Active foundering of a continental arc root beneath southern Sierra Nevada
This presentation is the property of its rightful owner.
Sponsored Links
1 / 11

Active foundering of a continental arc root beneath southern Sierra Nevada Zandt et al, 2004 PowerPoint PPT Presentation


  • 114 Views
  • Uploaded on
  • Presentation posted in: General

Active foundering of a continental arc root beneath southern Sierra Nevada Zandt et al, 2004. Removal of ultramafic root beneath southern Sierra Nevada Initiated between 10 and 3 Mya via Rayleigh-Taylor instability Process is consistent with observables at surface and depth

Download Presentation

Active foundering of a continental arc root beneath southern Sierra Nevada Zandt et al, 2004

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Active foundering of a continental arc root beneath southern sierra nevada zandt et al 2004

Active foundering of a continental arc root beneath southern Sierra Nevada

Zandt et al, 2004


Key points

Removal of ultramafic root beneath southern Sierra Nevada

Initiated between 10 and 3 Mya via Rayleigh-Taylor instability

Process is consistent with observables at surface and depth

Drip is asymmetric and migrating to the southwest

Key points


Surface observables

Garnet pyroxenite xenoliths of Miocene age found in local volcanic fields– density of 3.5-3.6 g/cm3

Later xenoliths from pliocene show no evidence of ultramafic root

Subsiding sub-basin in Great Valley migrating southwest

Alignment of features along direction of root migration

Surface observables


Seismic observables

Disappearance of moho beneath western foothills (“hole” in moho)

Increasing depth of moho (crustal thickening) in direction of hole

Maximum crustal thickness beneath Kings Volcanic Field (42km crustal welt)

Negative polarity arrivals move downward to the south (?)

Anisotropic layer at base of crust (?)

Seismic observables


Active foundering of a continental arc root beneath southern sierra nevada zandt et al 2004

2 possible explanations:

-Localized zone of low S wave velocity in uppermost mantle

-Moho topography scatters Ps conversion

-Synthetic modelling supports 2nd explanation


Verification

Created synthetic receiver functions for various structures

Processed synthetics in the same way as true data

Size of Moho cusp based on volume of entrained material seen in cross sections and previous models

V-shaped bulge of crust 50km wide and 25km deep would be sufficient to cause disappearing Moho

Verification


Sequence of events

Mesozoic: ultramafic phase of batholith formation produces dense root

Batholith + root formed strong microplate that persisted into Miocene

Miocene destabilization of root causes active foundering through present

Sequence of events


Possible causes of destabilization

Movement of volcanic are to north may have cause flux in Sierran lithosphere

Passing of Mendocino triple junction 20-10Mya exposed lithosphere to asthenosphere from slab window

Extensional faulting beginning at 15Mya weakens top of root

Possible causes of destabilization


  • Login