Anatectic pegmatites of the Oxford County pegmatite field, Maine, USA

Webber, Karen L.; Simmons, William B.; Falster, Alexander U.; Hanson, Sarah L.

doi:10.3749/canmin.ab00028

Cited by 42 publications

(16 citation statements)

References 2 publications

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“…This age difference between the Sebago Pluton and the pegmatites is in contrast to previous works (e.g., [20,28]), which suggested that these pegmatites were the product of fractional crystallization of the Sebago Pluton or pegmatitic leucogranites. Other authors (e.g., [29,30]) propose anatexis of the migmatites and metasedimentary host rocks as the origin for these pegmatites.…”

Section: Geological Settingmentioning

confidence: 96%

Garnet as Indicator of Pegmatite Evolution: The Case Study of Pegmatites from the Oxford Pegmatite Field (Maine, USA)

et al. 2021

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Almandine-spessartine garnets, from the Oxford County pegmatites and the Palermo No. 1 pegmatite, record significant compositional variations according to the degree of evolution of their hosting rock. Garnets from the most fractionated pegmatites (Mt. Mica, Berry-Havey, and Emmons) show the highest Mn, Nb, Ta, Zr, and Hf values, followed by those from the intermediate grade pegmatites (Palermo No. 1) and, finally, garnets from the barren pegmatites show the lowest values (Perham and Stop-35). Iron, Ca, and Mg contents follow an inverse order, with the highest contents in the latter pegmatites. Major element zoning shows increasing Mn values from core to rim in most garnet samples, while trace element zoning is not systematic except for some crystals which show a core to rim depletion for most of these elements. Chondrite normalized HREE (Heavy Rare Earth Elements) spectra show positive slopes for garnets from barren pegmatites, both positive and negative slopes for those associated with the intermediate pegmatite, and negative or flat slopes in garnets from the highly fractionated pegmatites. Ion exchange mechanisms, including Fe2+−1Mn2+1, (Fe2+, Mn2+)−1Si−1Li1P1; and, (Y, Ho3+)2(vac)1(Fe2+, Mn2+)−3, could explain most of the compositional variations observed in these garnets. These compositional variations are the reflection of the composition of the pegmatitic magma (barren pegmatites originate from a more ferromagnesian magma than fractionated pegmatites); and of the coexisting mineral phases competing with garnets to host certain chemical elements, such as biotite, schorl, plagioclase, apatite, Fe-Mn phosphates, Nb-Ta oxides, zircon, xenotime, and monazite.

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Section: Geological Settingmentioning

confidence: 96%

Garnet as Indicator of Pegmatite Evolution: The Case Study of Pegmatites from the Oxford Pegmatite Field (Maine, USA)

et al. 2021

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“…In contrast, chlorine contents are lower and are well distinguished between barren Mus-Mc-Ab and Rb-rich Mus-Ab pegmatite, with the latter displaying higher Cl contents (1200-1600 ppm) (Figure 8d). Furthermore, apatite F/Cl ratios of Rb-rich Mus-Ab pegmatite (20)(21)(22)(23)(24)(25)(26)(27)(28)(29) are much lower than those of barren Mus-Mc-Ab pegmatite (164-169) (Figure 8f). Most apatite grains from the studied samples are euhedral, and no prominent zonation was observed (Figure 6c,d), indicating a magmatic origin.…”

Section: Mineral Geochemistrymentioning

confidence: 99%

“…In this model, pegmatite is assumed to be linked genetically with fertile granite(s) exposed at the surface or buried at depth [1,3,[5][6][7][8][9]. The other model assumes an anatectic origin (e.g., in migmatitic terranes), whereby the pegmatites form by direct partial melting of metasedimentary rocks, and have no petrogenetic relation to the neighboring granite(s) [10][11][12][13][14][15][16][17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Geochemical Contrasts between Late Triassic Rb-Rich and Barren Pegmatites from Ningshan Pegmatite District, South Qinling Orogen, China: Implications for Petrogenesis and Rare Metal Exploration

et al. 2020

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The Ningshan pegmatite district in the South Qinling Orogen hosts numerous Rb-(Be) mineralized pegmatites. In this study, whole-rock geochemistry, mineral geochemistry, and zircon U–Pb isotopes of the Rb-rich and barren pegmatites were determined. The barren pegmatites consist mainly of muscovite, microcline, albite, quartz, and garnet, whereas the Rb-rich pegmatites are mainly composed of muscovite, albite, quartz, and beryl, with minor chrysoberyl, cassiterite and columbite-group mineral. The muscovite and albite are the main Rb-bearing minerals. The U–Pb zircon dating of the Rb-rich and barren pegmatites yielding an age of 212–203 Ma, which is similar to that of the neighboring two-mica monzogranites distributed in the Ningshan area. Compared with the two-mica monzogranites, geochemical features, such as the Zr/Hf, Rb/Sr and Nb/Ta ratios and trace element contents indicated that the Rb-rich and barren pegmatites derived from fractionation of the two-mica monzogranites. In combination, the current and previous results suggest that the fractionation of the two-mica monzogranites caused the generation of the affinitive residual melts that, finally, crystallized to form the pegmatites. Compared to those from the barren pegmatites, the apatite from the Rb-rich pegmatites have higher MnO (14.51–19.12 wt.%) and Cl (0.12–0.16 wt.%) contents and lower F/Cl rartios (20–29). We conclude that these differences reflect unique geochemical signatures, and the geochemical composition of the apatite can be used as exploration guidance for rare metal-rich pegmatites.

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“…For example if no potential parental granite is exposed; the granite occur to far away from the pegmatites (Ercit, 1999;Beurlen et al, 2014;Shaw et al 2016;Müller et al, 2017b;Konzett et al, 2018); or the pegmatites are significantly older or younger than an adjacent granite (Goodenough et al, 2014;Müller et al, 2017b;Webber et al, 2019). In addition, anatexis has been proposed as a possible genetic process in areas where classical chemical zoning of the pegmatite field is lacking (Roda et al, 1999;Shaw et al, 2016;Müller et al, 2017b;Fuchsloch et al, 2018;Webber et al, 2019) or where geochemistry suggest that the granite and pegmatites have different sources (Carson et al, 1997;Maas et al, 2015;Shaw et al, 2016;Fuchsloch et al, 2018;Konzett et al, 2018). Müller et al (2015; suggest that anatexis is an important model for the pegmatite genesis in southern Norway.…”

Section: Pegmatite Genesis Modelsmentioning

confidence: 99%

A Comparison of the Mica Geochemistry of the Pegmatite Fields in Southern Norway

Rosing-Schow

Müller

Friis

2018

The Canadian Mineralogist

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Anatectic pegmatites of the Oxford County pegmatite field, Maine, USA

Cited by 42 publications

References 2 publications

Garnet as Indicator of Pegmatite Evolution: The Case Study of Pegmatites from the Oxford Pegmatite Field (Maine, USA)

Garnet as Indicator of Pegmatite Evolution: The Case Study of Pegmatites from the Oxford Pegmatite Field (Maine, USA)

Geochemical Contrasts between Late Triassic Rb-Rich and Barren Pegmatites from Ningshan Pegmatite District, South Qinling Orogen, China: Implications for Petrogenesis and Rare Metal Exploration

A Comparison of the Mica Geochemistry of the Pegmatite Fields in Southern Norway

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