Framework Geologic Map and Structure Sections along the ... · mspy fys cy cpp vpp fmp cmp vy fpp...
Transcript of Framework Geologic Map and Structure Sections along the ... · mspy fys cy cpp vpp fmp cmp vy fpp...
U.S. Department of the InteriorU.S. Geological Survey
Scientific Investigations Map 3395Sheet 2 of 2
Pamphlet accompanies map
Framework Geologic Map and Structure Sections along the Bartlett Springs Fault Zoneand Adjacent Area from Round Valley to Wilbur Springs, Northern Coast Ranges, California
By Robert J. McLaughlin1, Barry C. Moring1, Christopher S. Hitchcock2, and Zenon C. Valin1
20181U.S. Geological Survey;2InfraTerra, Inc.
Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government
This plate is offered as an online-only, digital publication. Users should be aware that, because of differences in rendering processes and pixel resolution, some slight distortion of scale may occur when viewing it on a computer screen or when printing it on an electronic plotter, even when it is viewed or printed at its intended publication scale
Digital files available at https://doi.org/10.3133/sim3395
Suggested citation: McLaughlin, R.J., Moring, B.C., Hitchcock, C.S., and Valin, Z.N., 2018, Framework geologic map and structure sections along the Bartlett Springs Fault Zone and adjacent area from Round Valley to Wilbur Springs, northern Coast Ranges, California (ver 1.1, September 2018): U.S. Geological Survey Scientific Investigations Map 3395, pamphlet 60 p., 2 sheets, scale 1:100,000, https://doi.org/10.3133/sim3395.
ISSN 2329-132X (online)https://doi.org/10.3133/sim3395
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LIST OF MAP UNITS
See Description of Map Units (in pamphlet) for complete unit descriptions. Some unit exposures on the printed or plotted map are too small to distinguish the color for unit identification. These units are labeled where possible, and unlabeled units are attributed in the database. Note that many tiny units, primar-ily blocks, are covered by symbols.
UNCONSOLIDATED DEPOSITSArtificial fill (Holocene)
Landslide deposits (Holocene and Pleistocene)
ALLUVIAL DEPOSITSAlluvial deposits (Holocene and Pleistocene)
Older alluvial deposits (Holocene and Pleistocene)
TERRACE DEPOSITSAlluvial terrace deposits (Holocene and Pleistocene)
Younger alluvial terrace deposits and surfaces (Holocene?)
Older alluvial terrace deposits and surfaces (Pleistocene)
Very old alluvial terrace deposits and surfaces (Pleistocene)
FAN DEPOSITSAlluvial fan deposits (Holocene and Pleistocene)
Younger alluvial fan deposits and surfaces (Holocene?)
Older alluvial fan deposits and surfaces (Pleistocene)
Very old alluvial fan deposits and surfaces (Pleistocene)
GLACIAL DEPOSITSGlacial deposits, present locally (Pleistocene)
SPRING DEPOSITSHydrothermal deposits (Pleistocene and younger)
Travertine (Pleistocene and younger)
VOLCANIC ROCKSClear Lake Volcanic rocks (Pleistocene)
FLUVIAL AND LACUSTRINE FILLCache Formation (Pleistocene and upper Pliocene)
MARINE OVERLAP DEPOSITSSandstone and lignitic shale of the Covelo area (middle Miocene)
Marine sandstone and shale (Eocene)
Sandstone, shale, and conglomerate (Eocene and upper Paleo-cene)
Conglomerate (Eocene and upper Paleocene)
GREAT VALLEY COMPLEX Sandstone, siltstone, and mudstone (Upper Cretaceous,
Cenomanian and younger) Limestone (Upper Cretaceous)
Sandstone, siltstone, and mudstone with concretionary limestone and conglomerate (Upper and Lower Cretaceous, Ceno-manian to Hauterivian)
ELDER CREEK TERRANESiltstone, mudstone, minor sandstone, conglomerate, and
sedimentary serpentinite (Lower Cretaceous, Albian to Hauterivian)
Conglomerate (Lower Cretaceous, Albian to Hauterivian)
Bioclastic limestone, (Lower Cretaceous, Hauterivian)
Sedimentary serpentinite (Lower Cretaceous)
Argillite, siltstone, and sandstone (Lower Cretaceous, upper Valanginian, to Upper Jurassic, Tithonian)
Megabreccia (Upper Jurassic, Tithonian to Kimmeridgian)
Ophiolitic mélange (Lower Cretaceous)
Mafic volcanic rocks, including pillow basalt, diabase, and noncumulate gabbroic intrusive rocks
Undivided marine clastic rocks, commonly argillitic (Lower Cretaceous and Upper Jurassic)
Diabase, mapped locally
Gabbro, mapped locally
Radiolarian chert, mapped locally (Upper Jurassic, Kimme-ridgian)
Blueschist, mapped locally
Blocks of unknown lithology
COAST RANGE OPHIOLITEPelagic chert (Upper to Middle Jurassic, Tithonian to Bajocian)
Basaltic pillowed flows and flow breccias (Middle Jurassic)
Diabase dikes and sills (Middle Jurassic)
Gabbro and ultramafic rocks (Middle Jurassic)
Serpentinized ultramafic rocks (Middle Jurassic)
FRANCISCAN COMPLEX
CENTRAL BELTCentral Belt Mélange terrane (lower Tertiary and Upper
Cretaceous)Undivided mélange (lower Tertiary and Upper Cretaceous)
Sandstone and argillite (in part, Upper Cretaceous, Ceno-manian or younger; middle Cretaceous, Aptian or younger; and possibly, Upper Jurassic, Tithonian or younger)Radiolarian chert (Upper Cretaceous to Middle Jurassic)
Basaltic volcanic rocks (Jurassic)
Conglomerate (Lower Cretaceous and (or) Upper Jurassic or younger)Diabase (Cretaceous or Jurassic?)
Metasedimentary rocks (Lower Cretaceous? or younger)
Blueschist blocks (Jurassic)
Blocks of unknown lithology
Pomo terrane (Upper Cretaceous to Upper Jurassic)Basaltic breccia, sandstone, and shale (Upper Cretaceous, Maastrichtean)Alkalic pillow basalt, pillow-breccias, and minor diabase and chert (Jurassic)
Marin Headlands-Geysers terrane (Upper Cretaceous to Lower Jurassic)Sandstone and argillite (Upper Cretaceous, Cenomanian? or younger)Conglomerate (Upper Cretaceous, Cenomanian? or younger)Radiolarian chert (Upper Cretaceous, lower Cenomanian to Lower Jurassic, Pliensbachian)Basaltic volcanic rocks (Lower Jurassic)
Snow Mountain volcanic terrane (Lower Cretaceous, Valanginian or younger?)Basaltic to rhyolitic volcanics and intrusive rocks
Diabasic intrusive rocks, largely sill-like
Porphyritic basaltic rocks
Metasandstone and argillite
EASTERN BELTYolla Bolly terrane (Upper and Lower Cretaceous to Upper
Jurassic, Tithonian)Mélange of the Yolla Bolly terrane (Upper Cretaceous)
Blueschist
Conglomerate
Metachert (Early Cretaceous, Albian or Aptian, to Middle Jurassic, Aelenian)Gabbro
Limey mudstone
Metavolcanic rocks (Middle Jurassic, Aelenian or older)
Metaserpentinite blocks or lenses
Unidentified blocks
Metasandstone and argillite, locally conglomeratic (Upper and Lower Cretaceous, Cenomanian to Aptian, to Late Jurassic, Tithonian)
Metachert (Lower Cretaceous, Albian to Aptian, to Middle Jurassic, Aalenian)
Metavolcanic rocks (Middle Jurassic, Aalenian or older)
Mafic intrusive rocks (Early Cretaceous)
Pickett Peak terrane (Lower Cretaceous, Aptian to Barremian)
Undivided metasedimentary and metavolcanic rocks and metachert
Metachert
Basaltic metavolcanic rocks
Mendocino Pass terrane (Lower Cretaceous, Valanginian)
Foliated metasandstone, argillite, and minor undivided metachert and greenstone
Metachert and greenstone blocks
EXPLANATION OF MAP SYMBOLSContact—Solid where location is accurate; long-dashed where
approximate; short-dashed where inferred; dotted where concealed. Queried where identity or existence questionable
Fault—Solid where location is accurate; long-dashed where approximate; short-dashed where inferred; dotted where concealed. Queried where identity or existence questionable
Fault Lineament—Inferred from features on aerial photography. Dotted where projected beneath surficial deposits
Tuff of Clearlake Volcanic rocks (Qv)—Mapped in Cache Formation (QTc)
Active trace of Bartlet Springs Fault Zone (Lienkaemper, 2010)—Arrows show relative movement. In cross sections: circled minus, movement away from observer; circled plus, movement towards observer
Strike and dip of bedsInclined
Overturned
Horizontal
Vertical
Strike and dip of metamorphic fabric in sheared or foliated rocksInclined
Vertical
Location of block or lens too small to map in broken formation or mélange
Higher-grade metamorphic rock
Serpentinite
Volcanic rock
Sandstone
Conglomerate
Chert
Block of unknown lithology
Fossil Location—Map number corresponds to table 1
Hydrothermal bleaching (Quaternary)—Diffuse zone in sedimentary and metasedimentary rocks, characterized by quartz, carbonate, and clay mineral veins and veinlets. Associated with the Barttlet Springs Fault Zone in the vicinity of Neuman Springs
Sinter or silica carbonate rocks
Travertine•
40
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30
58•
CENTRAL BELT
Yolla Bolly Terrane
FRANCISCAN COMPLEX
Pickett PeakTerrane
Mendocino Pass Terrane
EASTERN BELT
MARINE OVERLAP DEPOSITS
FLUVIAL AND LACUSTRINE FILL
PomoTerrane
Central Belt Mélange Terrane
Marin Headlands-
GeysersTerrane
TERTIARY COASTRANGE
OPHIOLITEGREAT VALLEY COMPLEX
Miocene
Eocene
Eocene and Paleocene
Pleistocene and Pliocene
MESOZOIC
CENOZOIC
EarlyJurassic
ELDER CREEK TERRANERice Valley
CORRELATION OF MAP UNITS
UNCONSOLIDATED DEPOSITS
CRETACEOUS
EarlyCretaceous
JURASSIC
Holocene
VOLCANICROCKS
[See Description of Map Units (in pamphlet) for precise unit ages]
LateCretaceous
Pleistocene
TERRACEDEPOSITS
ALLUVIALDEPOSITS
FANDEPOSITS
GLACIAL DEPOSITS
SPRING DEPOSITS
Late Jurassic
Middle Jurassic
QUATERNARY
QUATERNARYAND TERTIARY
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PLASKETTRIDGE
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PLASKETTMEADOWS
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39°30'
39°15'
39°
Figure 2. Map showing quadrangles in map area and sources of geologic data.
SALTCANYON
WILBUR SPRINGSBENMORE CANYON
LODOGA
LEESVILLE
GILMOREPEAK
HOUGH SPRINGS
POTATO HILL
FOUTS SPRINGS
BARTLETTMOUNTAIN
BARTLETT SPRINGS
STONYFORDSAINT JOHNMOUNTAIN
CROCKETT PEAK
FELKNERHILL
KNEECAP RIDGEHULL MOUNTAIN
LAKEPILLSBURY
SANHEDRIN MOUNTAIN
BRUSHYMOUNTAINWILLIS RIDGE
FOSTERMOUNTAIN
VAN ARSDALERESERVOIR
POTTERVALLEY
REDWOODVALLEY
ELKMOUNTAIN
COWMOUNTAIN
UKIAH UPPERLAKE
LAKEPORT
HIGHLAND SPRINGS KELSEYVILLE
CLEARLAKEHIGHLANDS
LUCERNE
CLEARLAKE OAKS
LOWERLAKE
WILSONVALLEY
GLASCOCKMOUNTAIN
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6, 15
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5, 27
2, 16, 18
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12, 188
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AREA OFMAP
EXPLANATION1 Ohlin and others, 20102 Berkland, 1978; CDWR, 1966, 1968, and 19693 McLaughlin, R.J., unpublished mapping, 1980–1981 4 McLaughlin and others, 19905 Jayko and others, 1989; Clark, 19406 Ohlin H.N., 1989, unpublished mapping, 19857 Hitchcock, C.S., unpublished mapping, 2012–2013; McLaughlin, R.J., and Moring, B.C., aerial reconnaissance using Google Earth imagery, 20148 Etter, 1979; U.S. Forest Service, unpublished mapping9 Stanford, 199110 Berkland, 197311 Hearn and others, 1995; Sims and Rymer, 1976; Rymer, 198112 Brown and others, 1981; MacPherson, 198313 Brown, 196414 Suppe and Foland, 1978; Etter, 1979; U.S. Forest Service, unpublished mapping15 Blake and others, 199216 McLaughlin, R.J. and Moring B.C., mapping 2012–201317 Ohlin, H.N., unpublished field work, 1980–198118 McLaughlin and Moring, aerial reconnaissance using Google Earth imagery, 2012–201419 Ohlin, H.N., unpublished mapping, 1979–198120 McLaughlin, 1978; Ohlin H.N., and McLaughlin, R.J., unpublished mapping, 1978–198121 Lehman, 197422 McLaughlin, R.J., and Moring B.C., minor revisions23 Lawton, 195624 Swe and Dickinson, 197025 Shervais and others, 2005a, b26 Lienkaemper, 201027 Clark, 1940
1
4
4
6
6
3
2
5
39˚00’
122˚30’ 122˚0’
39˚30’
Figure 5. Map showing major structural features in map area and locations of structure and seismicity cross sections.
NORTHERN BARTLETT SPRIN
GS
(Hunting)
t5
t4
t3
t1
t2-6
A
A'
B
B'
B''C'
C
E'
E
D
D'
NORTHERN BARTLETT SPRINGS
LoganSprings
Kuikui
Pomo
Bad Ridge
Bear Valley Resort
Wilson Fault
Kennedy Fault
Sulphur Bank
Konocti Bay
Borax Lake
Collayomi
Wright Way
Big Valley
Scotts Valley
Clover Valley
Sanhedrin Mountain
Little Indian Valley
SOUTHERN BARTLETT SPRINGS
C
ross
S
prin
gs
EXPLANATION
MAJOR FAULTS
Active segments of the Bartlett Springs Fault Zone—From aerially interpreted geomorphic features (Lienkaemper, 2010)
Other faults, undifferentiated—Includes faults mapped in field and faults inferred from aerial lineaments. Includes faults discussed in this report, though not all named faults on figure are discussed
CROSS SECTION
Line of structure section
Line of seismicity cross section—See figure 5, 12 (Sheet 2) and figure 11 (pamphlet) for additional information
MAJOR FOLDS
Synforms
1 Bartlett Springs Synform
4 Middle Mountain Synform
5 Unnamed synform
Antiforms
2 Pacific Ridge Antiform
3 Wilbur Springs Antiform
6 Bartlett Mountain Antiform
EARTHQUAKE EPICENTERS
Magnitude 5.2 earthquake, August 10, 2016
Aftershock sequence, August 10, 2016–September 15, 2016
Epicenters 1984–2014
A A'
t1
MFZ ~5 Ma
MFZ PRESENTExhumed rocks of the Eastern Belt
Partiallyexhumed rocks of the Central Belt
CoastalBelt
CoastalBelt
CoastalBelt
KlamathBlock
Rice Valley
Rice Valley
Rice Valley
Round Valley
RoundValley Round
Valley
Middle Mountain
Middle Mountain
Middle Mountain
Lower Lake
Lower Lake Lower
Lake
Great Valley Complex andCoast Range ophiolite
Neogene Eel Riverforearc basin
Neogene Eel Riverforearc basin
APPROXIMATEAREA OF FIGURE 7
A PALEOCENE–EOCENE MARGIN B ~MIDDLE MIOCENE MARGIN C PRESENT MARGIN
EXPLANATION
Estuarine deposits of Round Valley area associated with former Neogene (Eel River) forearc basin (Middle Miocene)
Sandstone and shale, shallow to deep marine, associated with former Mesozoic–Paleogene Great Valley forearc basin (Eocene and Paleocene)
Sandstone shale and conglomerate, marine, and ophiolitic basement and mélange of former Great Valley forearc basin (Upper Cretaceous–Middle Jurassic)
Igneous and metasedimentary basement rocks of the Klamath Mountains (Jurassic and older)
FRANCISCAN COMPLEX
Central Belt (Upper Cretaceaous and older)
Eastern Belt (Upper Cretaceous–Upper Jurassic)
Coastal Belt (Tertiary and younger)
MAJOR FOLD AXES
Antiform
Synform
Figure 6. Geologic maps showing progressive deformation of the northern California margin during transition from subduction to right-lateral strike slip. The Northern Bartlett Springs Fault is viewed as having developed since the Miocene from deformation focused along the Bartlett Springs Synform, one of several northwest-trending folds that preceded northward encroachment of the Mendocino Triple Junction and the San Andreas Fault. The folding formed in response to northeast-southwest transpression across the subduction margin.
Dominated by east-west convergence, following exhumation of Eastern and Central Belts of Franciscan Complex from depth of 20–30 km. Yellow circled areas delineate Paleogene deposition near former western margin of the Jurassic–early Cenozoic Great Valley fore-arc basin.
Light-pink transparent overlay delineates former southeastern part of early Miocene and younger (Eel River) fore-arc basin based on erosional and tectonic remnants of the former Neogene fore-arc basin that includes yellow-circled Miocene remnant at Round Valley. The Neogene fore arc may have extended much farther to the southeast (Nilsen and Clarke, 1989) and deposition was on exhumed Franciscan and Paleogene rocks of older Great Valley fore-arc basin. Orientations of synforms and antiforms inboard of the subduction margin indicate major northeast-southwest transpression that accompanied or postdated Neogene fore-arc deformation. Slip along the Northern Bartlett Springs Fault is inferred to have right-laterally dismembered the Bartlett Springs Synform since middle to late Miocene formation, uplift, and erosion of the Neogene fore-arc basin. See figure 7 for details of slip restoration of the Bartlett Springs Synform.
Showing major strike-slip faults inboard of the San Andreas Fault, the Mendocino Triple Junction, the present subduction margin, and the remaining offshore and uplifted and eroded onshore Neogene (Eel River) fore-arc basin. The present Bartlett Springs Fault Zone extends beyond the Mendocino Triple Junction into the modern subduction margin and dismembers the Bartlett Springs Synform. Reconstruction of this dismemberment can be used to approximate total dextral displacement and approximate a long-term slip rate for the Northern Bartlett Springs Fault. MFZ, Mendocino Fault Zone.
0
0 5 10 15 MILES
10 20 30 KILOMETERS
Round Valley
Miocene
Lower Great Valley Complex
Paleogene
Circled areas include Paleogene marine strata deposited on Cretaceous and older Great Valley Complex or Coast Range Ophiolite, representing the former westward extent of the Jurassic-Eocene Great Valley forearc basin. Round Valley area also includes remnants of Miocene estuarine strata indicating the former southeastern extent of a Neogene forearc basin (Eel River basin) that formed in the Miocene further to the west (Nilsen and Clarke, 1989).
STRATIGRAPHIC AND STRUCTURAL RELATIONS CONSTRAINING RECONSTRUCTION OF NORTHERN BARTLETT SPRINGS FAULT ZONE DISPLACEMENT
PALEOCENE–EOCENE CON
VERGENT M
ARG
IN
MIOCEN
E–PALEOCENE CONVERGEN
T MA
RGIN
COASTAL BELT TH
RUST
SAN AN
DREAS FA
ULT
SAN
AN
DREA
S FAULT
PRESENT CO
NVERG
ENT M
A
RGIN
COASTAL BELT THRUST
BARTLETT SPRINGS FAULT
Maacam
a Fault
5
6
3
2
4
1
Figure 7. Schematic reconstruction of Bartlett Springs Synform configuration prior to its dismemberment along the Northern Bartlett Springs Fault Zone (fig. 6 B,C). Also shown are other subparallel folds northeast and southwest of the Bartlett Springs Synform discussed in this report. The restoration suggests a total cumulative oblique dextral slip of approximately 38–47 km for the Northern Bartlett Springs Fault Zone since the middle to late Miocene, based on linking remnants of Paleogene strata deposited along the uplifted and eroded former west margin of the Paleogene and older Great Valley fore arc. Slip could have begun earlier than the Miocene, however, and total displacement could be >50 km. See discussions in pamphlet on Wilbur Springs Dextral Hook and Northern Bartlett Springs Fault.
EXPLANATION
Nonmarine basin deposits, undifferentiated (Quaternary)
Volcanics and deposits of Clear Lake area (Holocene–Pliocene)
Estuarine deposits of Round Valley area (Middle Miocene)
Sandstone and shale, shallow to deep marine (Eocene and Paleocene)
Sandstone and shale, moderately to deep marine, turbiditic (Upper Cretaceous–Upper Jurassic)
Ultramafic and mafic rocks of Coast Range ophiolite and ophiolitic mélange (Lower Cretaceous and Upper–Middle Jurassic)
FRANCISCAN COMPLEX
Central Belt (Upper Cretaceous and older)
Mélange
Snow Mountain volcanic terrane
Eastern Belt (Upper Cretaceous–Upper Jurassic)
Yolla Bolly terrane (Upper Cretaceous–Upper Jurassic)
Metasandstone and slaty argillite
Mélange
Pickett Peak terrane (Lower Cretaceous–Upper Jurassic)
MAJOR FOLDS
Synform
Restored Bartlett Springs Synform
Middle Mountain Synform
Unnamed synform northeast of Rice Valley
Antiform
Pacific Ridge Antiform
Wilbur Springs Antiform
Bartlett Mountain Antiform
OTHER SYMBOLS
Faults
Points used to illustrate range in minimum strike–slip displacement for restoration of Bartlett Springs synform configuration
6
6
1
1
1
3
3
2
5
4
4
ClearLake
~47 Km~38 Km
Approximate range in the minimum amount of slip necessary to restore hypothetical Bartlett Springs synformconfiguration
Potter Valley
Little Indian Valley
Reservoir
Eden Valley
LakePillsbury
Lake Pillsbury
Round Valley
?
SNOW MOUNTAINVOLCANIC TERRANE
Middle Mountain
LowerLake
Rice Valley
Round
Valley
FUTURE NORTHERN BARTLETT SPRINGS FAULT
0
0 5 10 15 MILES
10 20 30 KILOMETERS
Round Valley
Miocene
Lower Great Valley Complex
Paleogene
Circled areas include Paleogene marine strata deposited on Cretaceous and older Great Valley Complex or Coast Range Ophiolite, representing the former westward extent of the Jurassic-Eocene Great Valley forearc basin. Round Valley area also includes remnants of Miocene estuarine strata indicating the former southeastern extent of a Neogene forearc basin (Eel River basin) that formed in the Miocene farther to the west (Nilsen and Clarke, 1989).
STRATIGRAPHIC AND STRUCTURAL RELATIONS CONSTRAINING RECONSTRUCTION OF NORTHERN BARTLETT SPRINGS FAULT ZONE DISPLACEMENT
A B
31-90°
Figure 8. Map showing Wilbur Springs Dextral Hook in context of regional structure and long-term transpressional deformation along the Northern Bartlett Springs Fault Zone. A, Partial map of California, showing major fault blocks associated with Miocene and younger development of the San Andreas Fault, northwestward translation of Salinian block, clockwise rotation of Western Transverse Ranges block (Colgan and others, 2012), and Upper Cretaceous–Neogene clockwise rotation of southern Sierra Nevada /Tehachapi block (Chapman and others, 2010). White box outlines Wilbur Springs Dextral Hook. B, An expanded view of Wilbur Springs Dextral Hook derived from figures 6 and 7, showing reconstructed Bartlett Springs Synform and other folds of the dextral hook. Orientations of folds suggest maximum compression was ~N. 41° E. to S. 41° W., ±16°. Geometry and approximate timing of Wilbur Springs Dextral Hook formation is similar to larger-scale dextral hook formed
by northward translation of the Salinian block since the early to middle Miocene. Upper Cretaceous–Paleogene rotations in southern Sierra Nevada-Tehachapi block, east-vergent crustal wedging, and unroofing of the Franciscan Complex accompanied shallow subduction of overthickened Farallon Plate and was followed by northward translation of the Salinian block during the Miocene (Chapman and others, 2010, 2012; Saleeby, 2003; Ernst and McLaughlin, 2012). See text for further discussion. Fault abbreviations: CASSZ, Cascadia Subduction Zone; GARFZ, Garlock Fault Zone; HAY-CAFZ, Hayward-Calaveras Fault Zone; MAAFZ, Maacama Fault Zone; MFZ, Mendocino Fault Zone; NBSFZ, Northern Bartlett Springs Fault Zone; NSAFZ, Northern San Andreas Fault Zone; RC-HLDFZ, Rodgers Creek-Healdsburg Fault Zone; SAFZ, San Andreas Fault Zone; SG-HFZ, San Gregorio-Hosgri Fault Zone; WW-KCFZ, White Wolf-Kern Canyon Fault Zone.
5 Ma
10 Ma15 Ma
Western Transverse Ranges block (present)
Wilber Springs Dextral Hook
SAFZ
NSAFZ
NSAFZ
SAFZSG-HFZ
GARFZ
WW
-KCF
Z
Mojave block
Southern Sierra Nevada/Tehachapiblock
Northern Sierra Nevada block
NBSFZ
NBSFZMAAFZ
MFZ
CASSZ
HAY-CAFZ
RC-HLDFZ
Salinian block
Coastal Belt
Salinian block
San Francisco
Eureka
Bakersfield
Monterey
San GabrielMountainsblock
Santa Rosa
Klamath block
Round Valley
FUTURE NBSFZ
FUTURE NBSFZ
Reconstructed Bartlett Springs synform
0
0 25 50 75 MILES
50 100 150 KILOMETERS
0
0 5 10 15 MILES
10 20 30 KILOMETERS
EXPLANATION
Nonmarine basin deposits (Quaternary)
Volcanics and deposits of Clear Lake area (Holocene–Pliocene)
Eel River forarc basin (Neogene)
Crystalline basement rock
Western Transverse Ranges block
Central Belt (Upper Cretaceaous and older)
Eastern Belt (Upper Cretaceous–Upper Jurassic)
Coastal Belt (Tertiary and younger)
Coast Range ophiolite and ophiolitic mélange (Lower Cretaceous and Upper–Middle Jurassic)
SYMBOLS
Upper Cretaceous—Neogene clockwise rotation in southern Sierra Nevada Batholith and Tehachapi Mountains block (Chapman and others, 2010)
Approximate location of buried tip of Franciscan tectonic wedge—Barbs on roof thrust side of wedge
Fault—Arrows show relative movement
Thrust fault
Vectors of maximum compression—From orientation of fold axes
MAJOR FOLD AXES
Antiform
Synform
31-90°
PACIFIC RIDGE ANTIFORM
PACIFIC RIDGE ANTIFORM
8/10/16 M 5.1 main shock
8/10/16 M 5.1 main shock
8/10/16 M 5.1 main shock8/10/16 M 5.1
main shock
8/10/16 M 5.1main shock
BARTLETT SPRINGS FAULT ZONE
BARTLETT SPRINGS FAULT ZONE
BARTLETT SPRINGSFAULT ZONE
Cross Section B–B’–B’’
BARTLETT SPRINGS FAULT ZONE
Snow Mountain
++
+
+
+ +
0
-5
-10
-15
-20
t4
t2-6
Dept
h (km
)
0
-5
-10
-15
-20
Dept
h (km
)
0
-5
-10
-15
-20
Dept
h (km
)
Distance (km) Distance (km)
Distance (km)
Distance (km)
0
-5
-10
-15
-20
Dept
h (km
)
0
-5
-10
-15
-20
Dept
h (km
)
t4t3t2-6t1
t5
t1
B' Part of structure section B–B’–B“ Part of structure section C–C’
Structure section E–E’
t3
Figure 12. Seismicity cross sections showing hypocentral depth distribution of earthquakes along sections t1, t2-6, t3, t4, and t5 (see fig. 5 for locations). Hypocenters are projected into seismicity cross sections along lines perpendicular to the sections from ~5 km north and south of the section lines. Depths of the 8/10/16 main shock and its aftershock sequence are, respectively, the large pink and small orange triangles. In t1, t2-6, t3, and t4, post-1984 hypocenters are plotted as small green dots. In section t5, red dots are hypocenters projected into the section from southwest of the plane of the cross section; green dots are hypocenters projected into the section from northeast of the cross-section plane. Intersection of
the Northern Bartlett Springs Fault with plane of t5 is approximated from intersection of the fault’s projection in t2-6, t3, and t4 with plane of t5 (magenta hexagon symbol). In seismicity cross sections t1, t3, and t5, we superpose parts of structure sections B–B'–B", C–C', and E–E', respectively, that correspond with the seismicity cross sections. See the structure sections for explanation of lithologic units. Note that the axis of a major antiform (Pacific Ridge Antiform) in Franciscan rocks northeast of the Northern Bartlett Springs Fault Zone forms prominent high topography in the hanging-wall block of the Northern Bartlett Springs Fault (sections t3 and t5).
EXPLANATION
EARTHQUAKE HYPOCENTERS
8/10/16 M 5.1 main shock
8/10/16 through 9/16/16 aftershock sequence
Microseismicity 1984–2011
Fault block motion toward observer
Fault block motion away from observer
Bartlett Springs Fault Zone—Arrows show relative strike-slip motion across fault
CROSS SECTION T5 (E–E‘) ONLY
Intersections of Northern Bartlett Springs Fault crossing northeast–southwest cross sections t1 (B–B‘–B‘‘), t2-6, t3 (C–C‘), and t4, with the plane of northwest–southwest section t5 (E–E‘)
Hypocenters located behind (northeast) of plane of E–E‘
Hypocenters located in front (southwest) of plane of E–E‘
BEN
D IN
SECT
ION
SECT
ION
E–E’
SECT
ION
B–B’
–B“
SECT
ION
C–C’
SECT
ION
E–E’
SECT
ION
t5
SECT
ION
E–E’
Distance (km)