The Time Averaged Field at the Equator: Ecuador

本研究将对厄瓜多尔赤道火山省的晚上新世-更新世熔岩流进行时间平均场（TAF）研究，那里丰富的火山活动提供了极好的采样可能性。厄瓜多尔有超过54座平流层火山，是安第斯火山带北段的一部分，被称为北部火山区（NVZ），从北纬50度延伸到南纬20度（覆盖哥伦比亚和厄瓜多尔的部分地区）。计划在至少40个地点进行40Ar/39Ar定年的古地磁采样和岩石采样。实地工作将在地球物理系教授（基多国立理工大学）Minard Hall博士的合作下进行，他是厄瓜多尔火山学方面知识和经验最多的人。他对该地区火山地层学的了解将加快和优化实地工作。古地磁和Ar/Ar实验室分析将在佛罗里达大学进行。古强度研究将在尽可能多的地点进行。这项研究将有助于填补赤道纬度古地磁数据库中合适的长期变化研究的空白。为了获得对磁场的非偶极子贡献（约占总磁场的5%）敏感的结果，本研究将应用现场工作、实验室和数据分析期间的最先进测量技术。根据长期变化模型G，赤道的角频散可以完全归因于四极谐波族，而不是主偶极子，从而使厄瓜多尔成为古磁场的一个战略观测点。在许多研究中观察到的当前磁场的角色散（相对于地球旋转轴）的纬度变化与古磁场之间的一致性将得到检验。该研究将有助于加强古地磁熔岩流数据库，该数据库目前似乎表明，尽管由于数据库的不足，最后5 Ma的TAF纵向结构与现在的场之间存在一致性。另一方面，过去二十年来磁场的变化导致一些人认为磁场正在发生逆转（Hulot et al., 2002），这很难被认为是磁场的正常状态。这项研究将在厄瓜多尔进行一项急需的长期变化研究，遵循严格的古地磁技术和出色的年龄控制。

OpdykeEAR-0229130This study will undertake a time averaged field (TAF) study of late Pliocene - Pleistocene lava flows in the equatorial volcanic province of Ecuador, where abundant volcanism offers excellent possibilities of sampling. More than 54 stratovolcanoes in Ecuador form part of the northern segment of the Andean volcanic belt, called the Northern Volcanic Zone (NVZ), which extends from 5o N to 2o S latitude (covering parts of Colombia and Ecuador). Paleomagnetic sampling and rock sampling for 40Ar/39Ar dating is planned on at least 40 sites. Fieldwork will be carried out with the collaboration of Dr. Minard Hall, professor of the Department of Geophysics (Escuela Politecnica Nacional, Quito), who is the person with the most knowledge and experience of the volcanology of Ecuador. His knowledge of the volcanic stratigraphy of the area will expedite and optimize fieldwork. Paleomagnetic and Ar/Ar laboratory analysis will be made at the University of Florida. Paleointensity studies will be carried out on as many sites as possible. This study will help to fill an existing gap in the paleomagnetic database of suitable secular variation studies at equatorial latitudes. State of the art measurements during fieldwork, laboratory and data analysis will be applied in this study in order to obtain results sensitive to non-dipole contributions of the magnetic field (about 5% of the total magnetic field). This study will comply with present day selection criteria of paleomagnetic databases According to model G of secular variation, angular dispersion at the equator can be attributed solely to the quadrupole family of harmonics and not to the main dipole, thus making Ecuador a strategic point of observation of the paleomagnetic field. The agreement observed in many studies between latitudinal variations of the angular dispersion (relative to the Earth's axis of rotation) of the present field and the paleomagnetic field will be tested. This study will contribute to enhance the paleomagnetic database of lava flows which at the present moment seem to indicate, although not conclusively due to deficiencies of the database, the coincidence between longitudinal structures in the TAF of the last 5 Ma and the present field. On the other hand changes of the present field in the last two decades have lead some to suggest an on-going reversal scenario (Hulot et al., 2002) which could be hardly considered a normal state of the magnetic field. This study will undertake a much-needed secular variation study in Ecuador, following rigorous paleomagnetic techniques with excellent age control.