1. introduction - tectonics observatory at caltech · cenozoic basins in sundaland are broadly...
TRANSCRIPT
What caused deep, long-lived subsidence during Sundaland basin formation?Fraser Keppie1, Michael Gurnis1
(1) California Institute of Technology
1. Introduction
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
North China Platform
South China Platform
Indochina
Sino/Malaya
Malay Peninsula
BorneoSumatra
Java
Gulf ofThailand
SundaShelf
Pattani Basin
Malay Basin
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
Topography(m)
(Overlay)Ocean Lithosphere
Age (Ma)
SUNDALAND
Borneo Basins
Gulf of Thailand & Indochina Basins
Sumatra and Java Basins
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
0255075
100125150
−7500−5000−2500
0250050007500
Figure 1: Map of Sundaland Cenozoic basins.
Cenozoic basins in Sundaland are broadly placed into three groups: (1) Sumatra and Javabasins, (2) Gulf of Thailand and Indochina basins, and (3) Borneo basins [1]. The Sumatraand Java basins parallel the Sumatra and Java trenches. The formation of these basins isrelated to subduction zone processes which include plate loading and flexure as well as back-arc extension [1]. Highly oblique convergence along the Sumatra Trench means strike-slipprocesses also play a role.
In contrast, the Gulf of Thailand, Indochina and Borneo basins do not appear to have formedclose to Sundaland subduction zones. The formation of these basins is enigmatic [1, 2]. Earlystages of basin formation appear to be rift-related [1] and may be explained by syn-rift thin-ning and subsidence [3]. Thermal relaxation of thinned lithosphere can explain some post-riftsubsidence [3] and basin growth. However, in central Sundaland, some basins are too deep(up to 18 km of sediment) and show too great a rate of post-rift subsidence (up to 1 kmMa−1)for millions of years to be accounted for by two-stage ”McKenzie-type” models of basin forma-tion [2]. Displacement on major normal or strike-slip faults is not associated with most of thesubsidence and present geotherms in Sundaland basins are high (30-75 oCkm−1) [2].
2. Pattani and Malay Basins
The Pattani and Malay basins are examples ofdeep basins with long post-rift growth in theGulf of Thailand. Stretching factors of 2 <
β < 4 are calculated from conventional back-stripping, whereas stretching factors of 1 < β <
1.5 are calculated from restoring throws on up-per crustal normal faults [2]. This suggeststhat depth-dependent extension or other basingrowth mechanisms are involved.
Figure 2: (left) Seismic profile from North Malay basin from [2] showing the transition fromsyn-rift to post-rift subsidence in the Oligocene; (right) Subsidence history of Pattani and Malaybasin (compared with North Sea Basins) from [2]
3. Cenozoic tectonics
The Cenozoic tectonics of the Sundaland region include many basin formation settings suchas subduction-related, rift and post-rift scenarios [1]. Lower crustal flow coupled to sedimentloading may be important for sustaining topography and sedimentation during long-term basingrowth in post-rift settings [2]. Southward-dipping subduction north of Borneo and northward-dipping subduction beneath Java are close together during the Oligocene and a compoundeffect due to doubly-convergent subduction on the development of Borneo basins may berelevent. Sundaland is a region of multi-slab descent into the mantle and slab avalanchesat the transition zone (660 km) may impact horizontal and lateral stresses in the lithosphereand lead to basin formation in both upper and lower plates.
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
0 Ma
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
15 Ma
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
30 Ma
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
45 Ma
90˚
90˚
100˚
100˚
110˚
110˚
120˚
120˚
130˚
130˚
140˚
140˚
150˚
150˚
160˚
160˚
−20˚ −20˚
−10˚ −10˚
0˚ 0˚
10˚ 10˚
20˚ 20˚
30˚ 30˚
Figure 3: Cenozoic reconstructions in a South China Platform reference frame for basic tec-tonic elements in Sundaland and associated basins.
4. Research Goals
erosion
Lower crustal flow
Top crust
Base crust
Top crust
Base lithosphere
Top crust
Base lithosphere
Base upper mantle (660 km)
Slab Avalanche Slab Avalanche
Rifting Inversion
Subsidence
A McKenzie “Two-stage” Rifting and thermal relaxation
C Coupled sediment-loading and lower crustal flow
D Doubly-convergent subduction
B Load-induced flexure
E Slab avalanche induced riftingin the lower plate
F Slab avalanche induced synchronous inversion and subsidence in the upper plate
Subsidence
Subsidence SubsidenceStage 1 = Thinning
Base lithosphere
flexure
flexure
load
load
load
flexure
Top crust
Stage 2 = Thermal RelaxationTop crust
Hot Asthenosphere
Rifting
Isostatic subsidence
Subsidence due to cooling
Post-rift
CompoundSubsidence
Effect?
Figure 4: Some basin formation mechanisms.
The purpose of this research is to use the thermo-mechanical, incompressible, Stokes Flowcode – GALE – to model: (1) rift and post-rift basin formation systems, and (2) subduction-related, double subduction-related and oblique subduction-related basin forming systems. TheGALE code is an open source modeling tool available to the geodynamics research commu-nity but its potential for modeling lithosphere and upper mantle scale problems needs to berealized. Hopefully, insight into basin forming processes relevant to Sundaland basins will beforthcoming and model templates for extension and subduction will be created forming thebasis for future, different directions of geodynamics research.
References
[1] Hall, R., and Morley, C.K., 2004. Sundaland basins. Geophysical monograph, 149, 55–85.
[2] Morley, C.K., and Westaway, R. 2006. Subsidence in the super-deep Pattani and Malay basins of southeastAsia: a coupled model incorporating lower-crustal flow in response to post-rift sediment loading. Basin Re-search, 18, 15–84.
[3] McKenzie, D., 1978. Some remarks on the development of sedimentary basins. Earth and Planetary ScienceLetters, 40, 25–32.
[4] Watts, A.B., Karner, G.D., Steckler, M.S., 1982. Lithospheric flexure and the evolution of sedimentary basins.Philosphoical Transactions of the Royal Society, 305 (1489), 249–281