ESTIMATES OF FLOW DIRECTION FOR CALC-ALKALINE WELDED TUFFS AND PALEOMAGNETIC DATA RELIABILITY FROM ANISOTROPY OF MAGNETIC-SUSCEPTIBILITY MEASUREMENTS - CENTRAL SAN-JUAN MOUNTAINS, SOUTHWEST COLORADO
ESTIMATES OF FLOW DIRECTION FOR CALC-ALKALINE WELDED TUFFS AND PALEOMAGNETIC DATA RELIABILITY FROM ANISOTROPY OF MAGNETIC-SUSCEPTIBILITY MEASUREMENTS - CENTRAL SAN-JUAN MOUNTAINS, SOUTHWEST COLORADO
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DOI：
10.1016/0012-821x(82)90133-9
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发表时间：
1982-01-01
影响因子：
5.3
通讯作者：
ELLWOOD, BB
中科院分区：
文献类型：
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作者：
ELLWOOD, BB
流动方向是通过测量106个样品的磁性结构来估计的，这些样品收集于科罗拉多州南部圣胡安山脉中部四个焊接凝灰岩单元的18个地点。估计假设凝灰岩通常直接从挤出口流出，凝灰岩内的磁性颗粒线代表了单个位置的流动方向。估计中的误差可能来自地形变化、凝灰岩内的流变性（侵位后的质量流动）和其他因素。磁性线化定义为磁化率最大方位角的部位平均各向异性。对单个单元的流动方向的测试是基于线条方位角的投影及其在已知凝灰岩源火山口内或附近的相交。4个单位的检测结果呈阳性。这些凝灰岩的古地磁结果可能是科罗拉多西南部（28.2-26.5 Ma）侵位期间地磁场方向的可靠指标。
Flow directions are estimated from the measurement of the magnetic fabric of 106 samples, collected at 18 sites in four welded tuff units in the central San Juan Mountains of southern Colorado. The estimates assume that the tuffs generally flowed directly away from the extrusive vents and that the lineations of magnetic grains within the tuffs represent the flow direction at individual sites. Errors in the estimation may arise from topographic variation, rheomorphism (post-emplacement mass flow) within the tuff, and other factors. Magnetic lineation is defined as the site mean anisotropy of magnetic susceptibility maximum azimuth. A test on the flow directions for individual units is based on the projection of lineation azimuths and their intersection within or near the known source caldera for the tuff. This test is positive for the four units examined. Paleomagnetic results for these tuffs are probably reliable indicators of the geomagnetic field direction in southwest Colorado, during the time (28.2–26.5 Ma) of emplacement.