Paleomagnetic of igneous rocks of ODP Leg 114@en

A paleomagnetic study was made of 12 samples of trachytic basalt from the base of ODP Hole 698A on the Northeast Georgia Rise (southwest Atlantic) and four samples of andesitic basalt and nine samples of volcanic breccia from the base of ODP Hole 703A on the Meteor Rise (southeast Atlantic). The magnetic intensities of the Hole 703A samples are anomalously low, possibly reflecting alteration effects. The mean magnetic intensity of the Hole 698A samples is high, and compatible with the model of Bleil and Petersen (1983) for the variation of magnetic intensity with age in oceanic basalts, involving progressive low-temperature oxidation of titanomagnetite to titanomaghemite for some 20 m.y. followed by inversion to intergrowths of magnetite and other Fe-Ti oxides during the subsequent 100 m.y. These results support the interpretation of the Hole 698A basalts as true oceanic basement of Late Cretaceous age rather than a younger intrusion. […]本研究对大西洋西南部东北乔治亚海隆大洋钻探计划（Ocean Drilling Program，ODP）698A孔底部的12件粗安玄武岩样品，以及大西洋东南部流星海隆ODP 703A孔底部的4件安山玄武岩样品与9件火山角砾岩样品开展了古地磁研究。703A孔样品的磁化强度异常偏低，可能受蚀变作用影响。698A孔样品的平均磁化强度较高，与Bleil和Petersen（1983）提出的洋壳玄武岩磁化强度随年龄变化模型相符：该模型指出，钛磁铁矿会经历约20百万年的逐步低温氧化，转化为钛磁赤铁矿，随后在后续的100百万年中发生逆转变，形成磁铁矿与其他铁钛氧化物的交生体。上述研究结果支持698A孔玄武岩为晚白垩世真实洋壳基底，而非后期年轻侵入体的解释结论。[…]