Cenozoic Soldiers Pass Volcanic Field, Central Utah—implications for the Transition to Extension-related Magmatism in the Basin and Range Province

The Basin and Range Province of the western United States is one of Earth’s most studied regions of continental rifting, and yet the timing and character of the onset of Cenozoic extension are still controversial. Some structural studies have concluded that extension in the Great Basin part of the Basin and Range Province is as old as 41–37 Ma (Rahl and others, 2002) or 32–30 Ma (e.g., Axen and others, 1993). Others have concluded that significant extension on large, high-angle normal faults started much later. For example, Parry and Bruhn (1986) concluded that the Wasatch fault has been active since about 17–18 Ma. The onset of lithospheric extension has both structural and magmatic aspects. Some aspects of the structural transition and many aspects of the magmatic transition (from subduction related to extension related volcanism) are recorded in the southern part of the Lake Mountains of western Utah, which lie near the eastern border of the Great Basin (figure 1). In the Soldiers Pass volcanic field, a Paleogene suite of silicic ignimbrites and intermediate-composition lavas is interlayered with lake and hot spring deposits (figure 2). Following a hiatus in magmatism, a mafic lava erupted as one of the oldest basaltic magmas in the eastern Great Basin. Our study aims to answer questions about the timing and nature of the onset of extension in the Great Basin by Eric H. Christiansen1, Nichelle Baxter1, Thomas P. Ward1, Elizabeth Zobell1, Matthew R. Chandler1, Michael J. Dorais1, Bart J. Kowallis1, Donald L. Clark2