Microstructural modal and geochemical changes as a result

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172 Roman Farka ovsk et al, of the original rocks Rutter 1999 Mylonite zones transfer during deformation can cause marked vol. at the surface represent fossil ductile high strain ume changes in the shear zones Shear deformation. shear zones that were exhumed during subsequent accompanied by volume loss is characteristic of. geological evolution Guermani Pennacchioni compressional tectonic regimes while volume gain. 1998 mylonitic zones are more typical of extensional tec. In general mylonites have strong foliation and tonic regime Hippertt 1998 where fluid enhanced. lineation that is already visible at macroscopic silicification is common Roberts Nissen 2006. scale Textures of polycrystalline rocks e g gran In the present contribution microstructural. itoids change by effect of shear deformation from modal and geochemical data obtained from the. protomylonites to ultramylonites with a progres Rolovsk shear zone in the ierna hora Mts are pre. sive reduction of grainsize Sibson 1977 Simpson sented This zone was active during several defor. 1985 Grainsize reduction during mylonitisation mational stages involving both compressional and. of granitoid rocks can be accomplished at first extensional regimes The final movements in the ex. through whole rock cataclasis and subsequent tensional regime were the result of stress relaxation. ly through ductile flow Goodwin Wenk 1995 after contraction in the area The aim of our study. A variety of microstructures can develop in natu was to present a synthesis of microstructural modal. rally deformed rocks Passchier Trouw 1996 and and geochemical changes observed in the gradually. are indicative of the metamorphic grade at which strained rocks from the undeformed and unaltered. deformation took place Pryer 1993 Weak rheol protolith to the strongly deformed ultramylonite. ogy is supported also by formation of fine grained Attention was paid also to transfer of chemical com. polyphase mineral aggregates often with preferred ponents in the shear zone and to possible volume. orientation and by mutual connection of dispersed changes during deformation. weak mineral phases Stunitz Tullis 2001 Oliot,et al 2010 Goncalves et al 2012 A softening ef. fect can be promoted by fluid assisted reactions and 2 Geological setting and evolution of. by mineral transformations due to syn kinematic the area. metamorphism Wintsch et al 1995 Tullis et al,1996 Wibberley 1999 Sassier et al 2006 Softening. reactions during mylonitisation of granitoid rocks The ierna hora Mts are located in the eastern. can be mica production at the expense of feldspar part of the Western Carpathians northwest of the. Hippertt 1998 Gueydan et al 2003 town of Ko ice Fig 1 and are part of Slovensk. Fluid activity is very important in many geologi rudohorie Mts In terms of geology the ierna hora. cal processes related to metamorphism and metaso Mts belong to the Veporicum tectonic unit of the. matism e g van der Straaten et al 2012 Halama et Western Carpathians The Veporic unit compris. al 2014 Deformation at low grade metamorphic es the Slovensk rudohorie Mts and the Kr ovo. conditions enables H2O rich fluid migration in the ho sk Tatry Mts crystalline basement in the west. shear zones through wetted crystal fluid micro as well as the ierna hora Mts in the east Strong. structures e g microfractures and grain bounda Alpine remobilisation is typical of the Veporic tec. ries Lee et al 1991 Goddard Evans 1995 In tonic domain The dynamo metamorphosed mylo. contrast deformation under medium to high meta nitised granitoid rocks were studied in detail main. morphic grades has a relatively dry character Bell ly in the western part of the Veporicum by Miko et. Cuff 1989 Fluid activity plays an important role al 1982 Puti et al 1997 and Koh t et al 2000. during deformation in the shear zones Fluids may Those authors observed that mylonitic deformation. enable dissolution of some minerals quartz feld of the granitoid rocks had a penetrative character. spar carbonates and transfer of chemical compo with development of wide shear zones similarly as. nents SiO2 alkalies in the shear zone Selverstone in the ierna hora Mts. et al 1991 Hippertt 1994 1998 Goddard Evans The ierna hora Mts consist of a crystalline com. 1995 Pressure of fluids enhances propagation of plex Upper Palaeozoic to Mesozoic cover forma. brittle fractures During ductile deformation fluids tions and isolated klippes of the Cho nappe Hron. enhance crystal plasticity and dynamic recrystalli icum Unit The Veporicum of the ierna hora Mts. sation Tullis Yund 1989 Low grade metamor is separated from the Gemeric unit in the southwest. phism in the presence of fluids can catalyse soften by Margecany shear zone In the north it is trans. ing reactions with the production of phyllosilicates gressively covered by sediments of the central Car. e g white mica and chlorite Wintsch et al 1995 pathian Paleogene Basin in the south and east by. Wibberley 1999 Arancibia Morata 2005 Mass sediments of the eastern Slovakian Neogene Basin. Microstructural modal and geochemical changes as a result of granodiorite mylonitisation 173. Fig 1 A Simplified geological map of the ierna hora Mts and adjacent area with the position of the section studied. B scheme of the same C tectonogram of predominant mylonite foliation planes and stretching lineations on. these Microscopic sense of shear markers indicate movement of the hanging wall of the shear zone towards the. 174 Roman Farka ovsk et al, The pre Carboniferous crystalline basement of the amorphosed in the shear zone in the contact area. ierna hora Mts consists of three local lithostructur of the crystalline complexes with cover formations. al complexes the Lodina Complex the Miklu ovce Voz rov Jacko in Pol k et al 1997 The cov. Complex and the Bujanov Complex Jacko 1985 er formations comprise Permian clastic volcanic. The Western Carpathian crystalline basement was and volcaniclastic rocks and Triassic and Jurassic. divided into the three basic Hercynian lithotectonic carbonate and clastic sediments Upper Palaeozoic. units compare Bez k 1994 According to analog rocks of the Hronic unit are preserved in the form. ical lithology and T P parameters of the Hercynian of isolated Cho nappe klippes on the cover forma. metamorphism the Lodina Complex is correlated tions of the ierna hora Mts. with the Middle lithotectonic unit MLU while the The geological setting of the ierna hora Mts is. Miklu ovce and Bujanov complexes correspond a product of several Hercynian but mainly Alpine. with the Upper lithotectonic unit ULU of the Ta tectonometamorphic stages Jacko 2007 During. troveporic Hercynian structure Jacko et al 1995 the Hercynian orogeny the ULU Miklu ovce and. The Lodina Complex Fig 1A is formed mainly Bujanov complexes was thrust onto the MLU. by intensively diaphtorised gneisses mica schists Lodina complex southvergently which was accom. and local intrafolial amphibolite bodies which are panied by syntectonic metamorphism in amphibo. the products of Hercynian metamorphism Jacko lite facies T P conditions Korikovskij et al 1990. 1985 T P conditions of the Hercynian metamor Jacko et al 2001 Jacko 2007 Next the intrafolial. phism reached temperatures of 520 540 C and granitoid bodies were emplaced into the ULU An. a pressure of up to 300 MPa Korikovskij et al age of 357 3 Ma was obtained from the ierna hora. 1990 The complex tectonic processes caused mul Mts biotite tonalite Broska et al 2013 The biotite. tiple repetition of rock types in the Lodina complex granodiorites of the section studied are a product of. profile as well as wide rock mylonitisation this stage Intrusions of granitoid bodies led to ex. The Miklu ovce Complex Fig 1A comprises tensive periplutonic changes of rocks of the ULU. migmatites gneisses and amphibolites developed also under metamorphic conditions of the amphib. during the same phase of the Hercynian synkine olite facies Korikovskij et al 1990 Consequently. matic metamorphism The complex was penetrated the ULU was rethrust further to the south Jacko et. later by intrafolial bodies of aplite granites Jacko al 2001 Jacko 2007 The mesoscopic structures. 1985 The Hercynian metamorphism reached T P of the stages mentioned are E W oriented folds as. conditions of amphibolite facies with tempera well as their axial plane cleavage sets representing. tures of 570 610 C and pressures of 530 600 MPa the pre Alpine subhorizontal schistosity. Korikovskij in Krist et al 1992 The rocks of the During Alpine orogeny tectonic evolution was. Miklu ovce complex were thrust onto the Lodina influenced by compression at first with typical. Complex during Hercynian orogeny The tectonic a north east vergent area reduction The superfi. contact of both complexes was repeatedly reacti cial Cho nappe was thrust onto the Veporic unit. vated by Alpine shear zones Jacko in Pol k et al Jacko 1988 and the rock complexes of the Gemer. 1997 icum were emplaced onto the slope of the Veporic. The Bujanov Complex Fig 1A is formed unit Jacko 2007 The rocks of the Veporicum with. mainly by intrusions of late orogenic Hercynian adjacent parts of the Gemeric unit and the Cho. granitoids which penetrate older metamorphic nappe were folded penetratively into mesoscopic. structures Jacko 1975 1985 Metamorphic rocks to regional NW SE folds Jacko 1975 Subsequent. especially biotite gneisses ophthalmic migmatites ly the imbrication structure was formed and the. and amphibolites participate in the complex com NW SE shear zones and Alpine cleavage came into. position to a lesser extent They are products of being dipping usually to the southwest Jacko et. Hercynian periplutonic metamorphism The tem al 1996 2001 Jacko 2007 The limit of the Alpine. peratures varied between 620 625 C pressures be mineral parageneses is 135 7 Ma Ar Ar muscovite. tween 400 450 MPa Jacko et al 1990 The rocks of age from granite mylonite of the Bujanov Complex. the Bujanov Complex are strongly tectonically de Maluski et al 1993 The older structures litholog. formed having developed a wide variety of brittle ical boundaries and tectonic zones were reactivated. to brittle ductile tectonites of granitoid rocks Jacko Jacko 1975 Jacko et al 1996 The development of. 1975 1985 Jacko et al 1996 Jacko in Pol k et al mylonitic shear zones in granitic rocks where shear. 1997 was localised along pre existing zones of weak. The Upper Carboniferous detritic metasedi ness aplite dykes joints veins cataclasite zones. ments rest on the crystalline complexes A signifi was described by Christiansen Pollard 1997. cant part of these rocks is strongly dynamically met Guermani Pennacchioni 1998 and others. Microstructural modal and geochemical changes as a result of granodiorite mylonitisation 175. The next movements in the shear zones were different types of granitoid brittle ductile tectonites. linked to the uplift of the Veporic basement and from protomylonites to ultramylonites. subsequent south vergent extensional unroofing,N meth et al 2000 N meth 2001 Shear zones.
were opened and hydrothermally silicified Jacko 3 Methodology. Bal 1993 Jacko 2007 Post collisional unroofing, in the western part of the contact zone of the Gemer The whole outcrop of the shear zone profile was. icum with the Veporic unit was dated as mid Cre first studied macroscopically in detail The aim of. taceous Pla ienka 1999 Finally the NW SE shear that macroscopic study was to identify structurally. zones were reactivated in brittle ductile to brittle different rocks with regard to their deformational. regime with the kinematics of subhorizontal strike reworking Then places for oriented sample taking. slips Jacko et al 1996 Farka ovsk 2005 2006 were selected Fig 1 The samples represented un. Jacko 2007 During this stage the mylonites were deformed or only slightly deformed rocks as well as. penetrated by the subhorizontal stretching linea the different types of brittle ductile tectonites my. tion of a NW SE direction Fig 1C The stretching lonites. lineation is a linking structural element of all my The mylonites in the section are rocks with. lonites in the area that retains constant orientation strong foliation and well marked traces of stretch. irrespective of orientation or dip of the planar ele ing lineation on the surface of the foliation planes. ments on which it occurs Farka ovsk 2013 For the purpose of microscopic study 25 oriented. The regional shear zones in the Veporicum thin sections were prepared in the planes parallel to. of the ierna hora Mts are the Roh ka S ubica the stretching lineation and normal to the mylonitic. Rolovsk Bujnisko and Margecany shear zones foliation in order to characterise microfabric defor. Fig 1A Shear zones tectonically detach crystalline mational reworking as well as mineralogical and. complexes of the ierna hora Mts and now they are modal composition of the tectonites Microscopic. the dominant tectonic structures in the region Fig observations were made using petrographic polar. 1A These mylonite zones have variable thickness ising microscope Olympus BX53. es of several metres to hundreds of metres In most The mylonites were classified according to met. cases borders of mylonite zones as well as transi amorphic grade of deformation and to their origi. tions of different types of tectonites to undeformed nal lithotype Further the mylonites were classified. wall rocks are not clear The mineral associations of following the porphyroclasts matrix ratio Sibson. the mylonites indicate very low to low grade meta 1977 Mylonites with a matrix content of 10 50 per. ally situated in planar shear zones that accommo date movement of relatively rigid wall rock blocks Slip along discrete fault zones and brittle deforma tion at lower metamorphic conditions is typical in the upper crust In the middle and lower crust shear deformation is distributed over more diffuse zones with a ductile character of deformation at higher metamorphic conditions Sibson 1977

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