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Geologic Unit: Alamos
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Map showing publication footprint
  • Usage in publication:
    • Alamos Tonalite
  • Modifications:
    • Named
    • Geochronologic dating
  • Dominant lithology:
    • Tonalite
  • AAPG geologic province:
    • Santa Maria basin
Publication:

Weaver, D.W., 1969, The pre-Tertiary rocks, IN Weaver, D.W., Doerner, D.P., and Nolf, Bruce, eds., Geology of the northern Channel Islands, southern California borderland: American Association of Petroleum Geologists, Pacific Section, Field Trip Guidebook, [no. 12], p. 11-13, (incl. geologic map, scale 1:24,000)


Summary:

[Probably named for Canada del Alamos.] Type locality is exposures 3.2 km north of Alamos Anchorage, south central Santa Cruz Island off southern coast of California. Composed of a highly quartzose, massive, coarse grained, somewhat metamorphosed quartz diorite. Is light-gray, with greenish tinge imparted by chlorite and epidote. Intrudes Santa Cruz Island Schist [new]. Assigned Late Jurassic age based on K-Ar age 145 +/-5 Ma of Willows Diorite [new].

Source: GNU records (USGS DDS-6; Menlo GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Alamos plagiogranite
  • Modifications:
    • Geochronologic dating
  • AAPG geologic province:
    • Santa Maria basin
Publication:

Mattinson, J.M., and Hill, D.J., 1976, Age of plutonic basement rocks, Santa Cruz Island, California, IN Howell, D.G., ed., Aspects of the geologic history of the California continental borderland: American Association of Petroleum Geologists, Pacific Section, Miscellaneous Publication, California Borderland Symposium, Santa Cruz Island, CA, September 22-26, 1975, no. 24, p. 53-58., Prepared in cooperation with USGS and Univ. California, Channel Islands Field Station


Summary:

Pb/U and Pb/Pb age determinations gave 194 +/-20, 144 +/-3 141 +/-3 Ma from Alamos plagiogranite. Samples collected from the East Fork of Laguna Canyon, 33 deg 59'57" N and 119 deg 47'59" W.

Source: GNU records (USGS DDS-6; Menlo GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Alamos Leucotonalite
  • Modifications:
    • Redescribed
    • Age modified
  • Dominant lithology:
    • Plagiogranite
  • AAPG geologic province:
    • Santa Maria basin
Publication:

Hopson, C.A., Mattinson, J.M., and Pessagno, E.A., 1981, Coast Range ophiolite, western California, IN Ernst, W.G., ed., The geotectonic development of California; Rubey memorial volume: Englewood Cliffs, NJ, Prentice-Hall, Inc., v. 1, p. 419-510.


Summary:

[Alamos Tonalite of Weaver (1969)] is redescribed as Alamos Leucotonalite. Composed of an intrusive mass of plagiogranite. Metamorphism shown by schistose margins, apophyses and albitization of primary zoned plagioclase. Intrudes the Santa Cruz Island Schist and maybe the Willows Plutonic Complex. Pb/Pb and Pb/U age determinations gave 201 +/-15, 148 +/-2, 144 +/-2 Ma. Younger samples were collected from apophyses of Alamos plagiogranite [Alamos Leucotonalite] dikes that intrude Willows Complex.

Source: GNU records (USGS DDS-6; Menlo GNULEX).


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