Magnetic properties of the oceanic igneous rocks (Table 1)

Hysteresis measurements have been carried out on a suite of ocean-floor basalts with ages ranging from Quaternary to Cretaceous. Approximately linear, yet separate, relationships between coercivity (Bc) and the ratio of saturation remanence/saturation magnetization (Mrs/Ms) are observed for massive doleritic basalts with low-Ti magnetite and for pillow basalts with multi-domain titanomagnetites (with x= 0.6). Even when the MORB has undergone lowtemperature oxidation resulting in titanomaghemite, the parameters are still distinguishable, although offset from the trend for unoxidized multidomain titanomagnetite. The parameters for these iron oxides with different titanium content reveal contrasting trends that can be explained by the different saturation magnetizations of the mineral types. This plot provides a previously underutilized and non-destructive method to detect the presence of low-titanium magnetite in igneous rocks, notably MORB.

本研究对一套时代跨度为第四纪至白垩纪的洋底玄武岩开展了磁滞测量（Hysteresis measurements）。针对赋存低钛磁铁矿（low-Ti magnetite）的块状辉绿玄武岩（massive doleritic basalts），以及含钛含量x=0.6的多畴钛磁铁矿（multi-domain titanomagnetites）的枕状玄武岩（pillow basalts），观测到矫顽力（coercivity, Bc）与饱和剩磁/饱和磁化强度比值（Mrs/Ms）之间存在近似线性但相互独立的相关关系。即便洋中脊玄武岩（Mid-Ocean Ridge Basalt, MORB）经历低温氧化（lowtemperature oxidation）作用形成钛磁赤铁矿（titanomaghemite），其相关参数仍可与未氧化的多畴钛磁铁矿的变化趋势相区分，仅存在一定偏移。不同钛含量的铁氧化物的相关参数呈现出截然不同的变化趋势，这可通过不同矿物类型的饱和磁化强度差异得到合理解释。该磁滞图提供了一种此前未被充分利用的非破坏性检测方法，可用于识别火成岩（igneous rocks）中低钛磁铁矿的赋存情况，尤其适用于洋中脊玄武岩。