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Wstępne wyniki badań petrograficznych archaicznych gnejsów Uivak (Prowincja Nain, Labrador)

Sałacińska A., Kusiak M. A.

Przegląd Geologiczny

2017

Vol. 65, nr 6

383--391

The Saglek Block of the Nain Complex in Northern Labrador forms the westernmost part of the North Atlantic Craton. It is one of the few regions on Earth where early Archaean crust is preserved. It consists of regionally metamorphosed gneisses to either granulite-facies from 2.74 to 2.71 Ga or amphibolite-facies at ca. 2.70 Ga. The Saglek Block is dominated by two suites of metaigneous gneisses: the Uivak I TTG suite (>3.6 Ga) and the Uivak II augen gneisses (ca. 3.4 Ga). Four samples offelsic Uivak I orthogneiss were selected to petrographi- cal and mineralogical studies: Johannes Point Cove (L1419), TigigakyukInlet (L1434; L1440) and Big Island (L1443). Sample composition (granodiorite-tonalite) and mineralogy (mostly plagioclase and quartz, with minor K-feldspar and biotite, and accessory zircon and apatite) for three of the four samples are consistent with published data of the Uivak I gneiss. Sample L1434 contains ferroean diopside and hornblende, which are absent in the other samples. Based on detailed mineralogical analyses, authors concluded that more mafic sample, can not belong to the suite of the Uivak I gneisses. Most probably it represents the younger Uivak II. Further, geochronological study is going to be conducted to characterise both, Uivak I and Uivak II gneisses isotopically.

W poszukiwaniu fragmentów najstarszej skorupy kontynentalnej na Labradorze

Kusiak M. A., Sałacińska A.

Przegląd Geologiczny

2016

Vol. 64, nr 11

896--901

There are few unresolved questions in the Earth Sciences which generate as much debate as the nature of the Hadean Earth: i.e. the rock record between the Earth’s formation and about 3.8 billion years ago. Current knowledge of the nature and origin of the earliest crust comes largely from studies of the mineral zircon (ZrSiO4). The oldest zircon grains on Earth (4.46 Ga) are found in Jack Hills, Australia. They represent a time capsule of what the Earth was like from ca. 4.4-4.0 Ga during the Hadean. The other ancien rocks (>3.8 Ga) are preserved in Antarctica, Canada, China, Greenland, Labrador, Western Australia and Swaziland, with the oldest known rochi on Earth from the Acasta gneiss in Northern Canada, dated at 4.03 Ga. Most likely, the second oldest rock record in the world (>3.9 Ga) may be derivedfrom the Nanok gneiss in the Nain Complex of the Saglek-Hebron area in the northern part of the Labrador Peninsula. Extensive investigation of these rocks will allowfurther characterizing the nature of the earliest preserved crust.