A Petrophysical Predictor for Degree of Serpentinzation

亚特兰提斯地块由非均质基性和超基性岩石组成，其特征是缓慢扩张的脊。现在沿大西洋中脊这部分露出的岩石是在地幔深处形成的，因此与通常在海底发现的熔岩具有非常不同的化学成分。这些地幔岩石与海水的反应被称为蛇纹石化反应，产生甲烷、氢气并产生热量，这些关键的反应可以在没有光和光合作用的情况下为生命的起源提供燃料。国际海洋发现计划将在今年10月至12月的任务专用平台远征357期间对这些岩石进行取样。在拟议的项目中，我们利用这次探险所产生的数据，试图调查和描述蛇形化后岩石物理性质的变化。在同行评审的文献中，先前的研究已经确定，在蛇纹石化过程中，随着新矿物的产生，磁化率会增加。岩石体积也会增加30%，因此岩石密度会降低。我们的项目将测试已发表的假设，即磁化率与密度呈负相关，并确定这是否可以应用于357考察期间取样的岩石。作为考察的一部分，我们将使用主要的数据来源，包括使用多传感器岩心记录器从整个岩心测量的磁化率和密度数据。在考察期间，岩心的密度数据将由在离散样品上测量的水分和密度（MAD）数据补充。这些物理性质（岩石物理）数据将与薄片岩石学分析相结合进行评估，以确定对磁化率信号及其模态比例有贡献的矿物。岩石学分析将首先使用船上的薄片检查矿物学。用于指导取样的子集，用于生成抛光的、未覆盖的薄片，以使用电子显微探针进行分析。微探针将是记录铁镍氧化物相关系随晶粒尺寸小的蛇纹石化程度变化的关键。通过将物性测量与岩性和矿物学信息相结合，我们的目标是开发一种基于物性输入的“蛇纹石化程度”预测工具，该工具可用于只有物性数据可用的情况。

The Atlantis Massif comprises heterogeneous mafic and ultramafic rocks that characterise slow spreading ridges. The rocks now exposed along this part of the Mid-Atlantic Ridge form deep in the Earth's mantle and therefore have very different chemistry to the lavas typically found at the sea floor. The reactions of these mantle rocks with seawater is known as serpentinization, produce methane, hydrogen and generate heat and these are key reactions that could fuel the initiation of life without light and photosynthesis. The International Ocean Discovery Program will core these rocks during the mission-specific platform Expedition 357 in October-December this year.In the proposed project using data generated as part of this expedition, we seek to investigate and characterise the changes in the rock physical properties following serpentization. Previous studies in the peer-reviewed literature have identified that, during serpentinization, magnetic susceptibility increases as new minerals are generated. The rock volume also increases by up to 30% and hence the rock density will decrease. Our project will test the published hypothesis that magnetic susceptibility is inversely correlated to density and determine whether this can be applied to application to rocks to be sampled during Expedition 357.We will use primary data sources, including magnetic susceptibility and density data measured from whole-round core using a multi-sensor core logger as part of the expedition. The density data from core will be supplemented by moisture and density (MAD) data measured on discrete samples also during the expedition. These physical property (petrophysical) data will be evaluated in tandem with petrographic analyses of thin sections to identify minerals contributing to the magnetic susceptibility signal and their modal proportions. The petrographic analysis will examine the mineralogy using the shipboard thin sections first. A subset used to guide sampling for generating polished, uncovered thin sections to analyse using the electron microprobe. The microprobe will be key for documenting changing Fe-Ni oxide phase relations with changing degree of serpentinization where grain size is small.By integrating physical property measurements with lithological and mineralogical information, we aim to develop a 'degree of serpentinization' predictive tool based on physical properties inputs that could be applied in situations where only physical property data is available.