Geomagnetic palaeointensity just prior to the Cretaceous normal superchron

被引:60
|
作者
Zhu, RX
Pan, YX
Shaw, J
Li, DM
Li, Q
机构
[1] Chinese Acad Sci, Inst Geol & Geophys, Beijing 100101, Peoples R China
[2] Univ Liverpool, Dept Earth Sci, Liverpool L69 7ZE, Merseyside, England
[3] China Seismol Bur, Inst Geol, Beijing 100029, Peoples R China
基金
中国国家自然科学基金;
关键词
palaeointensities; M0; China; lavas;
D O I
10.1016/S0031-9201(01)00287-4
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
A combined geochronologic (K-Ar) and palaeomagnetic study has been conducted on abasalt lava sequence at Zhuanchengzi in Liaoning province, northeastern China. The new K-Ar age obtained from these lava flows is 120.93 +/- 0.88 Ma (marine anomaly MO). Detailed investigations were conducted on two samples from each lava flow to determine their rock-magnetic properties. The temperature dependences of the saturation magnetization (J-T) and the initial susceptibility (K-T) show evidence of low-titanium magnetite and a Curie temperature of 560-585 degreesC with generally good reversibility of heating and cooling curves. Hysteretic properties, ratios of M-rs/M-s and Her/Hc, indicate that pseudo-single-domain (PSD) grains of magnetite are dominant in these lavas. Stepwise thermal demagnetization isolated well-defined characteristic magnetization (ChRM) in all the 20 lava flows with a mean direction of D/I = 174.9/-60.1 degrees with alpha (95) = 2.3 degrees. The modified version of the Thellier and Thellier palaeointensity method (Coe, 1967a) with systematic partial thermoremanent magnetization (pTRM) checks was used. Forty-two of 71 samples (59%) yielded reliable palaeointensity results. Virtual dipole moment (VDM) values range from 1.71 X 10(22) to 5.27 x 10(22) A m(2) with an average of (3.96 +/- 0.07) x 10(22) A m(2). This low dipole-field intensity value is approximately half the present day VDM, consistent with older results obtained from the Caribbean submarine basalt glasses for the period of 125 +/- 1 Ma (Pick and Tauxe, 1993). This suggested that a weak geomagnetic field probably occurred just prior to the Cretaceous normal superchron (CNS). (C) 2001 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:207 / 222
页数:16
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