Concluding Remarks on the Theory of Global Strike-Slip Tectonics

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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.

Orogenesis: a New Definition

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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.

Consistency Check I: The Mediterranean Area and the Vøring Basin

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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.