BMR Cruise 107: Seabed Morphology and Offshore Resources around Christmas Island, Indian Ocean

The Australian Territory of Christmas Island, a raised atoll with a population of about 2000 people, lies on oceanic crust about 1600 km north- north west of Australia's Northwest Cape, and 350 km south of western most Java (Fig. 1). The Australian Cocos-Keeling Islands group is 1000 km further west. Christmas Island resembles a 'T', with its stem running east-west (Fig. 4), has an area of 140 km2, and is up to 20 km across. Australia has declared a 200 mile fisheries zone around Christmas Island. The island is on the Indo-Australian Plate, which is moving 'north at about 7cm/year, and is being uplifted on the bulge in front of the Java Trench 150km to the north. It has the form of a plateau at 200-300 m above sea level,bounded by a series of sea cliffs and terraces. The plateau slopes to the south; the highest point is Murray's Hill (361 m) on the western end of the island. The natural vegetation is tropical rain forest. The island is at the eastern end of the submarine Christmas Rise, which extends south-south west for 700 km (Fig. 1). The Java Trench to the north is more than 6500 m deep, and the abyssal plains around the Christmas Rise are 5000-6000 m deep. The rise sits on oceanic crust of presumed LateCretaceous age, and both it and the pedestal of the island consist largely of volcanics. On the island the volcanics are overlain by Eocene limestone, and an extensive Miocene limestone which is associated with extensive phosphate deposits. These deposits produced nearly 1,000,000 tonnes a year of phosphate rock until 1987 when mining ceased. Mining resumed at asmaller scale in 1991. In early 1991, the Australian Department of Foreign Affairs and Trade requested BMR to undertake a study of the non-living seabed resources of the area around Christmas Island, as an aid to seabed boundary delimitation negotiations. This work arose from the request, and started in January 1992, using RV. Rig Seismic. A cruise narrative is provided in Appendix 7

圣诞岛领地（Australian Territory of Christmas Island）是一座抬升环礁，常住人口约2000人，坐落于澳大利亚西北岬以北西北向约1600千米、爪哇最西端以南350千米的洋壳之上（图1）。澳大利亚科科斯（基林）群岛（Cocos-Keeling Islands）群组位于其西侧1000千米处。圣诞岛外形呈“T”字形，其东西向延伸的主体如图4所示，面积140平方千米，最宽处达20千米。澳大利亚已在圣诞岛周边划定200海里渔业专属区。该岛位于印度-澳大利亚板块（Indo-Australian Plate）之上，板块以约7厘米/年的速率向北移动，且受北侧150千米处的爪哇海沟（Java Trench）前缘隆起影响而抬升。岛屿主体为海拔200-300米的高原，被一系列海崖与阶地环绕，高原向南倾斜，全岛最高点为岛西端的默里山（海拔361米）。原生植被为热带雨林。该岛位于海底圣诞海岭（submarine Christmas Rise）的东端，该海岭向南西方向延伸700千米（图1）。北侧的爪哇海沟最大水深超过6500米，海底圣诞海岭周边的深海平原（abyssal plains）水深介于5000-6000米之间。该海岭坐落于被认为属于晚白垩世（Late Cretaceous）的洋壳之上，海岭与岛屿基座主体均以火山岩为主。岛上的火山岩地层之上覆有始新世（Eocene）灰岩，以及与大规模磷酸盐矿床伴生的广泛分布的中新世（Miocene）灰岩。1987年采矿活动停止前，这些矿床每年可产出近100万吨磷矿石；1991年起，采矿活动恢复至小规模规模。1991年初，澳大利亚外交与贸易部（Australian Department of Foreign Affairs and Trade）请求澳大利亚矿产资源局（Bureau of Mineral Resources, BMR）开展圣诞岛周边海域非生物海底资源的研究，以协助海底边界划界谈判。本项工作即源于该委托，于1992年1月借助“里格号”地震勘探船（RV Rig Seismic）启动，附录7收录了本次航次的详细记述。