Upper plate deformation during blueschist exhumation, ancestral western California forearc basin, from stratigraphic and structural relationships at Mount Diablo and in the Rio Vista Basin

2021 ◽  
Author(s):  
Jeffrey Unruh
Keyword(s):  
San Francisco ◽  
Late Cretaceous ◽  
Normal Faults ◽  
Coast Range ◽  
Forearc Basin ◽  
Bay Area ◽  
The North ◽  
Early Tertiary ◽  
Local Equivalent ◽  
Structural Relief

ABSTRACT Late Cenozoic growth of the Mount Diablo anticline in the eastern San Francisco Bay area, California, USA, has produced unique 3D exposures of stratigraphic relationships and normal faults that record Late Cretaceous uplift and early Tertiary extension in the ancestral California forearc basin. Several early Tertiary normal faults on the northeast flank of Mount Diablo have been correlated with structures that accommodated Paleogene subsidence of the now-buried Rio Vista basin north of Mount Diablo. Stepwise restoration of deformation at Mount Diablo reveals that the normal faults probably root into the “Mount Diablo fault,” a structure that juxtaposes blueschist-facies rocks of the Franciscan accretionary complex with attenuated remnants of the ophiolitic forearc basement and relatively unmetamorphosed marine forearc sediments. This structure is the local equivalent of the Coast Range fault, which is the regional contact between high-pressure Franciscan rocks and structurally overlying forearc basement in the northern Coast Ranges and Diablo Range, and it is folded about the axis of the Mount Diablo anticline. Apatite fission-track analyses indicate that the Franciscan rocks at Mount Diablo were exhumed and cooled from depths of 20+ km in the subduction zone between ca. 70−50 Ma. Angular unconformities and growth relations in the Cretaceous and Paleogene stratigraphic sections on the northeast side of Mount Diablo, and in the Rio Vista basin to the north, indicate that wholesale uplift, eastward tilting, and extension of the western forearc basin were coeval with blueschist exhumation. Previous workers have interpreted the structural relief associated with this uplift and tilting, as well as the appearance of Franciscan blueschist detritus in Late Cretaceous and early Tertiary forearc strata, as evidence for an “ancestral Mount Diablo high,” an emergent Franciscan highland bordering the forearc basin to the west. This outer-arc high is here interpreted to be the uplifted footwall of Coast Range fault. The stratigraphic and structural relations exposed at Mount Diablo support models for exposure of Franciscan blueschists primarily through syn-subduction extension and attenuation of the overlying forearc crust in the hanging wall of the Coast Range fault, accompanied by (local?) uplift and erosion of the exhumed accretionary prism in the footwall.

Tectonics and paleogeography of a post-accretionary forearc basin, Coos Bay area, SW Oregon, USA

2021 ◽  
pp. 187-243
Author(s):  
John M. Armentrout
Keyword(s):  
Sediment Transport ◽  
Middle Eocene ◽  
North American Plate ◽  
Coast Range ◽  
Forearc Basin ◽  
Oregon Coast Range ◽  
Susceptibility Data ◽  
Bay Area ◽  
The North ◽  
Coos Bay

ABSTRACT This field guide reviews 19 sites providing insight to four Cenozoic deformational phases of the Cascadia forearc basin that onlaps Siletzia, an oceanic basaltic terrane accreted onto the North American plate at 51–49 Ma. The field stops visit disrupted slope facies, prodelta-slope channel complexes, shoreface successions, and highly fossiliferous estuarine sandstones. New detrital zircon U-Pb age calibration of the Cenozoic formations in the Coos Bay area and the Tyee basin at-large, affirm most previous biostratigraphic correlations and support that some of the upper-middle Eocene to Oligocene strata of the Coos Bay stratigraphic record represents what was differentially eroded off the Coast Range crest during ca. 30–25 Ma and younger deformations. This suggests that the strata along Cape Arago are a western “remnant” of the Paleogene Tyee basin. Zircon ages and biostratigraphic data encourages the extension of the Paleogene Coos Bay and Tyee forearc basin westward beyond the Fulmar fault and offshore Pan American and Fulmar wells. Integration of outcrop paleocurrents with anisotropy of magnetic susceptibility data from the middle Eocene Coaledo Formation affirms south-southeast to north-northwest sediment transport in current geographic orientation. Preliminary detrital remanent magnetism data show antipodal directions that are rotated clockwise with respect to the expected Eocene field direction. The data suggest the Eocene paleo-shoreline was relatively north-south similar to the modern shoreline, and that middle Eocene sediment transport was to the west in the area of present-day Coos Bay. A new hypothesis is reviewed that links the geographic isolation of the Coos Bay area from rivers draining the ancestral Cascades arc to the onset of uplift of the southern Oregon Coast Range during the late Oligocene to early Miocene.

Cr-spinel supply in the Brkini, Istrian and Krk Island flysch basins (Slovenia, Italy and Croatia)

2003 ◽  
Vol 140 (3) ◽  
pp. 335-342 ◽  
Author(s):  
DAVIDE LENAZ ◽  
VADIM S. KAMENETSKY ◽  
FRANCESCO PRINCIVALLE
Keyword(s):  
Oceanic Crust ◽  
Late Cretaceous ◽  
Type I ◽  
Backarc Basin ◽  
The North ◽  
Magmatic Rocks ◽  
Early Tertiary ◽  
Rifted Continental Margin ◽  
Internal Dinarides ◽  
Orogenic Belts

In Late Cretaceous times, subduction of oceanic crust occurred to the north of the Adria plate and was followed by the formation of ophiolitic complexes. Continental collision in Alpine orogenic belts lasted from Late Cretaceous to Early Tertiary times. The progressive contraction of oceanic crust caused the uplift of previously rifted continental margin and platforms and the formation of foredeep flysch basins. Detrital Cr-spinels are widespread in Eocene sandstones of the Brkini, Istrian and Krk Island foredeep flysch basins. On the basis of their TiO2 content and FeO/Fe2O3 ratio, spinels derived from peridotites and mantle-derived magmatic rocks were distinguished. The first are statistically more abundant and are considered to have been derived from type I and II peridotites. The second appear to be mainly related to backarc basin products. These results suggest that Cr-spinels were derived from the erosion of the Internal Dinarides, where type II and III peridotites are present, and also from the Outer Dinarides, where type I peridotites crop out.

Field and petrographic reconnaissance of Franciscan complex rocks of Mount Diablo, California: Imbricated ocean floor stratigraphy with a roof exhumation fault system

2021 ◽  
Author(s):  
John Wakabayashi
Keyword(s):  
Fault System ◽  
Normal Faults ◽  
Coast Range ◽  
Franciscan Complex ◽  
The North ◽  
Tectonic Window ◽  
Coast Range Ophiolite ◽  
Great Valley Group ◽  
Clastic Sedimentary ◽  
Great Valley

ABSTRACT Franciscan subduction complex rocks of Mount Diablo form an 8.5 by 4.5 km tectonic window, elongated E-W and fault-bounded to the north and south by rocks of the Coast Range ophiolite and Great Valley Group, respectively, which lack the burial metamorphism and deformation displayed by the Franciscan complex. Most of the Franciscan complex consists of a stack of lawsonite-albite–facies pillow basalt overlain successively by chert and clastic sedimentary rocks, repeated by faults at hundreds of meters to <1 m spacing. Widely distributed mélange zones from 0.5 to 300 m thick containing high-grade (including amphibolite and eclogite) assemblages and other exotic blocks, up to 120 m size, form a small fraction of exposures. Nearly all clastic rocks have a foliation, parallel to faults that repeat the various lithologies, whereas chert and basalt lack foliation. Lawsonite grew parallel to foliation and as later grains across foliation. The Franciscan-bounding faults, collectively called the Coast Range fault, strike ENE to WNW and dip northward at low to moderate average angles and collectively form a south-vergent overturned anticline. Splays of the Coast Range fault also cut into the Franciscan strata and Coast Range ophiolite and locally form the Coast Range ophiolite–Great Valley Group boundary. Dip discordance between the Coast Range fault and overlying Great Valley Group strata indicates that the northern and southern Coast Range fault segments were normal faults with opposite dip directions, forming a structural dome. These relationships suggest accretion and fault stacking of the Franciscan complex, followed by exhumation along the Coast Range fault and then folding of the Coast Range fault.

Taming the Wild West in the Late 1940s

2015 ◽  
Vol 92 (1) ◽  
pp. 27-52
Author(s):  
Christopher M. Sterba
Keyword(s):  
New York ◽  
San Francisco ◽  
Equal Opportunity ◽  
Political Conflict ◽  
Economic Security ◽  
Turn Of The Century ◽  
Lonely Crowd ◽  
The Great Depression ◽  
Bay Area ◽  
The North

In late 1945, a group of outraged citizens in the small city of El Cerrito formed a “Good Government League” to challenge the gambling and liquor interests who controlled City Hall. In the next few years the League achieved all of its agenda: a city manager plan, civil service reform, and the end of wide-open gambling. A movement like this was fairly typical of the Progressive Era. But the city in question was not a turn-of-the-century metropolis like New York or Chicago. These events happened in the late 1940s in a small bedroom community located just to the north of Berkeley. Within a few years, El Cerrito transformed its reputation from “Little Reno” to the squeaky-clean “City of Homes.” As a case study, the El Cerrito story is interesting for a number of reasons. Most importantly, it highlights how development in the San Francisco Bay Area has involved a regional periodization that differs from what we might traditionally associate with suburban growth. The city's Old West heritage was a major source of political conflict, while the activism of the city's new middle class contrasts with what sociologists called the politically quiescent “Organization Men” of the era's “Lonely Crowd.” The El Cerrito experience also lends insight into why the Bay Area has remained politically liberal since 1945. The city's reformers embraced much of the language and platform of the turn-of-the-century progressives. But they also lived through the Great Depression and the Second World War, and desired most of all to make public policy that would ensure economic security and equal opportunity. Their emphasis on an active public sector left a legacy that can still be felt today.

scholarly journals Volutoderminae (Gastropoda: Volutidae) of Coniacian through Maastrichtian age from the North American Pacific Slope

2008 ◽  
Vol 82 (2) ◽  
pp. 213-237 ◽  
Author(s):  
Louella R. Saul ◽  
Richard L. Squires
Keyword(s):  
San Francisco ◽  
Late Cretaceous ◽  
Gulf Coast ◽  
Shallow Marine ◽  
The North ◽  
Rudist Bivalves ◽  
Pacific Slope ◽  
Warm Temperate ◽  
World Distribution ◽  
A New Species

Specimens of the large, shallow-marine, volutid gastropod Volutoderma Gabb, 1877, herein recognized only from strata of Late Cretaceous (Coniacian through early Maastrichtian) age in British Columbia, Washington, California, and Baja California have commonly been identified as Volutoderma averillii (Gabb, 1864). This review of available specimens assigns them to two genera: Volutoderma and Longoconcha Stephenson, 1941.Twelve species, nine of them new, comprise three morphologic lineages of Volutoderma, i.e., 1) “Typical” includes V. querna n. sp., V. averillii (Gabb), V. blakei n. sp., V. jalama n. sp., V. perissa n. sp., and possibly Volutoderma? n. sp.; 2) “Angelica” includes V. angelica n. sp., V. elderi n. sp., and V. ynezae n. sp.; and 3) “Magna” includes V. santana Packard, V. magna Packard, and perhaps V.? antherena n. sp. A new species of Longoconcha, L. eumeka, is the first Pacific Slope record of this genus, which has a Gulf Coast and Tethyan Old World distribution. A smaller volutid, Retipirula Dall, 1907 is endemic to the study area and was formerly known only from its type species R. crassitesta (Gabb, 1869) of Paleocene age. Two new Retipirula are reported: R. calidula of latest Maastrichtian age and R. pinguis of Paleocene age.Only the Volutoderma lineage containing V. averillii has been found north of San Francisco. Recovery of rudist bivalves from formations yielding Volutoderma suggests that these volutes were warm-temperate to subtropical gastropods. Co-occurrences of these gastropods and rudistids may aid in placing the warm-temperate/subtropical boundary during the Late Cretaceous.

Different modes of the Late Cretaceous–Early Tertiary inversion in the North German and Polish basins

2005 ◽  
Vol 94 (5-6) ◽  
pp. 782-798 ◽  
Author(s):  
Stanislaw Mazur ◽  
Magdalena Scheck-Wenderoth ◽  
Piotr Krzywiec
Keyword(s):  
Late Cretaceous ◽  
The North ◽  
Early Tertiary

Late Cretaceous-early Tertiary stratigraphy of the Kangerdlugssuaq area, east Greenland, and the age of opening of the north-east Atlantic

1976 ◽  
Vol 132 (1) ◽  
pp. 85-102 ◽  
Author(s):  
N. J. SOPER ◽  
A. C. HIGGINS ◽  
C. DOWNIE ◽  
D. W. MATTHEWS ◽  
P. E. BROWN
Keyword(s):  
Late Cretaceous ◽  
East Atlantic ◽  
East Greenland ◽  
North East ◽  
The North ◽  
Early Tertiary

scholarly journals The Kap Washington Group volcanics

1981 ◽  
Vol 106 ◽  
pp. 65-68
Author(s):  
P.E Brown ◽  
I Parsons
Keyword(s):  
Late Cretaceous ◽  
Volcanic Rocks ◽  
Personal Communication ◽  
North Coast ◽  
Sr Isotopes ◽  
Fold Belt ◽  
The North ◽  
Early Tertiary ◽  
North Greenland

The Kap Washington Group volcanic rocks outcrop on the north coast of Johannes V. Jensen Land and Lockwood ø, where they are in thrust contact with Palaeozoic metasediments of the North Greenland fold belt. Their outcrop is limited, from west to east, to Lockwood Ø, Kap Kane, Kap Washington and Kap Cannon (fig. 21). The vo1canic rocks post-date basic dykes which cut Carboniferous and Permian sediments (Håkansson et al., this report) and their age, as determined by whole rock Rb-Sr isotopes in rhyolitic material, is 63 Ma (Larsen et al., 1978) i.e. early Tertiary. This is somewhat younger than the late Cretaceous age established by micropalaeontological evidence (D. Batten, personal communication) from shales, found in 1980, interbedded with the voicanics.

Asbestiform Minerals of the Franciscan Assemblage in California with a Focus on the Calaveras Dam Replacement Project

2020 ◽  
Vol 26 (1) ◽  
pp. 21-28
Author(s):  
R. Mark Bailey
Keyword(s):  
San Francisco ◽  
North American Plate ◽  
Tectonic Activity ◽  
Bay Area ◽  
The North ◽  
Rock Types ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Naturally Occurring Asbestos ◽  
Asbestiform Minerals

ABSTRACT The San Francisco Bay Area is underlain by bedrock of the Franciscan Assemblage, which outcrops in numerous places. A significant portion of these outcrops consists of rock types that contain both regulated and unregulated asbestiform minerals, including ultra-mafic serpentinites, various greenstones, amphibolites, blueschist, and other schists (talc-tremolite, actinolite, etc.). These rocks are a legacy of tectonic activity that occurred on the west coast margin of the North American plate ∼65–150 MY ago during subduction of the East Pacific and Farallon plates. The Calaveras Dam Replacement Project (CDRP), located in Fremont, California, is an example of an area within the Franciscan Assemblage that is substantially underlain by metamorphosed oceanic sedimentary, mafic, and ultra-mafic rocks in a tectonic subduction zone mélange with highly disrupted relationships between adjoining rock bodies with different pressure/temperature metamorphic histories. In order to protect the health of workers and residents in the surrounding area, an extensive effort was taken to identify, categorize, and monitor the types, locations, and concentrations of naturally occurring asbestos at the site. Using a combination of geologic field observations and transmission electron microscopy, energy dispersive X-ray, and selected area electron diffraction analysis of airborne particulate and rock/soil samples, the CDRP was discovered to contain chrysotile-bearing serpentine. It also had as a range of amphibole-containing rocks, including blueschist, amphibolite schist, and eclogite, with at least 19 different regulated and non-regulated fibrous amphibole minerals identified. The extensive solid solution behavior of the amphiboles makes definitive identification difficult, though a scheme was created that allowed asbestos mineral fingerprinting of various areas of the project site.

Northern California Coast Ranges, Domain 4

2007 ◽  
Author(s):  
Earl B. Alexander ◽  
Roger G. Coleman ◽  
Todd Keeler-Wolfe ◽  
Susan P. Harrison
Keyword(s):  
San Francisco ◽  
Northern California ◽  
Coast Range ◽  
Klamath Mountains ◽  
California Coast ◽  
Mountain Ranges ◽  
The North ◽  
Coast Ranges ◽  
California Coast Ranges ◽  
Great Valley

The Northern California Coast Ranges domain is in a mountainous region in which most of the mountain ranges are aligned north–south, or more precisely north, northwest– south southeast, curving around the Klamath Mountains into Oregon where the domain branches to north–south and northeast–southwest trends on the northwest side of the Klamath Mountains. It extends about 600km from the Golden Gate at the entrance to San Francisco Bay north to about the Coquille River in Coos County and nearly to the North Umqua River in Douglas County, Oregon. The domain corresponds to a physiographic region that is bounded by the Pacific Ocean on the west, the Coast Range of Oregon and Washington (Orr and Orr 1996) on the north, the Klamath Mountains on the northeast, the Great Valley of California on the southeast, and on the south by the drainage outlet of the Sacramento and San Joaquin rivers through the Carquinas Straight and San Pablo Bay. Serpentine is scattered in relatively small ultramafic bodies throughout the Northern California Coast Ranges and is concentrated along some of the major faults. For 200 or 300 km south from the Klamath Mountains, the Northern California Coast Ranges region is a rectangular strip 90–110 km wide between the Ocean and the Great Valley of California. The Klamath Mountains crowd the region to a narrow strip only 10 or 12 km wide in Del Norte County. Most of the mountain ranges have approximately concordant summits that are tilted up toward the east–northeast. Therefore, the highest altitudes are on the east, just south of the Klamath Mountains. North Yolla Bolly at 2397 m (7865 feet) and South Yolla Bolly at 2466 m (8092 feet) have the highest summits. Both of these and some neighboring mountains have cirques and moraines indicative of glaciation on their north slopes. There is no evidence of glaciation in any areas with serpentine rocks. Only the Rogue and Klamath rivers cut from east to west all of the way across the Northern California Coast Ranges, except for a few smaller streams such as the Chetco and Smith rivers that have headwaters in the Klamath Mountains.

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