Transcript New Geologic Mapping, Tahoe/Donner Region - Earth Science

New Geologic Mapping, Tahoe/Donner Region
Arthur Gibbs Sylvester1,
William S. Wise1, Jordan
Hastings2
And many UCSB
undergraduate geology
students
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1UCSB
Dept. of Geological Sciences
2UCSB Dept. of Geography
University of California, Santa Barbara
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Purposes of this Talk
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To present new
geologic maps of all or
parts of nine 7.5’
quadrangles in the
Tahoe/Donner area.
To present the major
geologic findings
resulting from the new
mapping.
Index Map
Yellow = UCSB 7.5’ mapping
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Purposes of the Mapping
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To investigate the
relation of volcanic
eruption centers to
basement structure.
To determine the
geologic history of the
area, including Tertiary
volcanism and faulting.
To complement the
geologic data base of
the greater Tahoe area.
Tahoe City 7.5’ Quadrangle
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Main Findings
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Tahoe/Truckee graben
is bounded on west by
Donner deformation
zone (Hudson, 1948).
Little evidence of
recent fault
displacement.
Norden 7.5’ Quadrangle
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Main Findings
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Tahoe/Truckee graben
is bounded on east by
major fault along state
line.
Much evidence of
recent faulting on other
faults (Schweickert et
al., 2000).
Kings Beach 7.5’ Quadrangle
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Main Findings
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Lake level was 75 m
higher during glacial
times than today
(Birkeland, 1964).
Ancient shorelines,
peperites.
Kings Beach 7.5’ Quadrangle
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Main Findings
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Oligocene rhyolite tuff in
Onion Creek, Emigrant
Meadow, Beacon Peak,
Boreal Ridge, and
Castle Valley areas
(Lindgren, 1897).
Nine separate tuffs.
Tuffs filled an Eocene
paleocanyon cut in
Cretaceous granite.
Norden 7.5’ Quadrangle
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Main Findings
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Presence of a major
volcanic debris
avalanche in Norden
quadrangle (Fosdick et
al., 2004; Rotberg et
al., 2004).
Derived between 13.4
- 7.5 Ma ago from
major volcano to SE
(Tinker Knob? Squaw
Peak?).
Norden 7.5’ Quadrangle
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Main Findings
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Graben filled with Tertiary
volcanic rocks of
Oligocene, Miocene,
Pliocene, and Recent age.
Seven major volcanoes:
 Four along Donner
deformation zone:
Tinker Knob, Squaw
Peak, KT22, Twin
Peaks.
 Three in the graben:
Mt. Pluto, Mt. Watson,
Martis Peak.
Martis Peak 7.5’ Quadrangle
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Main Findings
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Young tuff ring at Lake
Forest.
Kings Beach 7.5’ Quadrangle
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Main Findings
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Young tuff ring at Lake
Forest not far from seismic
activity in Carnelian Bay in
2003.
 Many small
earthquakes (< M.3)
 Deep earthquakes (~ 30
km)
 Indicative of volcanic
source.
2003
earthquake
swarm
Kings Beach 7.5’ Quadrangle
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Status of the Research
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Field mapping in
summer 2004 directed
to:
detailed work in basalt
fields in Truckee and
Martis Peak
quadrangles.
 details of glacial
deposits
 Map stateline fault
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Collect specific rocks
for radioisotopic dating
Truckee 7.5’ Quadrangle
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Status of the Maps
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All field maps now
compiled at scale of
1:24,000 in hand colored,
analog sheets of paper.
These maps now being
digitized using ArcMap 8.3
in GIS format.
Kings Beach quadrangle is
finished.
Others are raster images
posted at:
www.geol.ucsb.edu/projects/tahoe
Homewood 7.5’ Quadrangle
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Ultimate Intention
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Put all maps on Web
as Dynamic Digital
GIS documents that
can be queried for:
 age, type of rocks,
chemical analyses
 faults, geologic
structures
 outcrop and vista
images
Wentworth Springs 7.5’ Quadrangle
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Ultimate Objective
To complement the
collection of all
research in the
greater Tahoe
region available to
regional planners
and other users.
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