Submagmatic microfractures in granites

Bouchez, Jean‐Luc; Delas, Christian; Gleizes, Gérard; Nédélec, Anne; Cuney, Michel

doi:10.1130/0091-7613(1992)020<0035:smig>2.3.co;2

Cited by 290 publications

(141 citation statements)

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“…However granite fabrics study requires the establishment of the microstructures origin, either magmatic or eventually superimposed solid-state. Criteria for this distinction are presented in a number of papers (e. g. Blumenfeld and Bouchez, 1988;Bouchez et al, 1992;Paterson et al, 1989;Vernon, 2000) and the significance of the different microstructures is defined according to magma rheology considerations (Nicolas, 1992;Vigneresse et al, 1996). When the solid fraction of magma does not exceed a certain amount, about 60%, enough melt is supposed to be present to allow free crystal rotation, i.e.…”

Section: Petrography and Microstructural Studymentioning

confidence: 99%

Late-Variscan emplacement and genesis of the Vieira do Minho composite pluton, Central Iberian Zone: Constraints from U–Pb zircon geochronology, AMS data and Sr–Nd–O isotope geochemistry

Martins

Ovaia

Noronha

2013

Lithos

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In the Central Iberian Zone synorogenic (syn-and late-D 3 , the last deformation phase) composite batholiths of biotite-rich granitods with peraluminous character are well represented. We report here U-Pb zircon and monazite ages, geochemical, Sr-Nd-O isotopic data and Anisotropy of Magnetic Susceptibility (AMS) studies for the late-D 3 Vieira do Minho pluton, in northern Portugal. AMS reveals the paramagnetic behaviour of these granites and the magnetic fabric enhances the major role of NW-SE regional anisotropies on controlling the ascent and emplacement of the magmas. Magnetic anisotropy and medium temperature microstructures also point out the evolution of regional tectonics during crystallization of the magma. U-Pb zircon and monazite analyses yield consistent ages of 310 ± 2 Ma and 312 ± 2 Ma, interpreted as emplacement age. The Vieira do Minho pluton consists of two peraluminous monzogranites, the VMG and the MRG. Both have similar ε Nd values (VMG= −5.2 to −5.7; MRG =−4.98 to −5.96) but the VMG is slightly enriched in 87 Sr/ 86 i = 0.7087-0.7098 as well as in δ 18 O in the range of 10.6‰ to 11.0‰ than the MRG with 87 Sr/ 86 i =0.7064-0.7075 and δ 18 O=9.9‰-10.5‰. These granites are associated with coeval scarce grabroic intrusions and/or mafic microgranular enclaves which are not considered as mafic precursors of the associated granitic magmatism. Instead, a lower metaigneous crustal source, at different levels, is proposed based on the available data set.

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Section: Petrography and Microstructural Studymentioning

confidence: 99%

Late-Variscan emplacement and genesis of the Vieira do Minho composite pluton, Central Iberian Zone: Constraints from U–Pb zircon geochronology, AMS data and Sr–Nd–O isotope geochemistry

Martins

Ovaia

Noronha

2013

Lithos

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“…4a and b) which is typical for a submagmatic stage of deformation (Bouchez et al 1992). Thin section investigations of samples with visible magmatic foliation show parallel alignment of elongated feldspar crystals (Fig.…”

Section: Magmatic and Submagmatic Structuresmentioning

confidence: 82%

The emplacement mode of Upper Cretaceous plutons from the southwestern part of the Sredna Gora Zone (Bulgaria): structural and AMS study

Georgiev¹,

Henry²,

Jordanova³

et al. 2009

Geologica Carpathica

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Several plutons located in the southwestern part of the Sredna Gora Zone -Bulgaria are examples of the Apuseni-Banat-Timok-Sredna Gora type of granites emplaced during Late Cretaceous (86-75 Ma) times. The studied intrusive bodies are spatially related to and deformed by the dextral Iskar-Yavoritsa shear zone. The deformation along the shear zone ceased at the time of emplacement of the undeformed Upper Cretaceous Gutsal pluton, which has intruded the Iskar-Yavoritsa mylonites. A clear transition from magmatic foliation to high-, moderate-and low-temperature superimposed foliation and lineation in the vicinity of the Iskar-Yavoritsa and related shear zones gives evidence for simultaneous tectonics and plutonism. Away from the shear zones, the granitoids appear macroscopically isotropic and were investigated using measurements of anisotropy of magnetic susceptibility at 113 stations. The studied samples show magnetic lineation and foliation, in agreement with the magmatic structures observed at a few sites. Typical features of the internal structure of the plutons are several sheet-like mafic bodies accompanied by swarms of mafic microgranular enclaves. Field observations indicate spatial relationships between mafic bodies and shear zones as well as mingling processes in the magma chamber which suggest simultaneous shearing and magma emplacement. Structural investigations as well as anisotropy of magnetic susceptibility (AMS) data attest to the controlling role of the NW-SE trending Iskar-Yavoritsa shear zone and to the syntectonic emplacement of the plutons with deformation in both igneous rocks and their hosts. The tectonic situation may be explained by partitioning of oblique plate convergence into plate-boundary-normal thrusting in the Rhodopes and plate-boundary-parallel transcurrent shearing in the hinterland (Sredna Gora).

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“…3a, b). Beside this, internal fractures of plagioclase phenocrysts are filled by magmatic minerals (mostly hornblende and oligoclase), suggesting the presence of fluid during fracturing and deformation (e.g., Bouchez et al, 1992). The coexistence in equilibrium of high-temperature ductile deformation and fractures filled by a possible melt suggests that the microfabrics register the strain occurred from the submagmatic state to high-temperature solid state deformation.…”

Section: Emplacement Under Transtension In Cmdsmentioning

confidence: 99%

Transtension y transpresion del Jurasico Medio-Superior al Cretacico Inferior durante la construccion del arco magmatico en Chile central: evidencia a partir de enjambres de diques maficos.

Creixell¹,

Parada²,

Morata³

et al. 2011

Andgeo

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AbstrACt. The Middle-Late Jurassic mafic dike swarms of central Chile between 33º and 33º45'S register the tectonic activity of the contemporaneous arc represented by the Coastal batholith. These dike swarms evidence alternate episodes of transtension and transpression across NW-striking structures, which controlled the construction of the magmatic arc. The Middle-Upper Jurassic and Lower Cretaceous mafic dike swarms in the Coastal range of central Chile has been studied through field observations, geochronology and AMS (anisotropy of magnetic susceptibility) to document the tectonic and magmatic evolution of the Jurassic-Cretaceous arc at this latitude. Middle to Upper Jurassic dike swarms (Concón and Cartagena mafic dike swarms) were emplaced between 163 and 157 Ma, along NW-SE to WNW-ESE-striking host fractures, registering a first stage of magma emplacement under sinistral transtension. During this stage, dikes acquired a fabric characterized by magnetic foliation clockwise oblique to dike trend and gently plunging lineations. This stage was followed rapidly by dike emplacement under sinistral transpression, with associated steeply plunging lineations in the dikes, reverse shear zones in the country rocks and local occurrence of horizontal mafic dikes. On the other hand, the Lower Cretaceous El Tabo Dike Swarm was emplaced along tensile fractures that do not register shear displacements along their walls. These dikes were emplaced at shallower crustal levels along tensile fractures.Within each dike swarm, differences in the tectonic style of emplacement correlates with changes in the geochemical composition of the dikes, suggesting a strong coupling between tectonics and nature of magma supplies in the arc. Finally, the current results show that the Mesozoic evolution of the Coastal Batholith of central Chile occurred in several stages of deformation and not under a simple scenario of extensional tectonics. This magmatism and deformation were strongly controlled by NW-to WNW-striking fractures. These structures are spatially correlated with regional-scale Cenozoic lineaments that are oblique to the orientation of the Andean orogen. We suggest that these lineaments are features inherited at least from Jurassic times. Middle-late Jurassic to early cretaceous transtension and transpression during arc building in central chile... rEsuMEn. transtensión y transpresión del Jurásico Medio-superior al Cretácico Inferior durante la construcción del arco magmático en Chile central: evidencia a partir de enjambres de diques máficos. Los enjambres de diques máficos del Jurásico Medio-Superior de Chile central entre los 33º y 33º45'S registran la actividad tectónica del arco contemporáneo representado por el batolito costero. Estos enjambres de diques evidencian episodios alternados de transtensión y transpresión a lo largo de estructuras de rumbo NW, las cuales controlaron la construcción del arco magmático. Los enjambres de diques máficos del Jurásico Medio-Superior y del Cretácico Inferior de la Cordillera de la Costa...

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Submagmatic microfractures in granites

Cited by 290 publications

References 0 publications

Late-Variscan emplacement and genesis of the Vieira do Minho composite pluton, Central Iberian Zone: Constraints from U–Pb zircon geochronology, AMS data and Sr–Nd–O isotope geochemistry

Late-Variscan emplacement and genesis of the Vieira do Minho composite pluton, Central Iberian Zone: Constraints from U–Pb zircon geochronology, AMS data and Sr–Nd–O isotope geochemistry

The emplacement mode of Upper Cretaceous plutons from the southwestern part of the Sredna Gora Zone (Bulgaria): structural and AMS study

Transtension y transpresion del Jurasico Medio-Superior al Cretacico Inferior durante la construccion del arco magmatico en Chile central: evidencia a partir de enjambres de diques maficos.

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