Paper No. 5
Presentation Time: 2:45 PM
TEMPORAL RELATIONS OF THREE DIMENSIONAL MANTLE LITHOSPHERE DELAMINATION RESOLVED IN SOUTHEASTERN GREAT VALLEY'S SUBSIDENCE-UPLIFT HISTORY, SIERRA NEVADA MICROPLATE, CALIFORNIA
A synthesis of geophysical and geological data suggests that the eclogitic (arclogite) mantle lithosphere root that formed during Cretaceous arc magmatism beneath the southern Sierra Nevada (SN) and adjacent Great Valley (GV) has progressively delaminated in E to W, and subsequently in S to N directions during Pliocene-Quaternary time. Thermo-mechanical modeling predicts km-scale subsidence/uplift transients through the course of delamination. The current delamination hinge runs along the southeastern margin of the GV, and turns westwards towards the axial southernmost GV. The Tulare (sub-) basin of the GV lies west of the delamination hinge, above the area of lower crustal attachment of the residual arclogite root, with the delaminated portion of the root hinging down to the east and south into the underlying mantle. The “center” of Tulare basin records ~700 m of anomalous Pliocene-Quaternary tectonic subsidence, which occurred mainly during the E to W phase of delamination. The southern margin of Tulare basin is uplifted and eroded along the Kern Arch, a Quaternary epeirogenic uplift zone that continues eastwards into the western Sierra, where GPS monuments record the most rapid contemporary uplift rates of the entire SN. The southern segment of the delamination hinge curves westward and runs along the transition between Tulare basin and the Arch. Erosional truncation patterns of Cenozoic strata along the eastern margin of the Arch, along with subsurface data on: 1. mechanical granulation textures; 2. low grade metamorphic phases; 3. vitrinite reflectance; 4. detrital apatite (U-Th)/He ages; and 5. thermal modeling, - all indicate up to ~1500 m of Pliocene cryptic (total) subsidence and sedimentation prior to rapid Quaternary uplift of the Arch. The cryptic subsidence was in continuity with the anomalous subsidence recorded in Tulare basin, and follows the regional pattern of southward increasing sediment loading and total subsidence along the southern Great Valley. The Tulare-Kern Arch subsidence/uplift relationships record epeirogenic transients arising from the Pliocene phase of E to W delamination, followed by the Quaternary S to N phase of delamination. This transient pattern parallels rock uplift, and volcanic and thermal flux patterns of the adjacent southern SN.