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首页> 外文期刊>Physics and chemistry of the earth >Syn-folding remagnetization and the significance of the small circle test Examples from the Vocontian trough (SE France)
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Syn-folding remagnetization and the significance of the small circle test Examples from the Vocontian trough (SE France)

机译：顺折磁化和小圆弧试验的意义沃康天槽（法国东南部）的例子

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摘要

We present a detailed study of paleomagnetism and anisotropy of magnetic susceptibility of two cylindrical kilometric folds. These folds are located in the footwall of the Digne thrust, from the southern border of the Vocontian trough. We sampled Bajocian-Bathonian marly limestones at four sites. Rock magnetism is consistent with a mixture of single domain and super-para-magnetic grains of magnetite (Curie temperature at 580 ℃, unblocking temperature at about 450-500 ℃, wasp-waisted hysteresis cycles). Gentle limbs of the two folds show a magnetic foliation of sedimentary origin parallel to the bedding, while in steepest limbs magnetic foliation is oblique to the bedding and is of tectonic origin. We found well-defined paleomagnetic directions (B components) in both folds. Fold test and small circles test are performed in order to date the acquisition of the B component. Both folds exhibit syn-folding remagnetization when using fold test. Small circle tests give contrasted results. Untilting paths of B components follow two distinct small circles at Vaumeilh, which is not expected if the magnetization is related to cylindrical folding. We propose that a complex strain history is likely the cause of this unexpected behavior. By contrast, only one small circle is observed when untilting B components of Bayon fold. The overlapping paths of B components define a strip of uncertainty, which is compared to the range of expected inclinations for stable Eurasia. This allows to date the remagnetization from Tertiary at Bayon fold.
机译：我们目前对古磁性和两个圆柱公里褶皱的磁化率各向异性进行详细研究。这些褶皱位于迪格涅斯逆冲断层的下盘，从沃孔底海槽的南部边界开始。我们在四个地点采样了巴约西亚－巴松尼灰泥岩。岩石磁性与磁铁矿的单畴和超顺磁性晶粒的混合物一致（居里温度为580℃，解冻温度为约450-500℃，黄蜂腰部磁滞循环）。这两个褶皱的柔和肢体显示出与层理平行的沉积成因的磁性叶脉，而在最陡峭的肢体中，磁性成叶成因与层理倾斜，并且是构造成因。我们在两个褶皱中都找到了定义明确的古磁方向（B分量）。进行折叠测试和小圆圈测试，以便确定B组件的日期。使用折页测试时，两个折页均显示同折折磁化。小圆圈测试给出相反的结果。 B分量的直至路径在Vaumeilh处遵循两个不同的小圆圈，如果磁化与圆柱形折叠有关，则这是不希望的。我们建议复杂的应变历史可能是这种意外行为的原因。相比之下，当使Bayon的B组分折叠时，仅观察到一个小圆圈。 B分量的重叠路径定义了一条不确定性带，将其与稳定欧亚大陆的预期倾角范围进行比较。这样就可以从Bayon褶皱处的第三纪至今进行磁化。

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