Active Continental Extension of Eastern Papua New Guinea: Geologic Studies of Emerged Coral Reefs and Marine Sedimentary Rocks

0106518从狭窄、界限分明的板块边界处的海底扩张到大陆地壳的扩散裂陷，现今在世界范围内的三个地方发生了Mandarin横向过渡：红海、亚丁湾和巴布亚新几内亚东部。 这三个领域对于了解大陆如何断裂至关重要，因为从海底扩张到大陆裂谷的空间进展提供了对大洋扩张脊到大陆裂谷的时间和结构演变的见解。 这种认识并不容易从更广泛的活跃的陆内伸展区，如美国盆地和山脉省，那里的伸展还没有--也可能不会--最终进行到海底扩张的地步。 在这三个海底扩张到裂谷过渡区中，只有巴布亚新几内亚表现出扩张脊尖端与低角度正断层地震、海底环境中的活动低角度正断层和晚第三纪变质核杂岩之间的密切空间关联。 登特卡斯托群岛和巴布亚半岛位于大洋扩张和大陆裂谷作用的过渡地带，周边为晚第三纪沉积岩和晚第四纪珊瑚礁。 这些可进入的陆地区域提供了理想的地质环境，可以测试根据地震、核杂岩的辐射和结构研究以及海洋地球物理研究提出的几种对比鲜明的洋脊-裂谷扩展过渡构造模型。 这些先前提出的模型的主要内容包括海洋传播脊模型适用于这一地区的大陆地壳，本地化的变质核杂岩和地形隆起的传播脊的地区附近，和横向移动的裂谷和随后的扩展的位置。 我们正在使用晚第四纪珊瑚礁和晚新近纪沉积剖面的地质研究相结合的沿着数百公里的巴布亚新几内亚东部海岸线，以确定晚新近纪晚第四纪垂直构造历史，变形样式和构造机制的模式，以测试上述构造模型。 我们在这些研究中解决的关键问题包括：1）在D 'Entrecasteaux群岛和巴布亚半岛，最大的晚第四纪珊瑚礁隆起的区域在哪里，什么结构影响了它们？2)在这个地区的隆起模式中是否有可探测的空间迁移？在Sanaroa和Fergusson群岛附近的低角度正断层地震区，新近纪晚期海相岩石和珊瑚阶地本身是否存在低角度正断层？ 我们的研究结果将有助于解释活跃的脊传播或跳跃在其他活跃的裂谷地区，包括红海，东非裂谷，和亚丁湾的详细的珊瑚礁记录，如在巴布亚新几内亚是不可用的构造效应。

0106518MannThe lateral transition from seafloor spreading at a narrow, well defined plate boundary to diffuse rifting of continental crust occurs today in three localities worldwide: the Red Sea, the Gulf of Aden, and eastern Papua New Guinea. These three areas are critical for understanding how continents rupture because the spatial progression from seafloor spreading to continental rifting provides insights into the temporal and structural evolution of an oceanic spreading ridge to a continental rift. Such insights are not readily apparent from the more widespread zones of active intracontinental extension like the U.S. Basin and Range province where extension has not - and may not - eventually proceed to the point of seafloor spreading. Of these three seafloor spreading to rift transition areas, only Papua New Guinea exhibits a close spatial association between the tip of the propagating spreading ridge and low-angle normal fault earthquakes, active, low-angle normal faults in a submarine setting, and late Neogene metamorphic core complexes. The D'Entrecasteaux Islands and Papuan Peninsula, fringed by late Neogene sedimentary rocks and late Quaternary coral reefs, occupy the transition area between oceanic spreading and continental rifting. These accessible land areas provide an ideal geologic setting to test several contrasting tectonic models for spreading ridge-rift transitions proposed on the basis of earthquakes, radiometric and structural studies of core complexes, and marine geophysical studies. The main elements of these previously proposed models include oceanic propagating ridge models applied to this region of continental crust, localization of metamorphic core complexes and topographic uplift adjacent to areas of propagating ridges, and lateral shifts in the location of rifting and subsequent spreading. We are using a combination of geologic studies of late Quaternary coral reefs and late Neogene sedimentary sections along hundreds of kilometers of eastern PNG coastlines to determine the pattern of late Neogene to late Quaternary vertical tectonic history, style of deformation, and tectonic mechanisms in order to test the tectonic models described above. Key questions that we are addressing in these studies include: 1) Where is the area of maximum late Quaternary coral reef uplift in the D'Entrecasteaux Islands and Papuan Peninsula and what structures have affected them? 2) Are there detectable spatial migrations in the uplift pattern of this region? and 3) Are low angle normal faults present in the late Neogene marine rocks and the coral terraces themselves in the area of low angle normal fault earthquakes near Sanaroa and Fergusson Islands? Our results will aid interpretations of the tectonic effects of active ridge propagation or jumping in other active rift areas including the Red Sea, East African rifts, and Gulf of Aden where a detailed reef record such as in Papua New Guinea is not available.