DETRITAL ZIRCON GEOCHRONOLOGY OF BASEMENT AND COVER
ROCKS FROM THE SANTA LUCIA MOUNTAINS, CALIFORNIA; NEW
EVIDENCE FOR LIMITED TRANSPORT OF SALINIA
ALVARADO, Patricia1, BARBEAU, David1, ROBINSON, Cecil1, DUCEA, Mihai2,
GEHRELS, George2, GUYNN, Jerome2, HAGBO, Casey1, HE, Shudong2, HENNES,
Andrew1, and KRAWCIW, Olena2, (1) Department of Geosciences, Univ of Arizona,
Gould-Simpson Building,1040, E. Fourth St, Tucson, AZ 85721,
dbarbeau@geo.arizona.edu, (2) Geosciences, Univ of Arizona, Tucson, AZ 85721
Salinia is an out-of-place granitic terrane in California bounded by strike slip faults and
Franciscan rocks. Some 340 km of right lateral displacement are attributable to late
Cenozoic motion along the San Andreas system; prior to this, the Salinian block must
have been close to the Mojave region in southern California. Paleomagnetic and geologic
arguments suggest however, that Salinia could have originated much further south of the
Mojave, probably at the latitudes of southern Mexico; after 30 years of research, the
controversy of limited vs. significant travel for “orphan” Salinia, has not been settled. In
order to further address this problem, we used LA-MC-ICPMS techniques to determine
detrital zircon U-Pb ages on two samples from the Coast Ridge Belt (CRB), Santa Lucia
Mts.: (1) CONE, a quartzite from the Sur Series exposed in the vicinity of Cone Peak,
and (2) ESALEN, a sand-rich layer within the Maastrichtian cover that rests
unconfomably over the Salinian basement. The depositional age of the Sur Series is
unknown; arc-related granitic rocks in the CRB (92-80 Ma) constrain that age to be pre
Late Cretaceous. One hundred zircon grains were measured from each sample, yielding
168 ages that are of sufficient concordance and precision to provide provenance
information. CONE yields distinctive age peaks at 360-380, ~425, 1100-1200, ~1430,
1750-1900, and ~2700 Ma. ESALEN has distinctive peaks at ~93, ~135, ~155, 240-280,
~380, and 1400-1440 Ma. From a provenance point of view, the distribution of
Precambrian ages is consistent with a paleoposition near the SW US but are inconsistent
with an origin near southern Mexico. Other important age peaks in the two analyzed
samples are 360-380 Ma in CONE and 240-280 Ma in ESALEN; these are unusual
orogenic ages for the southwestern Cordillera. Locations that could have yielded Permian
ages are in areas where the eugeocline is present, e.g. in the vicinity of the El Paso
Mountains, northern Mojave desert. We suggest that during Late Cretaceous time, midand late Paleozoic magmatic assemblages may have been widespread along the
continental margin of SW US and NW Mexico.