Semi-pelitic rocks ranging in grade from the prehnite–pumpellyite to the greenschist facies from southeastern Otago, New Zealand, have been investigated in order to evaluate the reactions leading to formation and breakdown of stilpnomelane. Detrital grains of mica and chlorite along with fine-grained authigenic illite and chlorite occur in lower-grade rocks with compactional fabric parallel to ...

Seven eclogite facies samples from lithologically different units which structurally underlie the Semail ophiolite were dated by the Ar/Ar and Rb–Sr methods. Despite extensive efforts, phengite dated by the Ar/Ar method yielded saddle, hump or irregularly shaped spectra with uninterpretable isochrons. The total gas ages for the phengite ranged from 136 to 85 Ma. Clinopyroxene–phengite, epidote–...

An eclogite and its surrounding gneiss from the Malpica-Tuy zone, northwestern Spain, were studied. The eclogite contains besides garnet and omphacite, barroisitic amphibole, quartz, phengite with Si contents between 3.27 and 3.45 per formula unit (pfu), rutile, and accessory phases such as talc and (clino)zoisite-epidote. Garnet exhibits a chemical zonation with Alm59Prp13Grs24Sps4, Alm57Prp13...

A geochemical modeling of gold deposition was performed using the EQ3/EQ6 software package using conditions inferred from geological, petrographic, geochemical and fluid inclusion data from the Bloco do Butiá gold mine, Lavras do Sul, RS. Gold in the mine occurs only in the pyrite structure (invisible gold). The pyrite occurs associated with white mica (phengite) in the zone of phyllic alterati...

for the first time, an unusual assemblage of talc-phengite-chlorite-k-feldspar was found in quartz schists from the sanandaj-sirjan zone in the nahavand area in western iran. the talc-bearing quartz schists occur as small bodies or lenses within pelitic schist layers and contain talc, phengite, chlorite, k-feldspar and quartz as major mineral constituents with subordinate amounts of calcite ...

An exotic block of garnet-bearing schist has been found at the boundary between Early Triassic Takinosawa Unit Nedamo Belt and Jurassic Nakatsugawa Complex North Kitakami Belt, NE Japan. This is only second discovery schists in Belt; previously identified occur early Carboniferous Tsunatori units Belt. The characterized by a mineral assemblage garnet + phengite epidote albite quartz titanite. P...

Understanding the Earth’s geological nitrogen (N) cycle requires an understanding of how N behaves during dehydration subducted crust. We present first in situ measurements silicate minerals by secondary ion mass spectrometry, focusing on high pressure rocks representing oceanic investigate distribution between mineral phases, and combine analyses with other trace major elements order to constr...

The eclogite facies assemblage K-feldspar–jadeite–quartz in metagranites and metapelites from the SesiaLanzo Zone (Western Alps, Italy) records the equilibration pressure by dilution of the reaction jadeite+quartz=albite. The metapelites show partial transformation from a pre-Alpine assemblage of garnet (Alm63Prp26Grs10)–K-feldspar–plagioclase–biotite±sillimanite to the Eo-Alpine high-pressure ...