The Time Averaged Field at the Equator: Ecuador

OpdykeEAR-0229130这项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54多座层状火山，是安第斯火山带北段的一部分，称为北部火山带，从北纬50度延伸到S纬度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测年的古地磁采样和岩石采样。实地考察工作将在地球物理系(基多国家理工学院)教授Minard Hall博士的协作下进行，他是对厄瓜多尔火山学有最多知识和经验的人。他对该地区火山地层学的了解将加快和优化野外工作。古地磁和Ar/Ar实验室分析将在佛罗里达大学进行。将在尽可能多的地点进行古强度研究。这项研究将有助于填补在赤道纬度适合长期变化研究的古地磁数据库中的现有空白。为了获得对磁场(约占总磁场的5%)的非偶极子贡献敏感的结果，本研究将采用现场工作、实验室和数据分析过程中的最新测量。这项研究将符合当今古地磁数据库的选择标准。根据长期变化模型G，赤道角色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地磁场的战略观测点。在许多研究中观察到的现今磁场角散(相对于地球自转轴)的纬度变化与古地磁场之间的一致性将得到检验。这项研究将有助于加强熔岩流的古地磁数据库，该数据库目前似乎表明，尽管由于数据库的不足而不是决定性的，但最近5 Ma的TAF的纵向结构与现代场之间的重合。另一方面，在过去二十年中，电磁场的变化导致一些人提出了一种持续的反转情况(Hulot等人，2002年)，这几乎不能被认为是磁场的正常状态。这项研究将在厄瓜多尔进行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.