Provenance of the Neoproterozoic high-grade metasedimentary rocks of the arc-related Oriental Terrane of the Ribeira belt: Implications for Gondwana amalgamation

2015 ◽  
Vol 63 ◽  
pp. 260-278 ◽  
Author(s):  
Marcela Lobato ◽  
Monica Heilbron ◽  
Bernardo Torós ◽  
Diana Ragatky ◽  
Elton Dantas
Keyword(s):  
High Grade ◽  
Metasedimentary Rocks

scholarly journals Short Note: On the age and relation between metamorphic gneisses and the Trinity Peninsula Group, Bowman Coast, Graham Land, Antarctica

2008 ◽  
Vol 20 (5) ◽  
pp. 511-512 ◽  
Author(s):  
Michael J. Flowerdew
Keyword(s):  
Short Note ◽  
Geological Mapping ◽  
High Grade ◽  
Metasedimentary Rocks ◽  
Local Geology ◽  
Relationship Of ◽  
The Relationship ◽  
The Trinity

The Trinity Peninsula Group (TPG) of northern Graham Land, a weakly metamorphosed thick sequence of predominantly quartz- and feldspar-rich greywacke, has tentatively been correlated with metasedimentary rocks exposed along the Bowman Coast of Graham Land (Stubbs 1968). The base of the TPG is not observed but the Bowman Coast rocks, here newly defined as the Bowman Coast Succession (BCS), is proximal to high-grade gneisses, which may represent the local basement. Recent geological mapping along the Bowman Coast has allowed a revision of the local geology (Fig. 1) and this note focuses on the relationship of the BCS with the adjacent gneisses.

Comparative petrology of gneissic rocks in southwestern Newfoundland

1992 ◽  
Vol 29 (12) ◽  
pp. 2663-2676 ◽  
Author(s):  
J. Victor Owen
Keyword(s):  
Confining Pressure ◽  
Metamorphic Grade ◽  
High Grade ◽  
Grade Metamorphism ◽  
Metasedimentary Rocks ◽  
Gneiss Complex ◽  
High Grade Metamorphism ◽  
Tonalitic Gneiss ◽  
Silicate Layers ◽  
Bulk Chemistry

In southwestern Newfoundland, pelitic migmatites of the Meelpaeg Subzone of the Gander Zone are separated by faults and plutons from metasedimentary rocks of the Port-aux-Basques gneiss complex (PBGC). The PBGC is a polymetamorphic sequence of amphibolite-facies, pelitic, semipelitic, and psammitic rocks (and associated metabasic dykes). Maximum metamorphic grade surpassed the first sillimanite (i.e., staurolite-consuming) isograd. Metamorphic conditions approached 650–700 °C at Pmax approximately 6.5–8.5 kbar (1 kbar = 100 MPa).The Meelpaeg gneisses also include sillimanite-grade, two-mica rocks, but they lack the Barrovian mineralogy (e.g., kyanite, staurolite, rutile) characterizing parts of the PBGC. The Meelpaeg rocks attained temperatures similar to those of the PBGC, but confining pressure was substantially lower (approx. 4 kbar), indicating uplift from relatively shallow structural levels.Both groups of paragneisses also differ in some aspects of their bulk chemistry (notably CaO/K2O ratios) and their lithologic associations. The Meelpaeg metapelites are less calcic and relatively potassic (mean CaO/K2O = 0.32) compared with their counterparts in the PBGC (mean CaO/K2O = 1.12), but both groups of rocks have similar bulk Fet/(Fet + Mg) ratios (mean XFe ≈ 0.75). In contrast with the PBGC, which contains abundant metabasites and thin coticule-like (garnet + quartz) seams, the Meelpaeg metapelites are associated with biotite + garnet "tonalitic" gneiss and, despite their relatively lime-poor composition, calc-silicate layers and pods.In terms of contrasting lithologic associations and bulk chemistry, paragneiss of the PBGC is distinct from gneissic rocks in the Meelpaeg Subzone. This underscores difficulties in relating rocks in the Port-aux-Basques area to well-established lithotectonic entities elsewhere in Newfoundland. Despite apparent differences in their protoliths and contrasts in metamorphic pressure, available U–Pb data suggest that high-grade metamorphism in both areas occurred during the middle Silurian.

THE PROVENANCE OF HIGH-GRADE METASEDIMENTARY ROCKS, FIORDLAND, NEW ZEALAND

2016 ◽  
Author(s):  
David Trinidad Quezada ◽  
◽  
Joshua J. Schwartz ◽  
Mike Cho ◽  
Harold Stowell ◽  
...  
Keyword(s):  
New Zealand ◽  
High Grade ◽  
Metasedimentary Rocks

scholarly journals High-grade metasedimentary rocks (Gilgit Formation) in the vicinity of Gilgit, Kohistan, northern Pakistan.

1997 ◽  
Vol 92 (11) ◽  
pp. 465-479 ◽  
Author(s):  
Tahseenullah KHAN ◽  
M. Qasim JAN ◽  
M. Asif KHAN ◽  
A. Bakhsh KAUSAR
Keyword(s):  
High Grade ◽  
Northern Pakistan ◽  
Metasedimentary Rocks

scholarly journals The Malene metasedimentary rocks on Rypeø, and their relationship to Amîtsoq gneisses

1983 ◽  
Vol 112 ◽  
pp. 53-69
Author(s):  
R.F Dymek ◽  
R Weed ◽  
L.P Gromet
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Field Observation ◽  
Small Island ◽  
High Grade ◽  
Vertical Crustal Movement ◽  
Metasedimentary Rocks ◽  
Near Shore ◽  
Petrographic Study ◽  
Unconformable Contact

Two groups of Malene metasedimentary rocks on Rypeø, a small island south of Godthåb, have been studied in detail in order to evaluate their origin and relationship to older, adjacent Amîtsoq gneiss. Field observation shows that the metasediments range from massive to finely layered, and include an unusual pod-rock ('pseudoconglomerate'), which probably represents a series of deformed sedimentary layers (or lenses) of contrasting competence. Petrographic study indicates that the metasediments are quartz-rich, contain abundant plagioclase and biotite, and small but variable amounts ofsillimanite, muscovite, microcline and garnet. Rare earth elements (REE) in samples of four metasedimentary lithologies are similar to some published analyses of 'tonalitic' Amîtsoq gneiss. These observations suggest that the protolith of the Malene metasediments on Rypeø was dominated by sandstone type lithologies which evolved in a near-shore tidal to fiuviatile environment. These sediments were probably derived by weathering and erosion of Amitsoq gneiss and deposited unconformably on such a gneissic basement. Petrological study indicates that the Rypeø metasediments were metamorphosed to the beginning of Muse + Qtz breakdown (Musc-Sill-Kfsp transition zone), and locally underwent minor amounts of melting. The proposed original unconformable contact relationships, coupled with high-grade polymetamorphism - not only of the supracrustal rocks but also of Amitsoq gneiss - indicates substantial vertical crustal movement, perhaps as much as 75 km since the time of formation of Amitsoq gneiss at - 3750 Ma.

Age and contact-metamorphic effects of the Overflow Pond Granite: an undeformed pluton in the Dunnage Zone of the Newfoundland Appalachians

1983 ◽  
Vol 20 (11) ◽  
pp. 1639-1645 ◽  
Author(s):  
R. D. Dallmeyer ◽  
B. F. Kean ◽  
A. L. Odom ◽  
N. R. Jayasinghe
Keyword(s):  
Pressure Solution ◽  
Lower Grade ◽  
High Grade ◽  
Metamorphic Overprint ◽  
Metasedimentary Rocks

The Overflow Pond Granite intrudes deformed sedimentary and volcanic sequences in the central part of the Dunnage Zone of the Newfoundland Appalachians. Zircon and biotite in the pluton record similar ages (U–Pb and 40Ar/39Ar, respectively), which suggest an emplacement date of ca. 390 Ma. The concordant isotopic systems require relatively rapid post-magmatic cooling and indicate intrusion at shallow crustal levels. The metasedimentary rocks show a marked increase in grade in the vicinity of the pluton. Biotite within the higher grade terrane records 40Ar/39Ar ages identical to those within the pluton and suggests that the high-grade assemblages developed in response to emplacement of the granite. Whole-rock phyllite samples from lower grade portions of the sequence display variable discordant 40Ar/39Ar release spectra. These indicate a complex tectonothermal history, including formation of a pressure solution cleavage at ca. 410 Ma (with associated folding) and a contact-metamorphic overprint by the Overflow Pond Granite.

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