Suckling Dome and the Australian–Woodlark plate boundary in eastern Papua: the geology of the Keveri and Ada'u Valleys

Abstract

The Owen Stanley Fault Zone (OSFZ) is the low-angle thrust boundary between the Australian and Woodlark plates. The eastern extension of the OSFZ links with the Woodlark Basin spreading centre. Recent tectonic models of eastern Papua depict the OSFZ boundary passing through the Mt Suckling district, with the Keveri Fault a key component. Gravity data clearly show that the OSFZ and the Papuan Ultramafic Belt (PUB) pass north of Mt Suckling. Tectonised mafic and ultramafic rocks of the Mt Suckling district, previously referred to the PUB, are reassigned to the Awariobo Range Complex (new name). Extensive pillow basalts previously referred to the middle Eocene part of the Kutu Volcanics at the top of the PUB sequence are, in the map area, reassigned on lithological and biostratigraphic grounds to the late Oligocene–middle Miocene Wavera Volcanics. The detailed work reported here indicates that the Keveri Fault is unrelated to the OSFZ with no evidence for thrusting along the structure. The area's tectonic history has been dominated by large vertical displacements along the Keveri Fault. The commencement of late Miocene buoyant uplift of the Suckling Dome (new name), related to granite intrusion into thick crust of the eastern Papua region, marks the inception of the Keveri Fault and coincides with the initiation of Woodlark rifting. The fault facilitated much of the rapid vertical movement of the dome, with an estimated 8000 m of uplift (2.5 m/10³ a) since the late Miocene. Movement on the Keveri Fault is notably different from structures flanking other metamorphic core complexes in eastern Papua. There is no field evidence for the development of a low-angle, south-dipping detachment fault along the southern margin of the Suckling Dome. The Suckling Dome is the westernmost of the eastern Papua domes, localised within a broad extensional zone that continues to propagate westward along the OSFZ plate boundary.

欧文斯坦利(Owen Stanley)断裂带（OSFZ）是澳大利亚与伍德拉克(Woodlark)板块之间的低角度逆冲界线。该OSFZ的东延与伍德拉克盆地扩张中心连接。巴布亚东部近期构造模型显示出OSFZ边界穿过Mt. Suckling地区，Keveri断层是其重要组成部分。重力数据清楚地表明，OSFZ和巴布亚超基带（PUB）通过Mt. Suckling之北部。 Mt. Suckling 地区的经过构造运动的基性和超基性岩，以前被认为是POB，在此被重新归为Awariobo山脉复合体（新名词）。以前认为是PUB序列的顶部Kutu火山岩中始新世部分的广泛分布的枕状玄武岩，在地图区域，根据岩性和生物地层，重新归为晚渐新世 - 中新世中期Wavera火山岩。在这里详细工作的汇报表明Keveri断层与OSFZ无关，没有沿结构逆冲的证据。该地区地质构造历史一直以沿Keverie断层的垂直位移为主。Suckling圆穹（新名词）在晚中新世上浮抬升的开始与花岗岩侵入巴布亚地区东部厚地壳有关，标志着Keveri断层的开始，并恰逢伍德拉克裂谷作用的开始。故障大大促进了圆穹的快速垂直运动（2.5米/103）。据估计，自中新世隆起8000米。Keveri断层上的地质活动与巴布亚东部其它变质核复合体两侧的构造明显不同。没有野外证据来证明沿Suckling圆穹南缘有一个低角度南倾分离断层。Suckling圆穹是巴布亚东部圆穹的最西端，位于一个广阔的伸展区之内。该区沿OSFZ板块边界持续向西延续。

KEY WORDS:

• Australian plate
• Keveri Fault
• Owen Stanley Fault Zone
• Papuan Orogen
• Papuan Ultramafic Belt
• tectonics
• Woodlark plate

ACKNOWLEDGEMENTS

The author is grateful to three AJES reviewers for their comments; the constructive criticisms of Nathan Daczko and an anonymous reviewer were particularly important in improving the overall readability of my manuscript. Ken Campbell is thanked for his comments on the final text. Hugh Davies is thanked for his thoughts on chromitite rocks in Dimidi Creek and their absence in the PUB; Richard Moore mapped the felsic dykes in Dimidi Creek; George Chaproniere worked on the Ada'u Limestone biostratigraphic samples; Wolfgang Maier discussed his ideas on PGM occurrence in the PUB and the possible relationship of the Sadowa batholith with mineralisation; Ron Palmer, PGC Geophysical Consulting, Brisbane, produced an inversion model of TMI data (Figure 9b) and the base for the 1:50 000 geological map (Figure 4a); and Kevin McCue provided earthquake data for the Mt Suckling district. Cliff Ollier, Colin Pain and Ignacio González-Álvarez kindly reviewed early drafts of the manuscript. Fieldwork would not have been possible without the support of the landowning Ba'u and Keveri clans of Doma, Amau and Baiobo villages, inland Cloudy Bay district, Central Province. Many times our small exploration teams consisted only of villagers and myself. The support over the years of Elvin Nobake from Doma has been especially important. And thanks to the many helicopter pilots who skillfully managed to cross the Main Range despite the weather, especially David Inau who in 1992 landed me on one of the Mt Suckling peaks at an altitude of 11 028 ft and near the limits of our Hughes 500D helicopter.