Water of eastern Taiwan mud volcanoes. Part I. H, triple O, triple Sr isotopes, and trace elements of Lo-Shan mud volcano

Mud volcano (MV) is one of the most important passageways for deep seated volatile materials to migrate back to Earth’s surface in sedimentary basins and subduction zones. Waters of MV fluid emitted from 18 mud pools in MV Luo-Shan (LS) in eastern Taiwan were sampled from the year 2002 to the year 2021. Major and trace components as well as H, triple O (δ18O and Δ17O) and triple Sr isotopes (87Sr/86Sr and δ88Sr) were measured. The results show that major components of water are Cl-, Na and Ca. Compared with seawater, water of MV LS reveals similar chemical characteristics with low-temperature ridge-flank hydrothermal spring and marine pore water in reducing condition. Limited spatial and temporal variation of major components as well as H, triple O and 87Sr/86Sr indicates waters emitted by mud pools come from the same source regionally. Slightly radiogenic 87Sr/86Sr at southern mud pools and before the year 2003 denotes different fluid reservoir from northern ones. Small 87Sr/86Sr variation in waters of northern mud pools indicates near surface mixing from 2 fluid reservoirs. The correlation among all components reveals sediment component addition is the major factor and evaporation is the key factor for conservative elements. In summary, waters expelled by MV LS mud pools originate from the same regional source, and their trace element composition such as Mg, K, Sr as well as 87Sr/86Sr slightly varies, depending on the location of the reservoir they are hosted. A stable source with small vibration of fluid reservoir of MV LS is indicated during the 19-years investigation period.