Rapakivi texture: An indication of the crystallization of hydrosilicates, II

Elliston, John

doi:10.1016/0012-8252(85)90039-x

Cited by 25 publications

(3 citation statements)

References 19 publications

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“…The size of the K‐feldspar megacrysts decreases to a size only slightly larger than the groundmass crystals toward the contact with the trondhjemite. In this inner rim of the porphyritic granodiorite, both rapakivi and antirapakivi textures (Elliston, ) are displayed. The marginal fine‐grained granodiorite (max.…”

Section: Resultsmentioning

confidence: 99%

Crystal Mush Flow in Small Concentrically Expanded Pluton (Castle Crags Pluton; Klamath Mountains, CA, USA)

Machek

Závada

Roxerová

et al. 2019

Geochem Geophys Geosyst

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Understanding of the processes of magmatic fabric formation in crystal‐rich magmas and their reflection in rock magnetic properties are important for understanding pluton formation and intrusion mechanisms. On the example of small concentrically zoned Castle Crags pluton in the Klamath Mountains (CA, USA) we provide reconstruction of the flow/deformation mechanisms of the crystal‐rich magma and pluton growth based on detailed structural mapping and microstructural analysis employing the anisotropy of magnetic susceptibility, microstructural analysis, and crystallographic preferred orientation. Our study reveal microstructural evidence for progressive development of magmatic textures in the pluton core transitioning to submagmatic and eventually subsolidus fabric at the pluton periphery, that is interpreted in terms of the flow/deformation of the crystal mush. The documented magmatic textures are linked to anisotropy of magnetic susceptibility parameters and orientation. The recorded anomalous degree of anisotropy of magnetic susceptibility found in the pluton is attributed to tiling and plastic deformation of magnetite grains by the surrounding phenocrysts. The concentric structure of the pluton resulted from horizontal compaction and margin parallel stretching of the dense crystal mush around the vertically intruding trondhjemite magma in the pluton core. The Castle Crags pluton is interpreted as a concentrically expanded pluton, which grew at least by two increments of granodiorite and trondhjemite magma emplacement.

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Section: Resultsmentioning

confidence: 99%

Crystal Mush Flow in Small Concentrically Expanded Pluton (Castle Crags Pluton; Klamath Mountains, CA, USA)

Machek

Závada

Roxerová

et al. 2019

Geochem Geophys Geosyst

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“…A number of hypotheses have been proposed to explain rapakivi texture developed in Proterotoic rapakivi granites and in other occurrences (see reviews in Hibbard 1981;Elliston 1985). In line with several predecessors (e.g.…”

Section: Origin Of the Rapakivi Texture In Relation To The Mafic Enclmentioning

confidence: 94%

The rapakivi texture of feldspars in a plutonic mixing environment: A dissolution‐recrystallization process?

Bussy

1990

Geological Journal

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A new hypothesis is formulated to explain the development of rapakivi texture in and around the mafic enclaves of porphyritic granitoids, i.e. in environments involving magma mixing and mingling. The formation of a plagioclase mantle around alkali feldspar megacrysts is attributed to the localized presence of a melt resulting from the reaction of these megacrysts, with host hybrid magma with which they are in disequilibrium. This feldspathic melt adheres to the resorbed crystals and is virtually immiscible with the surrounding magma. Its composition is modified in terms of the relative proportions of KzO, Na,O, and CaO through selective diffusion of these elements, thus allowing the specific crystallization of andesine. With decreasing temperature, the K-feldspar, again stable, crystallizes along with the plagioclase, leading to mixed mantle structures.

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“…Additionally, granite can develop other less common textures, such as rapakivi. In the strictest sense, the rapakivi texture presents three main characteristics: (i) size and shape, ovoidal potash feldspar greater than 3 mm, (ii) crystallization process, overgrowth of plagioclase (oligoclase/andesine), with a thickness between 1 and 3 mm, around the k-feldspar, and (iii) crystallization order, the simultaneous occurrence of two generations of k-feldspar and idiomorphic quartz [22], [23].…”

Section: A Granite Rocksmentioning

confidence: 99%

Granite Weathering, Denudation Processes, and Associated Landforms in the Itu-Cabreúva Region, São Paulo, Brazil

Anjos,

Velázquez,

Azevedo Sobrinho

et al. 2023

EJGEO

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The Itu-Cabreúva region is located about 90 km northwest of the São Paulo city center. The geological setting is characterized by the expressive occurrence of Neoproterozoic granitic rocks. These intrusive rocks form large plutons that have given rise to flattened hills, valleys with concave-convex slopes, and superficial drainage systems. As part of this larger framework, several smaller landforms with unique appearances occur, which can be categorized into six groups: nubbin, boulder, balanced rock, castle koppie, cave, and minor form. Although these reliefs were formed under similar weathering conditions, the research results show that the physical properties of the lithology and the nature and density of the joints strongly influenced the shape and size of the blocks. These geoforms have exceptional scenic value and are situated in a geographically advantageous location for a range of educational and recreational activities that can be adapted to different levels of knowledge. The implementation of such proposals in the context of understanding the physical environment would result in a number of benefits, including (i) greater community involvement in the environment, (ii) valorization of the local landscape as a historical record of the planet's evolution, and (iii) improvement of urban geological risk prevention programs. Finally, these landforms are fascinating and offer conclusive evidence that can be observed on a wide range of scales, illustrating how the brittle deformation and magmatic fabric of the granite massifs influenced the development of the local landscape.

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Rapakivi texture: An indication of the crystallization of hydrosilicates, II

Cited by 25 publications

References 19 publications

Crystal Mush Flow in Small Concentrically Expanded Pluton (Castle Crags Pluton; Klamath Mountains, CA, USA)

Crystal Mush Flow in Small Concentrically Expanded Pluton (Castle Crags Pluton; Klamath Mountains, CA, USA)

The rapakivi texture of feldspars in a plutonic mixing environment: A dissolution‐recrystallization process?

Granite Weathering, Denudation Processes, and Associated Landforms in the Itu-Cabreúva Region, São Paulo, Brazil

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