Self-indentation of a heterogeneous continental lithosphere

Machado

et al. 2006

An. Acad. Bras. Ciênc.

Shear zones geometry in the Paraíba do Sul belt, southeastern Brazil, delineates a NE-trending fan-like structure. Shear zones dip towards SE in the northern limb, and towards NW in the southern one. This geometry has been interpreted either due to transpression or to late folding of flat-lying thrust surfaces. Stretching lineation plunges to ENE-ESE in the northern limb and towards NNE-NE in the southern one. Structural data in the southern limb of the divergent fan suggest a two stage kinematic evolution in high-temperature conditions: an earlier stage with top-to-SSW/SW sinistral thrusting and orogenic-parallel tangential motion, and a later stage with top-down to NNE/NE transtensional deformation. We propose a heterogeneous deformation model to explain the observed shear reversal, and suggest that the imposed transpressional displacement gradient may change during progressive deformation due to transient rheological inhomogeneities in bulk pure shear strain. In the earlier stage, the partially molten material could easily accommodate the imposed strain rates, giving rise fi rstly to the SW-directed shearing. As the thermal disturbance tended to vanish and the convergence increased, the NNE-directed transtensional shearing developed. We propose that the transtensional deformation characterized in this paper could be related to extrusion processes during regional transpressional strain.

Section: Geometric Overprint Relationships and Transtensional Shearinmentioning

confidence: 99%

Kinematics and geometry of structures in the southern limb of the Paraíba do Sul divergent structural fan, SE Brazil: a true transtensional shear

Machado

et al. 2006

An. Acad. Bras. Ciênc.

“…the Canadian Shield (Bokelmann and Wüstefeld, 2009), the Sao Francisco Craton (Vauchez et al, 1994), and in other settings suggests a lithospheric origin of anisotropy in those areas. Alternatively corre- to the east, in the Carpathian-Pannonian region (Stuart et al, 2007, Kovacs et al, 2012.…”

Section: Resultsmentioning

confidence: 99%

Correlated crustal and mantle deformation in the Tauern Window, Eastern Alps

Qorbani¹,

Kurz²,

Bianchi³

et al. 2015

AJES

“…Southern structure is different from northern one (from Vauchez et al, 1994) account for the late magmatism, no tectonic evidence has been found, such as normal faults or extensional shear zones, neither in the southern, nor in the northern part of the belt.…”

Section: Ii1 the Western Gondwanamentioning

confidence: 99%

“…A remarkable structural feature of this belt is the evolution of the deformation pattern from South to North. The southern part of the Ribeira-Araçuaí belt has a NE-SW trend and is characterized by a transpressional deformation regime that associates thrusting normal to the belt and dextral, orogen-parallel transcurent movements (Trompette, 1994;Vauchez et al, 1994;Egydio-Silva et al, 2002;Schmitt et al, 2004;Egydio-Silva et al, 2005). The northern part of this orogen, the Araçuaí belt, trends North-South, and involves high temperature (HT)…”

Section: -Introductionmentioning

confidence: 99%

Evolução estrutural e térmica de um batólito sin-cinemático no orógenos Neoproterozóico Araçuaí (leste do Brasil)

Mondou¹

AcknowledgementsMy first acknowledgments are for my two co-directors, Marcos Egydio-Silva, and Alain Vauchez, which permitted me to realize this work. I thank them to took me in a country that I enjoyed discover with them, especially during the field missions. And a special thank for their patience and their disponibility during the preparation of this manuscript and for their comments and reflexions in general.A great thank to Maria Irene Raposo who initiate me to the rock magnetism and help me to complete most of the experiments. Thank you for the discussions about sciences and other.I thank the correctors Ricardo Trindade and Jean-Luc Bouchez for accepting to criticize this work, and the others board members Jérôme Bascou, Maria-Helena Hollanda and Andréa Tommasi for their participation to the reflexion.I also thank all those who participated to this work, people from Geoscience Montpellier and from the Instituto de Geociências.Of course, I thank my family who supported me in my choices. My friends, from Brazil and France, for the precious moments of relaxation. And finally, thank you Lara, your support during this experience has been the greatest help I received. AbstractThe allochtonous domain of the Neoproterozoic Araçuaí belt involves large amounts of magma, widespread partial melting, granulitic facies and high geotherm, characterising this belt as a hot orogen. The Galiléia tonalitic suite, emplaced within host metasediments and deformed at magmatic state, represents a huge batholith that strongly influenced the mechanical behaviour of this middle crust. The anisotropy of magnetic susceptibility (AMS) measured through this batholith and used as a petrofabric proxy, combined to a detailed magnetic mineralogy investigation, permitted to characterize the paramagnetic behaviour of the Galiléia suite and therefore to highlight a complex 3D strain deformation. The observed structures developed within the viscous magma resulted from a combination of tangential tectonics induced by the compression, and gravitational forces arising from the load of the overlying crust. The kinematics of the batholith is compatible with that already described for ductile rocks of hot orogens. U/Pb dating on zircons and monazites together with 40 Ar/ 39 Ar dating on amphiboles, muscovites and biotites permitted to define the thermal evolution of the Galiléia batholith and its host metasediments and constrain the timing of the deformation. The Galiléia batholith emplaced during an important magmatic, tectonic and thermal event at ~580 Ma. Temperature remained high during the first ~50 Ma of the thermal evolution, promoting a seemingly constant deformation of the batholith at magmatic state during several tens of millions years. Such high temperature conditions and stable deformation kinematics during protracted periods of time are supposed to be characteristic of hot orogen. The slow cooling rate of ~10°C/Ma evidenced after ~500 Ma probably indicate a very slow exhumation probably only conducted by erosion. ResumoA faixa Araçuaí, ...