Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4724818 | Precambrian Research | 2006 | 17 Pages |
Abstract
Mafic garnet granulite xenoliths recovered from â¼500 to 600Â Ma old eastern Finland kimberlites provide direct information on the petrology and physical properties of the lower cust below the Archean Karelian craton. Mineral thermobarometry, together with isotopic, petrological and seismic velocity constraints, imply that the xenolith suite is derived from a geophysically-determined, dense, high-velocity layer at the base of the crust (40-58Â km depth). Single grain zircon U-Pb dates and Nd model ages (TDM) imply that this is a hybrid layer consisting of both Archean and Proterozoic mafic granulites. Zircon ages of up to â¼3.5Â Ga and Nd TDM model ages â¼3.7Â Ga of the xenoliths are equivalent to those of the oldest upper crustal assemblages. During the Proterozoic, transient heating of these Archean granulites by voluminous basic magmatic intrusions resulted in multiple younger zircon generations within individual xenoliths. The most important post-Archean lower crust growth took place during â¼1.9Â Ga accretion of the Svecofennian arc complex to the craton margin, when underplating Proterozoic basaltic magmas became mingled with pre-existing Archean mafic granulites. Later, post-orogenic (â¼1.80-1.73Â Ga) transient heating of the lower crust occurred as a response to magmas ponded at the uppermost lithospheric mantle. In conclusion, Karelian lower crust records the geological evolution of the craton margin environment through a period of nearly 4Â billion years. Our data add a new piece to the emerging picture that emphasises the global importance of the 3.5Â Ga crustal growth episode. We suggest that it represents a major mantle-plume event - more widespread than previously recognized - when a significant fraction of Paleoarchean continental crust was formed.
Keywords
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geochemistry and Petrology
Authors
Petri Peltonen, Irmeli Mänttäri, Hannu Huhma, Martin J. Whitehouse,