ND-SR ISOTOPIC AND TRACE-ELEMENT STUDY OF ROCKS AND FLUIDS FROM THE CONTINENTAL DEEP DRILLING PROJECT (KTB), GERMANY

Geochemical analyses were interpreted on the dominant lithological uni ts and on a deep crustal fluid from the Continental Deep Drilling Proj ect (KTB) Pilot Hole, situated at the western margin of the Variscan B ohemian Massif. The biotite gneiss (from 384 m depth) shows a rare ear th element pattern very similar to the European shale composite with N d model ages of 940 Ma (CHUR) and 1.4 Ga (DM). The lamprophyre dike in the upper profile (1549 m), a nepheline and olivine normative basalt, is geochemically and isotopically similar to rocks from the Tertiary Central European Volcanic Province, The lower metabasite sequence (357 5-4000 m), with an intrusion age of approximately 500 Ma, is made up p rimarily of highly metamorphosed subalkalic olivine basalts. The geoch emical characteristics of the metabasites are a (La/Yb)(N) of 5-10, an La concentration of 20-50 times chondrite as well as (Sr-87/Sr-86)(i) of 0.7035-0.7038 and epsilon(Nd)(T) of 4-6. These values suggest a de pleted mantle source for the igneous precursors, evolving by assimilat ion-fractional crystallization processes with up to 25% of upper crust into the ultramafic, basaltic, and intermediate rock types of the met abasite sequence, The strong geochemical and chronological similaritie s between the KTB metabasites and rocks from the Munchberg Massif sugg est that these units belong to the same lithological complex. The high salinity as well as the radiogenic Sr-87/Sr-86 ratio of 0.709413 in t he KTB fluid from 4000 m depth might be the result of migrating fluids reacting with the regional Permo-Mesozoic evaporite deposits, followe d by extensive Sr isotopic exchange with the upper crust.