Earth and Planetary Sciences ETDs

Publication Date

12-1-2015

Abstract

Input of deeply sourced (endogenic) waters can contribute significant quantities of salinity to groundwater, degrading water quality, with faults acting as conduits for subsurface fluid flow. Understanding the source, movement, and chemistry of groundwater is becoming ever more significant with changing climate and weather patterns. Systematic sampling was carried out on three groups of carbonic warm and hot springs in New Mexico, USA: 1) Tierra Amarilla springs (~ 20ºC), near San Ysidro south of Nacimiento Mountains, 2) Penasco springs (~ 20 ºC) along the Nacimiento fault west of the Nacimiento basement mountain block, and 3) Soda Dam, Jemez, and Indian hot springs (40-60 ºC) in San Diego Canyon along the Jemez River. Application of multiple hydrochemical tracers (including major/minor elemental chemistry and stable isotopes) was applied to quantitatively evaluate possible flow paths and mixing. The goal is to test three hypotheses for source and transport of waters to these carbonic springs: San Juan basin origin, meteoric flow from the Nacimiento high topography, and/or influence from the Valles Caldera geothermal system of the Jemez Mountains. Numerous geochemical plots show that all three carbonic spring groups are very different than meteoric and sedimentary aquifer waters. The springs are warm (20oC) to hot (60oC) and all deposit travertine, pH ranges from 5.38 – 6.94; conductivities range from 3300 - 20000µS and PCO2 ranges from -0.94 to 0.93. San Ysidro springs look similar in major anions and cations to Penasco springs (both along the Nacimiento fault) and each shows a different range of the same mixing trend. Soda Dam appears to anchor these mixing trends, but itself is part of a broader mixing trend with a Valles Caldera geothermal water end member. The main tracers that define mixing trends are: 1) major cations and anions (Piper diagram), 2) stable isotopes, 3) conservative tracers (Li, B, Br, Cl), 4) temperature, and 5) helium isotope ratios. In all of these tracers, the Tierra Amarilla and Penasco springs overlap with each other strongly and fall on well-defined mixing trends anchored by geothermal fluids of the Valles system. Stable isotope composition in the San Ysidro and Penasco springs ranges from δ13C= -8.71 to 2.698 and δ18O = -11.45 to -8.15 overlap with Soda Dam hot springs values fall on a mixing line with Valles Caldera geothermal waters. High lithium (0.1 to 10.4 ppm), boron (0.2 to 12.5 ppm), and bromine values all show the San Ysidro carbonic springs to have hydrochemical influence from the Jemez hydrothermal system (e.g. values are similar to Soda Dam and Jemez springs). Similarly, helium gas data show elevated 3He/4He values consistent with contributions from the Jemez volcanic system. However, in the San Ysidro and Penasco spring groups, plots of high Li and B versus chloride suggest that geothermal waters have acquired Cl from other sources, including salt and gypsum of the Paleozoic and Mesozoic rock aquifers. Thus we interpret these carbonic springs to be distal manifestations of fluid circulation along faults (e.g. the Soda Dam and Nacimiento faults) with a mixture of Jemez geothermal waters and waters sourced from either/both San Juan Basin aquifers and meteoric sources. Semi-confined fault conduits, especially of the Soda Dam/ Jemez and Nacimiento fault zones, provide connectivity between carbonic spring systems and help explain geochemical similarities and mixing trends between Valles Caldera, Soda Dam, and Jemez geothermal waters with more distal San Ysidro and Penasco carbonic spring waters. Penasco springs are interpreted to reflect a component of outflow from the geothermal system that crosses the Nacimiento Mountain basement block along NE- trending faults.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Advisor

Crossey, Laura

First Committee Member (Chair)

Karlstrom, Karl

Second Committee Member

Asmerom, Yemane

Third Committee Member

Gardner, Payton

Project Sponsors

National Science Foundation New Mexico Experimental Program to Stimulate Competitive Research (EPSCoR) New Mexico Geology Society

Language

English

Keywords

geochemistry, ground water, faults, mantle

Document Type

Thesis

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