Low-temperature oxidation of magnetite in rock weathering - a humidity proxy?

以前的工作提示，磁铁矿的低温氧化（LTO）是古湿度的潜在代表。在这个项目中，我们打算研究岩石风化过程中磁铁矿中的LTO。德干玄武岩（西印度）具有很强的磁性和相当的基岩岩性，跨越了年平均降水（MAP为~200 ~ bbb3000 mm/年）的大梯度，将作为研究区域。我们还将通过与中国西南部的玄武岩和石灰石进行比较，检查温度可能的影响，这些玄武岩和石灰石位于类似的MAP区域，但条件要冷得多。为了分析LTO效应，我们建议从非风化基岩、风化岩石表面和附近的分离物质沿风化梯度对磁铁矿蚀变进行系统研究，避免土壤形成的影响。在我们的一些地点，来自印度和中国的合作伙伴将增加集水区研究。我们认为LTO首先由于磁铁矿的磁赤化作用而提高磁铁矿的磁性硬度，然后转变为低磁性赤铁矿或针铁矿。人们可以通过批量测量来识别这些过程，这对于使用合适的快速测量参数来在合理的时间内获得高分辨率数据集是很重要的。该项目的研究成果可以为利用湖泊档案进行古气候研究提供重要的知识，也可以解释古土壤中的磁信号。

Previous work gave hints that low-temperature oxidation (LTO) of magnetite is a potential proxy of paleo-humidity. In this project, we intend studying LTO in magnetite during rock weathering. The Deccan basalts (W-India) providing strong magnetic und comparable bedrock lithology across a large gradient of mean annual precipitation (MAP of ~200 to >3000 mm/yr) shall serve as study area. We will also check for a possible influence of temperature by comparison with basalts and limestones in SW-China, located in a similar MAP regime but with much cooler conditions. To analyze the LTO effect we suggest performing a systematic study of magnetite alteration along a weathering gradient from non-weathered bedrock, weathered rock surfaces and nearby detached materials, avoiding influence of soil formation. At some of our locations, partners from India and China will add catchment studies. We assume that LTO first increases magnetic hardness of magnetite due to maghemitization, followed by transformation into lower magnetic hematite or goethite. One can identify these processes by bulk measurements, which will be important to use suitable fast-to-measure parameters sensitive for LTO for obtaining high-resolution data sets in reasonable time. The project results could provide important knowledge for paleoclimate studies using lacustrine archives, and may also explain magnetic signals in paleosols.