Pink manganian phengite in a high P/T meta-conglomerate from northern Syros (Cyclades, Greece)

• Verfasst von: Altherr, Rainer [VerfasserIn]
• Verfasst von: Soder, Christian [VerfasserIn]
• Verfasst von: Panienka, Sandra [VerfasserIn]
• Verfasst von: Peters, Daniel [VerfasserIn]
• Verfasst von: Meyer, Hans-Peter [VerfasserIn]
• Titel: Pink manganian phengite in a high P/T meta-conglomerate from northern Syros (Cyclades, Greece)
• Verf.angabe: Rainer Altherr, Christian Soder, Sandra Panienka, Daniel Peters, Hans-Peter Meyer
• E-Jahr: 2013
• Jahr: 31 July 2013
• Umfang: 12 S.
• Fussnoten: Gesehen am 12.05.2021
• Titel Quelle: Enthalten in: Contributions to mineralogy and petrology
• Ort Quelle: Berlin : Springer, 1947
• Jahr Quelle: 2013
• Band/Heft Quelle: 166(2013), 5, Seite 1323-1334
• ISSN Quelle: 1432-0967
• DOI: doi:10.1007/s00410-013-0929-7
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1757754210

Abstract

A new occurrence of Mn-rich rocks was discovered within the high-pressure/low-temperature metamorphic rocks on the Palos peninsula of Syros (Greece). Near the summit of Mount Príonas, a meta-conglomerate consists of calcite (~63 wt%), pink manganian phengite, blue-purple manganian aegirine-jadeite, microcline, albite and quartz. In addition, it contains abundant braunite-rich aggregates (up to ~1.5 cm in diameter) that include hollandite [(Ba0.98-1.02K<0.01Na<0.02Ca<0.03) (Mn1.02-1.523+Fe0.38-0.883+Ti0.29-0.92Mn5.11-5.764+)O16], barite and manganian hematite. Due to metamorphic recrystallization and deformation, the contacts between clasts and matrix are blurred and most clasts have lost their identity. In back-scattered electron images, many aegirine-jadeite grains appear patchy and show variable jadeite contents (Jd10-67). These pyroxenes occur in contact with either quartz or albite. Manganian phengite (3.41-3.49 Si per 11 oxygen anions) is of the 3T type and contains 1.4-2.2 wt% of Mn2O3. At the known P-T conditions of high-pressure metamorphism on Syros (~1.4 GPa/ 470 °C), the mineral sub-assemblage braunite + quartz + calcite (former aragonite) suggests high oxygen fugacities relative to the HM buffer (+7 ≤ ∆fO2 ≤ + 17) and relatively high CO2 fugacities. The exact origin of the conglomerate is not known, but it is assumed that the Fe-Mn-rich and the calcite-rich particles originated from different sources. Braunite has rather low contents of Cu (~0.19 wt%) and the concentrations of Co, Ni and Zn are less than 0.09 wt%. Hollandite shows even lower concentrations of these elements. Furthermore, the bulk-rock compositions of two samples are characterized by low contents of Cu, Co and Ni, suggesting a hydrothermal origin of the manganese ore. Most likely, these Fe-Mn-Si oxyhydroxide deposits consisted of ferrihydrite, todorokite, birnessite, amorphous silica (opal-A) and nontronite. Al/(Al + Fe + Mn) ratios of 0.355 and 0.600 suggest the presence of an aluminosilicate detrital component.