Hello Im a Title

1
(No Transcript)
2
Outline

• I. Summary of the inversion method for the 3-D
  seismic temperature structure of the
  oceanic lithosphere/upper mantle.
• II. Temperature structure as evidence for
  reheating in the Central Pacific.
• Cause of reheating?
• (Simulation of thermal boundary layer
  instabilities (TBI) by van Hunen, Zhong, and
  Huang.)

3
I. Inversion Method

• Data Rayleigh and Love wave group speeds. (20 -
  150 sec). Phase speeds (40 -150 s) from Harvard
  Utrecht Universities.
• Surface wave tomography creation of maps of
  surface wave speeds -- diffraction effects.
• Monte-Carlo inversion
• Seismic parameterization
• Temperature parameterization based on a thermal
  model

4
(No Transcript)
5
(No Transcript)
6
Surface Wave Speeds Relative to a Diffusively
Cooling Half Space (HSC Model)
7
II. Inversion Procedure Thermal Model
Temperature Parameterization
Location In the C. Pacific
8
(No Transcript)
9
Shear Velocity Structure
10
Temperature Structure
11
Uniqueness of the Temperature Structure of the
Pacific
12
III. Cause(s) of the Reheating of the Central
Pacific Lithosphere?

• Initial conditions.
• Small-scale, deep-seated processes plumes.

Large-scale, deep-seated processes global
convection. Small-scale, shallow processes
lithospheric instabilities, small-scale
convection (Richter rolls).
Shijie Zhong Jeroen van Hunen Jinshui Huang
13
(No Transcript)
14
Comparison of Thermal Structure Observed and
from Simulated Thermal Boundary Layer
Instabilities (TBI).

• TBI
• Sets on at 70 Ma.
• (Rayleigh )
• 2. After on-set, reheats
• the deep lithosphere.
• After about 25 My, no
• longer effectively
• heats the lithosphere.
• 4. Duration strength of reheating
• depend on rheology.
• Right Newtonian,
• effective E 120 KJ/mol.)

15
Historical Proximity to Known Active Hot Spots
Paleo-trajectories from Wessel Kroenke (1997)
Much of the W. Pacific at one time was near
known hotspots. Role of plumes in reheating C.
Pacific lithosphere ? direct thermo-mechanical
erosion, ? asthenospheric heating triggering
TBI.
16
Summary Conclusions
Seismic Evidence Pacific lithosphere, on
average,has experienced a two-stage cooling
history cooling 0-70 Ma, 100 - 135
Ma. reheating 70 - 100 Ma Reheating
dominantly at depth between 70 150 km This
cooling history appears to be unique to the
Pacific. 3-D Simulations of Thermal Boundary
Layer Instabilities (TBI) Thermal structure
depends on rheology. Can approximately match
observed average cooling history of the
Pacific. TBI is an important dynamical agent at
work in the C. Pacific Interplay between plumes
and TBI and the joint effect on lithospheric
temperatures remain poorly understood
requires further work.
17
(No Transcript)
18
Effect of Problem Specification on Dispersion
Maps (e.g., Rayleigh Phase 50 sec)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
(No Transcript)
28
(No Transcript)
29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
(No Transcript)
37
(No Transcript)
38
(No Transcript)