The Role of Manganese in the Paragenesis of Magmatic Garnet: An Example from the Old Woman-Piute Range, California: A Reply

Miller, Calvin F.; Stoddard, Edward F.

doi:10.1086/628645

Cited by 11 publications

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“…remains contentious (e.g. Abbott 1981b;Clemens & Wall 1982;• Miller & Stoddard 1981b, most workers concur with S Hall (1965) that an increase in the Mn content of the liquid } as a result of fractional crystallisation stabilises the crystallisj ation of late garnet from felsic magmas (Miller & Stoddard 11981a; Abbott & Clarke 1979;Abbott 1981aAbbott , 1985Zen 1988).…”

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confidence: 98%

Insights from igneous reaction space: a holistic approach to granite crystallisation

Hogan¹

1996

Earth and Environmental Science Transactions of the Royal Socie

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ABSTRACT:Petrological investigations of granite commonly reveal multiple periods of growth punctuated by resorption for many of the constituent minerals. Complementary to such textures are mineral compositional heterogeneity manifested by zoning or grain to grain variability. These features ultimately reflect changes in the intensive parameters or activities of components during melt solidification. Such complexities of granite crystallisation can be simultaneously modelled in a reaction space constructed from the set of linearly independent reactions describing the equilibria among all phases and components in the system of interest.The topology of the linearly independent reactions that define the reaction space for garnetmuscovite-biotite granites yields the following insights: (1) there is no one unique reaction that produces or consumes aluminous minerals (e.g. garnet); (2) minerals can alternate as reactants or products in different reactions accounting for textures indicating multiple periods of crystallisation separated by resorption; (3) mineral compositions are regulated by the reaction(s) producing them and vary as the stoichiometry of the reaction(s) producing them varies; (4) resorption of early crystallising garnet is likely to reflect decreasing pressure, presumably during magma ascent; (5) late crystallisation of garnet, at the expense of biotite, reflects an increase in melt aluminosity and does not necessarily require high Mn activities for the melt and (6) increasing melt H2O, at H2Oundersaturated conditions, favours the formation of biotite–muscovite granite.Application of the reaction space method to other granite types holds considerable promise for elucidating reactions that regulate mineral assemblages and compositions during crystallisation.

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confidence: 98%

Insights from igneous reaction space: a holistic approach to granite crystallisation

Hogan¹

1996

Earth and Environmental Science Transactions of the Royal Socie

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“…Although the exact nature of the reactions involved remains contentious (e.g. Abbott 198 lb;Clemens & Wall 1982;Miller & Stoddard 1981b, most workers concur with Hall (1965) that an increase in the Mn content of the liquid as a result of fractional crystallisation stabilises the crystallisation of late garnet from felsic magmas (Miller & Stoddard 1981a;Abbott & Clarke 1979;Abbott 1981aAbbott , 1985Zen 1988).…”

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confidence: 99%

Insights from igneous reaction space: a holistic approach to granite crystallisation

Hogan¹

1996

The Third Hutton Symposium on the Origin of Granites and Related Rocks

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Petrological investigations of granite commonly reveal multiple periods of growth punctuated by resorption for many of the constituent minerals. Complementary to such textures are mineral compositional heterogeneity manifested by zoning or grain to grain variability. These features ultimately reflect changes in the intensive parameters or activities of components during melt solidification. Such complexities of granite crystallisation can be simultaneously modelled in a reaction space constructed from the set of linearly independent reactions describing the equilibria among all phases and components in the system of interest.The topology of the linearly independent reactions that define the reaction space for garnetmuscovite-biotite granites yields the following insights: (1) there is no one unique reaction that produces or consumes aluminous minerals (e.g. garnet); (2) minerals can alternate as reactants or products in different reactions accounting for textures indicating multiple periods of crystallisation separated by resorption; (3) mineral compositions are regulated by the reaction(s) producing them and vary as the stoichiometry of the reaction(s) producing them varies; (4) resorption of early crystallising garnet is likely to reflect decreasing pressure, presumably during magma ascent; (5) late crystallisation of garnet, at the expense of biotite, reflects an increase in melt aluminosity and does not necessarily require high Mn activities for the melt and (6) increasing melt H 2 O, at H 2 Oundersaturated conditions, favours the formation of biotite-muscovite granite.Application of the reaction space method to other granite types holds considerable promise for elucidating reactions that regulate mineral assemblages and compositions during crystallisation.Petrological studies reveal complex crystallisation histories for granite. Many of the constituent minerals can exhibit evidence of multiple periods of growth punctuated by episodes of resorption. Rapakivi feldspars are one common example. Complementary to such textures are compositional heterogeneities exhibited by minerals (e.g. growth zoning in garnet). These features serve as witness that most granites are the integrated product of crystallisation over a range in values for P, T, fn l0 , f 02 , as well as other components of interest.The complex phase relationships of biotite-muscovitegarnet granites are discussed in this paper as an example. These granites typically exhibit the following crystallisation sequence: (1) early crystallising garnet, when observed, is replaced by biotite and muscovite; (2) near the end of crystallization, garnet rejoins the crystallising assemblage of biotite and muscovite; and (3) eventually biotite is eliminated from the final solidus assemblage, which crystallises as muscovite-garnet granite. Reaction relationships among these phases during crystallisation have been discussed in detail by numerous workers (Miller

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Remote sensing techniques and geochemical constraints on the formation of the Wadi El-Hima mineralized granites, Egypt: new insights into the genesis and accumulation of garnets

Khedr

Khashaba

El-Shibiny

et al. 2022

Int J Earth Sci (Geol Rundsch)

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The Wadi El-Hima Neoproterozoic I- and A-type granites in the Southern Eastern Desert of Egypt are rich in garnets (up to 30 vol%) and are cut by NW–SE strike-slip faults, as confirmed from structure lineament extraction maps. These mineralized granites and garnet mineralization zones can be successfully discriminated using remote sensing techniques. Spectral angle mapper and matched filtering techniques are highly effective for mapping garnet-rich zones and show that the highest garnet concentrations occur along the intrusive contact zone of NW–SE striking faults. El-Hima granites have high SiO2 (73.5–75.1 wt%), Al2O3 (13.4–15.3 wt%) and total alkali (6.7–8.7 wt%) contents, suggesting that they were sourced from peraluminous (A/CNK > 1) parental magmas. Garnet-bearing trondhjemites are metasomatic in origin and formed after I-type tonalite-granodiorites, which originated in a volcanic arc tectonic setting. Garnet-rich syenogranites and alkali-feldspar granites are both post-collisional A-type granites: the syenogranites formed from peraluminous magmas generated by partial melting of lower crustal tonalite and metasedimentary protoliths during lithospheric delamination, and the alkali-feldspar granites crystallized from highly fractionated, felsic and alkali-rich peraluminous magmas in the upper crust. Garnets in El-Hima mineralized granites occur in three forms: (1) subhedral disseminated crystals, (2) vein-type crystals, and (3) aggregated subhedral crystals, reflecting different mechanisms of accumulation. All are dominantly almandine in composition (Alm76Sps10 Prp7Grs6Adr1) and have high average concentrations of heavy rare earth elements (HREE) (ΣHREE = 1636 ppm), Y = (3394 ppm), Zn (325 ppm), Li (39.17 ppm) and Ga (34.94 ppm). Garnet REE patterns show strong negative Eu anomalies with HREE enriched relative to LREE, indicating a magmatic origin. These magmatic garnets are late-stage crystallization products of Al-rich hydrous magmas, and formed at low temperature (680–730 °C) and pressure (2.1–2.93 kbar) conditions in the upper continental crust. Peculiar garnet concentrations in syenogranites near and along contact zones with alkali feldspar granites are related to peraluminous parent hydrous magma compositions. These garnets formed by in situ crystallization from A-type granite melts, alongside accumulation of residual garnets left behind after partial melting of the host garnet-rich granites along the intrusive contact. Magmatic-fluid flow along the NW–SE striking fault of Najd system enhanced garnet accumulation in melts, which formed clots and veins of garnet.

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The Role of Manganese in the Paragenesis of Magmatic Garnet: An Example from the Old Woman-Piute Range, California: A Reply

Cited by 11 publications

References 0 publications

Insights from igneous reaction space: a holistic approach to granite crystallisation

Insights from igneous reaction space: a holistic approach to granite crystallisation

Insights from igneous reaction space: a holistic approach to granite crystallisation

Remote sensing techniques and geochemical constraints on the formation of the Wadi El-Hima mineralized granites, Egypt: new insights into the genesis and accumulation of garnets

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