The Central Atlantic Magmatic Province at the TriassicaaaJurassic boundary: paleomagnetic and ⁴⁰Ar/³⁹Ar evidence from Morocco for brief, episodic volcanism

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• 作者：Knight ; K.B. ; Nomade ; S. ; Renne ; P.R. ; Marzoli ; A. ; Bertrand ; H. ; Youbi ; N.
• 关键词：Triassic??????Jurassic ; Central Atlantic Magmatic Province ; paleomagnetism ; geochronology ; large igneous province
• 刊名：Earth and Planetary Science Letters
• 出版年：2004
• 出版时间：November 30, 2004
• 年：2004
• 卷：228
• 期：1-2
• 页码：143-160
• 全文大小：1.94 M

文摘

The Central Atlantic Magmatic Province (CAMP), one of the largest known flood basalt provinces formed in the Phanerozoic, is associated with the pre-rift stage of the Atlantic Ocean at the TriassicaaaJurassic boundary ca. 200 Ma. Paleomagnetic sampling targeted packages of CAMP lava flows in Morocco's High Atlas divided into four basic units (the lower, intermediate, upper, and recurrent units) from sections identified on the basis of field observations and geochemistry. Oriented cores were demagnetized using both alternating field (AF) and thermal techniques. Paleomagnetic results reveal wholly normal polarity interrupted by at least one brief reversed chron located in the intermediate unit, and reveal distinct pulses of volcanic activity identified by discrete changes in declination and inclination. These variations in magnetic direction are interpreted as a record of secular variation, and they may provide an additional correlative tool for identification of spatially separated CAMP lava flows within Morocco. ⁴⁰Ar/³⁹Ar analyses of Moroccan CAMP lavas yield plateau ages indistinguishable within 2aa error limits, sharing a weighted mean age of 199.9aa0.5 Ma (2aa), reinforcing the short-lived nature of these eruptions despite the presence of sedimentary horizons between them. Correlation of our sections with the E23n, E23r, E24 sequence reported in the Newark basin terrestrial section and St. Audrie's Bay marine section is suggested. Brief volcanism in sudden pulses is a potential mechanism for volcanic-induced climatic changes and biotic disruption at the TriassicaaaJurassic boundary. Combination of our directional group (DG) poles yields an African paleomagnetic pole at 200 Ma of aa(aaN)=73.0aa, aa(aaE)=241.3aa (Dp=5.0aa, Dm=18.5aa).