EVALUATING DETRITAL ZIRCON PROVENANCE OF PRE-MESOZOIC STRATA IN THE SIERRA NEVADA, EASTERN CALIFORNIA

Detrital zircon U/Pb geochronology of disrupted Paleozoic strata across the Sierra Nevada provides new constraints on the tectonic evolution of the SW Laurentian margin before the formation of Mesozoic arcs. To evaluate 32 new sample detrital ages, we have compiled 123 published sample ages from pre-Mesozoic strata spanning CA, NV, UT, and AZ. As this volume of data complicates comparison of sample ages, we have used multidimensional scaling to explore these data.

Sierra Nevada Paleozoic rocks form distinct stratigraphic groups trending ~NNW. From E-W these are: (1) more distal equivalents of inboard passive margin shelf deposits known as the Morrison Block; (2) deep-water strata similar to rocks of the Roberts Mountain (RMA) and Golconda allocthons; (3) displaced, para-autochthonous shallow-water strata of the Snow Lake Block; (4) deep-water strata of the Shoo Fly Complex and southern Sierra Kernville terrane; and (5) abyssal and ophiolitic rocks of the Western Metamorphic Belt.

Detrital ages synthesized with field data show that: (1) para-autochthonous rocks of the Morrison Block record provenance similar to shallow-water strata across the southwestern Laurentian margin until at least Devonian time; (2) their dissimilarity to RMA detrital ages suggests that RMA strata are not the distal equivalent of this section of the passive margin; (3) allochthonous deep-water strata overlying the Morrison Block record provenance divergent from RMA rocks that match Devonian rocks of the Klamath Mountains and southern British Columbia; (4) submarine sediments and volcaniclastics of likely Permian age are exposed in the eastern central Sierra; (5) deep-water strata of the El Paso terrane record provenance highly similar to allochthonous deep-water strata, supporting previous correlations with the RMA; (6) boundaries of the Snow Lake Block and Western Metamorphic Belt near the southern extent of the Shoo Fly Complex need to be reevaluated; (7) deep-water strata of the Kernville terrane show two distinct detrital age distributions with unique features relative to both deep- and shallow-water strata; and (8) at least some Paleozoic rocks presently exposed in the Sierra Nevada were likely displaced southward along the margin prior to formation of a regional Late Permian unconformity and arc initiation at ~255 Ma.