Objective

kraut.carlotta49

Objective

Presenter: Ting-Hsuan Hsu

2012/10/4


Reference

Upton, P., K. Mueller, and Y.‐G. Chen, Three‐dimensional

numerical models with varied material properties and erosion rates:

Implications for the mechanics and kinematics of compressive

wedges, J. Geophys. Res., 114, B04408,

doi:10.1029/2008JB005708. 2009b

Wilcox T., K. Mueller, P. Upton, Y. G. Chen, S. T. Huang, B. J.

Yanites, and G. Tucker , Linking Taiwan’s subcritical Hsuehshan

Range topography and foreland basin architecture, TECTONICS,

VOL. 30, TC4011, doi:10.1029/2010TC002825, 2011


Introduction

OUTLINE

Critical Wedge Model

Three-Dimensional Model

Discussion

Conclusion


Introduction

Objective

The relationship between the contemporary

presence of the Puli Topographic

Embayment and the varied material

properties and erosion rates

Approach

To model with different parameters of

material properties and erosion rate by

FLAC 3D


Introduction

Puli Topographic

Embayment – (PTE)

Previously recognized as

an anomalous portion of

the thrust belt.

[Deffontaines et al., 1994; Lu and Malavieille,

1994; Mueller et al., 2001; Lin and Watts, 2002;

Powell, 2003; Yanites et al., 2010]

50-km-wide

~1500 m lower than the

surrounding areas


Introduction

(1) Changhua thrust

(2) Chelungpu thrust

(3) Shuangtung thrust

(4) Shuilikeng thrust

Bold dashed lines—

Tuntzuchiao fault

Meishan fault


Introduction

A: north of

Tuntzuchiao fault

B: central

C: south of

Meishan fault


Introduction

Synorogenic strata –

Kcl – thickness different

Cs – uniform thickness

Cl、Tk – abrupt change in thickness


Critical Wedge Model

α = surface slope

β = dip of décollement


Critical Wedge Model

Shape control

Basal friction, strength of the wedge, internal

pore pressure, and fluxes of material.


Critical Wedge Model

Strength of wedge

Stronger than décollement – flatter wedge

Weaker than décollement – steeper wedge


Maintenance of

critical taper

(a) Steepness is

decreased by erosion and

normal faulting in the

upper part of the wedge.

(b) Steepness is

decreased by offscraping

and building out of the

wedge at the toe.

(c) Steepness is

increased by underplating

and internal thickening of

the wedge.


Subcritical state?

Definition

Surface erosion has a very strong control

over the internal organization of strain in

critical wedges, by focusing strain into

areas that exhibit a “subcritical” taper.


Subcritical state?

Examples

Glaciated regions undergoing rapid and

spatially limited erosion - St Elias orogen

in Alaska [Berger et al., 2008; Meigs et al., 2008]

Sharp orographic precipitation as driving

accelerated erosion inboard of the

leading edge of the Himalayas

[Thiede et al., 2004; Wobus et al., 2003]


Subcritical state?

“Negative taper” =strong erosion?


3D model

Elastic slab – subducting plate

Elastoplastic wedge – passive margin

sediments

Elastic Indentor – colliding volcanic arc

Bold dashed line – enhanced erosion rate

Lighter dashed line – region of weaker, less

dense sediments


3D model

Model 1:

weaker material

Deeper topographic

embayment inboard

Embayment width ≒

weaker material width


3D model

Model 2:

enhanced erosion

Broad effect on the

wedge kinematics

Strong erosion controls

over the internal

organization strain


3D model

Model 3:

weaker material +

enhanced erosion

Close to the condition

of western Taiwan

Topographic

embayment is at least

1000 m


Discussion

The results of our models suggest that focused erosion

may exert a stronger and broader influence on the

organization of strain across the entire width of an active

orogenic wedge than a change in material properties at

the leading edge of the orogen.

The subcritical portion of the Taiwanese thrust belt

formed at spatial scales of tens of kilometers, and this

scale is likely controlled by the spacing of individual

thrusts within the orogen [Upton et al., 2009b] and by

the spacing of preexisting normal fault arrays in the

foreland.


Discussion

Early stage: foreland template is set by varying subsidence along strike, with

thicker sequence of easily erodible sediment in central region

Intermediate stage: material is accreted into wedge initiating rock uplift. As

rocks are brought above local base level, different rheologies respond to

river incision at different rates and drainages are reorganized.

Proto‐Puli: all synorogenic sediment is flushed from uplifted region into the

foreland basin.


Conclusion

By using the three-dimensional numerical

model, they suggest the presence of the PTE

may reflect the presence of weaker and more

erodible sediments than those present along

strike in the orogen.


Thank you!

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