Kinematic markers III: Extension Nodes

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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

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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.