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Rock magnetic studies of the CY-4 drill hole: Through the Troodos ophiolite, Cyprus.

机译：CY-4钻孔的岩石磁研究：通过塞浦路斯Troodos蛇绿岩。

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摘要

Rock magnetic properties of 50 specimens from a continuous section through the lower layers of the Troodos ophiolite in the CY-4 drill hole, reveal an alteration and palaeomagnetic history consistent with ocean spreading. Anisotropy of magnetic susceptibility (AMS), low temperature demagnetization (LTD), high temperature demagnetization (TD), distinct Curie and Neel temperatures and hysteresis were the main rock magnetic techniques and were supplemented by thin section microscopy.; The steeply dipping CY-4 drill hole has a total depth of 2263 m from the surface through the sheeted dike complex, upper and lower gabbro rocks and ultramafic rocks. CY-4 was part of the Cyprus Crustal Study Project in the 1980s as a Cyprus Geological Survey of Canada-NATO collaboration.; The AMS results showed primarily oblate magnetic fabrics reflecting plutonic ductile flow and strain dominated by chlorite, magnetite, biotite and amphiboles. The bulk susceptibility (K) discriminates the four lithological zones very well, with the highest K in the diabase dikes. The AMS tensor means showed the overall magnetic fabric to be a strong L>S fabric with L ∼ vertical and the diabase dikes being the main contributor. The magnetic fabric became less pronounced with depth through the gabbros down to the mantle rocks, indicating weaker strain or flow influences on the fabric in the upper mantle.; Palaeomagnetism was studied by thermal demagnetization, low temperature demagnetization and detailed measurements of natural remanent magnetism (NRM) on 45 specimens. Characteristic and secondary magnetizations were isolated and palaeolatitudes were compared on the apparent polar wander path (APWP) of the Troodos microplate. Two main vector components were identified from NRM results, a stable and primary component A, with an unblocking temperature (Tub) >550°C and a secondary viscous remanent magnetism (VRM) component D, with a Tub 140°C. NRM palaeopoles for the diabase dikes were anomalous and did not contribute to the conclusions. Palaeopoles for the upper gabbros plot on the APWP as the oldest rocks suggesting that they cooled first, followed by the lower gabbros at about 75 Ma and the ultramafic rocks acquired their characteristic remanence at 55 Ma. Hydrothermal alteration on the NRM of Troodos varied with time and spreading distance from the ridge. The upper gabbros cooled and acquired their magnetizations before the anticlockwise rotation of the Troodos microplate. However, the lower gabbros were affected during the first rotation of about 60° whereas the ultramafic rocks were magnetized in the final approximately 30° rotation.; Curie and Neel temperatures identified specific iron and iron-titanium oxide magnetic minerals. These temperatures also indicate the degree of hydrothermal seafloor alteration vertically down the CY-4 drill hole. Magnetic hysteresis determined the grain size of magnetic minerals and their capacity for palaeomagnetization. Curie Balance results showed magnetite was most common followed by hematite, throughout CY-4. Ti-rich magnetite (TM60) was present as unoxidized and oxidized grains within the diabase dikes and upper gabbro rocks to a depth of 1060 m. Hysteresis results show an obvious trend of decreasing grain size with depth. However, the majority of samples fell within the psuedosingle domain (PSD) range. The ferromagnetic minerals at the bottom of the drill hole had strong, stable remanence value whereas the top of the hole had minerals with weaker memories (HcrHc). These results help to explain the large influence of the diabase dikes on the AMS fabric. Strong magnetization in the diabase dikes is due to TM60, which is identified to the base of the diabase dikes and into the top of the upper gabbroic rocks. The Curie temperatures also identified the hydrothermal alteration boundary at about 1060 meters; this alteration boundary is found 3500 meters below the sea floor in modern ocean-floor stratigraphy.;
机译：通过CY-4钻孔中Troodos蛇绿岩下层连续断面的50个标本的岩石磁特性显示出与海洋扩散一致的蚀变和古磁历史。磁化率的各向异性（AMS），低温退磁（LTD），高温退磁（TD），明显的居里和尼尔温度和磁滞是主要的岩石磁技术，并通过薄层显微镜进行了补充。陡峭的CY-4钻孔从地面穿过片状堤坝复合体，上下辉长岩和超镁铁质岩体的总深度为2263 m。 CY-4是1980年代塞浦路斯地壳研究项目的一部分，是加拿大-北约合作组织的塞浦路斯地质调查。 AMS结果显示主要是扁圆形的磁性织物，反映了由亚氯酸盐，磁铁矿，黑云母和闪石组成的青铜韧性流和应变。块体磁化率（K）很好地区分了四个岩性带，辉绿岩堤中的K最高。 AMS张量手段表明，整个磁性织物是坚固的L> S织物，其中L〜垂直，辉绿岩堤为主要贡献者。磁性织物在穿过辉长岩直至地幔岩石的深度上变得不那么明显，表明对上地幔中的织物的应变或流量影响较小。通过热去磁，低温去磁以及对45个样品的自然剩磁（NRM）进行详细测量，研究了古磁性。分离了特征和次级磁化强度，并在Troodos微孔板的表观极移路径（APWP）上比较了古纬度。从NRM结果中确定了两个主要矢量成分，一个稳定的主要成分A，其解链温度（Tub）> 550°C，一个次级粘性剩磁（VRM）成分D，一个Tub <140°C。辉绿岩堤防的NRM古极是异常的，对结论没有贡献。 APWP上辉长岩的古极点是最古老的岩石，表明它们先冷却，其次是辉长岩在约75 Ma冷却，超镁铁质岩石在55 Ma获得了特征剩磁。 Troodos NRM上的热液蚀变随时间和距山脊的扩散距离而变化。在Troodos微孔板逆时针旋转之前，上辉长球冷却并获得了其磁化强度。然而，下辉长岩在大约60°的第一次旋转中受到影响，而超镁铁质岩石在最后大约30°的旋转中被磁化。居里和尼尔温度确定了特定的铁和铁-钛氧化物磁性矿物。这些温度还指示了沿CY-4钻孔垂直向下的热液海底变化的程度。磁滞决定了磁性矿物的晶粒尺寸及其古磁化能力。居里平衡结果显示，在整个CY-4中，磁铁矿是最常见的，其次是赤铁矿。富钛磁铁矿（TM60）作为未氧化和氧化的晶粒存在于辉绿岩堤坝和上辉长岩中，深度为1060 m。磁滞结果显示出随深度减小晶粒尺寸的明显趋势。但是，大多数样本都落在伪单域（PSD）范围内。钻孔底部的铁磁矿物具有强而稳定的剩磁值，而钻孔顶部的矿物具有较弱的记忆力（HcrHc）。这些结果有助于解释辉绿岩堤防对AMS织物的巨大影响。辉绿岩堤防中的强磁化归因于TM60，它被识别为辉绿岩堤防的基础并进入上辉长岩的顶部。居里温度还确定了约1060米处的热液蚀变边界。在现代海底地层学中，这种蚀变边界位于海床以下3500米处。

著录项

  • 作者

    Trebilcock, Dawn-Ann.;

  • 作者单位

    Lakehead University (Canada).;

  • 授予单位 Lakehead University (Canada).;
  • 学科 Geology.; Geophysics.
  • 学位 M.Sc.
  • 年度 2006
  • 页码 118 p.
  • 总页数 118
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地质学;地球物理学;
  • 关键词

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