Calabozos caldera complex: geology, petrology, and geochemistry of a major silicic volcanic center and hydrothermal system in the Southern Andes
The Calabozos caldera complex, located in the central Chilean Andes, lies at the boundary between a province of silicic and intermediate volcanism to the north and predominantly basaltic volcanism to the south. Three ash-flow sheets, Units L (0.8 Ma), V(0.30 Ma), and S(0.15 MA) of the Loma Seca Tuff represent 1000 km/sup 3/ of high-K rhyodacite and dacite magmas which erupted there. Pre-eruptive magma chambers graded from biotite-bearing rhyodacite containing 4-5 weight% H/sub 2/O with Fe-Ti oxide equilibration temperature of 800/sup 0/C in their upper reaches to amphibole-bearing dacite with 3 weight% water and temperatures between 900 and 1000/sup 0/C in deeper parts of the chamber. Fractionation of the observed phenocrysts (plagioclase, clinopyroxene, orthopyroxene, titanomagnetite and ilmenite) in model proportions is a successful model for the differentiation of the entire compositional range. Calculated fractionation paths cannot, however, account for elevated Ba, Rb, and Zr concentrations and low ..delta../sup 18/O values of the rhyodacites. These data suggest that crystal fractionation was accompanied by small amounts of contamination by assimilation of wall rocks (or partial melts of wall rocks) that had been altered previously at high temperature in a meteoric hydrothermal system. Hot springs issue mainly along resurgence-related faults. Most of the springs are interpreted as mixtures of meteoric water with a parent reservoir water that contains 400 ppm Cl at 250C. Low concentrations of both trace metals in sinter deposits and metal-complex-forming ions in the thermal waters suggest that there is no economic mineralization at shallow depths. The dilute composition of the waters, high calculated subsurface temperatures, and longevity of the magmatic and hydrothermal system make the Calabozos caldera complex an attractive geothermal target.
- Research Organization:
- Stanford Univ., CA (USA)
- OSTI ID:
- 6801847
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ANDES
HYDROTHERMAL SYSTEMS
CHILE
GEOCHEMISTRY
GEOLOGY
PETROLOGY
BARIUM
FRACTIONATION
GEOLOGIC FAULTS
GEOLOGIC HISTORY
GEOLOGIC MODELS
HOT SPRINGS
METEORIC WATER
MINERALOGY
OXYGEN 18
RESERVOIR FLUIDS
RESERVOIR TEMPERATURE
RUBIDIUM
TUFF
VOLCANIC REGIONS
ZIRCONIUM
ALKALI METALS
ALKALINE EARTH METALS
CHEMISTRY
DEVELOPING COUNTRIES
ELEMENTS
ENERGY SYSTEMS
EVEN-EVEN NUCLEI
FLUIDS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOTHERMAL SYSTEMS
GROUND WATER
HYDROGEN COMPOUNDS
ISOTOPES
LATIN AMERICA
LIGHT NUCLEI
METALS
MOUNTAINS
NUCLEI
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
SEPARATION PROCESSES
SOUTH AMERICA
STABLE ISOTOPES
THERMAL SPRINGS
TRANSITION ELEMENTS
WATER
WATER SPRINGS
150202* - Geology & Hydrology of Geothermal Systems- Non-USA- (-1989)