Silica Sinter and the Evolution of Hot Springs in the Alvord/Pueblo Valleys, Southeast Oregon, USA

Leslie Allen Mowbray,Michael L Cummings

doi:10.3390/en14217186

Abstract

Hot springs in the Alvord/Pueblo valleys in southeastern Oregon are analogous to Basin-and-Range hydrothermal systems where heat source and permeable pathways are met through crustal thinning. Silica sinter deposition at Mickey Springs, Alvord Valley, predates the late Pleistocene high stand of pluvial Lake Alvord. At Borax Lake, Pueblo Valley, sinter deposition occurred during the Holocene. This study examines the evolution of springs at Mickey Springs, where three morphologies of sinter are present: (1) basalt clasts surrounded by sinter in interbedded conglomerate and sandstone, (2) pool-edge and aprons of sinter surrounding depressions (12–32 m diameter), and (3) quaquaversal sinter mounds with pool-edge sinter. The oldest sinter occurs in silica-cemented conglomerate and sandstone, where deposition occurred prior to 30 kya. Deposition around broad depressions and mounds occurred after 30 kya but before water levels began to rise in pluvial Lake Alvord. Thermoluminescence dates suggest sinter deposition ceased before 18 kya when silt and clay filled inactive vents and buried aprons. A few mounds hosted active springs after sinter deposition ceased but while submerged in pluvial Lake Alvord. Now, high-temperature springs, steam vents, and mud pots are concentrated in a 50 × 50 m area near the southern edge of the spring area.

Highlights

Surface and subsurface hydrogeological conditions of geothermal systems are recorded in silica sinters
While many studies have explored the micro-scale dynamics of silica sinter deposition and diagenesis (e.g., [16,17,18,19]), this study examines the meso-scale lifespan and migration of spring features at Mickey Springs
The geothermal systems of the Alvord/Pueblo valleys evolved within the context of the structural evolution of the northwestern Basin-and-Range Province and pluvial Lake

Summary

Introduction

Surface and subsurface hydrogeological conditions of geothermal systems are recorded in silica sinters. Remote locations, designated as Area of Critical Environmental Concern (ACEC) by the Bureau of Land Management, and ownership of Borax Lake by The Nature Conservancy protect the hot spring deposits and provide opportunities to investigate the timing and duration of silica sinter deposition relative to the evolution of the geothermal systems and Late Pleistocene pluvial Lake Alvord These temporal relations are within context of the tectonic evolution of the northwestern Basin-and-Range Province [6], ongoing deformation of the Alvord/Pueblo valleys [7,8,9,10], dynamics of fluid flow along active faults [11,12,13,14,15], and chronology and deformation of pluvial lake shorelines [9,10]

Objectives

Methods

Results

Discussion

Conclusion