Lithospheric structure and geodynamic evolution of the northern

EAE-03-A-10849
GD10-1MO2P-0123
Lithospheric structure and geodynamic evolution
of the northern Molucca Sea area constrained by 3-D gravity field inversion
of a combined sea-surface and satellite gravity dataset
C. Widiwijayanti 1), C. Tiberi 2), M. Diament 1), C. Deplus 1), V. Mikhailov 3), R. Louat 4), S. Tikhotsky 3), A. Gvishiani 3)
1) Labo. de Gravimétrie et Géodynamique, DGSP-UMR7096, IPG Paris, Case 89, 4 Place Jussieu, 75252 Paris Cedex 05, France ([email protected]/Fax: +33-144277340)
2) Labo. de Tectonique, UMR7072, Université Paris 6, France. 3) UIPE-RAS, 3 Molodejnaya, Moscow, Russia. 4) IRD, Paris, France
Introduction
The Molucca Sea Plate, which is now almost completely subducted, is squeezed between three converging plates: the
Philippine Sea, Eurasian and Australian ones. Its structural style is formed under collision of Sangiihe and Halmahera
subduction zones and evolves from the southern to the northern parts of the Sea. Although numerous geophysical and
geological studies have been carried out in the area, many details are still unclear. In particular, structure and origin of the
Central Ridge, the northward continuation of the Molucca Sea subduction zones, southern propagation of the Philippine
Fault, and structure and origin of the Snellius Plateau remain poorly understood.
REGIONAL GRAVITY STUDY :
Complete Bouguer anomaly map of the Molucca Sea area is based on gravity and
bathymetry data from the available ship cruises (MODEC and NGDC) complemented
with the satellite derived data (KMS 1998 for gravity and predicted bathymetry from
Smith and Sandwell). To extract the gravity signal from lithospheric structures, we
separated the complete Bouguer anomaly into 2 components of different wavelength
using the Kolmogorov-Wiener optimal filter (Gordin et al., 1980).
Regional Component of the Bouguer Anomaly
0
00
-2
0
00
00
-2
-20
0
00
-20
0
00
00
-2
-20
0
0
-20
00
0
0
-20
-2
0
0
126
-50
122
130
0
mGal
50
100
325
-150
-50
-20
00
-4
00
0
0
00
-20
rc
hera A
-2
00
0
0
126
-25
0
mGal
130
25
50
2
00
-70
0
00
00
-40
-50
00
0
4
A
6.13
e
1
Ridg
s
a
g
Mian
ge
al Rid
Centr
0
00
Pujada Ridge
Ridge
s
a
g
n
a
i
M
rc
0
Position and depth of the shallow lithospheric gravity sources were estimated from
local field component applying a new approach of the Euler deconvolution method
(Mikhailov et al., 2003) based on recently developed fuzzy logic method of
clustering, called RODIN (Gvishiani et al., 2002).
Mindanao
0
-300
0
-2000
00
Pujada Ridge
rc
hera A
Halma
Halma
al Rid
ge
ihe A
Miangas
Cantr
Sang
Pujada Ridge
Ridge
Sarangani
e Arc
Sangih
00
0
-40
00
00
-60
0
-200
Halmahera
00
-20
0
Objective: delineate the structural contacts
0
-2
00
-60
-8000
Tifore
Sulawesi
- Selection of Euler solutions.
-3
5.2
0
Miangas
5.41
- Structural Index = 2
(point mass)
- window size = 25'x25'
- tolerance = 10%
- depth: 0 km < z < 60 km
- maximum distance = 50'
-2000
-3000
-300
0
16
00
-30
0
6
Talaud
Snellius
Plateau
B
00
12
3.96
15
-20
19
00
Sangihe
13
14
00
-30
0
00
-1
20
3.4
00
-20
0
-1
18
Nanusa
Snellius
Plateau
11
0
00
0
00
17
-40
-2
0
TALAUD
4.1
3.8
00
-2000
00
-10
-10
00
0
00
-3
4.69
-30
4.5
5
0
00
-1
00
-1000
Nanusa
Islands
-20
4.9
00
-20
3.1
125.5
125.9
126.2
126.6
-20
127.0
00
127.3
127.7
128.0
mGal
-75
-50
-25
0
25
50
75
Local component of the Bouguer
anomaly map, superimposed by
bathymetry (contour interval 500m).
The OBS network locations are
shown by rectangles boxes and OBS
locations by red star symbols. Mean
delay time at each OBS stations is
expressed by crosses (negative
delay) and circles (positive delay);
the symbols are scaled to the
absolute value of the delay time.
Oblique convergence between Philippines and Eurasian
Plates results in partitioning between:
- a westward subduction located at the Philippines Trench
- a NW movement of the Snellius Plateau.
As a consequence:
1. deformation/segmentation of the Snellius Plateau
2. extension zones (south of Snellius Plateau)
3. strong compressive deformations in Talaud and Miangas
4. accumulation of sedimentary prisms to east of Miangas.
Pujada-Miangas Ridges: different structure orientation with
depth
- superficial structures: E-W
- deep structures: NW-SE.
150
Local component:
At the Central Ridge positive anomaly represents slices of the oceanic crust;
negative anomaly represents sedimentary prism. The change in orientation of
positive anomaly structure at the south of the Snellius Plateau is interpreted as a
superficial response of the slab tear zone beneath the Halmahera and the Morotai.
130°
05 04 03
10
00
South-Talaud:
North-Miangas:
Moho at 25 km depth;
Moho at 45 km depth;
NS pop-up structure.
Low velocity zone trending NE-SW,
dipping NW down to 35 km depth
inferred as ophiolitic zone bouded with
two sedimentary prisms.
-4
-100
00
00
-80
HALMAHERA
128°
Mayu
Regional component:
- A linear, roughly N-S, negative Bouguer Anomaly coincides with the Central Ridge
- In the south two minima flank the Central Ridge.
- Talaud coincides with a local positive anomaly.
- Near the Miangas: a single minimum borders the eastern side of the central ridge.
The "backstop" of the Halmahera and Sangihe subduction is identified
The Snellius Plateau seen as a positive anomaly is the result of oceanic crust
thickening.
ault
126°
Morotai
0
0
122
-325
0
-400
Morotai
-8
-2000
00
09
-6
-20
Halmahera
00
0
02
06
00
0
0
00
-3000
0
-3
5.6
-40
0
0
3
01
07
00
-20
0
MIANGAS
08
-2
00
0
0
Morotai
Basin
4
00
-2000
0
TalaudSnellius
Plateau
-2000
0
0
00
Miangas
Celebes Sea
0
Mayu
Tifore
Sulawesi
Snellius
Plateau
-4
-2000
6.0
00
0
-2000
00
-8000
00
0
-20
(Talaud) area.
-3
-20
Nanusa
00
0
00
MODEC experiment in 1994 (20 days): 2
OBS networks; 284 events in the northern
(Miangas) area ; 276 events in the southern
0
00
RESULTS
Objective : to study local seismicity
in two areas to characterize crustal
structure.
-40
00
-2
4
-2
ng F
124°
4
Snellius
Plateau
-2000
0
122°
0
-2°
00
92 mm/yr
-40
Gorontalo Basin
0
-60
Celebes Sea
Mayu
Soro
Talaud
Philippine
Sea
0
Miangas
-6000
8
-6
00
0
0
-40
0°
-2000
00
0
4
Tifore
SULAWESI
-4000
-60
ench
00
0
LOCAL TOMOGRAPHY
6.3
-6
-200
129°
esi Tr
-8000
127°
0
Mindanao
8
Philippines
Sea
00
0°
-2°
125°
-2000
00
0
0
-80
2. Gravity:
- Euler-solutions analysis
- 3D gravity field inversion
from a combined sea-surface
and satellite-derived data.
Gorontalo Basin
123°
0
HALMAHERA
Sulaw
-400
SULAWESI
2°
Local scale:
1. Local earthquake tomography
from OBS network data.
2°
Tifore
121°
Sangihe
00
4°
Morotai
Mayu
-4000
-2000
Talaud
ch
0
-6
0
0
-400
8
0
Regional scale:
Gravity study.
Nanusa
esi T
ren
4°
Celebes Sea
92 mm/yr
Snellius
Plateau
Mindanao
8
-6000
0
00
APPROACHES
Miangas
Sangihe
Philippine
Sea
Talaud
6°
Celebes Sea
00
0
-400
0
h
-6
0
Miangas
8°
0
-40
nc
Sulaw
Co
tab
Tr
en ato
ch
0
0
Tr
e
Philippine Trench
Philippine Trench
ult
e Fa
ppin
to
t
Phili
ba
tab
Fau ato
lt
Philipine Sea
MINDANAO
ta
Co
6°
Faul
10°
8°
0
0
- How do tectonic units inter-relate?
- Which processes perturbate the
convergence?
MINDANAO
pine
QUESTIONS
to describe the collision evolution
- What is the geometry of
tectonic units?
and identify processes responsible
What are their structure and origin?
for the oceanic basin closure
Co
p
Phili
OBJECTIVES
0
Local Component of the Bouguer Anomaly
-20
10°
3.24
125.70
0
126.42
10
127.14
20
30
Euler-solution depth (km)
127.86
40
50
Map of the local component of the Bouguer anomaly. Bathymetry
is superimposed. Euler solutions were represented in greytriangles, plot together with shallow seismicity from EHB-catalogue
in blue-squares and Harvard CMT solutions. Black-lines show the
locations of cross-sections (figure below).
REFERENCES:
Gvishiani, A. D., Diament, M., Mikhailov, V.O, Galdeano., A., Agayan, S.M.,
Bogoutdinov, Sh.R., and Graeva, E.M., 2002. Artificial Intelligence Algorithm for
Magnetic Anomaly Clustering, Izvestiya, Physics of the Solid Earth, 38, 7, 545559.
Widiwijayanti C., V. Mikhailov, M. Diament, C. Deplus, R. Louat, S. Tikhotsky, A.
Gvishiani, Structure and evolution of the Molucca Sea area: Constraints based on
interpretation of a combined sea-surface and satellite gravity dataset. Earth and
Planetary Science Letters, 2003, in press