Reassessment of Paleo- and Mesoproterozoic basin sediments of Arizona: implications for tectonic growth of southern Laurentia and global tectonic configurations

Abstract

Proterozoic crustal provinces that underlie much of the United States record prolonged southward growth of the North American craton (Laurentia) between ca. 1.8 and 1.0 Ga. Exposures throughout central Arizona's Tonto Basin represent multiple generations of sedimentary basins formed during Proterozoic accretion. However, complex structural geology, scattered outcrops of similar looking quartzite and shale, and under-appreciated unconformities have hindered local and regional correlations, resulting in a confusing range of locally derived names and correlation schema. For example, quartzite-slate successions of the Mazatzal and upper Alder Groups, lithologically similar, in structurally complex terrain, are sometimes misinterpreted for each other. Similarly, the Mazatzal Group and Four Peaks quartzite, separated by 45 km, appear lithologically similar but have some stratigraphic differences. Detrital zircon geochronology is now widely used for establishing minimum depositional ages and sediment provenance. Combined with other isotopic systems such as Lutetium-Hafnium, detrital zircon ages and isotopic compositions can help "fingerprint" sediment sources and provide a critical test of regional correlations. Metasedimentary rocks sampled across Tonto Basin resulted have identified remnants of a previously undated but potentially widespread Mesoproterozoic basin called the Yankee Joe Basin. Sediments of Yankee Joe Basin are particularly interesting because they have depositional age's ca. 200 m.y. younger than previously thought and because they are rich in detrital zircons with ages between 1.6-1.48 Ga, a time period not widely represented in the igneous record of Laurentia. Metasedimentary rocks with similar age and provenance are found in northern New Mexico and in the lower parts of the Belt Supergroup in northern Idaho, Montana, and Canada. Zircon ages and Hf isotopic characteristics suggest the distinctive 1.6-1.48 Ga grains might have been derived from non-Laurentian sources, most likely one or more formerly adjacent cratons such as north Australia. Circa 1.48-1.43 Ga units in the Yankee Joe Basin rest disconformably on Paleoproterozoic quartzite, and all were deformed together during northwest-directed foreland-style thrusting. This event was previously interpreted to represent the ca. 1.66-1.60 Ga Mazatzal orogeny. However, new findings challenge this view and suggest a major deformation event occurred ca. 1.47-1.45 Ga, possibly representing the Picuris orogeny as recently described in northern New Mexico. Regional thrust faulting during the Mesoproterozoic might have unroofed and removed significant portions of the Yankee Joe section, potentially shedding detritus north from the thrust front into the upper parts of the Belt-Purcell basin. These linkages between sedimentary basins and tectonic systems in southern and western Laurentia require further testing but raise the possibility of some intriguing and previously unconsidered regional relationships during the Proterozoic evolution of the continent. Detrital zircon ages and hafnium isotope compositions provide a critical test of sediment provenance and depositional age and were used to reassess sedimentary age and sources multiple Proterozoic unconformity-bound metasedimentary successions exposed across Arizona. These successions represent a series of ca. 1.75 to 1.3 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 3.3-1.8 Ga detrital zircon ages and initial epsilon Hf ([epsilon]Hf) values of +4 to -13 in both detrital grains of the Vishnu Schist and xenocrystic grains in plutons from cross-cutting plutons suggests the Vishnu Schist 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 Arizona, show a marked shift to strongly unimodal detrital zircon age distributions with initial [epsilon]Hf values ranging from +13 to -5, generally more positive and near-juvenile. Cross-cutting ca. 1.74-1.72 Ga plutons that intrude these rocks also have largely juvenile Hf isotopic signatures. The prominent ca. 1.73 Ga age peaks and relatively juvenile [epsilon]Hf values of detrital grains and plutons are consistent with first-cycle sediment derived from local arc systems formed during progressive assembly of the Yavapai province with the older Mojave province. The ca.1.66-1.63 Ga Mazatzal succession is more compositionally mature and contains broader unimodal detrital zircon age spectra, interpreted to represent increasing 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 tectonic lull in southwestern Laurentia ca. 1.6-1.5 Ga. Bimodal age spectra in this succession indicates widespread recycling of ca. 1.64 Ga Laurentian sources as well as input of significant 1.6-1.49 Ga detrital zircon representing non-Laurentian provenance. 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 Ma 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. Overall, the sedimentary successions represent relatively short-lived (10's of Ma) unconformity bounded syntectonic successions that provide a record of punctuated tectonic events within the 100's Ma accretionary history of southwestern Laurentia. In the northern Tonto Basin, detrital zircon age populations from similar looking quartzite and shale successions were used to develop new regional correlations. First, the Houdon Quartzite of the Alder Group was correlated to the Pine Creek Conglomerate. Second, the Mazatzal Group that unconformably overlies the Alder Group, was found to be deposited ca. 1631 ± 22 Ma, consistent with the White Ledges Formation and the quartzite succession at Four Peaks. Third, a new detrial zircon population collected from the upper part of the argillaceous section in the core of the Four Peaks synform yield ages between 1591-1560 Ma suggesting this section is correlative to the Yankee Joe Formation. It also requires the timing of the Mazatzal orogeny to be younger than 1560 Ma and likely associated with the estimate timing of deformation for the former Hess Canyon Group of the upper Salt River Canyon ca. 1470-1450 Ma. Fourth, recognition of deformation at 1470-1450 Ma and the subsequent regional intrusions of 1.4 Ga granites coincided with the rapid filling of the Belt-Purcell Supergroup. Detrital zircons isoplots and [epsilon]Hf data support the notion that southern Laurentia was a primary source of sediment.