constraining crustal rheology and lower crustal flow in the tibetan plateau n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Constraining crustal rheology and lower crustal flow in the Tibetan plateau PowerPoint Presentation
Download Presentation
Constraining crustal rheology and lower crustal flow in the Tibetan plateau

Loading in 2 Seconds...

play fullscreen
1 / 28

Constraining crustal rheology and lower crustal flow in the Tibetan plateau - PowerPoint PPT Presentation


  • 82 Views
  • Uploaded on

Constraining crustal rheology and lower crustal flow in the Tibetan plateau. Update from CIDER 2011: Dynamics of Mountain Building Marianne Karplus 1,2 , Warren Caldwell 1 , Flora Bajolet 3 , Whitney Behr 4 , Jiajun Chong 5,6.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Constraining crustal rheology and lower crustal flow in the Tibetan plateau' - lyre


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
constraining crustal rheology and lower crustal flow in the tibetan plateau
Constraining crustal rheology and lower crustal flow in the Tibetan plateau

Update from CIDER 2011: Dynamics of Mountain Building

Marianne Karplus1,2, Warren Caldwell1, Flora Bajolet3, Whitney Behr4, JiajunChong5,6

1 Stanford University, 2 University of Southampton, 3 Università Roma TRE, 4 University of Texas, 5 ESS, USTC, Hefei, China, 6Berkeley Seismological Lab, Berkeley, CA, United States.

outline cider 2011 crustal flow project
Outline: CIDER 2011 crustal flow project
  • Motivation
  • Observations bearing on crustal flow
  • Methods: literature review & flow law modelling
  • Results & discussion
  • Future work…
how is tibet deforming in response to the collision
How is Tibet deforming in response to the collision?

Terrane motion along strike-slip faults (e.g., Tapponnier et al., 2001)

Crustal flow outwards from the plateau (e.g., Clark & Royden, 2000)

= motion into the screen

= motion out of the screen

slide4

Proposed locations & directions of crustal flow:Southern Tibet (to Banggong-Jiali system): south-directed crustal flow driven by GPE, orographic exhumation and lithospheric underthrusting; Northern Tibet: east-directed mixed crustal & mantle flow driven by north-south compression and east-west extension

o bservations bearing on channel flow
Observations bearing on channel flow

Inferences bearing on channel flow

Geological observations

  • xenoliths
  • magma composition

Seismological observations

  • reflectivity (e.g., bright spots)
  • attenuation
  • tomography
  • anisotropy

Other geophysical observations

  • gravity
  • heat flow
  • thermal gradient
  • strength
  • composition
  • % H2O
  • viscosity
  • ductility
  • cumulative strain/ flow

Consistent with channel flow or not??

focus areas within tibet
Focus areas within Tibet

Qaidam

North

Central

East

South

channel flow model clark et al 2005
Channel flow model (Clark et al., 2005)

Suggested best fit channel flow model to explain magnitude of dynamic topography at the Eastern Plateau margin:

Flow rate divided by channel thickness gives us spatial gradients in velocity, which is strain rate.

  • channel viscosity of ~1018 Pa s
  • channel thickness of ~ 15 km
  • channel flow rate of 80 mm/yr
  • 80 mm/yr / 15 km = 2x10-13/s strain rate

These estimates of strain rate and viscosity allow us to test different experimental flow laws to see if we can place simple constraints on where in the middle or lower crust channel flow may be occurring

flow laws used and related assumptions
Flow laws used and related assumptions
  • Wet quartzite, assuming maximum water fugacity at all depths
  • If seismic anisotropy is observed, we use Hirth et al. (2001) quartzite flow law for dislocation creep
  • If anisotropy is weak or absent, we use Rutter & Brodie (2004) quartzite flow law for diffusion creep

Middle crust

Lower crust

  • Both wet and dry anorthite, assuming maximum water fugacity at all depths
  • If seismic anisotropy is observed, we use Rybacki & Dresen (2006) anorthite flow law for dislocation creep
  • If anisotropy is weak or absent, we use Rybacki & Dresen (2006) anorthite flow law for diffusion creep

Influence of melt

  • Assumed to scale exponentially and depends on melt fraction and dihedral angle
  • Dihedral angle assumed to be 18 for quartz and 25 for anorthite (from Holness, 2006)
bulk resistivity vs melt fraction
Bulk resistivity vs. melt fraction

Bulk resistivity as a function of melt fraction obtained from Archie’s law for melt resistivities of 0.1 and 0.3m. The shaded areas indicate the range of melt fractions required to explain the magnetotelluric data in the northern Lhasa block (left) and the southern Lhasa block and Qiangtangterrane (right)

Rippe & Unsworth, 2010

summary of results
Summary of results

In most of Tibet, models show 1018 Pa*s could be achieved for narrow depth intervals in lower crust.

  • Central: 55-60 km
  • East: 53-58 km
  • South: 48-58 km
  • North: 53-56 km
  • Qaidam Basin: 30-37 km, 43-47 km

Flow channel may be deeper in central Tibet compared to the margins (?)

Viscosity heavily dependent on: temperature, depth of top ‘lower crust’, crustal composition, strain rate

 (Future) 3-D cartoon of Tibet showing composition and intervals of possible flow in various regions of plateau

challenges
Challenges
  • Structural/ compositional disagreements & ambiguities in literature
  • Sparse data in Tibet
  • Constraining viscosity reasonable for channel flow
slide21

North-South cross sections

East-West cross sections

Yang et al., 2012

ideas for future work
Ideas for future work
  • Better constraints on crustal composition (literature)
  • Better constraints on viscosity required for channel flow (literature, topographic modelling for more regions of the plateau)
  • Improve temperature modelling (i.e., non-linear geotherm)
  • Compare results from flow laws used for Tibetan crust in the past with those we use
  • Measuring water content in xenoliths (new proposal)
slide28

Better constraints on composition

  • Measuring water content in xenoliths
  • Keying profiles to viscosity estimates from regional topography
  • See if Marin still thinks the numbers are valid (for “best fit” viscosity, channel thickness, etc.)
  • Compare to MT and Yang’s flow paper
  • 3-D figure!!!!! Showing where flow is… comparison to Yang or MT papers about where flow is.