USING LU-HF ISOTOPES IN ZIRCONS FROM PALEOPROTEROZOIC BASEMENT OF UTAH: NEW CONSTRAINTS ON THE TECTONO-MAGMATIC EVOLUTION OF THE FARMINGTON CANYON AND SANTAQUIN METAMORPHIC COMPLEXES

The Precambrian basement of Utah provides an ideal opportunity to interpreting crust formation, tectonic setting, and deformational histories of western Laurentia. Two of these metamorphic complexes are found in the footwall of the Wasatch Fault: the Santaquin Complex and Farmington Canyon Complex.

The Santaquin Complex is thought to represent a Paleoproterozoic volcanic arc where plutonism, metamorphism, and accretion to Laurentia took place between 1.7-1.67 Ga. Data from the Santaquin Complex suggest a volcanic arc origin.

The two prominent hypotheses presented for the Farmington Canyon Complex either interpret it to be a sequence of passive margin sediments shed from the Wyoming Craton or an accretionary melange complex formed during arc volcanism in the Wyoming Craton. Recent studies support a Paleoproterozoic depositional age and a prominent 1.7 Ga amphibolite grade metamorphic event. The provenance of the Farmington Canyon Complex has been assumed to be the Wyoming Craton, however currently no detrital zircon spectra exist to substantiate this hypothesis.

To further characterize the relationship between these two Proterozoic basement complexes, we will report U-Pb and Lu-Hf analyses for detrital zircons and magmatic zircons from various units in these metamorphic bodies.

U-Pb dating of detrital zircons has proven to be a powerful tool in identifying depositional provenance and differentiating between various lithologic units in complex tectonic settings. U-Pb ages coupled with Lu-Hf isotopes in zircon provides a method wherein the addition of juvenile material to the crust can be assessed. Furthermore, because the formation of juvenile crust predominately occurs in volcanic arcs, Lu-Hf isotopes can be used as a tool for tectonic discrimination with detrital sediments.

Applying these methods to the Farmington Canyon and Santaquin Metamorphic Complexes will aid in testing these petrogenetic models and aid in identifying the presence of Paleoproterozoic juvenile material from which these rocks were derived.