and diffusive transport). Developing tractable analytical equations for these processes requires simplifying as-Numerical simulations of transport and isotope fractionation prosumptions, which lead to analytical methods that are not vide a method to quantitatively interpret vadose zone pore water stable isotope depth profiles based on soil properties, climatic condi-easily adapted to field conditions. Previous numerical tions, and infiltration. We incorporate the temperature-dependent models have relied on assumptions such as neglecting equilibration of stable isotopic species between water and water vapor, the temperature dependence of isotope fractionation and their differing diffusive transport properties into the thermodyand treating the isotopic species as nonreactive tracers namic database of the reactive transport code TOUGHREACT. with concentrations defined by fixed partition coeffi-These simulations are used to illustrate the evolution of stable isotope cients. profiles in semiarid regions where recharge during wet seasons dis-Prior approaches to predicting the impact of infiltraturbs the drying profile traditionally associated with vadose zone pore tion water on stable isotope profiles include a semiemwaters. Alternating wet and dry seasons lead to annual fluctuations pirical model (Barnes and Allison, 1988), a mixing in moisture content, capillary pressure, and stable isotope composischeme (Mathieu and Bariac, 1996b), and an analytical tions in the vadose zone. Periodic infiltration models capture the effects of seasonal increases in precipitation and predict stable isotope model to predict overall average pore water isotope profiles that are distinct from those observed under drying (zero compositions (DePaolo et al., 2004). However, a more infiltration) conditions. After infiltration, evaporation causes a shift general approach is needed to link observed isotope to higher ␦ 18 O and ␦D values, which are preserved in the deeper pore compositions with dynamic hydrological processes, waters. The magnitude of the isotopic composition shift preserved in where precipitation events or temperature changes afdeep vadose zone pore waters varies inversely with the rate of infilfect the isotopic profile with depth. tration.We use the thermodynamic framework of the TOUGH-REACT transport code (Xu and Pruess, 2001;Xu et al.,

Velika Palagruza (Pelagosa) is the largest island of the Palagru2a arehipelago (central Adriatic Sea, Croatia). Despite its minute size the island bears a certain geological interest being the only exposed piece of land in the central part (Mid-Adriatic ridge) of the common Adriatic foreland of the Apenninic and the Dinaridic orogenic domains. The litho-. bio-, and chemostratigraphic (strontium and sulphur isotopes) characteristics of the sedimentary units, along with tectono-stnictural and geomorphic characteristics of the island, are described in (his paper. The oldest ¿ato unit is composed of highly deformed siliciclastics containing gypsum, and carbonates of Middle Triassic (Ladinian) age. This unit represents a transitional fluvial-to-shallow marine, occasionally evaporitic environment, typical of the Middle Triassic rifting phase of the Adriatic microplate. Soft and strongly deformed Zalo unit deposits are found along a probably still active, WN W-ESE striking, subvertical, oblique-slip tault that crosses the entire length of the island. The Zalo unit is probably in diapiric contact with the Lantema unit, poorly defined as Late Triassic. and characterized by dolomite with chert and dolomite breccia, presumably deposited in a transitional plattbnn-to-basin environment of an evolving Adriatic basin. The Lantema unit deposits are capped by Miocene biocalcarenites of the Salamandrija unit over an almost perpendicular discordance, possibly representing an unconformity, suggesting that an early deformational phase preceded a Miocene marine transgression. Talus, landslide deposits, and humic soil make up the cover of the bedrock sedimentary succession, and they represent the ultimate phase of emersion of the island, which probably occurred during Pliocene(?) to Quaternary times. An active neotectonic regime of the central Adriatic is evidenced by present-day seismicity. while recent uplifting of the island is shown by the presence of remnanis of pebbly palaeobeach deposits, marine (erosional) straths, and cyanobacterial supratidal encrustations (pelagosite) currently observed at various elevations above mean sea level.

Kea lavas were entered, the hole would remain in Mauna Kea to total depth. The drill sites were chosen to be (1) far from volcanic rift zones to avoid intrusive rocks, alteration, and high-temperature fluids; (2) close to the coastline to minimize the thickness of subaerial lavas that would need to be penetrated to reach the older, submarine parts of the volcano; and (3) in an industrial area to minimize environmental and community impacts. Drilling and Downhole LoggingThe main phase of HSDP2 drilling in 1999 consisted primarily of successive periods of coring to predetermined depths, followed by rotary drilling to open the hole for installation of progressively narrower casing strings (Fig. 2). No commercially available system could satisfy both the coring and rotary drilling requirements, so a hybrid coring system (HCS) was designed and fabricated. The HCS employed a rotating head and feed cylinder to drive the coring string, and it was attached to the traveling block of a standard rotary eastern part of the island of Hawaii, was chosen as the target (Fig. 1). The drill sites are located within the city of Hilo at elevations just a few meters above sea level. The project proceeded in three phases of drilling. What we refer to as "HSDP1" involved coring a pilot hole to a depth of 1052 meters below sea level (mbsl) in 1993 . The deep drilling project, referred to as HSDP2, took place in two phases. In the first phase a hole was core drilled in 1999 to a depth of 3098 mbsl (3110 m total depth; DePaolo et al., 2001b). In the second phase the hole was cased Site LocationAn abandoned quarry on the grounds of Hilo International Airport was chosen as the site for HSDP2. The HSDP1 pilot hole was located 2 km to the NNW, north of the airport, within fifty meters of the shoreline of Hilo Bay ( Fig. 1; Stolper et al., 1996;. Although the Mauna Kea volcanic section was the primary target, the HSDP sites in Hilo required drilling through a veneer of Holocene Mauna Loa flows. The Mauna Kea lavas are encountered at depths of 280-245 m. Because the volcanoes are younger to the southeast, and overlap with subsurface boundaries sloping to the southeast (Moore, 1987), it was expected that once Mauna Temperature survey (red line), done while the hole was flowing and still uncased below 1820 mbsl, suggests that water is entering the hole below ~2800 mbsl, and additional entry levels are at 2370 and 2050 mbsl. Circulation of cold seawater through the section below 600 mbsl is rapid enough to cool the rocks to temperatures 15°C-20°C below a normal geothermal gradient.

No abstract