The purpose of this thesis is to describe the preliminary results from the investigation of shallow (<20m) hydrothermal vents with a total venting area of about 0.5 km2 off the eastern tip of Kueishantao Island. The chemical compositions of hot fluids, sediments and rocks as well as a continuous record of fluid temperature of a fumarole were measured in order to understand the venting process of hydrothermal fluids. The continuous temperature records show that the attainment of the maximum temperature of the hot fluids is related to the tidal cycle. The temperature variation seems to be associated with changes in the boiling point of seawater, which is affected by changes in water pressure. Such a correlation has not been reported in the literature. The hydrothermal fluids reach their highest temperature about 3.5 hours after each high tide, which is indicative of a shallow infiltration of seawater since the time it takes the boiling seawater to exit is so short. The hottest temperature recorded in our study area is 116¢J, while the lowest pH is 1.75, both a record in the world amid shallow hydrothermal systems. And, 1.75 is the lowest pH been reported on hydrothermal systems in the literature. At one point, the temperature recorder was covered with sand as a result of an encroaching typhoon. This suggests that the topography of the study area is susceptible to external forces. Based on salinity, the source of the hot fluids is taken to be ambient seawater, with no meteoric water from the islet involved. Concentrations of major ions in the hydrothermal fluids are almost the same as those in the ambient seawater. Mg is slightly enriched, however, which is unlike other hydrothermal fluids where, as reported elsewhere, Mg is generally lower because it replaces Ca in the bedrock. Low concentrations of Si in the studied fluids make for another distinct feature. Compared with other hydrothermal fluids in the world, the concentrations of Si in our study area are much lower, possibly on account of there being insufficient time for the rock to dissolve in the infiltrated seawater. Black and white smokers have widely been reported in the literature, but here are found heretofore unheard of yellow smokers as high as 6 meters. Other than one vent which emits liquid sulfur and forms a sulfur chimney, some vent sulfur from sulfur mounds. Still others are low- temperature vents which do not emit sulfur whatsoever. The most active venting activities are off the eastern tip of the islet. There are no other large reliefs associated with the hydrothermal activity, except for the chimney and a depression down to 35m deep. the chimney and a depression down to 35m deep. The composition of gravel on the seafloor is andesite, which is the same as the rock on the islet. The major composition of the sediments collected from the seafloor is sulfur, which is different from the sediments of the hydrothermal systems in the Okinawa Trough. The sulfur particles observed in this study originate from the fumaroles. Besides, sulfur balls the size of softballs and with distinct growth rings are found near some vents. The formation mechanism of these rings at this time, however, remains unclear. The bubbles from the vents are mostly made up of CO2, which is different from the composition of the shallow hot springs on the beach of Green islet. The 3He/4He of the emitted gas is high, this indicates that the gas may have originated from the mantle.

This investigation focuses on two well-preserved impact structures developed in sedimentary target rocks: the ~23.5 Ma old Haughton structure, Canada, and the ~14.5 Ma old Ries structure, Germany. The aim of this study was to investigate the effects of hypervelocity impact into sedimentary targets. The study reveals that a series of different impactites are present at Haughton, the bulk of which comprise a groundmass of impact-generated melts (calcite + silicate glass ± anhydrite). Thus, carbonates, evaporites, sandstones, and shales underwent shock melting during the Haughton impact event. The shock melting of impure carbonates resulted in the generation of Mg–Ca–Si-rich melts that crystallized calcite during rapid cooling. The residual melt quenched to Mg–Si-rich glass. These impactites should, therefore, be classified as clast-rich impact melt rocks or impact melt breccias, and not clastic matrix breccias as previously held. Ries surficial suevites are reinterpreted as clast-rich impact melt rocks or impact melt breccias. Four main types of impact melt glass are present, in contrast to previous studies that recognized only one type. These results are at odds with the current, generally accepted, definition of suevite. Given that the Ries is the original type occurrence of ‘suevite’, some redefinition of the term suevite may be in order. Furthermore, it is clear that sedimentary rocks, as well as crystalline rocks, were shock melted during the Ries impact event. The results of this study are, therefore, incompatible with previous models in which the zone of melting is restricted to the crystalline basement. It is apparent that impact melting in sedimentary targets is much more common than previously thought. Furthermore, there is no unequivocal evidence for the decomposition of carbonates or evaporites at any terrestrial impact site. Many previous assumptions about the response of sedimentary rocks during hypervelocity impact events are, therefore, incorrect. The products of impact into sedimentary targets may appear very different from those developed in crystalline targets. However, microscopic imaging and analysis suggests that these seemingly different lithologies may be genetically equivalent. Thus, the apparent ‘anomaly’ between the amount of impact melt rocks formed in sedimentary and crystalline targets may be due to a misinterpretation of the rock record.