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M.C. Blake

Publications and source records attributed to M.C. Blake.

At least 19 recordsLinked to original sources
USGS2010

Correlation of early Cretaceous blueschists in Washington, Oregon and northern California

The protolith and metamorphic histories of Early Cretaceous blueschists that occur in Washington, Oregon, and California are remarkably similar. These blueschists are the Shuksan metamorphic suite of northwestern Washington, the Condrey Mountain schist of northern California and southern Oregon, and the Pickett Peak terrane of northern California and southwestern Oregon. We suggest that these bodies were coextensive during their formation. Dispersion of the blueschists occurred in Late Cretaceous time by lateral translation of up to 900 km along the continental margin in response to oblique plate convergence.

California, Oregon, Washington↗
USGS2010

Tectonics of formation, translation, and dispersal of the Coast Range ophiolite of California

Data from the Coast Range ophiolite and its tectonic outliers in the northern California Coast Ranges suggest that the lower part of the ophiolite formed 169 to 163 Ma in a forearc or back arc setting at equatorial latitudes. Beginning about 156 Ma and continuing until 145 Ma, arc magmatism was superimposed on the ophiolite, and concurrently, a transform developed along the arc axis or in the back arc area. Rapid northward translation of this rifted active magmatic arc to middle latitudes culminated in its accretion to the California margin of North America at about 145 Ma. This Late Jurassic episode of translation, arc magmatism, and accretion coincided with the Nevadan orogeny and a proposed major plate reorganization in the eastern Pacific basin. The high rate of poleward motion necessary to translate the Coast Range ophiolite to middle latitudes during this time implies that the ophiolite traveled north on a fast-moving plate of the eastern Pacific basin, here termed plate X. Plate X probably was driven by a cryptic ridge east-northeast of the Pacific-Farallon-Izanagi ridge triple junction. Structural relations indicate that following Late Jurassic time, parts of the Coast Range ophiolite were displaced from the west side of the Great Valley province and incorporated into the Central belt of the Franciscan Complex along steep-dipping to low-angle reverse faults having dominant components of dextral shear. A northwest trending eastern zone of these right-laterally displaced outliers shows strong affinities to the main Coast Range ophiolite of the northwestern Sacramento Valley (the Elder Creek terrane), in that the outliers include ophiolitic breccias of Oxfordian to Kimmeridgian age. A southwestern zone of outliers lacks ophiolitic breccia and instead includes latest Oxfordian or Kimmeridgian to Tithonian, arc-derived volcanic rocks like those found in the Del Puerto and Stanley Mountain terranes of the main ophiolite. Whereas outliers of the northeastern outlier zone are right-laterally displaced no more than 260 km from the western side of the Sacramento Valley, outliers of the southwestern zone are displaced a minimum of 169 to 249 km. This displacement occurred between about 60 and 52 Ma. Ophiolitic rocks in the Decatur terrane of western Washington that have recently been correlated with the Coast Range ophiolite and the Great Valley sequence of California were apparently displaced at least 950 to 1200 km from the west side of the Great Valley between early Tertiary and Early Cretaceous time. Derived rates of northward translation for the ophiolite outliers in California are in the range of 1 to 4 cm/yr. Rates for the Decatur terrane are in the range of 2.5 to 4 cm/yr if translation was initiated 90 Ma, but as much as 11.9 to 15 cm/yr if it was not initiated until 60 Ma. The lower rates for the Decatur terrane are consistent with the rates derived for the California outliers and with the northward component of relative motion between the Farallon and North American plates from 90 to 50 Ma. The higher rates require northward transport on the Kula plate or on a fast-moving microplate. The higher translation rates derived for the Decatur terrane are also consistent with paleomagnetically determined rates for some limestones of the Central belt. This may indicate that outliers of the Coast Range ophiolite dispersed in the Central belt of the Franciscan Complex record only part of the total displacement which occurred along the Late Cretaceous to early Tertiary western margin of North America.

California↗
USGS2010

Structure and metamorphism of the Franciscan Complex, Mt. Hamilton area, Northern California

Truncation of metamorphic isograds and fold axes within coherent terranes of Franciscan metagraywacke by intervening zones of melange indicate that the melange is tectonic and formed after the subduction-related metamorphism and folding. These relations are expressed in two terranes of blueschist-facies rocks of the Franciscan Complex in the Mt. Hamilton area, northern California-the Jurassic Yolla Bolly terrane and the structurally underlying Cretaceous Burnt Hills terrane. Local preservation in both terranes of basal radiolarian chert and oceanic basalt beneath continent-derived metagraywacke and argillite demonstrates thrust repetition within the coherent terranes, although these relations are scarce near Mt. Hamilton. The metagraywackes range from albite-pumpellyite blueschists to those containing well-crystallized jadeitic pyroxene, and a jadeite-in isograd can be defined in parts of the area. Primary bedding defines locally coherent structural orientations and folds within the metagraywacke units. These units are crosscut by thin zones of tectonic melange containing blocks of high-grade blueschist, serpentinite, and other exotic rocks, and a broader, but otherwise identical melange zone marks the discordant boundary between the two terranes.

California↗
USGS2002

Geologic map and map database of western Sonoma, northernmost Marin, and southernmost Mendocino counties, California

This digital map database, compiled from previously published and unpublished data, and new mapping by the authors, represents the general distribution of bedrock and surficial deposits in the mapped area. Together with the accompanying text file (wsomf.ps, wsomf.pdf, wsomf.txt), it provides current information on the geologic structure and stratigraphy of the area covered. The database delineates map units that are identified by general age and lithology following the stratigraphic nomenclature of the U.S. Geological Survey. The scale of the source maps limits the spatial resolution (scale) of the database to 1:62,500 or smaller.

Miscellaneous Field Studies Map↗
USGS2000

Geology of the Cape MendocinoGeology of the Cape Mendocino, Eureka, Garberville, and southwestern part of the Hayfork 30 x 60 minute quadrangles and adjacent offshore area, northern California, with digital database

Introduction These geologic maps and accompanying structure sections depict the geology and structure of much of northwestern California and the adjacent continental margin. The map area includes the Mendocino triple junction, which is the juncture of the North American continental plate with two plates of the Pacific ocean basin. The map area also encompasses major geographic and geologic provinces of northwestern California. The maps incorporate much previously unpublished geologic mapping done between 1980 and 1995, as well as published mapping done between about 1950 and 1978. To construct structure sections to mid-crustal depths, we integrate the surface geology with interpretations of crustal structure based on seismicity, gravity and aeromagnetic data, offshore structure, and seismic reflection and refraction data. In addition to describing major geologic and structural features of northwestern California, the geologic maps have the potential to address a number of societally relevant issues, including hazards from earthquakes, landslides, and floods and problems related to timber harvest, wildlife habitat, and changing land use. All of these topics will continue to be of interest in the region, as changing land uses and population density interact with natural conditions. In these interactions, it is critical that the policies and practices affecting man and the environment integrate an adequate understanding of the geology. This digital map database, compiled from previously published and unpublished data, and new mapping by the authors, represents the general distribution of bedrock and surficial deposits in the mapped area. Together with the accompanying text file (ceghmf.ps, ceghmf.pdf, ceghmf.txt), it provides current information on the geologic structure and stratigraphy of the area covered. The database delineates map units that are identified by general age and lithology following the stratigraphic nomenclature of the U.S. Geological Survey. The scale of the source maps limits the spatial resolution (scale) of the database to 1:100,000 or smaller.

California↗
USGS2000

Geologic map and map database of parts of Marin, San Francisco, Alameda, Contra Costa, and Sonoma counties, California

This digital map database, compiled from previously published and unpublished data, and new mapping by the authors, represents the general distribution of bedrock and surficial deposits in the mapped area. Together with the accompanying text file (mageo.txt, mageo.pdf, or mageo.ps), it provides current information on the geologic structure and stratigraphy of the area covered. The database delineates map units that are identified by general age and lithology following the stratigraphic nomenclature of the U.S. Geological Survey. The scale of the source maps limits the spatial resolution (scale) of the database to 1:62,500 or smaller general distribution of bedrock and surficial deposits in the mapped area. Together with the accompanying text file (mageo.txt, mageo.pdf, or mageo.ps), it provides current information on the geologic structure and stratigraphy of the area covered. The database delineates map units that are identified by general age and lithology following the stratigraphic nomenclature of the U.S. Geological Survey. The scale of the source maps limits the spatial resolution (scale) of the database to 1:62,500 or smaller.

Miscellaneous Field Studies Map↗
USGS1993

Northward displacements of forearc slivers in the Coast Ranges of California and Southwest Oregon during the late Mesozoic and early Cenozoic

North American-Farallon-Kula plate motion data, combined with estimated strikeslip displacements obtained from the obliquity of convergence along active circumPacific subduction zones, can be used to estimate the amount of strike-slip displacement along the forearc region of western North America. This evidence suggests a minumum of 500 km and maximum of 1600 km displacement with respect to the Farallon plate, and a minumum of 1600 km and a maximum of 4900 km with respect to the Kula plate (or some equivalent) from Late Jurassic to middle Eocene (145 Ma to 43 Ma). These displacements are consistent with pre-middle Eocene displacements of paleoforearc strata (Franciscan Complex, Great Valley sequence and related units), inferred from pa 1eomagnetic, petrologic, stratigraphic, and conglomerate pebble data. Tentative restorations suggest that the Elk outlier and Snow Camp terrane of southwest Oregon have affinities with the southern Klamath Mountains of northern California; that the Gold Beach terrane of southwest Oregon has affinities with central or southern California; that the Healdsburg terrane of the San Francisco area has affinities with southern California; that other Franciscan rocks of the San Francisco area have affinities with central or southern California; and that the Nacimiento block has affinities with the Peninsular Ranges or Vizcaino area of Baja California. These tentative correlations suggest about 600-1000 km of right-lateral displacement between Early Cretaceous and middle Eocene time which can be entirely accommodated by Farallon plate motions and (or) represent minimal displacement with respect to Kula plate motions (or some equivalent).

Book chapter↗
USGS1989

Deformation of the Eastern Franciscan Belt, northern California

The late Jurassic and Cretaceous Eastern Franciscan belt of the northern California Coast Range consists of two multiply deformed, blueschist-facies terranes; the Pickett Peak and Yolla Bolly terranes. Four deformations have been recognized in the Pickett Peak terrane, and three in the Yolla Bolly terrane. The earliest recognized penetrative fabric, D 1 , occurs only in the Pickett Peak terrane. The later penetrative fabrics, D 2 and D 3 , occur in both the Yolla Bolly and Pickett Peak terranes. D 1 and D 2 apparently represent fabrics that formed during subduction and accretion of the terranes. Fabrics from both D 1 and D 2 are consistent with SW-NE movement directions with respect to their present geographic positions. D 3 postdates blueschist-facies metamorphism of the terranes and may be related to emplacement of the terranes to higher structural levels. A broad regional warping, D 4 , is evident from the map pattern and folding of large metamorphosed thrust sheets. D 4 folds may be related to deformation associated with oblique convergence along the continental margin in late Cretaceous and (or) early Tertiary time.

Journal of Structural Geology↗
USGS1989

New evidence for polyphase metamorphism of glaucophane schist and eclogite exotic blocks in the Franciscan Complex, California and Oregon

The early metamorphic history of high-grade exotic blocks in the Franciscan Complex may be more complicated than previously supposed. The different assemblages of high-grade glaucophane schists, eclogite, amphibolite and hornblende schist are commonly considered to have formed at the same time from essentially unmetamorphosed oceanic crust. However, new textural and mineralogical data presented here suggest that high-grade glaucophane schist and eclogite have replaced an earlier epidote-amphibolite facies assemblage that is identical to the primary assemblages in many of the hornblende-rich blocks. At least some of the hornblende-rich blocks may therefore be well-preserved remnants of the earlier metamorphism. Comparison of the mineral assemblages and element partititioning in the mixed-assemblage blocks suggests that the glaucophane schist and eclogite metamorphism took place at slightly lower temperatures but at the same or higher pressures than the earlier, hornblende-forming stage. -Authors

Journal of Metamorphic Geology↗