The Origin of Rapakivi Feldspar by a Fluid-induced Coupled Dissolution–Reprecipitation Process

Mondal, Suman; Upadhyay, Dewashish; Banerjee, Atanu

doi:10.1093/petrology/egx058

Cited by 15 publications

(4 citation statements)

References 85 publications

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“…Garnet has formed from epidote and both minerals are replaced by chlorite. The rock has undergone extensive lowtemperature, fluid-induced alteration as seen from extensive sericitization of plagioclase grains, and alteration and coarsening of plagioclase exsolution lamellae in K-feldspar (Engvik, Putnis, Fitz Gerald, & Austrheim, 2008;Mondal, Upadhyay, & Banerjee, 2017;Plümper & Putnis, 2009).…”

Section: Bonai Granitementioning

confidence: 99%

The geological evolution of the Gangpur Schist Belt, eastern India: Constraints on the formation of the Greater Indian Landmass in the Proterozoic

Chakraborty

Upadhyay

Ranjan

et al. 2018

Journal Metamorphic Geology

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The Central Indian Tectonic Zone (CITZ) is a Proterozoic suture along which the Northern and Southern Indian Blocks are inferred to have amalgamated forming the Greater Indian Landmass. In this study, we use the metamorphic and geochronological evolution of the Gangpur Schist Belt (GSB) and neighbouring crustal units to constrain crustal accretion processes associated with the amalgamation of the Northern and Southern Indian Blocks. The GSB sandwiched between the Bonai Granite pluton of the Singhbhum craton and granite gneisses of the Chhotanagpur Gneiss Complex (CGC) links the CITZ and the North Singhbhum Mobile Belt. New zircon age data constrain the emplacement of the Bonai Granite at 3,370 ± 10 Ma, while the magmatic protoliths of the Chhotanagpur gneisses were emplaced at c. 1.65 Ga. The sediments in the southern part of the Gangpur basin were derived from the Singhbhum craton, whereas those in the northern part were derived dominantly from the CGC. Sedimentation is estimated to have taken place between c. 1.65 and c. 1.45 Ga. The Upper Bonai/Darjing Group rocks of the basin underwent major metamorphic episodes at c. 1.56 and c. 1.45 Ga, while the Gangpur Group of rocks were metamorphosed at c. 1.45 and c. 0.97 Ga. Based on thermobarometric studies and zircon–monazite geochronology, we infer that the geological history of the GSB is similar to that of the North Singhbhum Mobile Belt with the Upper Bonai/Darjing and the Gangpur Groups being the westward extensions of the southern and northern domains of the North Singhbhum Mobile Belt respectively. We propose a three‐stage model of crustal accretion across the Singhbhum craton—GSB/North Singhbhum Mobile Belt—CGC contact. The magmatic protoliths of the Chhotanagpur Gneisses were emplaced at c. 1.65 Ga in an arc setting. The earliest accretion event at c. 1.56 Ga involved northward subduction and amalgamation of the Upper Bonai Group with the Singhbhum craton followed by accretion of the Gangpur Group with the Singhbhum craton–Upper Bonai Group composite at c. 1.45 Ga. Finally, continent–continent collision at c. 0.96 Ga led to the accretion of the CGC with the Singhbhum craton–Upper Bonai Group–Gangpur Group crustal units, synchronous with emplacement of pegmatitic granites. The geological events recorded in the GSB and other units of the CITZ only partially overlap with those in the Trans North China Orogen and the Capricorn Orogen of Western Australia, indicating that these suture zones are not correlatable.

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Section: Bonai Granitementioning

confidence: 99%

The geological evolution of the Gangpur Schist Belt, eastern India: Constraints on the formation of the Greater Indian Landmass in the Proterozoic

Chakraborty

Upadhyay

Ranjan

et al. 2018

Journal Metamorphic Geology

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“…At grain scale, feldspar textures such as Rapakivi (alkali feldspar mantled by plagioclase or albite) or anti-rapakivi feldspar (plagioclase mantled by K-feldspar) are typically believed to form via a magmatic mixing process 33 . However, an external fluid-driven ICDR process was recently suggested to account for these textures 34 . Plümper et al 10 describe one ternary feldspar grain from the Larvik batholith, Norway, that shows a similar texture as in our experiments, with pristine feldspar replaced by porous albite, which is then further replaced by K-feldspar (Fig.…”

Section: Discussionmentioning

confidence: 99%

Kinetically driven successive sodic and potassic alteration of feldspar

et al. 2021

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The dynamic evolutions of fluid-mineral systems driving large-scale geochemical transformations in the Earth’s crust remain poorly understood. We observed experimentally that successive sodic and potassic alterations of feldspar can occur via a single self-evolved, originally Na-only, hydrothermal fluid. At 600 °C, 2 kbar, sanidine ((K,Na)AlSi3O8) reacted rapidly with a NaCl fluid to form albite (NaAlSi3O8); over time, some of this albite was replaced by K-feldspar (KAlSi3O8), in contrast to predictions from equilibrium reaction modelling. Fluorine accelerated the process, resulting in near-complete back-replacement of albite within 1 day. These findings reveal that potassic alteration can be triggered by Na-rich fluids, indicating that pervasive sequential sodic and potassic alterations associated with mineralization in some of the world’s largest ore deposits may not necessarily reflect externally-driven changes in fluid alkali contents. Here, we show that these reactions are promoted at the micro-scale by a self-evolving, kinetically-driven process; such positive feedbacks between equilibrium and kinetic factors may be essential in driving pervasive mineral transformations.

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“…The hematite formation is also recognized to be secondary at the above hydrothermal stage from the above textural evidence and recent de-tailed studies as already mentioned Engvik et al, 2008;Plümper and Putnis, 2009), although several origins were proposed (Deer et al, 1952;Smith, 1974;Hofmeister and Rossman, 1983;Rawat et al, 1996). The formation of such secondary hematite has been recently supposed to be products of metasomatic iron-bearing fluid-feldspar interaction in larger scales up to a crustal one Engvik et al, 2008;Plümper and Putnis, 2009;Mondal et al, 2017). The genetic process of the Fe-oxides in the four examined samples also needs individual future studies from geological or petrological viewpoints.…”

Section: And the Fe 2 O 3 Contents Inmentioning

confidence: 97%

Combined influences of iron-oxides and micropores on reddish coloration of alkali feldspars in granitic rocks

Nakano

Makino

Yokoyama

et al. 2019

Jour. Geol. Soc. Japan

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The international color parameters (L*, a*, and b*) of four granite alkali feldspars, determined by a new method using a scanner and personal computor system show a successive variation of reddish colors. Small reddish particles and whitish micropores were observed using a binocular microscope. Raman spectroscopy showed that the common reddish particles are hematite in all four feldspar samples, and showed maghemite in the G feldspar. Distributions of Fe-oxide particles and micropores were assessed by electron microprobe mapping, and their area percentages in the feldspars were obtained using image processing. The results suggest that the size distribution and number density of both hematite and micropores control the reddish color variation in the alkali feldspars, with some additional influencing factors such as the presence of maghemite.

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The Origin of Rapakivi Feldspar by a Fluid-induced Coupled Dissolution–Reprecipitation Process

Cited by 15 publications

References 85 publications

The geological evolution of the Gangpur Schist Belt, eastern India: Constraints on the formation of the Greater Indian Landmass in the Proterozoic

The geological evolution of the Gangpur Schist Belt, eastern India: Constraints on the formation of the Greater Indian Landmass in the Proterozoic

Kinetically driven successive sodic and potassic alteration of feldspar

Combined influences of iron-oxides and micropores on reddish coloration of alkali feldspars in granitic rocks

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