Paper No. 9
Presentation Time: 3:25 PM
RATES OF MAGMA EVOLUTION IN THREE DIFFERENT GRANITIC COMPLEXES: AN INSIDE INTO THE PETROLOGY OF GRANITE PLUTON CONSTRUCTION AND THERMAL EVOLUTION OF UPPER CRUSTAL MAGMAS
Concordant U–Pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth. Advances in zircon TIMS analysis along with enriched knowledge of the evolution of magmatic systems, allows a new approach to reevaluate and explore such processes like rates associated to the petrology of granitic plutons. This study is aimed to demonstrate an exploration of these possibilities by presenting new state of the art data on three granite complexes namely the St. Francois Mountain granite pluton (Precambrian), the Galway granite (Cambrian), and the Sithonia Plutonic Complex (Eocene). All listed plutons have similar size and range in composition, from quartz diorites through granodiorites and granites to alkali granite and show multiple intrusive episodes. Thermobarometric calculations point to upper crustal emplacement of the granites. Geochemical, isotopic and petrological data indicates different individual pulses from each pluton are able to be linked through their liquid line of decent and explained by fractional crystallization of predominantly plagioclase, K-feldspar, biotite, hornblende and some minor accessory mineral phases, magma mingling and mixing as well as crustal contamination. To obtain the temporal relationship we carried out High-precision CA-TIMS zircon geochronology on selected samples along the liquid line of decent. These data indicate a wide range of rates: Different pulses evolved on timescales of 10-30ka, but the construction time of the different complexes ranges from millions of years with prolonged tectonically inactive phases to very short lived of about ~300 ka. These obtained timeframes of the magmatic differentiation and of episodes of crystallization allows us to understand much better the constraints on the dynamics of the magmatic plumbing system and incorporate tested rates of crystallization into thermal models.