Temporal Constraints on Geomagnetic Filed Behavior From High-Precision 40Ar/39Ar Geochronology

该项目寻求通过获取精确的40Ar/39Ar年龄测定以及详细记录地球发电机行为的熔岩流的磁测量来改进古地磁记录。将解决三个问题：(1)将利用智利、塔希提岛、夏威夷和华盛顿的熔岩流序列中的许多新的增量加热数据来探索松山-布鲁内斯反转过程的持续时间和时间精细结构，这些数据显然是在反转过程中不同时间喷发的。(2)南半球的五个火山区将被开发为全球平衡阵列中的新记录点，旨在测量过去500万年来磁场的古分子变化。新的地质年代学将在确定熔岩记录的周期和极性状态方面发挥重要作用，熔岩对模拟磁场的时间平均行为至关重要。(3)反转尝试的频率、时间、持续时间和地理范围是模拟地球发电机的重要观测约束。因此，我们将加大努力，核实松山晚期发生的至少三个极性事件或次时间的时间和地理范围。其中包括最近提出的Punaruu(1.10 Ma)和Santa Rosa(0.92 Ma)事件，以及神户事件(0.90 Ma)。激光聚变和对新墨西哥州和加利福尼亚州硅质熔岩流中的闪锌矿斑晶的增量加热将提供所需的年龄分辨率和空间复盖率。

This project seeks to improve the paleomagnetic record through acquisition of precise 40Ar/39Ar age determinations coupled with magnetic measurements of lava flows that record in detail the behavior of the geodynamo. Three problems will be addressed: (1) The duration and temporal fine-structure of the Matuyama-Brunhes reversal process will be probed using many new incremental-heating data from lava flow sequences in Chile, Tahiti, Hawaii, and Washington that apparently were erupted at different times during the reversal. (2) Five volcanic areas in the southern hemisphere will be developed as new recording sites in a globally balanced array designed to measure paleosecular variation of the magnetic field over the past 5 million years. The new geochronology will play an important role in determining the periods and polarity states recorded by the lavas essential to modeling time-averaged behavior of the magnetic field. (3) The frequency, timing, duration, and geographic extent of reversal attempts are important observational constraints on modeling the geodynamo. Accordingly, we will expand efforts to verify the timing and geographic extent of at least three polarity events or subchrons in the late Matuyama chron. These include the recently proposed Punaruu (1.10 Ma) and Santa Rosa (0.92 Ma) events, and the Kamikatsura event (0.90 Ma). Laser fusion and incremental-heating of sanidine phenocrysts from silicic lava flows in New Mexico and California will provide the needed age resolution and spatial coverage.