东太平洋地区DSDP573孔始新世末期的微玻璃陨石  

THE MICROTEKTITES IN HOLE B AT SITE 573 OF DSDP IN THE EAST PACIFIC

作　　者：尹延鸿[1] 万天丰[2] 孙嘉诗[1] 

机构地区：[1]青岛海洋地质研究所,青岛266071 [2]中国地质大学,北京100083

出　　处：《海洋地质与第四纪地质》2001年第4期37-42,共6页Marine Geology & Quaternary Geology

基　　金：国家自然科学基金资助项目 ( 4 9776 2 94)

摘　　要：通过研究 DSDP5 73孔的岩心样品 ,首次在该孔始新世与渐新世的界线地层含金属粘土层中发现了微玻璃陨石 ,且主要富集在其底部。一个样品 (5 g)中最多可达 12粒。这些微玻璃陨石主要呈球形、椭球形。用电子探针测试了其化学成分 ,Si O2 含量为 2 9.6 4%～ 5 8.93%,Al2 O3 为 3.42 %～ 2 0 .96 %,Fe O为 9.98%～ 2 9.5 5 %,Mg O为 4.32 %～ 16 .0 5 %,Ir为 0 .0 6 %～ 0 .81%。总体来说 ,微玻璃陨石的化学成分变化较大 ,可能与靶岩的成分变化较大有关。始新世末期北美微玻璃陨石场的展布方向约为 2 5 0°,这与太平洋板块运动方向改变所需要的矢量变化(2 45°)仅相差 5°,推测很可能是始新世末期陨星的撞击引起了太平洋板块在该时期的运动方向由 NNW突然变为NWW。Samples of the strata from late Eocene to early Oligocene at site 573 of DSDP give the first discovery of microtektites in the layer of metalliferous claystone around the boundary between late Eocene and early Oligocene and the microtektites were more abundant at the bottom of the metalliferous claystone with a hole depth of 525 00～526 00 m than in any other part of th hole. At most 12 grains of microtektites were found in a 5 gram sample. The microtektites are black in color, and spherical, ellipsoid or droplet in shapes. They vary mainly from 0 063 mm to 0 3 mm in size. The chemical compositions of the microtektite were researched by EPMA. SiO 2 is 29 64%～58 93%,Al 2O 3: 3 42%～20 96%,FeO: 9 98%～29 55%,MgO: 4 32%～16 05%,and Ir 0 06%～0 81%. The chemical compositions of the microtektites have a large range which may be caused by the variable chemical compositions of the impact rock. As we all know, the microtektite strewn field is formed by meteorite impact, and the strewn field trending may show the direction of the impact. The trending of the North American microtektite strewn field at the end of Eocene is about 250°. The Pacific plate changed its movements from NNW to NWW at the end of Eocene. By a vector triangular diagram,we can see that a vector change of 8 7 cm/a in the direction of 245° is necessary for the Pacific plate to do so. This vector change surprisingly coincides with the trending ( about 250°) of North American microtektite strewn field. So it has a large possibility that the change of the moving direction of the Pacific plate might be caused by a meteorite's impacting the Pacific plate in the direction of 245° or 250° at the end of Eocene.

关 键 词：微玻璃陨石 含金属粘土层 始新世末期 太平洋板块 海洋沉积物 陨击事件 

分 类 号：P736[天文地球—海洋地质]