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Chloritoid–hornblende assemblages in quartz–muscovite pelitic rocks of the Central Metasedimentary Belt, Grenville Province, Canada
Author(s) -
THOMPSON P.H.,
LECLAIR A.D.
Publication year - 1987
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1987.tb00393.x
Subject(s) - geology , hornblende , geochemistry , pelite , staurolite , kyanite , muscovite , petrology , metamorphic rock , quartz , biotite , paleontology
Chloritoid–hornblende occurs in quartz–muscovite pelitic schist derived from sediment in a volcaniclastic sequence of the Grenville Supergroup and from reworked sedimentary and regolithic material above the unconformity at the base of the Flinton Group. Comparison of these samples with other pelitic rocks on triangular composition diagrams and in the ACNF and ACFM tetrahedra indicates that the presence of hornblende cannot be explained by unusually high CaO content. The rare assemblage is attributed to a combination of relatively low Al 2 O 3 and high K 2 O with high CaO/(CaO+Na 2 O) and FeO/(FeO+MgO). On two qualitative reaction grids derived from AFM diagrams projected through CaO and plagioclase, respectively, the P–T stability field of chloritoid–hornblende overlaps the first appearance of staurolite–biotite in normal pelitic rocks in the kyanite field. Staurolite–hornblende overlaps chloritoid–hornblende and extends to the higher temperatures and pressures of the kyanite–hornblende field. The phase relations in these rocks provide a link between the conventional hornblende‐absent grids for pelitic rocks and those for K 2 O‐poor (muscovite‐absent) pelitic and mafic amphibolitic rocks.