Structure of the Irian Jaya Mobile BElt, Irian Jaya, Indonesia

Abstract

Image interpretation and field investigation over the Central Ranges of Irian Jaya has provided a structural overview of the inaccessible and largely unmapped Irian Jaya Mobile Belt (IJMB) in the region bounded by longitudes 136°30′E and 141°00′E. Throughout much of the southern (para‐autochthonous) part of the belt, structural facing directions are visible on imagery through selective illumination of hogbacks and cuestas formed on thick‐bedded Mesozoic siliciclastics and extensive Late Cretaceous‐Neogene platform carbonate sequences. North of the regional Derewo Fault Zone, the Derewo Metamorphics are regarded in part as correlatives of the “metamorphosed Om Beds” in western Papua New Guinea and display a regional structural grain parallel to the orogen. The limited extent of spectrally anomalous features associated with ultramafic rocks indicate that ophiolites are confined to the southern part of the “Irian Jaya Ophiolite Belt”, which may be largely composed of metamorphic rocks. Interpreted macroscopic and megascopic structures suggest the presence of seven discrete structural domains in the IJMB. From north to south these are (1) North Coast Basin region, consisting of Paleogene‐Neogene volcanics and sediments overlain by a Pliocene‐Pleistocene successor basin sequence; (2) an allochthonous terrane composed of ophiolites and high‐grade metamorphic rocks; (3) the Derewo metamorphic assemblage, displaying polyphase deformation; (4) a complex marginal zone within Mesozoic‐Paleogene miogeoclinal sediments which includes steep duplex structures and remnant klippen; (5) a 40 to 50‐km‐wide partly inverted synclinorium composed of miogeoclinal sediments; (6) a regional south vergent overturned anticlinorium formed by incompetent Paleozoic sediments; and (7) a foreland thrust domain involving both Mesozoic‐Cenozoic miogeoclinal cover and a deformed Neogene foreland molasse basin sequence. The regional disposition of interpreted structures in the Irian Jaya Mobile Belt and reference to published mapping in western Irian Jaya and western Papua New Guinea strongly indicates polyphase deformation. Late Oligocene‐Miocene docking of metamorphics, island arc assemblages and ophiolites produced tectonically stacked E‐W trending structures thrust on to the north margin of the Australian continent with its miogeoclinal cover. Late Miocene‐Pliocene collision with the Melanesian Arc brought the accreted Australian margin into contact with the westward moving Pacific Plate and instituted a regime of oblique transpressional convergence. Resulting structures include E‐W sinistral wrenching and NW thrusts along lateral E‐W ramps.

Source-to-sink constraints on tectonic and sedimentary evolution of the western Central Range and Cenderawasih Bay (Indonesia)

“…To the North, in the south flank of the western Central Range, a 30-km-wide, 300km-long, basement-cored anticline, called the Mapenduma anticline (Figures 1 and 2C), has been thrust 35 km southward above the Akimeugah foreland basin (Hill et al, 2004;Kendrick, 2000;Nash et al, 1993;Quarles van Ufford, 1996;Weiland and Cloos, 1996). It exposes Precambrian to early Paleozoic sediments and metasediments.…”

“…It consists of pelitic rocks (Slate and Phyllites) containing graphite. The most widespread protoliths are Australian passive margin sediments (Kembelangan Group) metamorphosed under greenschist-facies conditions (Bär et al, 1961;Dow, 1977;Dow et al, 1988;Nash et al, 1993;Visser and Hermes, 1962;Warren and Cloos, 2007). The northern edge of the Derewo Metamorphic Belt is bounded by a thrust fault that places the Irian Ophiolite Belt above the metamorphic rocks ( Figure 1).…”

Tectonics of the New Guinea Region

“…Although its exact location, especially in northwestern New Guinea, is poorly known (Hill & Hall 2003), it has important relevance for how deformation is accommodated as collisional orogenesis proceeds. In some regions, it is clear where Precambrian Australian craton has been reworked, such as in the Mapenduma anticline of the southwest Central Ranges of the New Guinea highlands block (Nash et al 1993. In other regions, Precambrian zircons provide clues regarding the extent of reworked Australian craton in New Guinea.…”

Strike-slip faulting in the core of the Central Range of west New Guinea: Ertsberg Mining District, Indonesia

“…The 150-km-wide belt has rugged topography and numerous peaks over 3000 m in elevation. The Ruffaer metamorphic belt is a 1000-kmlong and 50-km-wide zone of deformed, low- temperature (Ͻ300 ЊC) metamorphic rocks that are bounded on the north by the Irian ophiolite belt and on the south by deformed, but unmetamorphosed, passive-margin strata (Dow et al, 1988;Granath and Argakoesoemah, 1989;Nash et al, 1993;Warren, 1995;Weiland, 1999). The Melanesian island-arc complex, built into the edge of the Pacific plate, is poorly exposed.…”