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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Magnetostratigraphy of the Miocene Corque basin, Bolivia: Implications for the geodynamic evolution of the Altiplano during the late Tertiary
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Magnetostratigraphy of the Miocene Corque basin, Bolivia: Implications for the geodynamic evolution of the Altiplano during the late Tertiary

机译：玻利维亚中新世盆地的磁地层学：对第三纪晚期高原的地球动力学演化的启示

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摘要

A magnetostratigraphic study of a thick Miocene continental red bed sequence (Totora Formation) located in the north central Altiplano (the Corque syncline) yielded quantitative determinations of the sedimentation rate and better constraints of the timing of the deformation within the Altiplano. Paleomagnetic results obtained in 653 samples from a composite 4.5 km thick red bed sequence across the Corque syncline indicate that most of the Totora sequence was deposited in the middle Miocene from 14 to 9 Ma with high sedimentation rates up to 970 m/Myr from 12 to 9 Ma. The high rate of infill of the Corque basin demonstrates active subsidence of the northern Altiplano during the middle Miocene. Deformation ceased in the northern Altiplano domain only at the end of the Miocene. Two major tuff beds within the sequence have been previously dated by ~(39)Ar/~(40)Ar of sanidine minerals [Marshall et al., 1992]. The excellent agreement between the magnetostratigraphic dating of the tuffs and the radiometric dating independently supports the age calibration of the geomagnetic reference timescale proposed by Cande and Kent [1995]. The numerous paleomagnetic results obtained in middle Miocene sediments within the Corque syncline, a structure which can be traced for more than 100 km along its axis, demonstrate that the Corque syncline rotated counterclockwise by 10.8 deg +- 2.9 deg since 9 Ma as a consequence of the internal deformation of the Altiplano. Inclination flattening of 17 deg is recorded in these red bed sediments. This result provides additional evidence that detrital magnetizations, especially in red beds, should be taken with caution when estimating paleolatitudes or long-term variations of the geomagnetic field.
机译：磁地层学研究了位于高原中部北部（Corque向斜）的中新世大陆红层厚层（托托拉组）的定量确定了沉积速率，并更好地限制了高原内变形的时间。在653个样品中，从横跨柯克向斜线的一个4.5 km厚的复合复合红层层序中的653个样品中获得的古磁结果表明，大多数Totora层序沉积于14〜9Ma的中新世中期，高沉积率高达12m〜12m的970 m / Myr。 9玛。 Corque盆地的高填充率表明，在中新世中期，北部高原的活跃沉降。仅在中新世末期，北部高原的变形才停止。序列中的两个主要凝灰岩层以前是由山梨素矿物质的〜（39）Ar /〜（40）Ar确定的[Marshall等，1992]。凝灰岩的磁地层测年和放射测年之间的极好的一致性独立地支持了Cande和Kent [1995]提出的地磁参考时标的年龄校准。在Corque向斜内中新世中期沉积物中获得的大量古磁结果表明，由于9 Ma，Corque向斜自9 Ma以来一直沿逆时针方向旋转了10.8度+-2.9度，这种构造可沿其轴线追踪100多公里。高原的内部变形。在这些红层沉积物中记录了17度的倾角平坦化。该结果提供了额外的证据，在估算古纬度或地磁场的长期变化时，应特别注意碎屑磁化，尤其是在红层中。

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