Concluding Remarks on the Theory of Global Strike-Slip Tectonics

Standard

The theory of Global Strike-Slip Tectonics is providing an alternative approach to global plate tectonics, in which internal deformation of plates is put forth of boundary processes. Strike-slip faults are considered being of primary importance in deciphering the structural geology of crustal fragments, while normal faulting and thrusting are only complimentary elements of plate-interior kinematics.

The classic plate tectonic framework commonly fails to explain the interaction of low hierarchy crustal fragments; as a consequence several inefficient regional tectonic models were generated, which have created confusion and paradox situations. Albeit, we have presented a few of such conflicting situations, particularly from the Mediterranean Basin, the scope of the present study did not permit to give an extensive worldwide review. That can be made, however, in the forthcoming issues of the JGSST journal, with your kindly contribution.

Relying on the aforementioned inadequate plate tectonic models, mysteries have propagated further into the domain of sedimentary geology as well, e.g. the origin of the Messinian Salinity Crisis also remained unrevealed, or basin modelling efforts failed to reproduce observed basin infill geometries.

For hydrocarbon and ore exploration, plate scale events are too large to deduce a consistent local scale model. Therefore, we have looked after the behavior of smaller scale tectonic units.

While approximating with a holistic approach and integrating several data types, as described in previous sections, we have discovered that established global plates can be broken down into low hierarchy crustal fragments, like nanoplates and pikoplates. These latter already can be readily used in the delineation of prospective trends and play assessment.

The concept of stress nodes was introduced to describe the spatial clustering of earthquake epicenters, while the concept of extension nodes is localizing and gives explanation to regions of intraplate magmatism, all related to aspects of the regional stress fields.

We have emphasized the importance of simple shear stress fields in providing space management solutions for the low hierarchy crustal fragment interactions. Beyond that pikoplates and nanoplates are kinematically integrated into microplates, we have found that all these low hierarchy elements are commonly integrated into kinematic chains, which can be made up of various oceanic and continental crustal fragments, occasionally linked by inactive rift segments. They are usually showing lateral kinematic constraints from the behalf of other kinematic chains, orchestrated by the Coriolis force.

Like trains, kinematic chains perform a constant eastward drift towards their backstop, identified in the Jade Dragon – Smith Mp – Sunda Arc lineament. Behind this backstop lineament, crustal fragments are intensively deformed and broken into small and arcuate units. In this area, as suggested by earthquake clustering and a P-wave tomographic profile from northeastern Japan, crustal fragments are rather performing strike-slip overriding along steep master faults, than real subduction, and the same might apply for the Western Pacific ‘subduction’ zone. True subduction, where oceanic plate is recycled into the asthenosphere may only happen along the western margin of the American continents. When contractional space problem occurs, oceanic crustal fragments either perform lateral duplexing like in the case of the Marquesas, Bismarck and Caribbean nanoplates, or may even override each-other, forming oceanic ridges (e.g. Laximi Ridge). Space problem in the continental domain is resolved in the similar way, by incipient various scale lateral duplexing, than vertical duplexing. Initial push-up ranges (proto-orogens) may advance into evolved orogens, like in the case of the Atlas Mountains, as proven by Ellero.

Herein, we have proposed the extension of Ellero’s model to the whole Tethys area, and gave a new definition for orogenesis, in the GSST approach.

In addition to the review of the orogenesis and subduction concept, we have drawn preliminary conclusions about the East African Rift strain patterns, as well. Selecting random rift zones from published articles through the East African Rift area, strike-slip tectonics related faulting and deformation is as common as elsewhere in the world; however the magnitude of fault-displacements seems less expressed. Here, the role of tension fracture components is more relevant, and these continental rifts are interpreted as microplate scale tension fractures. Because crustal thickness is much larger than elsewhere, structural deformation is slow, but still present along deep crustal faults, which either give birth to intraplate volcanism, or possibly produce punctual release of high-pressure mantle volatiles, as we have discussed in the impact crater related section.

Acknowledgements

We are grateful for NASA (SRTM), European Mediterranean Seismological Centre (earthquake database), Max Planck Institute of Geochemistry Mainz (Georoc database), Google Earth, UNAVCO (GPS measurments) for sharing their database over the internet. ADX Energy (Perth) is thanked for providing a close seismic study opportunity on the onshore and offshore geology of Tunis.

GSST: Impacts on Hydrocarbon and Ore Exploration

Standard
impactcr50

Distribution of proven (red) and unproven (blue) impact craters of the Earth (Reimold, 2014). Craters are clustered in several continental locations, and are showing good correlation with microplate and nanoplate boundaries, suggesting that at least one part of the craters is related to the escape of high-pressure mantle volatiles (Storetvedt, 1997).

After spending several years in the petroleum and mining industry it becomes obvious to anybody that structural geology is the α and Ω of exploration, because structural geology gives the platform where all the results of various analyses can be integrated. Besides local project details, structural geology has a large significance in predicting plate scale disposition of hydrocarbon and ore accumulations, delineating plays and structural trends. Structural geology is driving new venture acquisitions, exploration and forthcoming appraisal cycles, and even enhanced recovery projects.

Prospect generation is always based on preconceptions, and even object based geophysical processing is depending on structural modelling, thus building a robust regional and local structural model, without conflicts, mysteries and paradoxes is definitely important.

9.1. Hydrocarbon exploration

Global strike-slip tectonics (GSST) helps to better understand the cause of heat anomalies, explains the tectonic evolution of cool basins, like the Junggar, Transylvanian and Vienna basins. It gives a new approximation to the orogenesis process, and to the internal structuring of orogens.

The thermal history of basins is a basic input for source rock maturation studies; therefore it is critical to understand basin opening and later subsidence mechanisms. Heat transfer, for example it is more effective in convective systems, and a low stress (open) fracture network may provide effective conduits for fluid circulation.

Local stress field prediction is useful from many purposes. In order to identify active migration pathways, reservoir charging conditions we need to spot the low-stress regions, and in contrast, in case we are interested in the location of sealing faults, we need to search for high-stress zones. When working with tight reservoirs, identification of natural fracture zones not only provides sweet spot targets, i.e. higher hydrocarbon yields, but it is also reducing fracking costs and minimizing environmental risk. In addition, predicting the location of deep crustal faults helps with a better CO2 risk assessment.

There are several ways of characterizing, measuring local stress fields, but prediction for wildcut wells is more efficient approaching from a regional perspective. The nanoplate and pikoplate concepts can be very useful in delivering hydrocarbon play assessments.

9.2. Ore exploration

Channelways of primary dispersion and concentration of elements are indisputably provided by crustal faults and fractures, which are enabling the rising of mantle and lower crustal origin magmas or hydrothermal fluids to create magmatic and hydrothermal deposits. Therefore, it is not surprising that largest ore accumulations are related to strike-slip tectonics, after the so called impact craters, the origin of which seems disputable, and needs further research, however they are commonly related to cosmic origin.

Deep crustal faults are needed also to maintain the element budget of oceanic basins, and subsequently for charging marine sedimentary ore traps, like in the case of the Urgonian limestone hosted Zn-Pb deposit from Reocin, Basque Country (Velasco et al., 2003).

Delineation of second order structures related to crustal scale structures also involve structural geology techniques, because 1) breccia pipe deposits, for example, are related to fault intersections, which usually hold copper and uranium mineralization, or 2) anastomosing shear zones may host quartz–carbonate–sulphide veins and disseminated stockwork deposits (e.g. copper & gold in porphyry associated deposits), 3) ore plunge frequently might correlate with fold axis, and finally 4) extensional structures host order of magnitude variation in gold grade, for example, and therefore the evolution of paleo-stress fields is also important.

Fault systems are accumulating ore mineralization usually in low stress sites of brittle structures or cavities, in 1st, 2nd, 3rd order vein systems (Siddorn, 2010), which enable the circulation of hydrothermal fluids.

Presence of CO2 can induce immiscibility both within the magmatic volatile phase and in the hydrothermal systems, therefore CO2 may indirectly aid the process of metallogenesis by inducing phase separation (Lowenstern, 2001). Because orogenic gold deposits need CO2-rich H2S bearing low salinity fluids, mapping deep crustal CO2 conduits might help in prospecting gold.

Impact structures – further research direction

Considering that impact structures are holding the largest ore deposits on the Earth, it worth to take a glance at their origin, particularly to their disposition against microplate boundaries.

Apart from the widely known and largest impact craters Chicxulub (Mexico), Sudbury (Canada) and Vredefort (South Africa), there were identified dozens of impact craters across the world (Fig. 34), Reimold has identified 49 sites in Africa alone. From the 49 impact crater sites proposed in Africa, 28 already have been proved not to be of meteorite impact origin (Reimold and Koeberl, 2014); however they are concentrating in the same geographic area, e.g. South Africa.

An alternative explanation to the origin of these crater morphologies is provided by Storetvedt, who argues that the Chicxulub crater in Mexico (off Yucatan Peninsula) is a major blow-out crater of high-pressure mantle volatiles (Storetvedt, 1997), that kicked up billions of tonnes of sulfur (Ainsworth, 1994). The Chicxulub impact predates the K–T boundary by about 300 kyr (Keller et al., 2007).

Seismic images of Moho at Chicxulub are showing an upwarped mantle (Christeson et al., 2009), which come in the support of the blow-out model.

Similar structures in Sudbury, Canada also interpreted as cosmic impact product, are showing more than one generation breccia (Grieve et al., 2008), suggesting a repetitive event, which is indeed possible by mantle volatile activity. This crater is situated north of the Huron Lake, and shows an elongated crater, with pre-impact magnetic dykes, in radial disposition.

The associated breccia of Vredefort crater, South Africa is showing post impact deformation (Grieve et al., 2008).

In conclusion, considering the various pre-impact, post-impact features, mantle upwarp below the crater, the presence of high sulphur volumes, and the very high correlation with major crustal fragment boundaries, we find that the impact crater mystery might be solved with further research on GSST microplate/ nanoplate boundaries.

Published in: Kovács, J.Sz., 2015 (in press), Elements of Global Strike-Slip Tectonics: a Quasi-Neotectonic Analysis, Journal of Global Strike-Slip Tectonics, v1., Szekler Academic Press, Sfintu Gheorghe.

Diverging Margins – Review of the Rift Concept

Standard
Fig27 Edwarded

Strike-slip fault deformation pattern in the Pleistocene sediments of Lake Edward. Line drawing after a seismic profile published in the Journal of Sedimentary Research, McGlue et al., 2006. Green dotted lines are showing the original fault interpretation, red lines are evidencing our interpretation.

The East African Rift

The Eastern African Rift System is given in many places as the best example for continental rifting; hence it is worth considering its structural elements from a kinematic point of view.

The Turkana Corridor is found in eastern Africa, at the intersection of two different fault sets, and forms a geomorphological corridor between the Ethiopian and Kenyan highlands. The axis of the Turkana Corridor corresponds to the Y-shear of the Cretaceous Panglobal Fracture System.

The Turkana Rift (Fig. 30) is a minor N-S trending rift, which is situated in the continuation of the Kenya and Main Ethiopian Rifts, inside the Turkana Corridor. It is actually a younger rift that is superposing an older NE-SW trending rift, the Anza Rift, which is a Neocomian transtensional basin, a lateral ramification of the Cretaceous Panglobal Fracture System, born as a major tension fracture. During Late Cretaceous, the Anza Basin has undergone a phase of major fault activity, when older basins were partly cannibalized (Bosworth and Morley, 1994). Towards the Chalbi Desert area, the oldest known deposits are Cenomanian lacustrine carbonates (Morley et al., 1999a). On the western side of Lake Turkana Oligocene half-grabens were also outlined (Vétel, 2004).

Tectonic inversion has affected several basins in eastern Africa; it is present in the Rukwa and Anza Basins, but the strongest inversion among all of them occurred in the Turkana Basin, twice, in the Paleogene and the Plio-Pleistocene (Morley et al., 1999b).

In the case of the North Malawi Basin (Fig. 32), Mortimer links basin-orientation to the underlying Pan-African foliation, however he notes that opinions are differing about the timing and the effect of strike-slip kinematics on the basin development of the Malawi Rift (Mortimer, 2007). Based on multifold seismic profiles Wheeler states that some aspects of the Livingstone Basin (North Malawi or Nyasa Rift) resemble pull-apart, extensional duplex, and extensional imbricate fan fault geometries, as expected in an incipient strike-slip basin (Wheeler and Rosendahl, 1994). Fault striations are evidencing both normal and strike-slip displacement (Delvaux et al., 1992).

McGlue has studied the depositional systems of Lake Edward because, unlike the other larger rift basins, it shows only one undisturbed depositional system from a seismic stratigraphic point of view. However, it seems that rifting preconceptions may have biased at least the structural interpretation of seismic profiles. It is more likely the basin was deformed by a strike-slip fault system instead of classic normal faults (McGlue, 2006).

In our interpretation, the East African Rift is originating in the internal simple shear stress field of the African Plate, which has been generated by the velocity contrast of the different plate segments during their eastward movement. The main (Y) shear direction is roughly parallel to the Equator, and the principal displacement was materialized in the Cretaceous Panglobal Fracture Zone.

Other important principal displacement zones of Africa, showing similar Y-shear directions, can be identified at the Congo – Tanganyika, Tanganyika– Malawi, Malawi – Okavango microplate boundaries.

Cyclicity of the observed extensional and inversion periods can be translated into periods of transtension and transpression involving large separation regional strike-slip faults.

Congo Basin

The Congo Basin is one of the largest intracratonic basins with an almost complete Neoproterozoic to Recent sedimentary sequence. It is underlain by a ~200km thick lithosphere showing current seismic activity and tectonic dislocations (Kadima et al., 2011). Various mechanisms such as a downward dynamic force linked to a high-density lithospheric object (Downey and Gurnis, 2009) or downwelling mantle plume (Hartley and Allen, 1994) are invoked to explain subsidence observed in the Congo Basin.

According to Fig. 33, the last major simple shear stress related structural event of the Busira Subbasin happened in the early Paleozoic involving the Neoproterozoic – earliest Paleozoic deposits, as suggested by the onlapping sedimentary sequence (above the green unconformity). Strike-slip faults are reaching to the surface, indicating that the Paleozoic fault system has experienced some minor reactivations recently.

In our view, the structural style of the Congo Basin is perfectly fitting into the GSST model, because it is mapping the current stress field and it is compatible with that observed in the East African Rift area, despite the more reduced degree of deformation. Hence, subsidence history of the Congo Microplate should be interpreted in the common, codependent history of the Central African kinematic chain.

In conclusion, in any of the reviewed African ‘rift basins’ strike-slip tectonics is unequivocally present, and the basin opening and later deformations are related to the movement of the equatorial kinematic chains. Due to the irregularity of microplates local stress fields are variable along microplate boundaries. Thus, rift zones in the context of GSST are assimilated with simple shear tension fractures, and consequently, the East African basin evolution is guided by the movement of microplates and by their inherent low hierarchy plate fragments. The takeaway for the GSST approach it is that we should avoid applying the rift term for transtensional basins and incipient tension fractures, unless oceanic sea floor spreading can be proved.

Published in: Kovács, J.Sz., 2015 (in press), Elements of Global Strike-Slip Tectonics: a Quasi-Neotectonic Analysis, Journal of Global Strike-Slip Tectonics, v1., Szekler Academic Press, Sfintu Gheorghe.

Orogenesis: a New Definition

Standard

In GSST (Global Strike-Slip Tectonic) approach, orogenesis defines the main space shortening process of transpressional shear zones, involving the coalescence of various, different scale and hierarchy crustal fragments, i.e. piko-, nano- and microplates. Initial push-up ranges or (proto-orogenes) evolve into orogens by the means of horizontal and vertical duplexing mechanisms.

Consumption of Oceanic Plates – Review of the Subduction Concept

Standard

Fig24MarianaSubduction first of all it means recycling, i.e. recycling of crustal fragments into the asthenosphere. When oceanic crustal fragments are rising above baselevel, we speak about obduction processes, whilst in case crustal fragments are indeed melted into the asthenosphere we may speak about subduction processes.

According to the GSST theory, kinematic plate fragments are in constant motion, showing certain relative plate velocity contrasts. Under constraints of the Coriolis force, hence, due to their accumulated momentum, microplates tend to rather develop transpressional orogenic build-ups on their longer edges than forming subduction zones during their constant eastward drift. As a consequence, oceanic plate fragments instead of being recycled are rather preserved, being obducted into orogenic complexes, where they are forming suture zones. In other words, the presence of ophiolites in orogenic complexes is the proof of obduction processes, and only indirectly can be inferred the presence of subduction zones from mass balance considerations. Hence, it is not surprising that the peri-Tethys area is full of obducted ophiolite units; starting with the Vardar, Transylvanides, Dinarides, dozens of Asian (e.g. Anatolian) obducted ophiolites in the geological record are all product of transpressional strike-slip tectonics.

Because of global kinematic constraints, subduction may happen only perpendicularly to the principal plate drifting vector or more frequently, as a function of the principal drifting vector of kinematic chains. This means, that real subduction may only form roughly in N-S direction. Basically there are only two such kind of convergent plate boundary lineaments on the Earth, where plate recycling could happen: 1) at the western Pacific plate margin, 2) and at the eastern Pacific plate margin.

In section 3, we have already reviewed the main geological, geophysical, geodetic observations made regarding the evolution of the Japan Island. All these data are proving the significance of shear deformation in northeast Japan, where the intensity of fault activities is very pronounced, earthquake epicenters indicating the presence of E-W directed fault planes. Clustering of earthquake epicenters in stress nodes is generally present all along the Western Pacific subduction zones, from the Sumatra Arc to the Philippine subduction zone. Pacific plate velocity measurements might change with time as new GPS stations will be installed in the oceanic domain, and if the motion of smaller crustal units is also going to be integrated. The origin of the Mariana Trench and the Bonin Ridge is linked to the same strike-slip displacement, which was made along the irregular Hawaii North Mp/ Bonin Nanoplate boundary, in S to N direction. This irregular plate boundary in turn is the result of another plate velocity contrast, which is characterizing the Bonin Np–Hawaii North Mp and the North Philippine–Hawaii South Mp kinematic chains.

Therefore, structural features of the Japan Island and the whole southeastern Asia island-belt, suggest that instead of real subduction we are facing various transpressional space management processes, best described with the term of plate-overriding, i.e a mix of obduction, lateral escape, plate buckling mechanisms.

From a kinematic perspective, real subduction, where recycling of crustal fragments occurs it could only happen in the western margin of the American continents. Here, all the kinematic prerequisites of subduction are present: 1) the motor of subduction is present, and it can be identified in the Coriolis force, which is transferred and exploited by the momentum of plates, 2) there is an obvious density, hence a momentum contrast, between the oceanic and continental crustal fragments.

Momentum contrasts between plate fragments can play a significant role in the initiation of both oceanic spreading and subduction processes, in case the Earth suffers angular acceleration. Whether the angular acceleration of planets is a common planetary phenomenon or not, it is out of our knowledge, but certainly accidental larger meteoric impacts may affect the spinning velocity of the Earth.

Published in: Kovács, J.Sz., 2015 (in press), Elements of Global Strike-Slip Tectonics: a Quasi-Neotectonic Analysis, Journal of Global Strike-Slip Tectonics, v1., Szekler Academic Press, Sfintu Gheorghe.

The ‘Walled Basin’ Model of the Transylvanian Basin: Geodynamic Implications

Standard

Fogaras

In Central Asia several ‘walled basins’  (Carroll et al., 2010) exist which are recording thick lacustrine to alluvial deposits through geological times, and are actually showcasing the various types of strike-slip basins, in nature. Sedimentation is starting in some basins, like in the Junggar Basin, already in the Late Permian (Hendrix et al., 1992), in others during the Mesozoic (Fig. 28, 29). In western China strike-slip basins are contractional in origin, while in eastern China basins are younger pull-apart basins; the interior of these basins practically had stayed undeformed, only basin margins evolved into high to very high orogenic build-ups (Carroll et al., 2010). According to Carroll, many terms have been used to describe these basins ‘broken foreland’, ‘cornered foreland’,  ‘Chinese-type basin’, ‘collisional successor basin’.

If we recall, such walled basins can be seen in the Mediterranean area, as well, like in the case of the South Adriatic basin.

The Neogene Transylvanian Basin it is also a good candidate, in terms of basin mechanism, quality of sedimentary infill. It shows  very similar ‘walled basin’ margin character in all directions, a lacustrine-alluvial sedimentary infill, and it was called for a long time as a back-arc basin, assuming the Roydenian tectonic model. Herein, we propose to adopt the ‘walled basin’ model for the Neogene Transylvanian basin because many of the characteristics traditionally considered as mysterious  are getting a robust explanation, like 1) basin geometry, 2) sediment infill, 3) subsidence rates, 4) thickening of the lithosphere, 5) low heat flux, 6) uplift mechanism of the Southern Carpathians, 7) Peri-Carpathian basin geometry and many others that are going to be presented  in a separate paper.

We need to note, that the geodynamic evolution of the Southern Carpathians was generally neglected from the geodynamic models, because did not really fit into the back-arc model of the Pannonian-basin.  Secondly, it is obvious that the highest mountains of the Earth should share something in common regarding their origin, and geodynamic history. The Tian Shan Mts. are showing peaks of 7000m, the Caucasus has peaks above 5000m, the Atlas is rising above 4000m, the Alps have peaks of 3000m, and finally the highest peaks of Romania are found in the Southern Carpathians (above 2500m). All these very  high and relatively narrow mountain ranges are bounded by steep transpressional fault systems, just as in the case of the Southern Carpathian Mts.

Published in: Kovács, J.Sz., 2015 (in press), Elements of Global Strike-Slip Tectonics: a Quasi-Neotectonic Analysis, Journal of Global Strike-Slip Tectonics, v1., Szekler Academic Press, Sfintu Gheorghe.

Consistency Check I: The Mediterranean Area and the Vøring Basin

Standard
Fig15Herodotus

Strike-slip fault system of the South Mediterranean area (Matruh and Herodotus Basin), extracted from composite seismic profile published by Tari et al., 2012. Two different fault systems can be identified; the primary one is the regional strike-slip system. The secondary deformation events, materialized as listric faults and thrustings, are also triggered by strike-slip tectonics: 1) gravitational sliding in the transtensional stress field sector, 2) and contractional vertical and lateral duplexing in the transpressional stress field sector.

The thinning of the Mediterranean crust below the Sirte Basin and the Ionian Sea  has been evidenced recently by gravity inversion (Cowie and Kusznir, 2012). Cowie and Kusznir have also noted that the nature of the crust could be either oceanic or thinned continental. On their second profile, which transects the Herodotus Basin the transform nature of the basin margin i.e the sudden increase of crustal thickness is more prominent, as a consequence most probably the masterfault of basin opening was localized on the southern basin margin of the Mediterranean Sea.

In our interpretation, gravity profile from Fig.20 is showing additional arguments for the transtensional origin of the Mediterranean crust. Here, contrary to the southern margin, crustal thinning was enabled by overstepping strike-slip faults. The crustal thinning mechanism cannot be understood solely from the published profiles, but certainly must be sought in those of transtensional strike-slip basins.

Southern transform margin of the Mediterranean Basin (Matruh-Herodotus Basin)

An ENE-ESE opening of the East Mediterranean area related to a transform margin was documented by several authors (Longacre et al., 2007; Walley, 1998, 2001) in (Tari et al., 2012), and indeed strike-slip tectonics suggested by gravity profiles (Cowie and Kusznir, 2012) is supported by seismic profiles as well. Reinterpreting a composite profile across the Matruh-Herodotus Basin margin, we have concluded that  it is likely, that an important amount of the structural traps identified in the Matruh Basin were generated by the local Neogene transpressional stress regime. Actually, down-dip contractional horses interpreted by (Tari et al., 2012) might originate partly in strike-slip deformation than solely in gravitational sliding on a Cretaceous shale detachment, as indicated by the presence of numerous antithetic faults. The NNE-SSW Matruh Canyon itself, described by Tari as an aborted syn-rift basin, it is overlaying a Jurassic(?)-Cretaceous transtensional shear zone, most probably initiated as a plate-scale tension fracture, which is depicting the whole coeval North African stress regimes. Interestingly, the main strike of the basin is parallel with those of the NOSA zone in Tunis, which also belongs to the Sirte Microplate in our plate tectonic subdivision.

Eratosthenes Seamount

The Eratosthenes Sea Mount of the Levantine basin was reimaged recently with modern processing techniques (Peace et al., 2012). Around the Eratosthenes seamount, two sets of strike-slip faults can be differentiated highlighting the transpressional origin of the seamount. This crustal fragment initially it constituted a footwall segment of the Levantine Basin, related to a major transtensional fault, which later got inverted  with the evolution of the local stress-regime along the main displacement zone. Stratigraphy given in Fig. 22 is very uncertain; layering is rather reflecting seismic packages than established stratigraphic units.

Northern margin of the Mediterranean Basin

The Corinth Trough (Fig. 26) can be described as a 1-2 Ma old, ~100X30km high-strain band, which shows 5-15mm/year N-S extension (Bell et al., 2009), and segmented, overstepping boundary faults in plain view. Bell is referring to three prevailing theories which are used to explain basin extension: 1) back-arc extension related to the Hellenic Trench, 2) westward propagation of the North Anatolian fault (Dewey and Şengör, 1979), 3) gravitational collapse of the Hellenide orogeny lithosphere (Jolivet, 2001).

In the frame of GSST, the Corinth Trough is interpreted as an internal shear zone of the South Anatolian Nanoplate, which has developed internally an overstepping fault network in the principal displacement zone (PDZ), instead of a continuous masterfault. Given the significant space created in the releasing bend of the PDZ, gravitational collapse proposed by Jolivet (2001) is regarded as a complimentary effect of the regional strike-slip tectonic deformation.

The Vøring Basin, offshore Norway

Within the Vøring Basin, several compressional (Cenomanian-Turonian, Maastrichtian-Paleocene, Middle Miocene) and extensional collapse phases (Paleozoic, Late Jurassic, Early Cretaceous hyperextension, Late Paleocene, Early Eocene) have been documented (Lundin et al., 2013). Overviewing Lundin’s data, we have noted that the ‘early’ (Permian–Jurassic) tension fractures in many places have evolved into overstepping strike-slip faults and several isolated subbasins formed. It should be also noted, that main (SSW-NNE trending) sedimentary trenches, are cut by  further W-E striking strike-slip systems in the continuation of mid-oceanic transforms, giving birth to complex structural patterns. During  periods of inversion, i.e. when structural blocks have arrived into restraining phase, some fault blocks evolved into push-up ranges, like the Vema Dome (Fig. 24), which has been formed in the Middle Miocene.

Published in: Kovács, J.Sz., 2015 (in press), Elements of Global Strike-Slip Tectonics: a Quasi-Neotectonic Analysis, Journal of Global Strike-Slip Tectonics, v1., Szekler Academic Press, Sfintu Gheorghe.

Definition of Micro-, Nano-, Pikoplates and Kinematic Chains

Standard
kchain

Marquesas Mp-Ganges Mp kinematic chain is found south of the Cretaceous Panglobal Fracture Zone, and incorporates microplates of the Pacific Ocean, South America, Atlantic Ocean, Africa, India and the Indian Ocean

Being involved into various shear zones during continental drift, world tectonic plates area broken into smaller and smaller tectonic units with time. Contact zones of microplate are marked by pushup ranges and evolved orogenes, deep sedimentary basins, and transform fault scars on the oceanic floor. Most probably, a great percentage of fault-scars preserved on the surface of the Earth are somewhat older than Holocene, and ocean-floor fault scars are even older. The ‘quasi-neotectonic’ term points to this timing uncertainty.

Size of these crustal fragments is varying within a wide range, thus a plate hierarchy can be established according to their size ranges. In GSST we propose the simultaneous usage of conventional ‘plate‘ name to refer to the classic large plate tectonics units. For mid-size plate fragments we also keep the ‘microplate‘ term. In order to study the movement of the even smaller, but well individualized crustal fragments, we propose the use of the ‘nanoplate‘ term, without any direct reference to the absolute plate size range. Nanoplates usually appear in areas of long lasting contractional stress, and are made up of incipient or well developed plate duplex horses.

‘Pikoplates’ are the internal components of nanoplates, smaller with about one order of magnitude. These are the most important elements of structural hydrocarbon plays and are driving the regional distribution of hydrocarbon and ore accumulations. What we know as hydrocarbon trends, for example, are related usually to the presence of pikoplates.

Example: The Marquesas Mp-Ganges Mp kinematic chain is found south of the Cretaceous Panglobal Fracture Zone, and incorporates microplates of the Pacific Ocean, South America, Atlantic Ocean, Africa, India and the Indian Ocean.

Published in: Kovács, J.Sz., 2015 (in press), Elements of Global Strike-Slip Tectonics: a Quasi-Neotectonic Analysis, Journal of Global Strike-Slip Tectonics, v1., Szekler Academic Press, Sfintu Gheorghe.

Kinematic markers III: Extension Nodes

Standard
Columnar basalts at Racoșul de Jos/ Alsórákos are yielding a 1200 ka to 600 ks old (Harangi et al., 2013)  effusive product in one of the  Perșani Mountain tension nodes, tracing the location of cross-cutting strike-slip  faults

Columnar basalts at Racoșul de Jos/ Alsórákos are yielding a 1200 ka to 600 ka old (Harangi et al., 2013) effusive product in one of the Perșani Mountain tension nodes, tracing the location of cross-cutting strike-slip faults

In the GSST approach, rising of magmas is related to the opening of crustal scale tension fractures. Because pure shear related stress field and deformation is unlikely to exist in nature, even within compressional belts there will exist some transtensional fracture components, which are characterized by significantly lower stress values. These tension fractures always form perpendicularly to the σ3 direction, and will serve as pathways for rising of magmas.

Cross-cutting fault systems are quite common in nature. While in regional compressional fault intersections stress nodes may form, in tensional fault intersections, extension nodes may appear. Here, in these extension nodes magmas have the highest chance to rich to the surface. As a consequence, volcanic craters are the best markers of regional extension nodes. In addition to volcanic craters, other parts of the volcanic build-ups may also serve as passive kinematic indicators, because of the pronounced hardness and brittleness of lavas and volcano sedimentary successions, in comparison to the surrounding environment.

Example: Columnar basalts at Racoșul de Jos/ Alsórákos are yielding a Pleistocene, 1200 ka to 600 ks old (Harangi et al., 2013) effusive product in one of the Perșani Mountain tension nodes, tracing the location of cross-cutting strike-slip faults.

Published in: Kovács, J.Sz., 2015 (in press), Elements of Global Strike-Slip Tectonics: a Quasi-Neotectonic Analysis, Journal of Global Strike-Slip Tectonics, v1., Szekler Academic Press, Sfintu Gheorghe.

Kinematic markers II: Stress Nodes

Standard

Fig2Stress Node Map

There are at least 20 locations in Europe where the EMSC earthquake database is recording a spatial concentration of earthquake epicenters, like in the Vrancea Stress Node in Romania. We term these high activity seismogenic locations as ‘stress nodes’, because earthquake epicenters are sites of stress accumulation and release. High velocity bodies below a strike-slip zone are not uncommon (Hadley and Kanamori, 1977, in Kearey and Vine, 1996). Hadley has documented a high velocity body below the Transverse Ranges which was seismically active even at 100km.

A similar phenomenon happens in the Vrancea area, which serves as a meeting point for three different nanoplates, hence cross-cutting strike-slip faults. In this area, seismic gaps should be interpreted as oversteps of faults, as suggested in the case of the Calaveras fault (Reasenberg and Ellsworth, 1982). The occurrence of stress nodes in corner positions of microplates and nanoplates could be already predicted by GSST logics as well, without consulting the earthquake database, because significant structural deformation is also more likely to be present in corner locations.

Just nearby the Haute Provence Stress Node, in Southeastern France, 6 distinct deformation domains were isolated from the inversion of 89 focal mechanism (Baroux et al., 2001), which fits completely into the expected structural configuration, outlined by GSST techniques. This great variety of the recorded deformation domains is depicting the whole strike-slip stress field, including conjugate fault activity.

In the current study we have isolated the following Stress Nodes: 1) Vrancea Stress Node, Eastern Carpathians, Romania, 2) South Silesian Stress Node, Poland, 3) Lower Silesian Stress Node, Poland, 4) Po Valley Stress Node, Italy, 5) Cuneo Stress Node, Alpi-Marittime, Italy, 6) Haute Provence Stress Node, Alpes-de-Haute-Provence, France, 7) Pyrenees Stress Node, Spain, 8) Umbria Stress Node, Apennines, Italy, 9) Lipari Stress Node, Tyrrhenian Sea, Italy, 10) Monte Negro Stress Node, 11) Albanian Stress Node, 12) Gulf of Corinth Stress Node, Greece, 13) Keffalonia Stress Node, Greece, 14) Zakinthos Stress Node, Greece, 15) Crete Cluster of Stress Nodes, Greece, 16) Soma Stress Node, Turkey, 17) Şenköy Stress Node, Turkey, 18) Çameli Stress Node, Turkey, 19) Sapientza Stress Node, Greece, 20) Pamukkale Stress Node, Turkey, 21) Elazig Stress Node, Turkey, 22) Tabriz Stress Node, 23) Van Lake Stress Node, Turkey, 24) Qushm Stress Node, Iran, 25) Karakul Stress Node, Pamir Mts. China-Tajikistan, 26) Badakhshan Stress Node, Pamir Mts., Tajikistan, 27) Islamabad Stress Node, Himalaya Mts., Pakistan.

A systematic description of stress nodes listed above does not represent the objective of the present study.

Published in: Kovács, J.Sz., 2015 (in press), Elements of Global Strike-Slip Tectonics: a Quasi-Neotectonic Analysis, Journal of Global Strike-Slip Tectonics, v1., Szekler Academic Press, Sfintu Gheorghe.