RELAÇÕES ENTRE CISALHAMENTO, MAGMATISMO E ANATEXIA: EXEMPLO DA ZONA DE CISALHAMENTO CRUZEIRO DO NORDESTE, PROVÍNCIA BORBOREMA, BRASIL

The Borborema Province, northeastern Brazil, exhibit an extensive framework of shear zones in spatial proximity with syn-tectonic magmatism that makes it a perfect place to understand their relationship. In the eastern portion of this province an important dextral shear zone, that divides into two terranes, was originated during an escape tectonics after an oblique collision after a tectonic transport to NW. The recrystallization of quartz and feldspar shows a remarkable increase towards the shear zone, interpreted as a temperature increase during deformation. Thermodynamic modelling coupled with field relationship shows that high strain migmatitic textures such as stromatic structure was formed at ~650 °C and ~0.9 GPa prior to the shear development. Whereas low strain migmatites with schollen texture was formed at ~750 °C and ~0.7 GPa. We propose that the presence of melt during an oblique collision facilitated the emplacement of shear structures due to a thermal anomaly during the emplacement of syn-tectonic plutons.

FAULT SYSTEMS IN THE UPPER CRUST OF THE FENNOSCANDIAN SHIELD, THE EAST EUROPEAN PLATFORM

Directions of 683 faults located in the southeastern part of the Fennoscandian (Baltic) shield were statistically analyzed, and three orthogonal associations of fault systems were identified in the study area. According to the dynamic analysis of the fault systems and their associations, the main NW-striking faults belong to the fault network originating mainly from the early Paleoproterozoic. These faults functioned in the Paleoproterozoic during four main deformation stages: D1 – sinistral shear transtension and asymmetric rift genesis (2.1–1.9 Ga); D2 – sinistral shear transpression under oblique accretion and convergence (1.9 Ga); D3 – sinistral shear transpression under oblique collision (1.89–1.80 Ga); D4 – dextral strike-slip displacements at the background of complex escape tectonics of the late collision stage (1.80–1.78 Ga). The regional stress field changed as follows: D1 – northeast- or east-trending extension; D2 – northeast compression; D3 – sub-latitudinal compression; D4 – sub-meridian compression. Changes in dynamic loading conditions led to multiple kinematic inversions of the fault networks. Widespread transtension and transpression settings in the southeastern parts of the Baltic Shield give evidence of asymmetric rifting, oblique accretion and collision in the Paleoproterozoic, which must be taken in to account in geodynamic reconstructions.

Cenozoic tectonic evolution of the Ecemiş fault zone and adjacent basins, central Anatolia, Turkey, during the transition from Arabia-Eurasia collision to escape tectonics

The effects of Arabia-Eurasia collision are recorded in faults, basins, and exhumed metamorphic massifs across eastern and central Anatolia. These faults and basins also preserve evidence of major changes in deformation and associated sedimentary processes along major suture zones including the Inner Tauride suture where it lies along the southern (Ecemiş) segment of the Central Anatolian fault zone. Stratigraphic and structural data from the Ecemiş fault zone, adjacent NE Ulukışla basin, and metamorphic dome (Niğde Massif) record two fundamentally different stages in the Cenozoic tectonic evolution of this part of central Anatolia. The Paleogene sedimentary and volcanic strata of the NE Ulukışla basin (Ecemiş corridor) were deposited in marginal marine to marine environments on the exhuming Niğde Massif and east of it. A late Eocene–Oligocene transpressional stage of deformation involved oblique northward thrusting of older Paleogene strata onto the eastern Niğde Massif and of the eastern massif onto the rest of the massif, reburying the entire massif to >10 km depth and accompanied by left-lateral motion on the Ecemiş fault zone. A profound change in the tectonic setting at the end of the Oligocene produced widespread transtensional deformation across the area west of the Ecemiş fault zone in the Miocene. In this stage, the Ecemiş fault zone had at least 25 km of left-lateral offset. Before and during this faulting episode, the central Tauride Mountains to the east became a source of sediments that were deposited in small Miocene transtensional basins formed on the Eocene–Oligocene thrust belt between the Ecemiş fault zone and the Niğde Massif. Normal faults compatible with SW-directed extension cut across the Niğde Massif and are associated with a second (Miocene) re-exhumation of the Massif. Geochronology and thermochronology indicate that the transtensional stage started at ca. 23–22 Ma, coeval with large and diverse geological and tectonic changes across Anatolia.

Supplemental Material: Cenozoic tectonic evolution of the Ecemiş fault zone and adjacent basins, central Anatolia, Turkey during the transition from Arabia-Eurasia collision to escape tectonics

Consists of geochronology and thermochronology data, and methods related to those data. Geochronology data are from ⁴⁰Ar/³⁹Ar dating of volcanic rocks and U-Pb analysis of detrital zircons, while thermochronology data are from apatite and zircon fission-track and apatite helium cooling ages.

Supplemental Material: Cenozoic tectonic evolution of the Ecemiş fault zone and adjacent basins, central Anatolia, Turkey during the transition from Arabia-Eurasia collision to escape tectonics

Consists of geochronology and thermochronology data, and methods related to those data. Geochronology data are from ⁴⁰Ar/³⁹Ar dating of volcanic rocks and U-Pb analysis of detrital zircons, while thermochronology data are from apatite and zircon fission-track and apatite helium cooling ages.

A SUÍTE CÓRREGO TAQUARI NO ANTICLINAL DE ITACAMBIRA, BACIA DO RIO MACAÚBAS (MG): MAGMATISMO BÁSICO TARDI-EDIACARANO (CA. 560 MA) NO DOMÍNIO EXTERNO DO ORÓGENO ARAÇUAÍ

No setor central do cinturão de dobramentos e empurrões da Serra do Espinhaço, domínio externo ocidental do Orógeno Araçuaí, situa-se o Anticlinal de Itacambira onde foi identificado um conjunto de diques gabróicos, pouco deformados e metamorfisados na fácies xisto verde. Um desses diques, englobados na Suíte Metaígnea Córrego do Taquari, tem assinatura litoquímica de toleíito intraplaca, idade-modelo Sm-Nd (TDM) em torno de 1,8 Ga e épsilon Nd negativo. Deste dique extraiu-se grãos de zircão para datação pelo método U-Pb (SHRIMP). Alguns destes grãos são herdados e evidenciam assimilação de cristais de zircão do Paleoproterozóico e Mesoproterozóico. A maior parte dos grãos são cristais euédricos, magmáticos, e suas análises U-Pb resultaram na idade de 560 ± 6 Ma para a cristalização magmática da Suíte Córrego Taquari. Esta suíte registra um sítio transtensivo formado e preenchido pelo magma máfico no limiar dos estágios sincolisional e tardi-colisional do Orógeno Araçuaí, provavelmente relacionado ao início dos fenômenos de escape lateral que afetaram este orógeno.Palavras-chave: diques máficos, Ediacarano, Orógeno AraçuaíABSTRACT: THE CÓRREGO TAQUARI SUITE IN THE ITACAMBIRA ANTICLINE, MACAÚBAS RIVER BASIN, MINAS GERAIS STATE: LATE EDIACARAN (CA. 560 MA) MAFIC MAGMATISM IN THE EXTERNAL TECTONIC DOMAIN OF THE ARAÇUAÍ OROGEN. In the central sector of the Serra do Espinhaço fold-and-thrust belt, western tectonic domain of the Neoproterozoic Araçuaí orogen, occurs the Itacambira anticline where a swarm of Late Ediacaran metamafic bodies were recently discovered, the Córrego Taquari meta-igneous suite. Most of these bodies occur as dykes cutting across units of the Espinhaço Supergroup and Macaúbas Group, and show incipient deformation and low greenschist facies metamorphism. The lithochemical and Sm-Nd isotopic data (negative epsilon Nd and TDM model age around 1.8 Ga) point to a tholeiitic intraplate signature. Twenty two zircon grains, extracted from a sample of a gabbroic dyke and analysed by the U-Pb (SHRIMP) method, show a small population of Paleoproterozoic and Mesoproterozoic inherited grains, and a major population of magmatic euhedral crystals. The less discordant, euhedral zircon crystals yielded the U-Pb (SHRIMP) age of 560 ± 6 Ma for the magmatic crystallization age of the Córrego Taquari Suite. This mafic magmatism records a Late Ediacaran extensional episode, probably related to the beginning of the lateral escape tectonics that took place in the late collisional stage of the Araçuaí orogen.Keywords: mafic dykes, Ediacaran, Araçuaí Orogen