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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Paleomagnetism of the Central Metasedimentary Belt, Grenville Province, Ontario: Differential uplift or collision of terranes?
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Paleomagnetism of the Central Metasedimentary Belt, Grenville Province, Ontario: Differential uplift or collision of terranes?

机译：安大略省格伦维尔省中部沉积带的古磁性：地层的隆升或碰撞？

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摘要

A paleomagnetic traverse across the Central Metasedimentary Belt of the Precambrian Grenville Province in southern Ontario, linked to an earlier study of the adjoining Central Gneiss Belt, sampled 54 sites in the Frontenac, Sharbot Lake, Mazinaw, Elsevir and Bancroft terranes. Ar-40/Ar-39 thermochronometry indicates differential unroofing of these terranes, with slow cooling (1.0-1.5 degrees C/Ma) along parallel temperature-time paths. Presently exposed rocks cooled through; approximate to 500 degrees C around 1100 Ma (Frontenac), 1010 Ma (Elsevir), 960 Ma (Central Metasedimentary Belt boundary zone) and 930 Ma (Mazinaw) [Cosca, M.A., Sutter, U., Essene, E.J., 1991. Cooling and inferred uplift/crosion history of the Grenville orogen, Ontario: constraints from 40Ar/39Ar thermochronology, Tectonics 10 (1991) 959-977]. 1100-930 Ma was a time of rapid paleolatitude shift but the various terranes do not have distinct paleomagnetic signatures. Frontenac, Sharbot Lake and Mazinaw terranes have similar reverse-polarity paleopoles in the central part of the Grenville polar wander track. Frontenac and Sharbot Lake normal poles are typical Pz 1000 Ma Grenville A poles, while Mazinaw normal poles seem to be somewhat older. Frontenac poles bear no resemblance to 1100 MaKeweenawan poles. The Elsevir pole and some Frontenac poles resemble Grenville B poles (600-800 Ma). Although Ar-49/Ar-39 homblende ages were reset thermally between 1100 and 930 Ma during differential uplift of terranes, the terranes were not remagnetized at these same times. Frontenac, Sharbot Lake and Mazinaw terranes (like much of the boundary zone and the Central Gneiss Belt) seemingly were all remagnetized between approximate to 1000 and approximate to 900 Ma, perhaps by a widespread thermochemical event. A 600-800 Ma event affected Elsevir and part of the Frontenac, at the western and eastern extremes of the traverse, but not areas between. The lack of correlation between Ar-40/Ar-39 ages and paleomagnetic results for the Frontenac, Sharbot Lake, Mazinaw and Elsevir casts doubt on the thermochronometric age calibration of the Grenville apparent polar wander path, which is based on the assumption that the magnetic and isotopic systems respond in similar ways to slow cooling during uplift so that their blocking temperatures can be directly compared. The most discordant results - those of the Frontenac - could be reconciled if the Frontenac terrane acquired its A magnetization around 1100 Ma before it docked with Laurentia. This is geologically plausible but the match between the Frontenae poles and 900-1000 Ma Grenvillian poles seems too close to be coincidental.
机译：横跨安大略省南部前寒武纪格伦维尔省中央准沉积带的古磁横断面，与对毗邻的中片麻岩带的较早研究有关，在Frontenac，Sharbot Lake，Mazinaw，Elsevir和Bancroft地层中采样了54个地点。 Ar-40 / Ar-39热计时表明这些地层的差异顶开，并沿平行的温度-时间路径缓慢冷却（1.0-1.5摄氏度/马）。目前暴露的岩石已冷却。大约在1100 Ma（Frontenac），1010 Ma（Elsevir），960 Ma（中央沉积区带边界带）和930 Ma（Mazinaw）周围约500摄氏度[Cosca，MA，Sutter，U.，Essene，EJ，1991。并推断了安大略省格伦维尔造山带的隆升/破坏历史：40Ar / 39Ar热年代学的局限，《构造》（Tectonics）10（1991）959-977）。 1100-930 Ma是古纬度快速变化的时期，但各种地层没有明显的古磁特征。 Frontenac，Sharbot Lake和Mazinaw地层在Grenville极地漂移轨迹的中部具有相似的反极性古极。 Frontenac和Sharbot Lake的正常杆是Pz 1000 Ma Grenville A的典型杆，而Mazinaw的正常杆似乎有些老。 Frontenac杆与1100 MaKeweenawan杆没有任何相似之处。 Elsevir极和某些Frontenac极类似于Grenville B极（600-800 Ma）。尽管在地层的差异抬升过程中，Ar-49 / Ar-39球体年龄在1100Ma和930Ma之间被热重置，但这些地块并没有在同一时间被重新磁化。 Frontenac，Sharbot Lake和Mazinaw地貌（与大部分边界带和中片麻岩带相似）似乎都在大约1000至900 Ma之间被磁化了，这可能是由于广泛的热化学事件造成的。一个600-800 Ma的事件影响了Elsevir和Frontenac的一部分，在导线的西端和东端，但不影响两者之间的区域。 Frontenac，Sharbot Lake，Mazinaw和Elsevir的Ar-40 / Ar-39年龄与古磁结果之间缺乏相关性，这使人们对格伦维尔视极极地游走路径的热年代法年龄标定产生了怀疑，这是基于以下假设：同位素系统以类似的方式对隆升过程中的缓慢冷却做出反应，因此可以直接比较它们的阻隔温度。如果Frontenac地层在与Laurentia对接之前在1100 Ma左右获得A磁化强度，那么最不一致的结果-Frontenac的结果可能会得到调和。这在地质上是合理的，但是弗隆特涅两极和900-1000 Ma Grenvillian极之间的匹配似乎太紧密了，以致无法巧合。

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