Paleomagnetism of the Jurassic Transantarctic Mountains revisited - Evidence for large dispersion of apparent polar wander within less than 3Myr
Paleomagnetism of the Jurassic Transantarctic Mountains revisited - Evidence for large dispersion of apparent polar wander within less than 3Myr
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重新审视侏罗纪横贯南极山脉的古地磁学 - 证据表明表观极地漂移在不到 3 马来西亚里的范围内大范围分散
DOI：
10.1016/j.gr.2015.01.002
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发表时间：
2016
影响因子：
6.1
通讯作者：
N. Petersen
中科院分区：
文献类型：
--
作者：
O.S. Lemna;V. Bachtadse;U. Kirscher;C. Rolf;N. Petersen
横跨北极的山脉主要由侏罗纪大陆洪泛玄武岩(Kirkpatrick)和盘古大陆分裂早期侵位的岩床(Ferrar)组成。基于各种年代学方法的已发表年龄都相当吻合，聚集在180 Ma左右，表明侵位时间相当短，不超过300万年。然而，大多在上世纪60年代至90年代进行的古地磁研究，得出了两组明确但明显不同的古地磁磁极位置，要么在中纬度(A)，要么在超过60°S的纬度(B)。属于A组的极点位置通常被解释为原生起源，而B组极点的意义尚不清楚。本文报道了南极维多利亚州北部柯克帕特里克玄武岩的新资料，在那里采集了15 7个定向古地磁样品，覆盖了盖尔台地(73.4666°S；162.8666°E)约800m的地层和23个火山流。去除具有相当低的矫顽力的陡峭的磁叠印后，在22个点的151个样品中发现了完全向投影原点方向发展的直线段。最大解封温度不超过580℃，最大矫顽力不超过60 mT。由此得到的盖尔台地的平均虚地磁极位于66.4°S；227.7°E(α95=6.2°，k=25.7)，与B组的极点相当。反射光学显微镜显示，所分析样品的磁性矿物以磁铁矿为主，表现出收缩的裂隙和宽阔的钛铁矿片层，后者被诊断为高温氧化。对所获得的22个极点位置的分布分析表明，长期变化被成功地平均(Sb=115.9°)，这表明这里所研究的岩石记录了中侏罗世早期的时间平均地磁场。根据这些新的结果，我们假设A和B团的磁极位置都反映了原始磁化作用，盖尔台地的Kirkpatrick玄武岩被定位在相当短的正常极性时间间隔3米。如果我们的推理是正确的，那么最新的早侏罗世的明显的极地漂移路径可能比之前想象的要复杂得多。这种复杂性是否为地块真极地漫游的证据，仍是一个猜测。
The Transantarctic mountains predominantly consist of Jurassic continental flood basalts (Kirkpatrick) and sills (Ferrar) emplaced during the earliest phase of the break-up of Pangea. Published ages, based on a variety of geochronological methods all agree rather well and cluster around 180 Ma suggesting emplacement during a rather short time interval of not more than 3 Myr. Paleomagnetic studies, mostly carried out between the 60s and 90s of the last century, however, yield two well defined but significantly different groups of paleomagnetic pole positions plotting either in intermediate latitudes (A) or at latitudes exceeding 60°S (B). Pole positions belonging to group A are generally interpreted to be of primary origin whereas the significance of group B poles remains unclear. Here we report new data from the Kirkpatrick basalts of Northern Victoria Land, Antarctica, where 157 oriented paleomagnetic samples were taken, covering about 800 m of stratigraphy and 23 volcanic flows in Gair Mesa (73.4666°S; 162.8666°E). After removal of a steep magnetic overprint with rather low coercivities straight linear segments of exclusively normal polarity trending toward the origin of projection are identified in 151 samples from 22 sites. Maximum unblocking temperatures do not exceed 580 °C andmaximum coercivities not 60 mT. The resulting mean virtual geomagnetic pole (VGP) for the Gair Mesa plots at 66.4°S; 227.7°E(α95of 6.2°,k= 25.7) comparable to group B poles. Reflecting light microscopy reveals that the magnetic inventory of all samples analyzed is dominated by magnetite showing shrinking cracks and broad ilmenite lamellae, the latter being diagnostic for high temperature oxidation. Analysis of the distribution of the 22 pole positions obtained here shows that secular variation has successfully been averaged (Sb= 15.9°) suggesting that the rocks studied here have recorded the time averaged geomagnetic field during early mid Jurassic times. Based on these new results we postulate that both clusters A and B of pole positions reflect primary magnetizations and that the Kirkpatrick basalts of Gair Mesa have been emplaced in a rather short normal polarity time interval of 3 Myr. If our reasoning is correct, the apparent polar wander path for the latest early Jurassic might be more complex than previously thought. Whether this complexity is evidence for massif True Polar Wander remains speculative.
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影响因子：
5.3
作者：
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DOI：
10.1144/gsl.sp.1996.108.01.04
发表时间：
1996
期刊：
Geological Society, London, Special Publications
影响因子：
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作者：
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通讯作者：
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影响因子：
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作者：
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影响因子：
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作者：
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