Indigenous source of late-stage dikes and veins in granitic plutons

Hibbard, M. J.

doi:10.2113/gsecongeo.75.3.410

Cited by 16 publications

(6 citation statements)

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“…These late crystallizing minerals may rotate during local flow, due to their small size. In addition, external force may produce microstructures such as microfractures or microveins during this regime [ Hibbard , 1980; Bouchez et al , 1992]. …”

Section: Discussionmentioning

confidence: 99%

Magnetite microexsolutions in silicate and magmatic flow fabric of the Goyozan granitoid (NE Japan): Significance of partial remanence anisotropy

2006

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[1] Anisotropy of magnetic susceptibility (AMS) has been widely used to infer magmatic flow patterns of granitoids where an appropriate AMS axis is parallel to an alignment of mafic minerals or magnetite. The magmatic flow fabric in Cretaceous granitic plutons from northeastern Japan was verified using an analysis of anisotropy of partial anhysteretic remanent magnetization (ApARM) which further isolates the magnetite subfabrics according to magnetite grain size. The preferred orientation of polysynthetic twins in plagioclase laths and clinopyroxene is discordant with the bulk AMS fabric along outer marginal zones of the granitoid, as shown by image analysis of microphotographs from thin sections cut in orthogonal planes. This suggests that the uncorroborated use of bulk AMS to detect flow fabric in granitoids has risks. Scanning electron microscopy (SEM) reveals that submicroscopic, needle-shaped magnetite inclusions exsolved in anhedral plagioclase and clinopyroxene may explain such anomalous exceptions to the validity of AMS fabrics. Our ApARM measurements show that the ApARM alignment of relatively high-coercive, submicroscopic magnetite inclusions is concordant to the linear orientation of anhedral plagioclase and clinopyroxene. The combination of SEM, AMS, and ApARM was required to confirm the magmatic and submagmatic flow pattern of granitoids in this study and is generally preferable to the use of AMS alone.Citation: Usui, Y., N. Nakamura, and T. Yoshida (2006), Magnetite microexsolutions in silicate and magmatic flow fabric of the Goyozan granitoid (NE Japan): Significance of partial remanence anisotropy,

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Section: Discussionmentioning

confidence: 99%

Magnetite microexsolutions in silicate and magmatic flow fabric of the Goyozan granitoid (NE Japan): Significance of partial remanence anisotropy

2006

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“…Relações de truncamento mostram que eles são de várias gerações (Foto 16). Seu cará ter co-magmático é atestado pelo sutil início a partir da matriz granítica e pelo fato de os megacristais de feldspato não serem truncados pelas paredes dos diques (Hibbard 1980, Hibbard & Waters 1985. Em regiões pouco deformadas, eles podem ter qualquer orientação (Foto 16), o que provavelmente resulta da liberação de fluidos em diferentes estágios de cristalização (Hibbard 1980), mas em regiões mais deformadas são rotacionados e tendem a adquirir uni paralelismo com a foliação milonítica.…”

Section: Mecanismo De Deformaçãounclassified

A Zona De Cisalhamento Tauá, Ceará: Sentido E Estimativa Do Deslocamento, Evolução Estrutural E Granitogênese Associada

Neves¹

1991

RBG

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The Taua shear zone (TSZ) comprises a subverlical minylonitic belt more than 5 km wide whose development marks the transition from a tangencial to a transcurrent tectonics at the end of the Braziliano (Pan-African) Cycle. Numerous kinematic indicators point to a sinistral sense of shear, with a stimated 30 to 35 km of horizontal displacement. The main features of the TSZ are interpreted as resulting froin progressive deformation. As time evolved, the present level of exposure was carried to successively shallower structural levels, and the deformational regime changed from ductile (plastic deformation of all minerals) to semiductile (beggining of brittle deformation in feldspars; Production of S-C mylonhes) and, then, to semibrittle (cataclasis predominates over dynamic recrystallization; pseudotachylytes are formed). During the mail, stages of deformation, granitic magmas ascendend toward the surface throughout the subvertical foliation of the TSZ. Arriving at the intrusion level they suffered flow differentiation and originated the synteclonic Pedra Lisa granites. During the crystallization of these rocks, deformation continued showing local variations in intensity. When the semibrittle regime was reached high strain areas were localized in narrow shear bands, so preserving the early formed structures. Fine-grained late-tectonic granites were possibly intruded along extension fissures formed at this stage. Brittle faults can represent the continuation of the deformalional history until the brittle regime or result from a late, unrelated, event.

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“…Hightemperature mylonites were derived from various kinds of pre-existing rocks: metasedimentary rocks, metabasites and pre-to synkinematic intrusive rocks. In the high-temperature mylonites a continuous transition from magmatic to solidstate flow is marked by: (a) microfractures filled with quartz and feldspar in K-feldspar porphyroclasts, suggesting formation due to stress concentrations at contacts between grains in the submagmatic stage [31,32]; (b) crystal plastic deformation (Fig. 3c) and dynamic recrystallization of plagioclase, myrmekite growth along the boundaries of Kfeldspar porphyroclasts, indicating that ductile deformation occurred under high-temperature [33,34].…”

Section: Shear Zone Fabricmentioning

confidence: 99%

Major Structural Features and the Tectonic Evolution of the Bossangoa-Bossembele Basement, Northwestern Central African Republic

Hubert¹

2011

TOGEOJ

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Planar structures (foliations and shear zones) and linear structures (lineations, fold axes) around the Bossangoa and Bossembele area (northwestern part of the Central African Republic) in the North Equatorial fold belt have been investigated and analyzed with the aim of unraveling the major structural elements and the tectonic evolution of the basement. The foliations show two major trends, an older flat-lying granulitic layering of uncertain age reworked by later, Neoproterozoic NE-SW ductile, sinistral shearing and mylonitization. The related lineation is conspicuous and corresponds to a mineral and stretching lineation. It trends N0-30°E with a moderate plunge (0-15) towards the north. F 1 folds occur only as decimeter-sized isoclinals folds; their axial traces are roughly parallel to the lineation. The brittle phase characterized by NW-SE-trending open and partially filled fractures is younger than the mylonitization. Quartzofelsdpathic anatectic veins or planes are commonly boudinaged, and the shape of boudins rather suggests non-coaxial deformation. The mylonitic foliation with associated stretching lineation and the ductile shear zone are recognized for the first time and support a tectonic evolution in which ductile deformation was overprinted by brittle failure accompanied by the emplacement of some intrusives.

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Indigenous source of late-stage dikes and veins in granitic plutons

Cited by 16 publications

References 0 publications

Magnetite microexsolutions in silicate and magmatic flow fabric of the Goyozan granitoid (NE Japan): Significance of partial remanence anisotropy

Magnetite microexsolutions in silicate and magmatic flow fabric of the Goyozan granitoid (NE Japan): Significance of partial remanence anisotropy

A Zona De Cisalhamento Tauá, Ceará: Sentido E Estimativa Do Deslocamento, Evolução Estrutural E Granitogênese Associada

Major Structural Features and the Tectonic Evolution of the Bossangoa-Bossembele Basement, Northwestern Central African Republic

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