Date File Created Name of Creator 11/7/2007 Taylor Brown GeoRef Data 2007-028096 DN GeoRef TI "New U-Pb radiometric dates of the Bear Mountain intrusive complex,Klamath Mountains, California" AU "Chamberlain, Kevin R; Snoke, Arthur W; Barnes, Calvin G; Bushey,Jonathan C" AF "University of Wyoming, Department of Geology and Geophysics, Laramie,WY, United States (USA)" AF "Texas Tech University, United States (USA); Texas Tech University,United States (USA)" MT "Geological studies in the Klamath Mountains province, California andOregon; a volume in honor of William P. Irwin" ED "Snoke, Arthur W; Barnes, Calvin G" AF "University of Wyoming, Department of Geology and Geophysics, Laramie,WY, United States (USA)" SO "Special Paper - Geological Society of America, vol.410, pp.317-332,2006" IS 0072-1077 CD GSAPAZ IB 0813724104; 978081372410 DE absolute age; Bear Mountain Complex; Bear Mountain Pluton; California;crystallization; dates; dikes; diorites; faults; igneous rocks;intrusions; Jurassic; Klamath Mountains; magmas; magmatism; Mesozoic;nesosilicates; Nevadan Orogeny; oblique-slip faults; Orleans Fault;orthosilicates; Paleoproterozoic; patterns; plutonic rocks; plutons;Precambrian; precision; Proterozoic; silicates; South Siskiyou ForkFault; tear faults; thrust faults; titanite; titanite group; tonalite;U/Pb; United States; upper Precambrian; variations; zircon; zircongroup AB "New, high-precision U-Pb titanite (sphene) and zircon dates from fivesamples of the Bear Mountain intrusive complex establish the timingand duration of magmatism. The oldest, magmatic date (150.5+ or -0.6Ma) comes from dark-colored titanite from a biotite-hornblendetonalite that is part of a composite pluton that intrudes the BlueRidge ultramafic-gabbroic intrusion. Pale titanite and zircon fromthis sample yielded a distinctly younger date of 149.3+ or -0.3 Ma. Asimilar pattern of mineral dates is also apparent in two samples ofthe areally extensive Punchbowl unit of the Bear Mountain pluton.Dark-colored titanite in one of these samples yielded a date of 149.5+or -0.6 Ma, whereas the dates of pale titanite and zircon are 147.4+or -0.3 Ma. The second sample of the Punchbowl unit only contained asingle morphology of pale titanite, which yielded the same date aszircon (148.2+ or -0.3 Ma). The U-Pb zircon date of the Buck Lake unitof the Bear Mountain pluton, 148.2+ or -0.2 Ma, supports fieldevidence that the Buck Lake unit was emplaced synchronously with thePunchbowl unit. A lower age limit on magmatism in the Bear Mountainintrusive complex comes from a 145.4+ or -0.4-Ma zircon date from alate crosscutting mafic dike. All samples exhibit slight inheritancein the zircon data, with 152- to 150-Ma minimum ages. The mafic dikecontains inherited components that are at least 264 Ma and possiblyPaleo-proterozoic in age. The new dates constrain magmatism in theBear Mountain intrusive complex to the period from 151 to 147 Ma, witha minimum duration of 1.5 m.y. and a maximum of 6 m.y. The datesestablish that the emplacement and crystallization of the BearMountain intrusive complex post-dated regional thrust faulting(Orleans fault) associated with the Nevadan orogeny, including theSouth Siskiyou Fork fault, which is interpreted as an oblique-sliptear fault associated with the Orleans (thrust) fault system. Thepattern of mineral dates from the composite pluton intruded into theBlue Ridge intrusion as well as the areally more extensive Punchbowlunit indicate that crystallization of these bodies occurred over 1.5-2m.y., due to either insulating effects of the intrusive complex and/ormagma recharge." LA English FE "References: 48; illus. incl. 2 tables, geol. sketch maps" PY 2006 PT Serial; Analytic CP United States (USA) LL "Latitude:N410000,N430000 Longitude:W1230000,W1243000" CL "03, Geochronology" CY "GeoRef, Copyright 2007, American Geological Institute." UD 200708 DO 10.1130/2006.2410(15) AN 2007-028096 JV 410 JP 317-332 Sample Data Item LatDD LongDD Loc_prec Age Max_age Min_age Age Max_age Min_age Location_Name Rock_Class Rock_Type Sample_Description Collected_by Material State Units DD DD Ma Ma Ma Ma Ma Ma Method 1 1 2 2 2 3 3 3 Sample Name DP2-20z 41.76227696 -123.7451993 0.0001 149.33 149.62 149.04 150.5 151.11 149.89 Blue Ridge ultramafic-gabbroic intrusion Tonalite Plutonic Biotite-Hornblende Tonalite Chamberlain Mineral Montana DP4-8z 41.80288665 -123.6695683 0.0001 147.43 147.76 147.1 149.5 150.14 148.86 Punchbowl Unit Gabbro Plutonic Pyroxene-Hornblende Gabbro Chamberlain Mineral Montana DP4-10z 41.80369287 -123.670323 0.0001 148.24 148.54 147.94 147.9 148.5 147.3 Punchbowl Unit Gabbro Plutonic Pyroxene-Hornblende Gabbro Chamberlain Mineral Montana DP1-13z 41.79850206 -123.7256258 0.0001 148.17 148.38 147.96 Buck Lake Unit Diorite Plutonic Biotite-Two-Pyroxene Quartz-Bearing Diorite Chamberlain Mineral Montana DP1-35z 41.81293866 -123.7041539 0.0001 145.43 145.85 145.01 Inner aureole of the Bear Mountain intrusive complex Diorite Plutonic Hornblende-Quartz Diorite Dike Chamberlain Mineral Montana Method Data 1 TABLE 2007-028096 2 U-PB6:ZIRC 486 3 U-PB6:SPHENE 486