Seminar

Integration of zircon isotopes and trace elements records with U-Pb geochronology makes zircon a key petrochronometer to evaluate temporal shifts in magma composition and evolution of magma reservoirs. Nevertheless, significant debates remain on the role of internal (e.g., shortening, crustal thickness, delamination), or external factors (e.g., plate motions, slab dynamics, mantle flow) on the evolution of magmas, particularly in subduction zones where complex interactions may affect geochemistry. The central Patagonia (45°S – 48°S) is an excellent location to test the impact of external and internal factors on the changes of magma. Indeed, extensive continental arc magmatism is recorded in this area since the Late Triassic, and arc migration through time indicates alternating phases of slab dip with a duration of <50 Myrs. Furthermore, no change of crustal thickness has been observed until the Miocene. Thus, U-Pb geochronology, trace elements and Hf-O isotope analyses on detrital zircon from central Patagonia were used as fingerprint for monitoring the impact of slab dip variations on magma changes. Long-lasting trends (~70 Myrs) obtained show that the importance of internal and external factors on the magma reservoirs is dependent of crustal thickness, with a dominance of internal factors in a thick crust and of external factors in a thin crust.

Additional information: Dr. Marie C. GENGE, mcgenge@hku.hk