The Formative Cause Of Native Sulfur Chimney Near Kueishan Island Off Northeastern Taiwan

The Kueishantao hydrothermal activity zone lies in the west extended part of the Okinawa Trough, Where Philippine Sea Plate is subducting under the Eurasia Plate. There are some prominent characters about Kueishantao hydrothermal activity: high content native sulfur (up to 99%) in the chimneys, the highest temperature of fluid is up 116℃, which contains a lot of bubble. It is the main objective that to investigate the material origin and formative cause of native sulfur. The exterior of native sulfur sample is observed with electro-microscope, the main element and microelement content of samples are decided with X-fluorescence spectroscopic analysis and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) respectively. Two methods, burning and sublimation, are employed to pretreat high-background sample. To discuss the material origin of native sulfur and hydrothermal fluid, as well as the formed sequence of chimney, we decide sulfur isotope, some elements and hydrogen-oxygen isotope of solid sample and fluid sample, respectively. It can be concluded that the hydrothermal activity near Kueishantao is relative with volcanic activity, the gas component of hydrothermal fluid which undergoes the mixing process seawater and meteoric water is from magma degassing. The new formed hydrothermal fluid, dissolving some elements from the passed andesites, up to seafloor and meeting ambient seawater. Then the hydrothermal fluid, which contains a lot of elements, is precipitating or reacting by some chemical reactions, forms the native sulfur chimney.