Paper No. 5
Presentation Time: 2:00 PM
DETRITAL ZIRCON CHARACTERISTICS OF UNCONFORMITY-BOUND PROTEROZOIC METASEDIMENTARY SUCCESSIONS IN CENTRAL ARIZONA: RELATIVELY SHORT-LIVED SYNTECTONIC BASINS AS KEY ELEMENTS IN THE PROTEROZOIC TECTONIC EVOLUTION OF SOUTHWESTERN LAURENTIA
Detrital zircon ages and hafnium isotope compositions provide a critical test of sediment provenance and depositional age in multiple Proterozoic unconformity-bound metasedimentary successions exposed across Arizona. These successions represent a series of ca. 1.75 to 1.1 Ga basins that span the Proterozoic accretionary provinces of southwestern Laurentia, representing key elements in the tectonic evolution of the continental margin. The ca. 1.75 Ga Vishnu Schist contains a bimodal detrital zircon age distribution with prominent Archean (2.5 Ga) and Early Paleoproterozoic (1.8 Ga) populations and minor juvenile 1.75 Ga input. The predominance of 1.8-3.3 Ga detrital zircon ages and εHf model ages in both detrital grains of the Vishnu Schist and xenocrystic grains in plutons that intrude the Vishnu Schist confirms that the succession was derived primarily from recycling of the Mojave and other older basement provinces, possibly including one or more outboard cratons. In contrast, the ca. 1.74–1.72 Ga Jerome and ca. 1.72 Ga Alder successions of central AZ show a marked shift to strongly unimodal detrital zircon age distributions; εHf model ages of basin detritus are ca. 1.84 Ga, and plutons that intrude these rocks also have juvenile εHf model ages (1.74 - 1.72 Ga). The prominent ca. 1.73 Ga age peaks and near-juvenile εHf model ages of detrital grains and plutons indicate first-cycle input from arc systems formed during progressive assembly of the Yavapai province. The ca.1.66–1.63 Ga Mazatzal succession is compositionally mature and contains broader unimodal detrital zircon age spectra, signifying increased regional crustal recycling following the culmination of the Yavapai orogeny. The ca.1.48–1.36 Ga Yankee Joe succession reflects renewed deposition following a ca. 100 Ma (1.6-1.5 Ga) tectonic lull. Bimodal age spectra represent recycling of ca. 1.64 Ga Laurentian sources as well as arrival of grains from non-Laurentian 1.60–1.49 Ga sources. Tilting and layer-parallel shearing in this basin occurred between 1.48 and 1.44 Ga and marks the early stages of regional 1.45-1.35 Ga tectonism. A regional angular unconformity developed before deposition of the 1.33 Ga lower Apache Group marks unroofing of southern Laurentia following uplift associated with 1.45-1.35 Ga orogenesis.