Geology of Yerington District, Nevada & Basin Range Extension
Discover the detailed geology of the Yerington district in Nevada, including the timing of Basin and Range extension. Explore the mechanism of extension based on geometries observed in the area, such as normal faults and stratigraphic layers. The district covers a 200 km2 area with extensive geological data, including Quaternary to present sedimentary formations, Miocene ignimbrites, Oligocene conglomerates, and Mesozoic basement rocks. Learn about the structure of the Cenozoic rocks, East-dipping normal faults, and fault styles affecting the region.
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Presentation Transcript
Photo courtesy of UNAVCO CENOZOIC GEOLOGY OF THE YERINGTON DISTRICT, NEVADA, AND IMPLICATIONS FOR THE NATURE AND ORIGIN OF BASIN AND RANGE FAULTING John M. Proffett Jr., 1977
Motivation Describe the geology of the Yerington district in detail Discern the timing of Basin and Range extension in this area Touch on the mechanism of extension in the Basin and Range based on geometries seen in Yerington area
Yerington district 200 km2 area Mapped at 1:12,000 scale 30,000 m of core and cuttings logged i.e. a very large amount of geologic data to describe in 10 min
Generalized Stratigraphy Age Lithologies Thickness, etc. Quaternary to present Alluvial fans, and basin sediments Conglomerate and sandstone, Capped by basalt flows 8 11 Ma 200 m Hornblend andesite Flows, breccias, and intusions (porphyrys) Olivine pyroxene basalt flows And breccias Miocene 400 m + Probably late tertiary ~200 m Sequence of ignimbrite sheets Divided into 10 distinct units Overlain by dacite breccia Oligocene Up to 1,400 m Conglomerate, sedimentary breccia, And minor basalt Early Tertiary ~400 m Metamorphic and granitic rocks Triassic to Cretaceous age Unknown Mesozoic Basement
Cenozoic structure East dipping normal faults Steep west dipping strata Rocks overlying Miocene angular unconformity are more shallow west dipping Present day distance along this section is 7.3km, prefaulting distance measured along Cenozoic surfaces is ~17.3 km, so 10km of extension has taken place here
Fault style East dipping Primarily dip- slip More gently dipping faults displace units up to 4,000m (gently dipping faults are older) Steeply dipping faults displace units up to 1,200m (interpreted as younger Curvature of fault planes allow for westward tilting of strata
Fault style East dipping Primarily dip- slip More gently dipping faults displace units up to 4,000m (gently dipping faults are older) Steeply dipping faults displace units up to 1,200m (interpreted as younger Curvature of fault planes allow for westward tilting of strata
Geologic history 17-11 Ma 17Ma 18-17Ma 19-18Ma Basin and Range faulting begins 18-17Ma, This comes from the fact that units older than this are all offset the same amount I the area 11-8 Ma By 11 Ma early faults are rotated so much that they are too flat for continued faulting Present In present time, steeply dipping range front faults are still active
Discussion/Implications Timing of Basin and Range extension constrained by structures in Yerington district to 18-17Ma Prior theories of Basin and Range mechanism dispelled, and basis of current idea is hashed out Ultimately, Basin and Range northern extent during formation roughly coincides with latitude of Mendocino triple junction, as well as the projection of the spreading centers b/w Mendocino and Murray fractures
