Makhavinekh Lake pluton, Labrador, Canada: geological setting, subdivisions, mode of emplacement, and a comparison with Finnish rapakivi granites

Abstract

Abstract Makhavinekh Lake pluton is an oval Elsonian (∼1322 Ma) granitic intrusion within the Nain Plutonic Suite of central coastal Labrador. The pluton comprises at least five textural/mineralogical subdivisions dominated by quartz monzonite and granite and it is surrounded by a well-defined pyroxene hornfels thermal aureole. Fayalite and clinopyroxene are common constituents of the eastern half of the Makhavinckh Lake pluton; hornblende is present throughout the whole pluton and is the dominant mafic mineral in the western half of the intrusion. The hornblende-rich parts of the intrusion appear to be a consequence of late- to post-emplacement hydration of originally olivine-bearing rocks. Textural, mineralogical and geochemical features are similar to the rapakivi granites of Finland. The Makhavinekh Lake pluton has the morphology of a sheath, separating an external gneissic country-rock complex from an internal basic plutonic suite. It is proposed that the Makhavinekh Lake pluton developed through cumulate processes and was emplaced as a hot, dry, crystal-charged mush via a mechanism of cauldron subsidence. Block faulting that allowed ascent of the pluton, may have been related to crustal bulging from an underlying mafic magma pond.