Full vector paleomagnetic estimation from the Paraná-Etendeka Large Igneous Province, southern Brazil: Implications on the onset of Cretaceous Normal Superchron

IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Luis M. Alva-Valdivia , Jairo F. Savian , Camila R. Tomé , Arnaldo Hernández-Cardona , Caroline D.K. Tolotti , Marcia E.B. Gomes , J. Antonio González-Rangel
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Abstract

Comprehensive paleomagnetic study from the Paraná-Etendeka Igneous Province (PEIP), Serra Geral Formation, southern Brazil (∼ 135 Ma) adds to the scarce southern hemisphere paleomagnetic database. Twelve paleomagnetic sites from the exposed stratigraphy of the PEIP were recovered from basaltic lava flows in northern Rio Grande do Sul state. These volcanic rocks erupted between 131.5 and 135.6 Ma. The reliability of the rock magnetism data was confirmed before being accepted for paleo-intensity analysis. The Thellier-Coe paleointensity protocol was applied to 109 collected specimens, and 26 individual samples from 9 sites were selected to test for consistency of the paleointensity determinations. The new high-quality mean paleointensity value of 30.6 ± 7.2μT corresponds to a virtual dipole moment (VDM) of 5.75 ± 0.49 × 1022 Am2. These values correspond to approximately 72% of the present-day Earth's magnetic field and suggest that the Earth's magnetic field strength was slightly elevated compared to the long-term average geomagnetic field that prevailed during the Cretaceous Normal Superchron. The calculated paleomagnetic pole (Plong = −27.5° and Plat = −78.6°, A95 = 3.5°) presents an angular difference of 22° with respect to the expected pole declination with an inclination of 5°. This difference may correspond to secular variations considering the confidence cones. Our results, when compared with previous paleomagnetic data, approach the accuracy of recent models for the Cretaceous interval.

Abstract Image

巴西南部Paraná-Etendeka大型火成岩省的全矢量古地磁估计:对白垩纪正超时开始的意义
巴西南部Serra Geral组Paraná-Etendeka火成岩省(PEIP) (~ 135 Ma)的综合古地磁研究增加了稀缺的南半球古地磁数据库。从南里奥格兰德州北部的玄武岩熔岩流中恢复了PEIP暴露地层的12个古地磁点。这些火山岩在131.5 - 135.6 Ma之间喷发。岩石磁学资料的可靠性得到证实,可用于古强度分析。采用Thellier-Coe古强度方案对109个采集的样品进行分析,选取9个测点的26个样品进行古强度测定的一致性检验。新的高质量平均古强度值为30.6±7.2μT,对应的虚偶极矩(VDM)为5.75±0.49 × 1022 Am2。这些值大约相当于现今地球磁场的72%,表明地球磁场强度与白垩纪正常超时期间盛行的长期平均地磁场相比略有提高。计算得到的古磁极(Plong = - 27.5°,Plat = - 78.6°,A95 = 3.5°)与预期的磁极偏角相差22°,倾角为5°。考虑到置信锥,这种差异可能对应于长期变化。我们的结果,当与以前的古地磁数据比较时,接近白垩纪区间的最新模型的准确性。
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来源期刊
Physics of the Earth and Planetary Interiors
Physics of the Earth and Planetary Interiors 地学天文-地球化学与地球物理
CiteScore
5.00
自引率
4.30%
发文量
78
审稿时长
18.5 weeks
期刊介绍: Launched in 1968 to fill the need for an international journal in the field of planetary physics, geodesy and geophysics, Physics of the Earth and Planetary Interiors has now grown to become important reading matter for all geophysicists. It is the only journal to be entirely devoted to the physical and chemical processes of planetary interiors. Original research papers, review articles, short communications and book reviews are all published on a regular basis; and from time to time special issues of the journal are devoted to the publication of the proceedings of symposia and congresses which the editors feel will be of particular interest to the reader.
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