Marine carbonates in the form of breccias, fossiliferous limestone and conglomerates were found at depths of 1,337-1,491 m (4,120-4,889 ft) bsl. The presence of shallow water foraminifera associated with the deposits suggest that this material formed in a lagoon or beach environment (pers. comm. J. Resig, 1990). The presence of shallow-water carbonates may be interpreted in several different ways, e.g., (1) Kilauea has subsided by 4/889 ft (1,491 m) and is much older than previously thought; (2) faulting has occurred and has displaced the old shoreline; and (3) the deposits represent the contact between Mauna Loa and Kilauea along an o!4 Mauna Loa shoreline. Using current subsidence rates of 2.4 mm/yr (Moore and Thomas, 1988) would yield ages of 557,083 to 621,250 years B.P. An alternative viewpoint is that the subsidence rates are too modest and that the sinking of the island has occurred at greater rates to arrive at the currently accepted age of Kilauea at approximately 250,000 to 400,000 years. LOGGING SPECIFICS The average core recovery rate for the entire SOH 4 drill hole is 93.6% (Fig. 5). Figure 2 is a sample core log illustrating the symbols used to depict different lithologies and descriptive terminology for the unit types. All graphical \AA, 3% plagioclase, «1% ol ivine phenocrysts land mi crogabbros in a gray Feldspathic ^aroundmass \AA, 5% plagioclase phenocrysts, laths and 3X ol ivine V AA, 3% p 1 og i oc 1 ase phsnocrysts, 1 aths, 3% o 1 i v i ne phenocrysts i n a 1 i ght gray Fe 1 dspath i c groundmass. CLINKER, with 5% plagioclase as laths, m i crogabbros, groundmass : bluish gray AA, 5% p 1 ag i oc 1 ase 1 aths, 5% o 1 i v i ne phenocrysts and rare ol ivine-plagioclase; groundmass is dark gray Depth Feet § 100 Temp(C)
Thirty-eight hydrothermal minerals were identified from 356 drill-core specimens that were obtained from three Scientific Observation Holes (SOH-1, SOH-2, and SOH-4) drilled along the lower East Rift Zone (ERZ) of Kilauea Volcano, Hawaii. The minerals formed during alteration of basaltic rocks and glass by hot, circulating, waters in aquifers consisting of variable mixtures of meteoric water and sea water. Several zeolites, hydrated calcium silicates, carbonates, clays, silicates, sulfates, sulfides, and other minerals were found filling open spaces of vesicles, fractures, and between breccia fragments of the recovered drill core; many specimens that originally consisted of glass are completely altered to some of these minerals, especially clays. Several hydrothermal minerals (erionite, mordenite, truscottite, smectite, chlorite-smectite, chalcedony, anhydrite, and hematite), occur in the SOH drill holes at higher measured temperatures than the same minerals are found in geothermal drill holes of Iceland or other geothermal areas, suggesting that temperatures within the ERZ geothermal system have increased since the minerals formed. Fluid-inclusion freezing data for quartz, anhydrite, and calcite from the three SOH holes show that composition of the inclusion fluids ranges from dilute meteoric water to highly modified sea water concentrated by boiling. Comparison of measured drill-hole temperatures with fluid-inclusion homogenization-temperature data indicates that only about 15% of the fluid inclusions could have formed under the present thermal conditions. The majority of fluid inclusions studied apparently formed during one or more temperature fluctuations associated with the emplacement of nearby dikes and their subsequent cooling. Bacteria-like particles at 1734.6 m depth in SOH-4 could be very significant because the particles occurred at much hotter temperatures (about 265°C) than the generally accepted 110°C limit for survival of bacteria. The presence of Cl in the particles suggests that they might have lived in a saline environment and did not result from contamination by the fresh water drilling fluids. We reccomend that future drilling and subsequent handling of drill hole specimens in the ERZ and elsewhere employ controls to minimize and(or) recognize bacterial contamination.
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