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首页> 外文学位 >MAGNETIZATION AND REMAGNETIZATION PROCESSES IN SOME EARLY PALEOZOIC LIMESTONES FROM THE GREAT BASIN.
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MAGNETIZATION AND REMAGNETIZATION PROCESSES IN SOME EARLY PALEOZOIC LIMESTONES FROM THE GREAT BASIN.

机译：大盆地早期某些古生界石灰岩的磁化和再磁化过程。

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摘要

Paleomagnetic data from Early Paleozoic rocks in North America are scattered, and the causes of this scatter are controversial. Several related studies of Cambrian and Ordovician strata, in which the focus was on determining the origin and nature of the magnetization by emphasizing geologic controls, are reported herein. The rock types sampled are mostly gray limestones, which have been little used in paleomagnetism because of their very weak magnetization, but which can now be routinely measured on cryogenic magnetometers. As such rock types are extremely common in the geologic record, the potential data base for paleomagnetic study is greatly broadened if they can be employed; additionally, much is known about the diagenetic history of such rocks, so that geologic constraints are easier to establish on the magnetization.;In western Utah, a contact aureole in late Cambrian limestone surrounds a granitic rock at Notch Peak. Samples farthest from the pluton yield a "Paleozoic" magnetization. In contrast, the only consistent magnetization inward from this is a low-blocking temperature magnetization that is rather scattered, has steep inclination with both polarities present, and that appears to reside in very fine-grained hematite. This magnetization is inferred to reflect a very late oxidation related to the intrusion, possibly from the mobilization of groundwater. Directions of magnetization from the pluton itself are similar in that they are scattered, two-polarity, and steep, but they appear to reflect the original thermoremanent magnetization (TRM) in magnetite.;Late Cambrian limestones from eastern Tennessee, sampled across "biomere boundary" defined by contrasting trilobite faunas, yield a consistent, "Paleozoic" magnetization that appears to reside in detrital magnetite. The average directions derived from sites in different thrust sheets differ, however, suggesting that relative tectonic rotation has occurred between the two sites. Further, comparison of other paleomagnetic data from North America from at or near this biomere boundary reveals gross discrepancies between the paleomagnetic poles from these nearly coeval rocks.;Cratonic Cambrian strata from tectonically complicated areas in southern Nevada appear to have been completely remagnetized. Red sandstone in the Bright Angel Shale yields a consistent magnetization that resides in diagenetic hematite; magnetization residing in magnetite in the overlying Jangle and Muav Limestones appears to be a VPTRM imposed during the late Tertiary.;Cambrian and Ordovician miogeoclinal carbonate rocks from the Desert Range of southern Nevada yield a well-grouped characteristic magnetization that appears to reside in detrital magnetite; its paleomagnetic pole is near late Paleozoic poles and it appears to reflect remagnetization at that time, probably from a viscous partial thermoremanence (VPTRM) that was imposed during regional uplift. In the Ordovician strata, the magnetization is younger than bedding disruption by major, late, through-going stylolites. Remagnetization is also grossly consistent with the degree of heating inferred from conodont color alteration index. A secondary component of magnetization, having lower blocking temperature and also residing in magnetite, is also present in the Desert Range Strata and probably reflects a VPTRM imposed during Cretaceous thrusting and uplift.;The studies carried out herein yielded ancient magnetizations that could in most cases be shown to result from remagnetization long after deposition. Upon reviewing the published literature on early to mid-Paleozoic paleomagnetism in North America, it appears that the scatter of published paleomagnetic poles from the early Paleozoic results from pervasive remagnetizations and tectonic rotations. I conclude that careful paleomagnetic study must be integrated with geologic data if reliable paleomagnetic data are ever to be derived from rocks as old as Early Palezoic.
机译：来自北美早期古生代岩石的古磁数据是分散的，这种散射的原因是有争议的。本文报道了寒武纪和奥陶纪地层的几项相关研究，其重点是通过强调地质控制来确定磁化作用的起源和性质。所采样的岩石类型大多为灰色石灰石，由于磁化强度很弱，因此在古磁铁矿中很少使用，但现在可以用低温磁力计进行常规测量。由于这类岩石在地质记录中极为常见，因此如果可以使用，则可能大大拓宽了潜在的古磁研究数据库。此外，人们对这类岩石的成岩史知之甚少，因此在磁化作用上更容易建立地质约束。在犹他州西部，寒武纪晚期石灰岩中的接触金环围绕着Notch Peak的花岗岩。离胶子最远的样品会产生“古生代”磁化强度。相反，向内唯一一致的磁化强度是低阻塞温度磁化强度，该磁化强度相当分散，倾斜存在两个极性，并且似乎存在于细粒赤铁矿中。推断该磁化反映了与入侵有关的非常晚的氧化，可能是由于地下水的流动。来自岩钉本身的磁化方向相似，因为它们是分散的，两极且陡峭的，但是它们似乎反映了磁铁矿中的原始热剩磁化（TRM）。；田纳西州东部的晚寒武纪石灰石，跨“生物素边界采样”通过对比三叶虫动物区系来定义”，会产生一致的“古生代”磁化强度，该磁化强度似乎位于碎屑磁铁矿中。但是，从不同推力板中的位置得出的平均方向是不同的，这表明在两个位置之间已经发生了相对的构造旋转。此外，通过比较从该生物石边界附近或附近的北美其他古地磁数据，可以发现这些近代岩石的古地磁极之间存在明显差异。内华达州南部构造复杂的地区的寒武纪寒武纪地层似乎已被完全磁化。明亮天使页岩中的红色砂岩产生一致的磁化强度，并存在于成岩赤铁矿中。上覆的Jangle和Muav石灰岩中磁铁矿中的磁化作用似乎是第三纪晚期施加的VPTRM .;内华达州南部沙漠地区的寒武纪和奥陶纪含碳酸盐岩产生了分组良好的特征磁化作用，似乎存在于碎屑磁铁矿中;它的古磁极靠近古生代极，并且似乎反映了当时的再磁化现象，这可能是由于区域隆升过程中施加的粘性局部热剩磁（VPTRM）所致。在奥陶纪地层中，磁化作用比主要的，晚期的，贯穿的陨石对地层的破坏还年轻。再磁化也大致与根据牙形变色指数推断出的加热程度一致。沙漠范围地层中也存在磁化作用的次要成分，它具有较低的阻隔温度，也存在于磁铁矿中，可能反映了白垩纪逆冲和隆升过程中施加的VPTRM。被证明是由于沉积后很长时间的磁化作用。在回顾了有关北美古生代早期至中期古磁铁矿学的文献后，看来早古生代已出版的古磁极的散布是由于普遍的磁化作用和构造旋转造成的。我的结论是，如果要从早古生代的岩石中获得可靠的古磁数据，就必须将仔细的古磁研究与地质数据结合起来。

著录项

  • 作者

    GILLETT, STEPHEN LEE.;

  • 作者单位

    State University of New York at Stony Brook.;

  • 授予单位 State University of New York at Stony Brook.;
  • 学科 Geology.
  • 学位 Ph.D.
  • 年度 1981
  • 页码 521 p.
  • 总页数 521
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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