Linking the Pinware, Baraboo, and Picuris orogens: Recognition of a trans-Laurentian ca. 1520–1340 Ma orogenic belt

Abstract

It is proposed that the Pinware orogen of eastern Canada, the Baraboo orogen of the midcontinent, and the Picuris orogen of the southwestern United States delineate a previously unrecognized, ~5000-km-long, ca. 1520–1340 Ma trans-Laurentian orogenic belt. All three orogenic provinces are characterized by Mesoproterozoic sedimentation, magmatism, metamorphism, and deformation—the hallmarks of a tectonically active plate margin. Tectonism was diachronous, with the earliest stages beginning ca. 1520 Ma in eastern Canada and ca. 1500 Ma in the southwest United States. Magmatic zircon age distributions are dominated by Mesoproterozoic, unimodal to multimodal age peaks between ca. 1500 and 1340 Ma. The onset of magmatism in the Pinware and Baraboo orogens was ca. 1520 Ma, and onset for the Picuris orogen was ca. 1485 Ma. Detrital zircon age distributions within each orogenic province yield maximum depositional ages between ca. 1570 and 1450 Ma. Minimum depositional ages generally fall between ca. 1500 and 1435 Ma, as constrained by crosscutting intrusions, metatuff layers, or the age of subsequent metamorphism. Metamorphic mineral growth ages from zircon, garnet, and monazite yield peak ages between ca. 1500 and 1350 Ma and tend to be older in the Pinware and Baraboo orogens than in the Picuris orogen. The 40Ar/39Ar cooling ages for hornblende, muscovite, and biotite yield significant peak ages between ca. 1500 and 1350 Ma in the Baraboo and Picuris orogens. We propose that the Pinware-Baraboo-Picuris orogen formed in a complex, diachronous, convergent margin setting along the southern edge of Laurentia from ca. 1520 to 1340 Ma.

Recently Identified Mesoproterozoic Strata in South‐Central Idaho Document Late‐Stage Rifting of the Nuna Supercontinent in Western Laurentia

“…Alternatively, the Goat Mountain sandstone could be correlated with the lower Jahnke Lake member of the Apple Creek Formation, and the ∼1,381 Ma age would be expected given our ∼1,400–1,380 results for the underlying Bonner and McNamara Formations. In either case, this DZ signature and inferred depositional age suggest that the youngest ∼1,440 age mode was derived from a source that was not syndepositional (Figure 5; Daniel, Aronoff, et al., 2023; Daniel, Indares, et al., 2023).…”

“…Dominant sediment sources for the Belt Supergroup are generally interpreted to be 1,900–1,600 Ma southwestern Laurentian Paleoproterozoic orogenic belts such as the Yavapai‐Mazatzal and Mojave terranes (Figure 4; e.g; Link et al., 2007, 2016; Stewart et al., 2010). Additionally, recently identified Mesoproterozoic Picuris orogenesis in the southwestern US likely contributed ∼1,435 Ma age zircon along similar sediment routing pathways to those exploited by Paleoproterozoic sources after reorganization of the drainage network (Figures 4 and 5; Daniel, Aronoff, et al., 2023; Daniel, Indares, et al., 2023; Hirtz et al., 2023; Jones et al., 2015). Grains between 1,610 and 1,490 Ma are within the hypothesized North American Magmatic Gap, and are attributed to western non‐Laurentian sources during the proto‐SWEAT (Southwestern United States and East Antarctica) configuration of Nuna (e.g., Brennan et al., 2021; Ross & Villenueve, 2003; Figures 1 and 4).…”

“…Age modes at 1,435–1,450 Ma are commonly interpreted to represent zircon formed during syndepositional magmatism (e.g., Link et al., 2016), but their provenance is uncertain. Recent work in southwestern North America (Daniel, Aronoff, et al., 2023; Daniel, Indares, et al., 2023; Doe & Daniel, 2019; Doe et al., 2013) suggests that magmatism associated with Picuris orogenesis occurred at 1,425–1,435 Ma (Figure 5). This is similar to the younger age mode in most Missoula Group samples, and thus we suggest that these grains were also derived from southwestern Laurentia and likely traveled by the same pathway as Yavapai‐Mazatzal attributed grains after reorganization of continental drainage networks at 1,430–1,410 Ma (Hirtz et al., 2023).…”

“…(2023) and Daniel, Indares, et al. (2023), with a weighted mean of the youngest mode shown below the distribution, calculated in IsoplotR. DZ age modes beyond the blue box are younger than the ∼1,435 Ma Picuris orogenic belt age mode and may have been derived from regions that are not within the southwestern Laurentian sources interpreted to have sourced many of the older age components.…”

“… Map of the outline of Belt basin outcrops (modified from Lonn et al., 2020; outcrop outline from Burmester et al., 2016) with detrital zircon age distributions for the most prevalent sources (from Brennan et al., 2021; Daniel, Aronoff, et al., 2023; Daniel, Indares, et al., 2023) and their generalized paleoflow directions shown by boxes and arrows. The 87 Sr/ 86 Sr = 0.706 isopleth is interpreted to represent the pre‐Phanerozoic boundary of North America.…”