems, basement structures and rift evolution in the Hailar‐Tamtsag Rift, northeast Asia. We identify three distinct rift segments which are defined by three rift‐related fault systems and accompanied by three underlying basement structure systems. We recognize three phases of basement reactivation and three types (including five styles) of interactions between basement structures and rift‐related faults. Our study shows that rift segmentation has been caused by reactivation of multiple basement structure systems which not only influence the orientation of rift segments and type of rift architecture, but also control the location, strike, dip and style of the major rift‐related faults. Rift segmentation was completely achieved through multiple phases of basement reactivation, while the main structural framework of segmentation was established through ‘extensive reactivation’ during the second phase extension. Our study examines how multiple basement structure systems control rift segmentation at both individual fault and sub‐basin scales, which can significantly improve our understanding of relationship between structural inheritance and rift segmentation.

Stress-strain state of the earth’s crust of the Central Asian mountain belt: distant effect of the tectonic impact of the Indo-Eurasian collision

In recent decades, extensive geological, geophysical and geochronological data have been obtained that characterize in detail the results of the distant tectonic impact of the Indo-Eurasian collision on the lithosphere of Central Asia, which led to the formation of the mountain systems of the Pamirs, Tien Shan, Altai-Sayan region and Transbaikalia from the Late Paleogene (about 25 million years ago). It has been established that the formation of the structure of Central Asia occurred as a result of the transmission of deformations from the Indo-Eurasian collision over long distances according to the “domino principle” through the rigid structures of Precambrian microcontinents located among the Paleozoic-Mesozoic folded belts. The study of peneplain surfaces deformed into simple folds on high-mountain plateaus surrounded by rugged mountain ranges made it possible to reveal the parameters of the deformations of the earth’s crust, the interrelationship of the formation of relief and sedimentary basins. Apatite track dating data, structural and stratigraphic analyses of Late Cenozoic sediments in the basins prove a period of intense tectonic activation the entire lithosphere of Central Asia from the Indian continent to the Siberian platform starting from the Pliocene (about 3.5 million years). As a result of reactivation of the heterogeneous basement of Central Asia, high seismicity was manifested, which is concentrated mainly along the border of the microcontinents (Central Tianshan, Junggar and Tuva-Mongolian) and the Siberian craton, as well as in the zones of articulation of regional faults.

The mechanical behaviour of the lithosphere beneath the Chad Basin and the Bangui Magnetic Anomaly. Insights from Moho depth and effective elastic thickness estimates

We used high-resolution gravity data to analyse crustal structure beneath the Bangui Magnetic Anomaly (BMA) and the Chad Basin within the North-Central African region. Moho depths and effective elastic thickness values, calculated respectively by a regularized non-linear inversion method and by analysis of the coherence function between gravity and topography, have been interpreted with reference to seismic data, previous gravity studies and regional geology. Our aim is to determine the crustal architecture and to analyse its mechanical behaviour. Estimated Moho depths range from 30 to 43 km in the North-Central African region. Beneath the uplift zones (Adamawa-Yade plateau, Ouaddaï, Tibesti, Hoggar, Tuareg shield) and the Congo Craton, the Moho depths range between 35 and 37 km. These values can be interpreted by tectonic and seismic events recorded along the regional shear zones; but also to the remobilization of the Precambrian basement. Analysis of the coherence function between the Bouguer gravity and the topography shows two different domains of rigidity: the highest values (100 km < Te < 180 km) are observed in Central African Republic, Chad, Niger, Algeria, and Egypt; the lowest values (20 < Te < 100 km) are observed in Cameroon, Nigeria, and Sudan. The lithosphere beneath the Chad Basin has a higher rigidity, similar to that observed in Central African Republic. In Chad and the Central African Republic, there is a positive correlation between the Te and the Moho depths; this indicates that cratonic remnant (Chad craton) beneath the Chad Basin is well preserved and covered by the sediments. The low Te values in Cameroon and the constant value in the Moho depth, are a proof of the reactivation of the Precambrian basement. This reactivation is related to the tectonic, seismic and thermal events occurred during the Eburnean and Pan-African orogenies. The contrast between the Te values in Cameroon compared to others regions (Chad, Central African Republic, Niger, Egypt, Algeria) show the magnitude of these events on the crustal architecture. This being defined by the presence of cratonic cores, the Cameroon Volcanic Line (CVL) and hot spots as well as large regional shear zones, explain the fact that thermo-tectonic and seismic events that occurred at the northern edge of the Congo Craton in Cameroon, are more intense than in the Central African Republic. So according to the geodynamic process in Cameroon and Central African Republic, related to the hot spots along the CVL, thermo-tectonic and seismic events recorded along the regional shear zones (Sanaga Shear Zone and the Central Cameroon Shear Zone) and the Congo Craton, the BMA is associated to two different geotectonic contexts. The sources of the BMA are closely linked to the Congo Craton; they bottom should not exceed −37 km depth. The present results agree with previous studies which allow us to understand the evolution of the Saharan metacraton and the preservation of cratonic remnants (Murzuq, Al-Kufrah, Chad); similarly the estimated Moho depths is an important step that would serve as an input to model the sources of the Bangui Magnetic Anomaly.

Multiple tectonomagmatic reactivation of the unexposed basement in the northern Siberian craton: from Paleoproterozoic orogeny to Phanerozoic kimberlite magmatism

ABSTRACT Zircon xenocrysts from two diamond-barren kimberlite pipes (Leningrad and Ruslovaya) in the West Ukukit kimberlite field opened a ‘window’ to the buried crustal basement in the northern Siberian craton. Zircon U-Pb ages reveal a close affinity of the basement of the Khapchan belt to the Archaean Anabar province and a significant tectonomagmatic reworking in the Paleoproterozoic (~2.1–1.8 Ga) due to collision between the Anabar province and the Olenek province. The West Ukukit kimberlite field experienced multiple tectonomagmatic reactivation from ~670 to 144 Ma, which can be attributed to interaction of the deep crust with mantle-derived melts. Hf isotope composition of zircon xenocrysts reveals significant addition of juvenile material into the crust during the Paleoproterozoic orogeny in diamond-barren kimberlite fields, which is different from the reworking crust in the southern Yakutia diamondiferous kimberlite fields. Eruption of the Leningrad and Ruslovaya pipes were constrained as the Late Jurassic, much later than the well-known Late Silurian-Earth Devonian kimberlites in the West Ukukit kimberlite field. A NE-trending, >2000 km long kimberlite corridor is proposed to account for a prolonged lithospheric channel for episodic eruption of kimberlites in the Siberian craton. The diamond storage in the lithosphere beneath the West Ukukit kimberlite field may have been largely reduced by the Paleoproterozoic orogeny and Phanerozoic reworking.

Crustal Configuration and Seismic Stability of the Eastern Indian Shield and Adjoining Regions: Insights for Incidents of Great Earthquakes in the Nepal-Bihar-Sikkim Himalaya

The Eastern Indian Shield (EIS) is comprised of the intracratonic (coal-bearing) Damodar Gondwana basin, rift-controlled extensional Lower Gangetic basin (LGB), and the downward flexed Indo-Gangetic basin (IGB). The present study involves the computations and mapping of the basement configuration, sediment thickness, Moho depth, and the residual isostatic gravity anomaly, based on 2-D gravity modeling. The sediment thickness in the area ranges between 0.0 and 6.5 km, and the Conrad discontinuity occurs at ∼17.0–20 km depth. The depth of the Moho varies between 36.0 and 41.5 km, with the maximum value beneath the Upper Gangetic basin (UGB), and the minimum of ∼36 km (uplifted Moho) in the southeastern part beneath the LGB. The maximum residual isostatic anomaly of +44 mGal in the southern part indicates the Singhbhum shear zone, LGB, and Rajmahal trap to be under-compensated, whereas the northern part recording the minimum residual isostatic anomaly of –87.0 mGal is over-compensated. Although the region experienced a few moderate-magnitude earthquakes in the past, small-magnitude earthquakes are sparsely distributed. The basement reactivation was possibly associated with a few events of magnitudes more than 4.0. Toward the south, in the Bay of Bengal (BOB), seismic activities of moderate size and shallow origin are confined between the aseismic 85 and 90°E ridges. The regions on the extreme north and south [along the Himalaya and the equatorial Indian Ocean (EIO)] are experienced moderate-to-great earthquakes over different times in the historical past, but the intervening EIS and the BOB have seismic stability. We propose that the two aseismic ridges are guiding the lithospheric stress fields, which are being further focused by the basement of the EIS, the BOB, and the N-S extended regional fault systems into the bending zone of the penetrating Indian lithosphere beneath the Himalaya. The minimum obliquity of the Indian plate and the transecting fault systems in the Foothills of the Himalaya channelize and enhance the stress field into the bending zone. The enhanced stress generates great earthquakes in the Nepal-Bihar-Sikkim Himalaya, and on being reflected back through the apparently stable EIS and BOB, the stress field creates deformation and great earthquakes in the EIO.

Early Paleozoic reactivation of the Precambrian basement on the northern margin of the Qilian block: Evidence from phase equilibria and zircon U-Pb dating of meta-mafic rocks

Early Paleozoic reactivation of the Precambrian basement on the northern margin of the Qilian block: Evidence from phase equilibria and zircon U-Pb dating of meta-mafic rocks

Quantifying and modelling the effects of pre-existing basement faults on folding of overlying strata in the Surat Basin, Australia: Implications for fault seal potential

Ancient basement fault geometry has a systematic effect on the folding of overlying sedimentary successions. Using aeromagnetic, Bouguer gravity, as well as 2D and 3D seismic datasets, the characteristics of the basement structure underlying the Jurassic-Cretaceous Surat Basin were examined and used to contextualise the nature of its folded strata. Using Fault-Forward modelling software, the deformation of the basement structural layers was modelled and analysed for its influence on the reactivation of faulting. The results show that the major fault trends in the eastern Surat and Bowen basins consist of five key features with N- and NE-trending orientations: the Goondiwindi, Moonie, Undulla Transition Zone, Burunga-Leichhardt, and Cockatoo fault systems. Most of the major fault deformation ceased in the Late Triassic. However, some faults (i.e., the Moonie and Goondiwindi fault systems) were variably reactivated along their lengths during the Jurassic. Three models of pre-existing basement reactivation are proposed to explain the observed variability in folding style with application to different parts of the basin. Ancient fault systems with dip angles greater than 45° were readily reactivated and produced tight monocline structures with high strain (ε > 0.35) and fault throw (>60 m) (e.g. Moonie Fault System), while faults with small dip (<30°) or large apical angles generated folds with low strain and uplift of the hanging wall. This variability in fault reactivation according to differences in fault throw potentially influences across-fault juxtaposition of strata and sealing potential for CO2 storage. Modelling such as this should be undertaken elsewhere in situations where trishear structural domains are expected, to better understand and predict the deformation of overlying stratal successions.

Sequence stratigraphy of a Middle to Upper Ordovician foreland succession (Ottawa Embayment, central Canada): Evidence for tectonic control on sequence architecture along southern Laurentia

AbstractThe Middle to Upper Ordovician foreland succession of the Ottawa Embayment in central Canada is divided into nine transgressive‐regressive sequences that defines net deepening of a platform succession over ~15 m.y. from peritidal to outer ramp settings, then a return to peritidal conditions over ~3 m.y. related to basin filling by orogen‐derived siliciclastics. With a backdrop of net eustatic rise through the Middle to Late Ordovician, there are several different expressions of structural influence on sequence development in the embayment. During the Middle Ordovician (Darriwilian), foreland‐basin initiation was marked by regional onlap with abundant synsedimentary deformation across a faulted trailing‐margin platform interior; subsequent craton‐interior uplift resulted in voluminous influx of siliciclastics contemporary with local structurally influenced local channelization; then, a formation of a platform‐interior shale basin defines continued intrabasin tectonism. During the Late Ordovician (Sandbian, early Katian), structural influence was superimposed on sea‐level rise as indicated by renewed local development of a platform‐interior shale basin; differential subsidence and thickness variation of platform carbonate successions; abrupt deepening across shallow‐water shoal facies; and, micrograben development coincident with foreland‐platform drowning. These stratigraphic patterns are far‐field expressions of distal orogen development amplified in the platform interior through basement reactivation along an inherited buried Precambrian fault system. Comparison of Upper Ordovician (Sandbian‐lower Katian) sequence stratigraphy in the Ottawa Embayment with eustatic frameworks defined for the Appalachian Basin reveals greater regional variation associated with Sandbian sequences compared to regional commonality in base level through the early Katian.

Coeval deposition of transgressive and normal regressive stratal packages in a structurally controlled area of the Viking Formation, central Alberta, Canada

AbstractVariability in accommodation and sedimentation rates within a basin generates significant deviations in the along‐strike stratal stacking patterns of systems tracts. This variability can lead to coeval depositional units that record the juxtaposition of transgressive (retrogradational) and regressive (progradational) stratal stacking patterns. In scenarios where transgressive and regressive units are deposited concurrently, challenges arise when attempting to correlate and place systems tracts into a sequence stratigraphic framework. In these scenarios, the maximum flooding surface records a high level of diachroneity, with the position of the surface variable throughout the stratigraphic column. In this study, Viking Formation (late Albian) deposits in the Western Canada Sedimentary Basin, central Alberta, Canada, preserve significant along‐strike variability of palaeoshorelines that developed in response to autogenic processes as well as allogenic controls that were active during deposition. Specifically, structural reactivation of Precambrian basement structures during Viking deposition led to significant variability in depositional environments along the palaeoshoreline. The incremental basement reactivation of the Precambrian Snowbird Tectonic Zone influenced sedimentation patterns and the creation of anomalous zones of accommodation in localized areas of the basin. Across fault boundaries and within the anomalously thick strata, both progradational and retrogradational stacking patterns occur within broadly contemporaneous deposits, complicating the correlation of stratigraphic units. While the concomitant deposition of transgressive and regressive units has been documented in a number of modern marine analogues, the concept is rarely applied to ancient successions. By identifying along‐strike variabilities in shoreline geometries and incorporating the autogenic and allogenic controls that were active during deposition, a more accurate sequence stratigraphic framework can be proposed.

Newly emerging cases of hydraulic fracturing induced seismicity in the Duvernay East Shale Basin

Hydraulic fracturing (HF) in the Duvernay Formation near Fox Creek, Alberta, Canada, has produced some of the most prolific clusters of induced seismicity. In this paper, we describe newly emerging clusters of events occurring in previously quiescent (and undeveloped) areas of the Duvernay Formation. In the Duvernay East Shale Basin, an industry supplemented waveform database is examined using a variety of seismological techniques. Here, strike-slip events as large as 4.18 ML have been felt in nearby cities. Temporal relationships suggest these clusters are almost certainly (>99.7% confidence) caused by nearby HF. Spatially, these earthquakes tend to occur in the strata directly overlying the Duvernay Formation and laterally near a horizontal well. One exceptional cluster clearly delineates a 1.5 km offset between its centroid and the inducing horizontal well, raising questions about the earthquake triggering mechanism. Westward in the Duvernay, two minor clusters within the Willesden Green region appear to be tenuously related to HF completions. This study also places constraints on the structural geology of faulting occurring in the Rocky Mountain House Seismogenic Zone – a region of induced seismicity related to secondary recovery in the Strachan D-3A pool. Here, our moment tensors and double difference relocations describe thrust-slip on a fault underlying the target formation. Last, the largest event (4.27 ML) in our study area was likely natural, due to its deeper hypocentral depth (~15 km) and non-correspondence with industrial operations. Overall, the newly emerging clusters are consistent with reactivation of basement rooted faults.

Broadband seismic imaging around the Banda Arc: changes in the anatomy of offshore fold-and-thrust belts

Abstract The complicated geology of the Banda region results from complex collision between the Eurasia, Australia and Pacific plates, ongoing in the region since the Late Oligocene but particularly in the study area since the Middle Miocene (from 15 Ma). Regional 2D broadband seismic data have provided improved imaging of Mesozoic and Cenozoic sedimentary successions in the region. The region comprises the deep and ultra-deep Banda Sea enclosed by a magmatic inner arc and an outer deformed zone, comprising a series of orogens. This outer orogenic zone comprises islands with extended and sometimes hyperextended continental crust, a series of marginal foredeeps and intervening fold-and thrust belts. This paper illustrates how the offshore fold-and-thrust belts that bound the fore-deeps change in size, shape and degree of basement reactivation in a clockwise sense around the Banda Arc.

Morphotectonics in the Central-East Region of South Brazil: Implications for Catchments of the Lava-Tudo and Pelotas Rivers, State of Santa Catarina

The catchments of the Lava-Tudo and Pelotas rivers are located on the eastern edge of the Paraná Sedimentary Basin, central-east of the Brazilian state of Santa Catarina. This region comprises Mesozoic volcanic rocks from the Paraná Large Igneous Province (LIP) deformed by Cenozoic joints and faults. Morphometric analysis carried out using remote sensing and structural data showed the influence of tectonics on the geomorphological framework of the target catchments, which therefore provided a morphological characterization of the area. Deformation of the topography was determined from changes in topographic surface, drainage basin asymmetries, disturbances on longitudinal profiles and anomalies in drainage patterns associated with NE-SW and NW-SE faults derived from reactivation of the Proterozoic basement, as well as other neotectonically formed structures trending mainly N-S and E-W. The asymmetry recognized in the studied catchments results from tectonic tilting marked by oblique NE-SW faults. The deformation pulses resulted in the dismantlement of an extensive local Paleogene planation surface, also known as the Sul-Americana Surface. In the southeastern and southern regions of Brazil, morphotectonic evolution has been associated with tectonic pulses that took place between the Upper Cretaceous and Upper Pleistocene.

Tectonic framework of the Paraná basin unveiled from gravity and magnetic data

The Paraná Basin, one of the most important Brazilian sedimentary basins, was created during the formation of Western Gondwana. Until recently, its tectonic framework has been studied mainly through indirect studies using geophysical data such as gravity, magnetic, as well as seismic reflection, and bore hole data. However, the last years, new geophysical data with better resolution became available, enabling new studies on the Brazilian sedimentary basins. To this end, the objective of this work is to contribute with new information on regarding the central and northern areas of the Parana basin and to investigate the major tectonic structures of its basement, as to understand the role of the Precambrian basement structures on its reactivation and geodynamics. For this purpose, quantitative and qualitative analysis of gravity and magnetic data were conducted using the Matched-Filter technique associated with enhancement filters, such as Total Horizontal Gradient and Tilt Derivative of the Total Horizontal Gradient. These geophysical products allowed interpreting the main geophysical lineaments and their depth. We identified structural patterns related to basement reactivation associated with the evolution of Western Gondwana. The NNE-SSW trending structures are related to reactivations of the Transbrasiliano and Paraíba do Sul Strike-slip Systems in the Late Ordovician. The NW-SE trending lineaments were generated with the tectonic growth of the Western Gondwana in the Triassic to the Late Jurassic, which started in the region of the Ponta Grossa Arch. This event was followed by the intracontinental magmatism in the Early Cretaceous. The E-W trending structures are related to the drifting of the South American Plate in the Late Cretaceous-Neogene and the faults originated from it, forming dextral binaries inside the plate pertaining to the Neotectonic Strike-slip System. The NNE-SSW, NE-SW, and NW-SE trending lineaments close to the border between the Paranapanema Block, the Goiano Domain, and the Araguaia, Paraguay, Brasília and Ribeira Belts are associated with suture zones. Thus, this work provides additional information related to the continuity of fault systems and crustal domain limits, as well as the extent of the crustal blocks in the basement of the Paraná Basin. It highlights the reactivation influence of the structures inherited from the Precambrian basement based on the results from both, gravity and magnetic data.

Evidence for Basement Reactivation during the Opening of the Labrador Sea from the Makkovik Province, Labrador, Canada: Insights from Field Data and Numerical Models

The onshore exposures adjacent to modern, offshore passive continental margins may preserve evidence of deformation from the pre-, syn-, and post-rift phases of continental breakup that allow us to investigate the processes associated with and controlling rifting and breakup. Here, we characterize onshore brittle deformation and pre-rift basement metamorphic mineral fabric from onshore Labrador in Eastern Canada in the Palaeoproterozoic Aillik Domain of the Makkovik Province. Stress inversion (1) was applied to these data and then compared to (2) numerical models of hybrid slip and dilation tendency, (3) independent calculations of the regional geopotential stress field, and (4) analyses of palaeo-stress in proximal regions from previous work. The stress inversion shows well-constrained extensional deformation perpendicular to the passive margin, likely related to pre-breakup rifting in the proto-Labrador Sea. Hybrid slip and dilatation analysis indicates that inherited basement structures were likely oriented in a favorable orientation to be reactivated during rifting. Reconstructed geopotential stresses illuminate changes of the ambient stress field over time and confirm the present paleo-stress estimates. The new results and numerical models provide a consistent picture of the late Mesozoic-Cenozoic lithospheric stress field evolution in the Labrador Sea region. The proto-Labrador Sea region was characterized by a persistent E–W (coast-perpendicular) extensional stress regime, which we interpret as the pre-breakup continental rifting that finally led to continental breakup. Later, the ridge push of the Labrador Sea spreading ridge maintained this general direction of extension. We see indications for anti-clockwise rotation of the direction of extension along some of the passive margins. However, extreme persistent N–S-oriented extension as indicated by studies further north in West Greenland cannot be confirmed.

Characterizing Seismo-stratigraphic and Structural Framework of Late Cretaceous-Recent succession of offshore Indus Pakistan

Abstract Regional seismic reflection profiles and deep exploratory wells have been used to characterize the subsurface structural trends and seismo-stratigraphic architecture of the sedimentary successions in offshore Indus Pakistan. To improve the data quality, we have reprocessed the seismic data by applying signal processing scheme to enhance the reflection continuity for obtaining better results. Synthetic seismograms have been used to identify and tie the seismic reflections to the well data. The seismic data revealed tectonically controlled, distinct episodes of normal faulting representing rifting during Mesozoic and transpression at Late Eocene time. A SW-NE oriented anticlinal type push up structure is observed resulted from the basement reactivation and recent transpression along Indian Plate margin. The structural growth of this particular pushup geometry was computed. Six mappable seismic sequences have been identified on seismic records. In general, geological formations are at shallow depths towards northwest due to basement blocks uplift. A paleoshelf is also identified on seismic records overlain by Cretaceous sediments, which is indicative of Indian-African Plates rifting at Jurassic time. The seismic interpretation reveals that the structural styles and stratigraphy of the region were significantly affected by the northward drift of the Indian Plate, post-rifting, and sedimentation along its western margin during Middle Cenozoic. A considerable structural growth along the push up geometry indicates present day transpression in the margin sediments. The present comprehensive interpretation can help in understanding the complex structures in passive continental margins worldwide that display similar characteristics but are considered to be dominated by rifting and drifting tectonics.

40Ar-39Ar dating of Archean iron oxide Cu-Au and Paleoproterozoic granite-related Cu-Au deposits in the Carajás Mineral Province, Brazil: implications for genetic models

40Ar-39Ar dating of biotite from IOCG and granite-related Cu-Au deposits in the Carajas Mineral Province provides evidence for the timing of mineralization and constraints on genetic models of ore formation. Ages of biotite from greisen and quartz-rich vein and breccia deposits, Alvo 118—1885 ± 4 Ma, Breves—1886 ± 5 Ma, Estrela—1896 ± 7 Ma, and Gameleira—1908 ± 7 Ma, demonstrate the close temporal relationship between Cu-Au mineralization and subjacent A-type granites. Mineralization is hosted within granite cupolas (Breves) or in vein/breccia systems emanating from the cupolas (Estrela and Gameleira), consistent with a genetic relationship of mineralization to the B-Li-F-rich granites. Plateau and minimum ages of biotite from IOCG deposits, including Igarape Bahia, Cristalino, Corta Goela, and GT34, range from 2537 ± 6 Ma to 2193 ± 4 Ma. The 40Ar-39Ar age of biotite from Igarape Bahia (2537 ± 6 Ma) is similar to a previous SHRIMP 207Pb-206Pb age for monazite of 2575 ± 12 Ma when the uncertainties in the respective analyses and standards are taken into account. The age spectrum for biotite from Cristalino shows increasing ages for successive steps, consistent with post-crystallization Ar loss, and the age of 2388 ± 5 Ma for the last three steps is considered a minimum age for Cu-Au mineralization. The age of biotite from the GT34 prospect (2512 ± 7 Ma) coincides with a previously identified period of basement reactivation and may indicate the formation of Cu-Au mineralization at this time or resetting of biotite from an older mineralization event at this time. At Corta Goela, within the Canaa Shear Zone, the biotite age of 2193 ± 4 Ma lies between the ages of IOCG (2.57–2.76 Ga) and granite-related Cu-Au (~ 1.88 Ga) deposits elsewhere in the Carajas district but is similar to previously reported 40Ar-39Ar ages for amphibole from Sossego, possibly indicating that mineralization at both Sossego and Corta Goela was affected by a thermal event at this time. The Paleoproterozoic Cu-Au deposits are commonly hosted within Neoarchean IOCG alteration systems and the common occurrence of potassic alteration (especially biotite) in both types of deposits means that special care is required in interpreting the paragenesis of alteration in both types of deposits. The Paleoproterozoic Cu-Au deposits are reduced, and sulfur- and quartz-rich deposits lacking in major amounts of iron oxides and are therefore unlike IOCG deposits. Instead, they share many characteristics in common with widespread Paleoproterozoic Sn-W deposits in the Amazon Craton, including close spatial and temporal relationships with reduced A-type B-Li-F granites, and the occurrence of greisen and quartz-rich vein/breccia systems within and above granite cupolas. The occurrence of sericitic alteration in the Paleoproterozoic Cu-Au deposits is not evidence for an upward transition to sericitic alteration in IOCG deposits in the Carajas Mineral Province.

Asymmetric continental deformation during South Atlantic rifting along southern Brazil and Namibia

Plate restoration of South America and Africa to their pre-breakup position faces the problem of gaps and overlaps between the continents, an issue commonly solved with implementing intra-plate deformation zones within South America. One of these zones is often positioned at the latitude of SE/S Brazil. However, geological evidence for the existence of a distinct zone in this region is lacking, which is why it remains controversial and is not included in all modeling studies. In order to solve this problem we present a study of multiple geological aspects of both parts of the margin, SE/S Brazil and its conjugate part NW Namibia at the time of continental breakup. Our study highlights pronounced differences between these regions with respect to Paraná-Etendeka lava distribution, magmatic dyke emplacement, basement reactivation, and fault patterns. In Namibia, faults and dykes reactivated the rift-parallel Neoproterozoic basement structure, whereas such reactivation was scarce in SE/S Brazil. Instead, most dykes, accompanied by small-scale grabens, are oriented margin-perpendicular along the margin from northern Uruguay to São Paulo. We propose that these differences are rooted in large-scale plate movement and suggest a clockwise rotation of southern South America away from a stable northern South America and Africa, in a similar way as proposed by others for a Patagonian continental section just prior to South Atlantic rifting. This rotation would produce margin-parallel extension in SE/S Brazil forming margin-perpendicular pathways for lava extrusion and leading to the asymmetric distribution of the Paraná-Etendeka lavas. NW Namibia instead remained relatively stable and was only influenced by extension due to rifting, hot spot activity, and mantle upwelling. Our study argues for significant margin-parallel extension in SE/S Brazil, however not confined to a single distinct deformation zone, but distributed across ~1000km along the margin.

Paleogene and Neogene kinematics of the Alpine-Carpathian fold-thrust belt at the Alpine-Carpathian transition

In this study we analyze a ~300km long segment of the Alpine-Carpathian orogen using novel outcrop data and regional seismic profiles from the West Carpathians to unravel the kinematics and timing of Eocene to Late Miocene deformation of the fold-thrust belt. Comparison with data from the Eastern Alps and the Vienna Basin leads to an updated tectonic model for the Paleogene and Neogene of the Alpine-Carpathian transition, which includes three stages:(1) Eocene to Early Oligocene NNW-directed foreland-propagating thrusting. Thrusts are directed perpendicular to the strike of the European foreland in the Outer West Carpathians (OWC) and sub-parallel to thrusts observed in the Eastern Alps west of the Vienna Basin.(2) Continued Late Oligocene to Early Miocene NNW-directed foreland-propagating thrusting simultaneous with sinistral strike-slip reactivation of former nappe boundaries in the hinterland of the active thrusts. This deformation corresponds to the early stage of eastward lateral extrusion of the Eastern Alps. The ENE-striking sinistral faults in the OWC are kinematic equivalents of the SEMP fault system in the Eastern Alps, which was active at the same time. The latest stage of thrusting is characterized by SSE-directed out-of-sequence thrusts in the hinterland of the OWC and the reactivation of Variscan basement thrusts in the European foreland as SSE-directed backthrusts.(3) Formation of (N)NE-striking sinistral strike-slip faults which are kinematically linked to (N)NE-directed out-of-sequence thrusts post-dating NNW-directed thrusting. The sinistral faults formed coeval with the opening of the Vienna pull-apart basin during the Middle to Late Miocene stage of lateral extrusion.Unlike proposed in previous studies the West Carpathians do not appear to be affected by Oligocene to Early Miocene crustal-scale wrenching of the Pieniny Klippen Belt. Our data show that the deformation of the PKB is in line with the Eocene to Late Miocene tectonic evolution reconstructed for the OWC.

3D seismic analysis of gravity-driven and basement influenced normal fault growth in the deepwater Otway Basin, Australia

We use three-dimensional (3D) seismic reflection data to analyse the structural style and growth of a normal fault array located at the present-day shelf-edge break and into the deepwater province of the Otway Basin, southern Australia. The Otway Basin is a Late Jurassic to Cenozoic, rift-to-passive margin basin. The seismic reflection data images a NW-SE (128–308) striking, normal fault array, located within Upper Cretaceous clastic sediments and which consists of ten fault segments. The fault array contains two hard-linked fault assemblages, separated by only 2 km in the dip direction. The gravity-driven, down-dip fault assemblage is entirely contained within the 3D seismic survey, is located over a basement plateau and displays growth commencing and terminating during the Campanian-Maastrichtian, with up to 1.45 km of accumulated throw (vertical displacement). The up-dip normal fault assemblage penetrates deeper than the base of the seismic survey, but is interpreted to be partially linked along strike at depth to major basement-involved normal faults that can be observed on regional 2D seismic lines. This fault assemblage displays growth initiating in the Turonian-Santonian and has accumulated up to 1.74 km of throw.Our detailed analysis of the 3D seismic data constraints post-Cenomanian fault growth of both fault assemblages into four evolutionary stages: [1] Turonian-Santonian basement reactivation during crustal extension between Australia and Antarctica. This either caused the upward propagation of basement-involved normal faults or the nucleation of a vertically isolated normal fault array in shallow cover sediments directly above the reactivated basement-involved faults; [2] continued Campanian-Maastrichtian crustal extension and sediment loading eventually created gravitational instability on the basement plateau, nucleating a second, vertically isolated normal fault array in the cover sediments; [3] eventual hard-linkage of fault segments in both fault arrays to form two along-strike, NW-SE striking fault assemblages, and; [4] termination of fault growth in the latest Maastrichtian. We document high variability of throw along-strike and down-dip for both fault assemblages, thereby providing evidence for lateral and vertical segment linkage. Our results highlight the complexities involved in the growth of both gravity-driven normal fault arrays (such as those present in the Niger Delta and Gulf of Mexico) and basement-linked normal fault arrays (such as those present in the North Sea and Suez Rift) with the interaction of an underlying and reactivating basement framework. This study provides an excellent example of spatial variability in growth of two normal fault assemblages over relatively short spatial scales (∼2 km separation down-dip).