| Title | Late Paleozoic igneous rocks at Clarke Head, Nova Scotia: magmatism at an arc to back-arc transition |
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| Author | Pe-Piper, G ;
Piper, D J W |
| Source | Geological Society, Special Publication vol. 542, 2023 p. 1-20, https://doi.org/10.1144/sp542-2022-351  Open Access |
| Image |  |
| Year | 2023 |
| Alt Series | Natural Resources Canada, Contribution Series 20220446 |
| Publisher | Geological Society of London |
| Document | serial |
| Lang. | English |
| Media | paper; digital; on-line |
| File format | pdf; html |
| Province | Nova Scotia |
| NTS | 21H/01; 21H/08 |
| Area | Clarke Head |
| Lat/Long WENS | -64.4858 -64.0344 45.4283 45.2481 |
| Subjects | Science and Technology; mineralogy; general geology; magmatism; Meguma-Avalon; Paleozoic |
| Illustrations | location maps; photographs |
| Program | GSC Atlantic Division |
| Released | 2023 07 24 |
| Abstract | This study re-examines a reported mylonitic 'metabasic granulite' block in a megabreccia that is the most outboard igneous rock outcrop in the Avalon terrane, near the Meguma-Avalon terrane boundary in
the northern Appalachians. The block of foliated gabbro is one of several igneous rock blocks in a largely dissolved salt wall and in style of deformation, mineralogy, lithogeochemistry and Sm/Nd isotopes resembles foliated and locally mylonitized
late Devonian-early Carboniferous gabbro plutons along the Cobequid Shear Zone to the north. Garnet porphyroclasts in the foliated gabbro are exceptional, with a distinctive composition of Alm55 Pyr25 Grs13 And4 Sps3. Inclusions of pyroxene, andesine
and ilmenite, lack of zoning and corroded rims suggest the garnets are antecrysts. Elsewhere in the world, garnets of similar composition in arc-related andesites are interpreted to be from disintegration of comagmatic cumulate material at 0.8-1.0
GPa under hydrous conditions. The Clarke Head foliated gabbro has two mafic components, one resembling arc-related hydrous magma and the other with tholeiitic back-arc character, similar to coeval rocks in the Cobequid Highlands. The gabbro is a
product of complex mixing in crustal magma chambers and rapid rise of magma containing lower crustal antecrysts along strike-slip faults. |
| Summary | (Plain Language Summary, not published)
A rock containing the mineral garnet was previously interpreted as having formed at a depth of 25 km. We demonstrate that the garnet is of the type found
in some volcanoes and has no such depth significance. It does, however, tell us important things about the location of the boundary between the Avalon and Meguma terranes of the Appalachians. |
| GEOSCAN ID | 331253 |
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