SZÉKELYFÖLD FELTÁRÁSRA VÁRÓ SZÉNHIDROGÉN KÉSZLETEI: FESZÜLTSÉGTEREK JÁTÉKA / YET TO FIND HYDROCARBON RESOURCES OF SZEKLERLAND: A GAME OF STRESS-FIELDS

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Székelyföldi  Geológus Találkozó, Sepsiszentgyörgy, 2018. október 26-28.

A szénhidrogénkutatást nemcsak Székelyföldön, hanem a világ számos pontjában a földtani, geofizikai, mélyfúrástechnikai ismeretek birtoklása mellett számos egyéb természetű tényező is meghatározza, esetenként gátolja vagy éppen segíti. Az akut háborús politikai környezetekben jellemzőn alacsony vagy részben alacsony a területek kőolajföldtani megkutatottsága (pl. Burma, Afganisztán, Irak-Irán egyes időszakokban), az instabil demokráciákban és diktatúrákban pedig a befektetések elmaradása, a gátolt technológiai tudásáramlás fogja vissza a kőolajkutatást – sokszor a szabadverseny hiányának köszönhetően – jóesetben időszakosan.

A környezettudatosság elveinek megjelenésével újabb megkerülhetetlen tényezővel kell számolnunk, mert nemcsak civil csoportosulások tudnak élni vele, néha és néhol teljesen jogosan, néha tudatlanul, de különböző lobbycsoportok is könnyűszerrel visszaélhetnek, alaptalanul. Ugyanakkor számos makroökonómiai sikertörténet is született már, és még mindig születik, kőolajipari motorral: Tunézia kőolajiparára támaszkodva lett turistaparadicsom, Kazahsztán építészetileg világkuriózum számba illő új fővárost teremthetett, és Vietnam is így emelkedik.

A fentiek fényében egész biztosan elmondható, hogy akárcsak a világ többi részén, Székelyföldön is mindezen tényezőknek feszültségterei vannak, számolnunk kell velük, a földtaniakon túl és fontossági sorrendben a földtaniakat megelőzően.

A kommunista központosított Román állam számára a politikai tényezők nem jelentettek problémát, így teljes gőzzel haladhatott a kőolajipar, sőt még a baráti államoknak is jutott a felhajtóerőből – a gondok más téren jelentkeztek. Ebben az időszakban az Erdélyi-medence és a Kárpátok előtere tálcán kínálta a könnyű falatokat, nagy volumenben. A mezőgazdasági földek, legelők és kaszálók sem a geofizikai szeizmikus mérések számára, sem a mélyfúrások logisztikája számára nem jelentettek jelentős technikai kihívást. Nem csoda tehát, hogy éppen Marosszék és Udvarhelyszék területei vannak a legalaposabban kőolajföldtani szempontból átkutatva, míg az erdőborította Háromszék és Csíkszék kevésbé. A keleti mezsgyéken csupán a gelencei kőolajmező felfedezése nevezhető sikertörténetnek. A nehéz falatok még hátra vannak.

Mert Gelence földtani mezőnye (play) nem ér véget a mező határainál, trendje felszínileg is térképezhető. Ráadásul mai tudásunk szerint rétegtani és szerkezet földtani szempontból is több mezőnnyel számolhatunk.

Jelen munkámban Székelyföld kőolajföldtani mezőnyeit kívánom számba venni, hogy a kőolajföldtani kutatásoknak Székelyföldön újabb lendületet adhassunk, ezek közül nevezetesen ‘a még fel nem tárt’ és ’a tüzetesen meg nem kutatott’ mezőnyökkel kívánok foglalkozni, a melyeket az angolszász irodalom a ’yet to find’ szókapcsolattal illet.

Székelyföld kinetikus modelljét (fenti ábra) a 2015-ben publikált globális kéregeltolódási tektonika (GSST) [1] alapelveire támaszkodva építettem fel. Ez a modell – tulajdonképpen mellőzve a Kelet-kárpáti szubdukció történetét – két egymásra kvázi merőleges eltolódásos rendszert feltételez, amelyek szimultán vagy éppen felváltott működése eredményeképpen jön létre az a szerkezetföldtani felszültségtér, amely a csapdák kialakulásának, valamint a szénhidrogének felhalmozódásnak kedvez, de nemcsak, mert ugyanebbe a feszültségtérbe illeszthető a Persányi vulkanizmustól kezdve az Olt-völgyi vulkanitok mindegyike, és tulajdonképpen az egész KGH vulkáni vonulat. Ebben a repedés és vetőhálóban jelöltem ki azokat a helyeket, amelyek földtani szempontból megkutatásra leginkább érdemesek, számszerint 45 kvázi-determinisztikus (a területek nagysága szempontjából némiképp sztochasztikus, randomszerű, de földtani térképek által irányított, ezért determinisztikus) mezőt.

Egy előzetes készletbecslést is mellékelek a térképhez. A székelyföldi termelő mezőket valamint a nemkonvencionális mezőnyöket leszámítva, 5 playtípusban 465 millió hordónyi átlagban 38.39 API nehézségű kőolajat és 354.9 bcf szabad földgázt helyezhetünk el (rizikófaktorral nem súlyzott OOIP, OGIP értékek), ebből 244 millió hordót az alátolódott Vráncsa-takaró paleogénjében, 220 millió hordót az alátolódott Tarkő-takaró paleogénjében, 175bcf alsókréta földgázt a Teleajen-takaróban, 75 bcf földgázt a KGH vulkanoszedimentek alatti miocénben és 43 bcf földgázt a Középső Dacidák urgoni valamin Stramberg típusú mészkőtárolóiban. A playtípusok közül kettő, az erdélyi medence bádeni anyakőzetéhez valamint a Vráncsa-takaró oligocénjéhez köthető bizonyított, a Tarkő-takaró oligocénjéhez köthető valószínű kategóriájú. Két playtípus lehetséges besorolású, mind a tárolók és mind az anyakőzetek lehetségesek és elméletileg megalapozottak. A medenceperemi mezozoós karbonátok az erdélyi-medence miocén forrásaiból töltődhetnek, míg a Teleajen-takaró albai homokkövei kréta óceáni anoxikus eseményekhez (OAE1, OAE2) köthető forrásokból, mindkettő jelen van a Keleti Kárpátok takarórendszerében.

[1] Elements of Global Strike-Slip Tectonics: a quasi-neotectonic analysis (Journal of Global Strike-Slip Tectonics, 1 k., 1. szám, Székely Akadémiai Kiadó, Sepsiszentgyörgy) Letölthető online: szekler-resources.ro

 

Bioszedimentáris események az Erdélyi-medence felsőeocén-alsóoligocén üledékeiben (Kolozsvár-Bánffyhunyad térség). Rétegtani szekvenciák paleoökológiai tanulmánya

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#háromszékikutatók #doktoridisszertáció
A doktori dolgozatom 10 oldalas magyar nyelvű kivonata itt érhető el: https://szeklerresources.files.wordpress.com/2018/06/hkdt_kovacs.pdf
 
#2007-ben a Háromszéki kutatók doktori disszertációi I. kötetben jelent meg a Háromszéki Magyarok Világtalálkozója alkalmából. A határidős szorítások, meg a nyomdák közti ping-pong miatt végül pre-press korrektúra nélkül jelent meg, még a tartalomjegyzékből is kézen-közül kivágódtam, ez már csak a sors iróniája :).
 
 

The Final Brick has Arrived

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The final brick of our knowledge-base has arrived 🙂.

Szekler Resources aims to provide Geo-Logics backed geoscience services during the whole Exploration – Field Appraisal – Stochastic Reservoir Modeling – Reservoir Simulation field life-cycle of oil and gas accumulations.

While traditional companies are losing momentum and information due to the large number of the contributing specialists, Szekler Resources is prepared for the quick revision of oil and gas assets, in order to pinpoint and solve the weak links of projects and entire portfolios.

Szekler Resources Ltd is working virtually on all geoscience platforms (including petrophysics), from vintage poor quality datasets to present industry standard 3D data, depending on the licenses and datasources available to the Client.

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Thin-section Collection to Back-up Your Business

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IMG_7307Szekler Resources Ltd is continuously developing its thin-section database, comprising various, mainly limestone, facies of the Triassic-Miocene Tethys realm, but also including sandstone, conglomerate, Fe-Mn hardground environments from 10 countries of Eurasia. Thin-sections of a wide range of magmatic and metamorphic rocks and ore samples can be delivered on request.

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.

GSST: Impacts on Hydrocarbon and Ore Exploration

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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

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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

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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.

Consumption of Oceanic Plates – Review of the Subduction Concept

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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.