Hydrothermal brecciation in the Jemez Fault zone, Valles Caldera, New Mexico: Results from CSDP (Continental Scientific Drilling Program) corehole VC-1
Paleozoic and Precambrian rocks intersected deep in Continental Scientific Drilling Program corehole VC-1, adjacent to the late Cenozoic Valles caldera complex, have been disrupted to form a spectacular breccia sequence. The breccias are of both tectonic and hydrothermal origin, and probably formed in the Jemez fault zone, a major regional structure with only normal displacement since mid-Miocene. Tectonic breccias are contorted, crushed, sheared, and granulated; slickensides are commmon. Hydrothermal breccias, by contrast, lack these frictional textures, but arej commonly characterized by fluidized matrix foliation and prominent clast rounding. Fluid inclusions in the hydrothermal breccias are dominantly two-phase, liquid-rich at room temperature, principally secondary, and form two distinctly different compositional groups. Older inclusions, unrelated to brecciation, are highly saline and homogenize to the liquid phase in the temperature range 189 to 246/sup 0/C. Younger inclusions, in part of interbreccia origin, are low-salinity and homogenize (also to liquid) in the range 230 to 283/sup 0/C. Vapor-rich inclusions locally trapped along with these dilute liquid-rich inclusions document periodic boiling. These fluid-inclusion data, together with alteration assemblages and textures as well as the local geologic history, have been combined to model hydrothermal brecciation at the VC-1 site.
- Research Organization:
- Utah Univ. Research Inst., Salt Lake City (USA). Earth Sciences Lab.
- DOE Contract Number:
- FG02-86ER13467
- OSTI ID:
- 6386155
- Report Number(s):
- DOE/ER/13467-T1; ESL-87005-JP; ON: DE87012101
- Resource Relation:
- Other Information: Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CALDERAS
GEOLOGIC STRUCTURES
GEOTHERMAL SYSTEMS
HYDRAULIC FRACTURING
GEOLOGIC MODELS
INCLUSIONS
CHEMICAL COMPOSITION
BOREHOLES
DRILL CORES
GEOLOGIC FAULTS
GEOTHERMOMETRY
HYDROTHERMAL ALTERATION
JEMEZ MOUNTAINS
CAVITIES
COMMINUTION
FEDERAL REGION VI
FRACTURING
GEOLOGIC FRACTURES
MOUNTAINS
NEW MEXICO
NORTH AMERICA
USA
Geothermal Legacy
150201* - Geology & Hydrology of Geothermal Systems- USA- (-1989)
152003 - Geothermal Data & Theory- Rock-Water-Gas Interactions