STRIKE-SLIP FAULTING AND COLLISIONAL DELAMINATION IN THE CENTRAL RANE OF WEST PAPUA,
PROCEEDINGS JOINT CONVENTION BALI 2007
The 32nd HAGI, The 36th IAGI, and The 29th IATMI Annual Conference and Exhibition
STRIKE-SLIP FAULTING AND COLLISIONAL DELAMINATION IN
THE CENTRAL RANE OF WEST PAPUA,
Benyamin Sapiie1
1Department of Geology - ITB
ABSTRACT
Most of the Cenozoic tectonic evolution of the New Guinea region is the result of obliquely convergent motion that led to an arc-continent collision between the Pacific and Australian plates. The Central Range is commonly described as a fold-and-thrust belt, as spectacular folding is evident on aerial photographs and satellite images. No outcrop-scale structural analysis had been done in west New Guinea until this investigation, which was made possible by the construction of mining roads (Sapiie, 1998). This paper describes a new tectonic evolution model proposed for New Guinea Island based on field observation in the Central Range of Papua.
The details of the Cenozoic tectonic evolution in New Guinea are the subject of debate, as several kinematic models have been proposed. The most commonly published scenario is the subduction polarity reversal (“arc reversal”) model that entails movement of the Australian continental crust into a northward-dipping subduction zone, followed by collision and initiation of southward subduction of the Pacific plate at the New Guinea Trench. An alternative model proposed to explain relationships in eastern New Guinea postulates that the island is underlain by a doubly subducted slab of oceanic lithosphere (“zippering” model), which would be the westward continuation of the Solomon Sea plate. Proposed a third model that is similar to the one involving northward-dipping subduction of the Australian plate, but in their model, subduction reversal has not occurred. In this scenario, the northward-subducted Australian lithosphere is thought to be dipping vertically.
The accumulating record of seismicity of the region does not delineate the southward subduction of the Pacific plate as envisioned by most workers. Sapiie et al. (1999) presented an analysis of the distribution of moderate and larger earthquakes (M> 4) from 1987 to 1997. Seismic activity is concentrated along the northern part of the island and near the eastern and western ends of the Central Range. In west New Guinea, there are few events deeper than 50 km, and there is remarkably little seismicity beneath where the Central Range elevations are higher than 1000 m. The overall seismicity indicates that most of the motion between the Australian and Pacific plates is accommodated by left- lateral slip along the Yapen and Bewani-Torricelli fault zones, which are connected by a wide convergent bend beneath the Mamberamo region near the international border. The Cendrawasih Bay area is a wide extensional bend bounded to the south where left-lateral slip occurs along the
Tarera-Aiduna fault zone in the Bird’s Neck region.
The profound change in deformation style from regional folding to localized strike-slip offset is interpreted to be a manifestation of a short-lived change in the relative plate motion between the Australian and Pacific plates at 4 Ma. We think that the strike-slip regime was the product of transform movement between the Australian plate and a broken off prong of the Pacific plate north of the island. This piece, the Caroline plate, had a short life as a distinct kinematic entity, from ~4 to ~2 Ma.
The concept advocated here is that strike slip movements were distributed across the Central Range between ~4 Ma and ~2 Ma as part of reoriented movements (well-dated by the opening of the Bismarck and Woodlark spreading centers) associated with collisional orogenesis. The most important tectonic effect was the temporary formation of the Caroline plate as a distinct kinematic entity north of the island; this event caused a change from convergent to left lateral transform motions. Since 2 Ma, the broken corner became reattached to the Pacific plate, and Australian-Pacific relative motion has been mostly accommodated by slightly convergent transform motion along the northern margin of the island.
The proposed model starts when North-dipping subduction of the oceanic end of the Australian plate began at ~30 Ma at an intraoceanic subduction zone, following a subduction reversal. Jamming of the subduction zone by underthrusting of the Australian continental plate began at ~8 Ma. The subducted oceanic end of the Australian plate continued to sink and broke off. The subterranean rifting, or delamination, of the Australian plate caused a magma generation event beneath the western Central Range from 7 to 4 Ma. This process followed by regional uplift of ~2.5 km of the collision- generated fold belt caused a profound change in regional sedimentation, forming molasses deposits in base of the mountain (Cloos et al., 2005).
Collisional delamination is a common and fundamental plate-tectonic process that occurs when subduction zones are jammed by continental margins or very large oceanic arc/plateau complexes.
The 32nd HAGI, The 36th IAGI, and The 29th IATMI Annual Conference and Exhibition
STRIKE-SLIP FAULTING AND COLLISIONAL DELAMINATION IN
THE CENTRAL RANE OF WEST PAPUA,
Benyamin Sapiie1
1Department of Geology - ITB
ABSTRACT
Most of the Cenozoic tectonic evolution of the New Guinea region is the result of obliquely convergent motion that led to an arc-continent collision between the Pacific and Australian plates. The Central Range is commonly described as a fold-and-thrust belt, as spectacular folding is evident on aerial photographs and satellite images. No outcrop-scale structural analysis had been done in west New Guinea until this investigation, which was made possible by the construction of mining roads (Sapiie, 1998). This paper describes a new tectonic evolution model proposed for New Guinea Island based on field observation in the Central Range of Papua.
The details of the Cenozoic tectonic evolution in New Guinea are the subject of debate, as several kinematic models have been proposed. The most commonly published scenario is the subduction polarity reversal (“arc reversal”) model that entails movement of the Australian continental crust into a northward-dipping subduction zone, followed by collision and initiation of southward subduction of the Pacific plate at the New Guinea Trench. An alternative model proposed to explain relationships in eastern New Guinea postulates that the island is underlain by a doubly subducted slab of oceanic lithosphere (“zippering” model), which would be the westward continuation of the Solomon Sea plate. Proposed a third model that is similar to the one involving northward-dipping subduction of the Australian plate, but in their model, subduction reversal has not occurred. In this scenario, the northward-subducted Australian lithosphere is thought to be dipping vertically.
The accumulating record of seismicity of the region does not delineate the southward subduction of the Pacific plate as envisioned by most workers. Sapiie et al. (1999) presented an analysis of the distribution of moderate and larger earthquakes (M> 4) from 1987 to 1997. Seismic activity is concentrated along the northern part of the island and near the eastern and western ends of the Central Range. In west New Guinea, there are few events deeper than 50 km, and there is remarkably little seismicity beneath where the Central Range elevations are higher than 1000 m. The overall seismicity indicates that most of the motion between the Australian and Pacific plates is accommodated by left- lateral slip along the Yapen and Bewani-Torricelli fault zones, which are connected by a wide convergent bend beneath the Mamberamo region near the international border. The Cendrawasih Bay area is a wide extensional bend bounded to the south where left-lateral slip occurs along the
Tarera-Aiduna fault zone in the Bird’s Neck region.
The profound change in deformation style from regional folding to localized strike-slip offset is interpreted to be a manifestation of a short-lived change in the relative plate motion between the Australian and Pacific plates at 4 Ma. We think that the strike-slip regime was the product of transform movement between the Australian plate and a broken off prong of the Pacific plate north of the island. This piece, the Caroline plate, had a short life as a distinct kinematic entity, from ~4 to ~2 Ma.
The concept advocated here is that strike slip movements were distributed across the Central Range between ~4 Ma and ~2 Ma as part of reoriented movements (well-dated by the opening of the Bismarck and Woodlark spreading centers) associated with collisional orogenesis. The most important tectonic effect was the temporary formation of the Caroline plate as a distinct kinematic entity north of the island; this event caused a change from convergent to left lateral transform motions. Since 2 Ma, the broken corner became reattached to the Pacific plate, and Australian-Pacific relative motion has been mostly accommodated by slightly convergent transform motion along the northern margin of the island.
The proposed model starts when North-dipping subduction of the oceanic end of the Australian plate began at ~30 Ma at an intraoceanic subduction zone, following a subduction reversal. Jamming of the subduction zone by underthrusting of the Australian continental plate began at ~8 Ma. The subducted oceanic end of the Australian plate continued to sink and broke off. The subterranean rifting, or delamination, of the Australian plate caused a magma generation event beneath the western Central Range from 7 to 4 Ma. This process followed by regional uplift of ~2.5 km of the collision- generated fold belt caused a profound change in regional sedimentation, forming molasses deposits in base of the mountain (Cloos et al., 2005).
Collisional delamination is a common and fundamental plate-tectonic process that occurs when subduction zones are jammed by continental margins or very large oceanic arc/plateau complexes.
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