Abstract The Rodinia supercontinent broke apart during the Neoproterozoic. Rodinia break-up is associated with widespread intraplate magmatism on many cratons, including the c. 720–719 Ma Franklin large igneous province (LIP) of Laurentia. Coeval magmatism has also been identified recently in Siberia and South China. This extensive magmatism terminates ∼1 myr before the onset of the Sturtian Snowball Earth. However, LIP-scale magmatism and global glaciation are probably related. U–Pb isotope dilution–thermal ionization mass spectrometry (ID-TIMS) baddeleyite dating herein identifies remnants of a new c. 724–712 Ma LIP on the eastern Kalahari Craton in southern Africa and East Antarctica: the combined Mutare–Fingeren Dyke Swarm. This dyke swarm occurs in northeastern Zimbabwe (Mutare Dyke Swarm) and western Dronning Maud Land (Fingeren Dyke Swarm). It has incompatible element-enriched mid-ocean ridge basalt-like geochemistry, suggesting an asthenospheric mantle source for the LIP. The Mutare–Fingeren LIP probably formed during rifting. This rifting would have occurred almost ∼100 myr earlier than previous estimates in eastern Kalahari. The placement of Kalahari against southeastern Laurentia in Rodinia is also questioned. Proposed alternatives, invoking linking terranes between Kalahari and southwestern Laurentia or close to northwestern Laurentia, also present challenges with no discernible resolution. Nevertheless, LIP-scale magmatism being responsible for the Sturtian Snowball Earth significantly increases.

ABSTRACT This field trip traverses a cross section of northern Sierra Nevada geology and landscape along two major corridors, Highway 49 (Yuba Pass) and Highway 70. These highways, and adjacent roadways, offer roadcuts, outcrops, and overviews through diverse pre-Cenozoic metamorphic rocks along the Laurentian margin, Mesozoic batholithic rocks, and Miocene volcanic rocks. Observing this array of rocks on a single trip provides an opportunity to examine the progression of tectonic forces in this region since the Paleozoic Era. Inspiration for this trip is a 1:100,000-scale geologic map and geophysical maps of the Portola 30′ × 60′ quadrangle that integrate decades of published and unpublished mapping with new geophysical data. The quadrangle map will seamlessly depict a geologically complex region along the boundary between the Sierra Nevada and Basin and Range provinces, dominated by transtensional tectonics of the Walker Lane. This field trip highlights many of the major units of the geologic map and will also feature new geochronological data on plutonic rocks.