Timing and origin of midcontinent rift alkaline magmatism, North America: evidence from the Coldwell Complex

Article Abstract:

Five samples from the Coldwell Complex, the largest midcontinent associated alkaline intrusion, were analyzed using uranium-lead and zircon/baddeleyite dating. Results indicate that the intrusion infiltrated a cold Archean crust at around 1108 Ma and probably underwent rapid quenching. Isotopic composition of minerals from different phases of the complex display variation which may have been brought about by magmas of different composition. However, rocks from similar phases in the complex exhibit uniform composition indicative of a principal, well mixed plume in the mantle.

History, Intrusions (Geology)

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Volatiles associated with the alkaline-carbonatite magmatism at Alno, Sweden: a study of fluid and solid inclusions in minerals from the Langarsholmen ring complex

Article Abstract:

A ring-type intrusion at Langarsholmen in Sweden that is part of the Alno alkaline-carbonatite complex appears to have a somewhat different magmatic history than the main intrusion as evidenced by petrological, geochemcial and fluid/solid inclusion studies. The Langarsholmen rocks are composed of ijolite, sovite and pyroxenite, from youngest to oldest. Details of the geochemical evolution of the rocks and their emplacement from the magmas are given.

Usage, Sweden, Observations, Carbonatites, Analytic geochemistry

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Proterozoic zircon growth in Archean lower crustal xenoliths, southern superior craton - a consequence of Matachewan ocean opening

Article Abstract:

The U-Pb zircon ages for four granulite-facies xenoliths discovered from a Jurassic kimberlite pipe in the south-central Superior craton of the Canadian Shield are studied. Results show that granulite facies anorthositic to mafic xenoliths in a Jurassoc kimberlite pipe have Neoarchean protolith ages. Xenoliths also witnessed Paleoproterozoic metamorphic activity marked by zircon growth at 2416 +/- 30 Ma and 2497 +/- 25 Ma.

Geology, Stratigraphic, Stratigraphy, Rocks, Igneous, Zircon, Facies (Geology), Geologic facies, Xenoliths, Canadian Shield

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