High-resolution paleomagnetic investigation in the Iceland Basin

Based on discrete samples, we report new high-resolution records of the ~185 kyr Iceland Basin (IB) geomagnetic excursion from Ocean Drilling Project (ODP) Site 1063 on the Bermuda Rise (sedimentation rate 32 cm/kyr) and from ODP Site 983 in the far North Atlantic (sedimentation rate 18 cm/kyr). Two records from Holes 1063A and 1063B are very consistent, and provide the highest resolution of the detailed field behaviour during the IB excursion obtained so far. Inclination records from Holes 983B and 983C in the far North Atlantic are also very consistent, whereas declination anomalies deviate more notably. The pseudo-Thellier (PT) technique was applied along with more conventional palaeointensity proxies (NRM/ARM and NRM/kappa) to recover relative palaeointensity (RPI) estimates from Hole 1063A and Hole 983B. As expected, these proxies indicate that the field intensity generally dropped at both sites during the IB excursion, but also that the history of RPI from the two sites is different. VGPs from Site 1063 indicate that the field at this location experienced some stop-and-go behaviour between patches of intense vertical flux over North America and the tip of South America, areas which coincide fairly well with patches of preferred transitional VGP clustering from reversals and zones of high seismic velocity in the lower mantle. Changes in RPI at this location were generally gradual, possibly due to the proximity of these flux patches, and the first period of VGP-clustering over North America was accompanied by a conspicuous increase in RPI. VGPs from Site 983 track along a different path, and the associated RPI changes are very abrupt and completely synchronous with the onset and termination of the excursion. The differing VGP paths from Sites 1063 and 983 indicate that the global field structure during the IB excursion was not dominated by a single dipole.本研究基于离散样品，报道了来自百慕大隆起区大洋钻探计划（"Ocean Drilling Project", ODP）1063站位（沉积速率32 cm/kyr）以及北大西洋远端ODP 983站位（沉积速率18 cm/kyr）的约185 kyr冰岛海盆（"Iceland Basin", IB）地磁漂移高分辨率新记录。1063A与1063B两口钻井的记录一致性极佳，为目前已获取的IB漂移期间精细地磁场演化行为提供了迄今最高分辨率的数据。 北大西洋远端983B与983C钻井的倾角记录同样吻合度较高，但偏角异常的偏差更为显著。本研究采用伪塞勒（"pseudo-Thellier", PT）技术，结合更为常规的古强度代理指标（天然剩余磁化强度/非磁滞剩余磁化强度（"NRM/ARM"）与天然剩余磁化强度/磁化率（"NRM/kappa"）），从1063A钻井与983B钻井中恢复得到相对古强度（"relative palaeointensity", RPI）估算值。正如预期，这些指标显示两处站位的地磁场强度在IB漂移期间均普遍下降，但两处的RPI演化历史存在显著差异。 1063站位的虚地磁极（"Virtual Geomagnetic Poles", VGPs）数据显示，该区域的地磁场在北美与南美尖端区域的强垂直通量斑块之间呈现间歇性停滞行为；上述区域与反转事件中过渡阶段虚地磁极聚集的优选斑块以及下地幔高速异常带的分布区域高度吻合。该区域的RPI变化整体较为平缓，这可能与这些通量斑块的邻近性有关；而北美上空首次出现虚地磁极聚集阶段，伴随有RPI的显著升高。983站位的VGPs沿不同路径移动，相关的RPI变化则极为突兀，且完全与漂移的起始和终止同步。1063与983站位的VGPs路径差异表明，IB漂移期间的全球磁场结构并非由单一偶极子主导。