Paleofluids and Recent fluids in the upper continental crust: Results from the German Continental Deep Drilling Program (KTB)

Abstract

Abstract. The two German Continental Deep Drilling Program (KTB) boreholes provided samples for studies of fluid inclusions (paleofluids), "free fluids" of the crystalline basement, and their fingerprints on the chemical and isotopic composition of minerals and rocks to 910t m depth, which allowed reconstruction of the evolution of fluids, their migration pathways, and their sources. Aqueous fluids were largely lost during the Devonian amphibolite facies metamorphism. Thereafter, radiogenic, nucleogenic, and fissiogenic gases, together with NH afixed nitrogen, were released from host rocks and partly enclosed in secondary inclusions.During the Hercynian uplift, Na-Cl fluids (formation water) infiltrated and dissolved noble gases and N 2 largely originating from the host rocks. In the course of the Cretaceous denudation, highsalinity Ca-Na-CI brines, possibly derived from Permo-Carboniferous sediments but altered by fluid/rock interaction, migrated into their present position. This fluid introduced low-maturity hydrocarbons released together with nitrogen from early metamorphic organic-rich sediments. The 4000-m fluid from the KTB pilot hole pumping test, which was analyzed chemically and isotopically, seems to be a mixture of an ascending basement brine and a descending paleometeoric water, from which the late alteration minerals calcite and laumontite precipitated in fractures. The calcite is neither chemically nor isotopically in equilibrium with the recovered "free fluid." Hydraulic tests indicate a communicating system of fractures between the boreholes with a distinct matrix and fracture porosity.

Magnetotelluric investigations for the seismically active area in Northern Miyagi Prefecture, northeastern Japan

“…However, the origin of fluids in the crust cannot be generally identified uniquely as suggested by drilling and geochemical studies (e.g. Frape and Fritz, 1984;Möller et al, 1997). For example, ancient meteoric water and brine deposited in the study area are other promising candidates for the origin of the crustal conductor (Fujimoto, Personal comm.).…”

Groundwater in fractured crystalline rocks, the Clara mine, Black Forest (Germany)

“…In general, the permeability of fractured crystalline basement is relatively high and permits groundwater advection and large-scale fluid flow (Manning and Ingebritsen 1999;Caine and Tomusiak 2003;Stober and Bucher 2007). The information on chemical properties of groundwater in the basement comes from shallow near surface wells (Banks and Banks 1993), scientific deep drilling (Möller et al 1997), research for nuclear waste disposal (e.g., Nordstrom et al 1989), prospection for geothermal energy (e.g., Stober and Bucher 2004) and deep mines (Fritz and Frape 1987;Negrel and Casanova 2005).…”

Sealing of fluid pathways in overpressure cells: a case study from the Buntsandstein in the Lower Saxony Basin (NW Germany)

“…Additional fluids can be released by the maturation of organic components producing hydrocarbons (Bredehoeft et al 1994;Law and Spencer 1998). Besides these intrinsic processes, basin scale advective fluid flow of meteoric waters is common, usually along fractures (Gross et al 1992, Mo¨ller et al 1997. In a sedimentary basin, a number of processes may produce deviations from hydrostatic pore pressure and thus drive fluid flow along a hydraulic gradient, for example topography (gravity-driven flow), compaction, thermal gradients (e.g.…”