A re-evaluation of arc–continent collision and along-arc variation in the Bismarck Sea region, Papua New Guinea

Abstract

The Bismarck Sea region of Papua New Guinea is marked by recent arc–continent collision giving rise to a highly dynamic tectonic environment, characterised by complex plate interactions that are yet to be fully understood. We present a new crustal and upper mantle crustal architecture model for northeastern Papua New Guinea and western New Britain that reveals complex tectonic geometries of overprinting slab subduction and partial continental subduction, resulting in a unique setting in which to investigate along-arc magmatic variation. Earthquake hypocentre databases are combined with detailed topography and seafloor structure together with geology and regional-scale gravity to unravel the sub-surface structure of northeastern Papua New Guinea. These data are used in conjunction with an updated 3-D slab map of the region to propose a new interpretation of the area whereby Australian continental crust extends as an underthrust block beneath the accreted Finisterre Terrane. The subducting continental crust combined with slab stagnation has resulted in a complex pattern of arc-related geochemical signatures from east to west along the Bismarck arc. In the east, where the Solomon Sea plate is subducting beneath New Britain, the sedimentary component is low, whereas in the west, the arc volcanics exhibit a greater sedimentary component, consistent with subduction of Australian crustal sediments. As a result, a new plate reconstruction is provided for the region together with a forward-looking reconstruction of the Papuan peninsula, the Solomon Sea plate and New Britain that illustrates that the same process will likely be repeated in some 5–10 m.y.

巴布亚新几内亚的Bismarck海区以近期岛弧-大陆碰撞为标志。这次碰撞导致了活动性大的构造环境，其特征是复杂的还未完全了解的板块互动。我们提出了巴布亚新几内亚东北部和新不列颠西部的一个新的地壳和上地幔地壳构造模式，发现了板块俯冲和部分大陆俯冲的复杂板块构造特性，导致了一个独特的可研究沿岛弧岩浆变化的环境。为探索巴布亚新几内亚东北部的地下构造，我们将地震震源资料、地貌细节、海底构造、地质学和区域范围重力特征综合起来。我们运用这些资料和该地区的最新三维板块图，提出了对这一地区的新解释：澳大利亚大陆地壳作为下推块体延展于加积的Finisterre地体之下。大陆地壳俯冲和板块停滞一起导致了沿Bismarck岛弧从东到西的与岛弧相关的复杂地化模式。在东部，所罗门海板块俯冲于新不列颠之下，沉积岩组份低，而在西部，岛弧火山岩表现出较高的沉积岩组份，与澳大利亚地壳沉积物的俯冲相一致。结果，我们提出了该区新的板块重建，以及期待中的巴布亚半岛、所罗门海板块和新不列颠的重建。后者可以显示大约500-1000万年之后同样的地质过程可能会重演。

KEY WORDS:

• Papua New Guinea
• Bismarck arc
• arc–continent collision
• gravity
• seismicity
• arc geochemistry.

关键词:

• 巴布亚新几内亚
• Bismarck岛弧
• 岛弧-大陆碰撞
• 重力
• 地震强度
• 岛弧地球化学

ACKNOWLEDGEMENTS

We would like to thank Nautilus Minerals for providing data from the Hamme Cruise. We also thank Carl Spandler, Thorsten Becker, Patrice Rey, Gideon Rosenbaum and Robert Hall and an anonymous reviewer for helpful criticisms and suggestions.