Paleomagnetic mapping of late Miocene-Pliocene basalt flows in the northwestern Basin and Range: Determining structural and topographic controls on the distribution of volcanic activity

Brent Ritzinger
April 2013

Purpose and Introduction

The primary goal of this research is to better understand the relationship between extensional faulting and volcanic activity during the initial stages of continental rifting. Volcanism is both temporally and spatially associated with large-scale extension that has occurred throughout the Basin and Range (e.g., Gans, 1987). However, most of the province has undergone large-magnitude extension along normal faults, resulting in the development of deep, sediment-filled basins that obscure many of the structures developed during the initiation of extension (Fig. 1). Yet these early structures, and their detailed relationship to volcanic activity, provide critical insight into the mechanisms by which the rifting process begins in continental crust and how it evolves.

The western margin of the Basin and Range is still actively extending, and is thus a place where rift initiation can potentially be explored. Surprise Valley is located along this margin in northeastern California (Fig. 2) and provides a unique opportunity to assess the relationship between faulting and volcanism in detail, because presumably inactive structures representing nascent extension can be observed along the northeastern boundary of Surprise Valley in the Larkspur Hills. Extension initiated in the mid-Miocene in this region, but a second phase occurred ca. 3-4 Ma (Egger & Miller, 2011), roughly contemporaneous with the eruption of well-dated 3-8 Ma low-K olivine tholeiites (LKOTs) in the Larkspur Hills (Fig. 3) (Carmichael et al., 2006).

In the Larkspur Hills, I will conduct field mapping and paleomagnetic sampling and analyses in order to:

  • Determine the correlation between faulting and LKOT flows in the Larkspur Hills

  • Construct detailed cross-sections illustrating the temporal relationships between faulting and LKOT flows

  • Determine the progression of extensional processes that occurred in the Larkspur Hills and how they relate to the evolution and localization of extension within Surprise Valley

Full Thesis Proposal (PDF format)