Karl Mueller QUATERNARY RIFT FLANK UPLIFT OF THE PENINSULAR RANGES IN BAJA AND SOUTHERN CALIFORNIA BY REMOVAL OF MANTLE LITHOSPHERE

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1 QUATERNARY RIFT FLANK UPLIFT OF THE PENINSULAR RANGES IN BAJA AND SOUTHERN CALIFORNIA BY REMOVAL OF MANTLE LITHOSPHERE August 2013

2 Quaternary Rift Flank Uplift of the Peninsular Ranges in Baja and Southern California by Removal of Mantle Lithosphere TECTONICS, Mueller, Rockwell, Kier and Jones, 2009, 28, doi: /2007tc002227

3 Rift Flank Model Started with the OBT where coastal uplift was considered as a possible indicator of recent activity. Subsequently sought to determine where coastal uplift ended to the south relative to existing offshore blind thrust models Determined that uplift continued 400 kilometers into Baja Made the connection between high topography in the Peninsular Ranges and uplift along the Pacific Coast, best explained as flank uplift - common to many rifts, here the Gulf of California Undertook flexural modeling to assess sources of bouyancy in the crust and mantle lid. Most of the bouyancy that drives uplift must come from the mantle.

4 Rift Flanks Karl Mueller

5 Modeling Flexure Requires constraints on processes and crustal structure that drives changes in bouyancy. These include: Crustal thickness and how it changes Geometry and height of rift flank Timing and extent of coastal uplift (sea level as a datum) Extensional basin geometry and fill Crustal thinning and erosion Estimates of effective elastic thickness and flexural rigidity

6 Crustal thickness from receiver functions (seismology) Lewis et al., 2001

7 Geometry and Height of Rift Flank Post Eocene Erosion Surface

8 Timing and Extent of Coastal Uplift San Diego Cabo Colonet Punta Baja Punta Rosalilita to Cabo (no uplift)

9 Timing and Extent of Coastal Uplift

10 Modeling approach See Tectonics paper p for details, equations and tradeoffs for forces acting on Peninsular Ranges 4D 4D 4 m f g m f g 4 3 ET ET e 3 e D

11 Contributions to buoyancy for a line load that produces flexure similar il to erosional surface. Crustal processes balance out, so a large positively buoyant mantle source is required.

12 Started with simple models with constant Te (line loads & blocks) Got more complicated, thin Te across rift, migrated westward Extension in Salton Trough - crustal thinning (receiver functions) Infilling by sediments (refraction data) Erosion of rift flank Metamorphism of sediments (minor) Karl Mueller Chemistry of mantle (xenoliths) at Pinacates and San Quintin suggest normal lithosphere, so buoyancy must by driven by thinning of mantle lid or heating, not a phase change (i.e. mineralogy) as has been proposed for the Sierra Nevada. Regardless, a 10% decrease in density (replace Lithosphere with Asthenosphere) was used.

13 Te = 15, 20, 30 kilometers, varied negative e mantle loads

14 Best fit and more realistic models Te = 10 km rift, 24 km Penin Ranges Mantle load moves westward

15 Simple best-fit flexural model Karl Mueller Inferred mantle load is for entire post Eocene history of Peninsular Ranges and GoC, includes Miocene extension, followed by spreading. Rock uplift due to Pliocene flank uplift likely less than current topography. Regardless, mantle contribution is dominant contribution to uplift (i.e. crustal loads balance out).

16 Validity of models (do they fit what we see) We can fit topography to flexural models High topography matches coastal uplift in Baja Crustal thickness is well defined Timing of onset of coastal uplift matches flank uplift further south (Pliocene and younger) uplift further south (Pliocene and younger)

west Other sources of uncertainty exist, does not consider small crustal root under Sierra Juarez, assumes

17 What isn t realistic Models produce symmetric flank uplifts, we only see one on the west side of the GoC Geometry of mantle anomaly likely to be much more complicated than a simple block, also biased towards west Other sources of uncertainty exist, does not consider small crustal root under Sierra Juarez, assumes flat erosion surface prior to extension (some seaward gradient likely), earlier flank due to Miocene extension.

18 Caveats and implications for seismic hazards Problem requires separating flank uplift signal from local sources such as the San Joaquin Hills. Question of how rapidly signal dies out to the north is important. Model results are extreme and less mantle heating/thinning likely occurs than shown in Tectonics paper (i.e. earlier extension, crustal root, assumption of perfectly flat Eocene surface).

Quaternary rift flank uplift of the Peninsular Ranges in Baja and southern California by removal of mantle lithosphere

TECTONICS, VOL. 28,, doi:10.1029/2007tc002227, 2009 Quaternary rift flank uplift of the Peninsular Ranges in Baja and southern California by removal of mantle lithosphere Karl Mueller, 1 Grant Kier, 1