updated 10/24/2006 Gabriel Rotberg Date File Created Name of Creator 10/24/2006 Gabriel Rotberg Georef Data 2004-085330 AU Mihai, Ducea N.; Kidder, Steven; Zandt, George TI Arc composition at mid-crustal depths: insights from the Coast Ridge Belt, Santa Lucia Mountains, California AF University of Arizona, Deptartment of Geosciences, Tucson, Arizona, United States SP Geophysical Research Letters SO 30(13) (July 01, 2003) IS 0094-8276 AB [1] The Coast Ridge Belt (CRB, Santa Lucia Mts., central California) comprises mid-crustal rocks (750-800degreesC and 0.8 GPa) of the California magmatic arc. We estimated the bulk composition of the CRB and converted our results to seismic velocities expected at the observed pressures and temperatures. The bulk composition of this arc section changes abruptly at 25 km depth from a granodiorite to a quartz-diorite or diorite. These data are in agreement with results from other Cordilleran batholiths suggesting 1.5 to 2 times thicker felsic columns than interpreted for modern continental arcs, and a relatively sharp transition from a felsic upper crustal batholith, and a mafic deep crust. This implied rheological boundary may have significant implications for intracrustal faulting or convective removal of the roots of batholiths. CD PB American Geophysical Union, Washington, DC LA English PY 2003 FE References: 27; illus. incl. geol. sketch maps, 1 table, sect. PT serial analytic CP United States USA DE batholiths; California; Coast Ridge Belt; crust; diorites; emplacement; faults; granites; granodiorites; igneous rocks; intrusions; mafic composition; plutonic rocks; rheology; Santa Lucia Range; United States CL Igneous and metamorphic petrology CY GeoRef, Copyright 2004, American Geological Institute. UD 2003 Sample Data Item Age Max_age Min_age Age Max_age Min_age LatDD LongDD Loc_prec SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O P2O5 Location Name rock_class material Rock_Type State Unit Ma Ma Ma Ma Ma Ma DD DD Wt % Wt % Wt % Wt % Wt % Wt % Wt % Wt % Wt % Wt % Method 1 1 1 2 2 2 3 3 3 4 4 4 4 4 4 4 4 4 4 Sample Name 709.2 85 91 80 36.04830556 -121.4889722 0.01 49.5 1.8 19.3 9.9 0.1 3.3 8.1 3.8 1.6 0.6 Santa Lucia Mountains diorite whole rock plutonic California 813.1O 85 91 80 36.04830556 -121.4889722 0.01 49.5 2.1 18.9 10.2 0.1 3.6 7.7 3.8 2.2 0.4 Santa Lucia Mountains diorite whole rock plutonic California 814.2 85 91 80 36.01463889 -121.5083333 0.01 46.2 1.5 13.2 9.5 0.2 7.8 15.2 1.8 0.5 0 Santa Lucia Mountains gabbro whole rock plutonic California 814.9 85 91 80 36.01613889 -121.5041667 0.01 41.9 2.2 18.7 10.6 0.1 6.6 12.8 2.2 0.5 0.1 Santa Lucia Mountains cumulate whole rock plutonic California 802.6 85 91 80 36.04186111 -121.5013056 0.01 46.5 0.2 25.5 3.4 0.1 5.1 13.9 1.4 1.1 0 Santa Lucia Mountains gabbro whole rock plutonic California 808.7 85 91 80 36.04111111 -121.4943611 0.01 54.85 1.62 18.72 4.8 0.129 4.07 7.74 4.93 0.52 0.3 Santa Lucia Mountains diorite whole rock plutonic California 817.1 85 91 80 36.036 -121.4847222 0.01 48.3 2.1 19.8 9.6 0.2 3.8 8 3.1 0.9 0.5 Santa Lucia Mountains diorite whole rock plutonic California 730.3 85 91 80 36.01530556 -121.4980833 0.01 44.1 1.6 19.3 11 0.2 6.8 11 2.1 0.8 0.2 Santa Lucia Mountains gabbro whole rock plutonic California 813.2 85 91 80 36.04916667 -121.4937778 0.01 43.8 2.9 18 10.6 0.2 6.5 9.8 2.5 1.4 0.2 Santa Lucia Mountains amphibolite whole rock metamorphic California 630.4 85 91 80 93 96 90 36.05716667 -121.4951944 0.01 63.23 0.76 17.43 9.21 0.067 2.36 5.25 4.3 0.38 0.22 Santa Lucia Mountains gneiss whole rock metamorphic California 718.3 85 91 80 36.0285 -121.4863889 0.01 60.6 1.6 16.9 7.7 0.2 2 5.3 2.8 1.1 0.4 Santa Lucia Mountains gneiss whole rock metamorphic California 814.11 85 91 80 36.01527778 -121.5058056 0.01 59.35 1.03 17.82 5.26 0.094 3.14 5.78 4.03 0.59 0.34 Santa Lucia Mountains gneiss whole rock metamorphic California 814.12 85 91 80 36.01527778 -121.5058056 0.01 51.4 1 14.8 8.6 0.01 7 9.1 2.9 0.5 0.4 Santa Lucia Mountains gneiss whole rock metamorphic California 711.3 85 91 80 36.06138889 -121.4985833 0.01 82.2 0.2 6.5 6.3 0.01 1.6 0.4 1 0.3 0 Santa Lucia Mountains quartzite whole rock metamorphic California 815.3B 85 91 80 36.01066667 -121.5026667 0.01 82.8 0.3 7.1 3 0.01 1.2 0.6 0.6 2.9 0.1 Santa Lucia Mountains quartzite whole rock metamorphic California Method Data 1 MC_ICP_MS 196 2004-052910 Kidder et al., 2002 2 TIMS_ID 196 2004-052910 Kidder et al., 2002 3 NN 2004-085330 4 XRF 196 2004-052910 Kidder et al., 2002 Reference Data Georef# 2004-052910 AU Kidder, S; Ducea, M; Gehrels, G; Patchett, P J; Vervoort, J TI Tectonic and magmatic development of the Salinian Coast Ridge Belt, California AF University of Arizona, Department of Geosciences, Tucson, AZ, United States; SP Tectonics SO 22(5) (October 2003) IS 0278-7407 CD PB American Geophysical Union, Washington, DC AB We present new field, structural, petrographic, and geochronologic data on a rare midcrustal (?25 km) exposure of a Cordilleran arc, the Coast Ridge Belt, located in the Santa Lucia Mountains of central California. The study area is composed primarily of a deformed suite of upper amphibolite to granulite facies rocks (the Sur Series), which is dominated by metaigneous tonalites, diorites, and gabbros with subordinate metasedimentary quartzite and marble. Inherited zircons in magmatic rocks suggest that the provenance of framework rocks is drawn heavily from miogeoclinal formations and that sedimentation occurred in the late Paleozoic or later. Minor magmatism in the Coast Ridge Belt began in the Early or Middle Cretaceous, but magmatic activity was most intense during a short period time from 93 to 81 Ma, based on U-Pb zircon ages of a felsic gneiss and two less-deformed diorites. The time period 93 81 Ma also brackets a period of extensive thickening and high-temperature ductile deformation. While a thrusting cause for ductile deformation cannot be ruled out, we favor the hypothesis that the exposed rocks correspond to a zone of return flow of supracrustal rocks locally displaced by granitoid plutons in the shallower crust. Magmatism ended throughout Salinia between 81 and 76 Ma, coincident with the attainment of peak pressure and temperature conditions of 0.75 GPa and 800 C. Exhumation followed immediately, bringing the Coast Ridge Belt to the surface within 8 My at a rate of at least 2 3 mm/yr. Exhumation was coincident with an episode of extensional collapse that has been documented elsewhere in the southern California arc during the early Laramide orogeny and that may be related to underthrusting of the forearc at that time. LA English FE References: 83; illus. incl. 5 tables PY 2003 PT serial analytic CP United States DE absolute age; amphibolite facies; batholiths; California; Central California; Coast Ranges; Coast Ridge Belt; crust; deformation; facies; faults; granites; granulite facies; igneous rocks; intrusions; magmatism; metamorphic rocks; middle crust; nesosilicates; North America; North American Cordillera; orthosilicates; Paleozoic; petrography; plutonic rocks; Salinian Block; San Andreas Fault; Santa Luca Mountains; silicates; subduction zones; tectonics; thrust faults; U/Pb; United States; upper Paleozoic; zircon; zircon group CL Structural geology, Igneous and metamorphic petrology CY GeoRef, Copyright 2004, American Geological Institute. UD 2003