Palaeomagnetism and ⁴⁰Ar/³⁹Ar age from a Cretaceous volcanic sequence, Inner Mongolia, China: Implications for the field variation during the Cretaceous normal superchron

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• 作者：Rixiang Zhu ; Yongxin Pan ; Huaiyu He ; Huafeng Qin ; Shoumai Ren
• 关键词：Palaeointensity ; Cretaceous normal superchron ; ⁴⁰Ar/³⁹Ar dating ; Inner Mongolia
• 刊名：Physics of the Earth and Planetary Interiors
• 出版年：2008
• 出版时间：August 2008
• 年：2008
• 卷：169
• 期：1-4
• 页码：59-75
• 全文大小：2558 K

文摘

An integrated palaeomagnetic and ⁴⁰Ar/³⁹Ar dating study was carried out on an Early Cretaceous volcanic lava sequence from the Suhongtu section, Inner Mongolia, to determine the field behavior within the Cretaceous normal superchron (CNS). ⁴⁰Ar/³⁹Ar ages were obtained from 12 lava flows, indicating that the studied lava was formed around 114.1 ± 0.3 Ma for the lower interval and 110.6 ± 0.1 Ma for the upper interval. Rock-magnetic experiments and electron microprobe analyses indicate that the primary Fe–Ti oxides are the main magnetic carriers. All lava flows carry normal palaeomagnetic directions, which can be grouped into 31 units by an F-test, with a Fisher mean characteristic remanent magnetization (ChRM) of D/I = 12.8/58.6° (α₉₅ = 2.3°). The corresponding palaeomagnetic pole is located at 80.3°N and 200.3°E (A₉₅ = 3.2°, K = 64.4), which is indistinguishable at the 95 % confidence level from the Eurasia pole derived from the apparent polar wander path for the early Cretaceous. Using a modified Thellier palaeointensity method with stringent acceptance criteria, we obtained two time-series of palaeointensity records from 15 independent palaeomagnetic units (total 136 samples). The virtual dipole moment (VDM) values varied from 2.53 × 10²² Am² to 9.92 × 10²² Am². The mean VDMs for the upper and lower intervals are (5.38 ± 2.06) × 10²² Am² and (4.61 ± 2.67) × 10²² Am², respectively. The observed time-series of palaeointensity, together with the previously available data for the CNS, suggest that magnetic field strength during the CNS fluctuated significantly with time.