Feldspar thermometry in pegmatites: truth and consequences

London, David; Hunt, Lindsey; Schwing, Christine R.; Guttery, Brandon M.

doi:10.1007/s00410-019-1617-z

Cited by 23 publications

(18 citation statements)

References 48 publications

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“…Low temperature of crystallization, below 400°C, is suggested by the values obtained by coexisting albite and nonperthitic microcline in one of the Santa Elena samples. This temperature is lower than the hydrous minimum melt temperatures of about 600°C suggested for pegmatites by Jahns and Burnham (1969), but agrees with several more recent estimations on Li-bearing, fluid-rich pegmatites based on mineral geothermometry and fluid inclusion data (Nabelek et al 1992;Tindle and Breaks 2000;Sirbescu and Nabelek 2003;Simmons and Webber 2008;London et al 2020). The abundance of Li, Cs, B, P and F (as in the case of Santa Elena and Tres Tetas pegmatites) has been experimentally demonstrated to depress, to a significant extent, the liquidus and solidus of hydrous haplogranite systems (Černý, 1991a;London, 1992).…”

Section: Insights Into Petrogenesis Of Santa Elena and Tres Tetas Pegmatitessupporting

confidence: 90%

“…Moreover, crystallization temperatures of 350-400°C, at 2-3 kbar, are also suggested by , based on the stability of Li-bearing mica and spodumene in the Santa Elena pegmatites. These low temperatures, below 400°C, may correspond to the conditions of crystallization following undercooling to about 250°C below the liquidus, as found for similar thin pegmatite dykes by London et al (2020). Henry and Guidotti (1985) for discrimination of the different tourmaline-bearing rock types.…”

Section: Insights Into Petrogenesis Of Santa Elena and Tres Tetas Pegmatitessupporting

confidence: 62%

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Rare element minerals’ assemblage in El Quemado pegmatites (Argentina): insights for pegmatite melt evolution from gahnite, columbite-group minerals and tourmaline chemistry and implications for minerogenesis

et al. 2021

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The pegmatite district of El Quemado (NW Pampean Ranges, NW Argentina) hosts several Ordovician pegmatite bodies of the LCT (Li, Cs, Ta) type. We present paragenetic assemblages for a set of samples from two of the El Quemado pegmatite groups, Santa Elena and Tres Tetas, and mineral chemistry analyses for gahnite, columbite-group minerals, tourmaline, micas, albite, microcline, and discuss the relation between their major element composition and the degree of evolution of pegmatite melts. The chemical composition of rare element minerals allows recognizing an evolutive trend reaching highly differentiated compositions, with complex paragenetic assemblages including Li-, Zr-, U-, Zn-, P-, Mn- and Ta-bearing minerals. The temperature of crystallization during the magmatic phase was below 400 °C. Non-pervasive hydrothermal alteration, testified by a moderate presence of phyllosilicates, affected the pegmatite bodies. Chlorite geothermometry indicates that the circulation of post-magmatic hydrothermal fluids occurred at a temperature ranging between 200 °C and 250 °C. The mineralogical features recognized in the El Quemado pegmatite rocks have implications for the metallogenesis of the region, suggesting that the pegmatites potentially contributed to the genesis of Ta-Nb oxide placer mineralizations.

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Section: Insights Into Petrogenesis Of Santa Elena and Tres Tetas Pegmatitessupporting

confidence: 90%

Section: Insights Into Petrogenesis Of Santa Elena and Tres Tetas Pegmatitessupporting

confidence: 62%

Rare element minerals’ assemblage in El Quemado pegmatites (Argentina): insights for pegmatite melt evolution from gahnite, columbite-group minerals and tourmaline chemistry and implications for minerogenesis

et al. 2021

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“…In this latter respect, precise pressure condition estimates are not available for the Peloritani Mountains granitoids, also due to the lack of suitable mineral assemblages but, according to [47] and [65], the~310 Ma trondhjemite magmas intruded the migmatite host rocks after leucosome solidification and migmatite equilibration at~0.5 GPa (i.e.,~14 km) (e.g., [69,70]). On the other hand, final crystallization of the~300 Ma granites is likely to have occurred at upper crustal levels, at a pressure of~0.3 GPa (i.e.,~8 km), as suggested by the occurrence of local granophyric and graphic textures, which are typically associated to crystallization under strong undercooling conditions (e.g., [132,133]). Low-pressure crystallization of the granitic magmas is also supported by the occasional presence of magmatic andalusite in the studied low-Ca granitoid rocks.…”

Section: Supra-to Sub-solidus Deformation In Granitoids Cooling At MImentioning

confidence: 99%

Submagmatic to Solid-State Deformation Microstructures Recorded in Cooling Granitoids during Exhumation of Late-Variscan Crust in North-Eastern Sicily

Fazio¹,

Fiannacca²,

Russo³

et al. 2020

Geosciences

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Late-Variscan granitoid rocks of trondhjemitic and granitic composition, intruded in migmatitic paragneisses in the north-eastern Peloritani Mountains (southern Italy) at ~310 Ma and ~300 Ma, respectively, exhibit a range of deformation microstructures developed under a shear regime at decreasing temperatures. Non-coaxial deformation is documented by sigmoidal feldspar porphyroclasts, mica fish, and asymmetric boudins affecting tiny andalusite crystals. Late-Variscan shearing during granitoid cooling is constrained by largely represented chessboard patterns in quartz and, especially, submagmatic fractures in plagioclase, indicating deformation at high-temperature conditions (T > 650 °C), in the presence of melt. Submagmatic deformation was extensively superseded by deformation at lower temperatures. Examples of solid state-high temperature deformation-related microstructures (T > 450 °C) include feldspar bulging, quartz grain boundary migration, and subgrain rotation recrystallization. Finally, low temperature subsolidus microstructures (T < 450 °C) consist of quartz bulging, mica kinks, and feldspar twinning and bending. A complete sequence of deformation, operating from submagmatic to low-temperature subsolidus conditions is recorded in both the older and younger granitoids, suggesting a duration of ~20 Ma for shear zone activity during post-collisional exhumation of the Variscan middle crust in southernmost Italy.

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“…Genetic relation between granitic pegmatites and granites, i.e. a search for the source of particular pegmatite body in some neighboring granite pluton, is the topic of a long-term debate (London 2008). Despite intense search, localities enabling to study the direct transition from granite pluton to rare-element pegmatite dykes are scarce.…”

Section: Case Study 4 -Estimation Of Mineralmentioning

confidence: 99%

Automated mineralogy and petrology - applications of TESCAN Integrated Mineral Analyzer (TIMA)

Hrstka¹,

Gottlieb²,

Skála³

et al. 2018

Jour. Geosci.

166

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The collection of representative modal mineralogy data as well as textural and chemical information on statistically significant samples is becoming essential in many areas of Earth and material sciences. Automated Scanning Electron Microscopy (ASEM) systems provide an ideal solution for such tasks. This paper presents the methods and techniques used in the recently developed TESCAN Integrated Mineral Analyzer (TIMA-X) with Version 1.5 TIMA software. The benefits from the use of a fully integrated quantitative energy-dispersive X-ray spectrometry (EDS) and an advanced statistical approach to ASEM systems are demonstrated. Typically, the system can handle more than 500,000 X-ray events per second. Using a common spectral total of 1000 events this represents the acquisition of 500 spectra per second. A number of measurement modes is available to make the most effective use of these spectra depending on the application. For a back-scattered electrons (BSE) map combined with EDS data with spatial resolution of 10 µm, this represents the high-resolution measurement of c. 1 cm 2 of a thin section or a polished rock surface in 30 minutes. A patented X-ray spectrum clustering algorithm that lowers the chemical detection limit is described and an example of its use is shown. The modal and textural (liberation, association, size etc.) data produced are statistically robust and provide information across a broad range of Earth and material sciences. A comparison with some other available instruments is also provided together with a number of case studies.

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Feldspar thermometry in pegmatites: truth and consequences

Cited by 23 publications

References 48 publications

Rare element minerals’ assemblage in El Quemado pegmatites (Argentina): insights for pegmatite melt evolution from gahnite, columbite-group minerals and tourmaline chemistry and implications for minerogenesis

Rare element minerals’ assemblage in El Quemado pegmatites (Argentina): insights for pegmatite melt evolution from gahnite, columbite-group minerals and tourmaline chemistry and implications for minerogenesis

Submagmatic to Solid-State Deformation Microstructures Recorded in Cooling Granitoids during Exhumation of Late-Variscan Crust in North-Eastern Sicily

Automated mineralogy and petrology - applications of TESCAN Integrated Mineral Analyzer (TIMA)

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