Beschreibung
The Collisional Orogeny in the Scandinavian Caledonides (COSC) scientific drilling project is investigating mountain building processes at mid to lower crustal levels in a deeply eroded Paleozoic collisional orogen of Himalayan dimensions. Two fully cored COSC boreholes will provide a unique circa 5 km deep composite section from a subduction related allochthon through the underlying continental margin, mostly cover-derived nappes, and the basal décollement into Precambrian crystalline basement. Utilising the Caledonides as an analogue to comparable tectonic settings, such as the Himalaya, will advance our understanding of orogenic systems and how they affect the stability of the living environment. COSC-1, drilled in 2014, investigated the emplacement of the high-grade (UHP) metamorphic allochthons. COSC-2 (this proposal) will define the character and age of deformation of the underlying greenschist facies thrust-sheets, the main Caledonian décollement and the Precambrian basement. The upper part of the borehole will sample a Cambro-Silurian succession, including both distal shelf sedimentary formations typical of the Baltoscandian platform and also foreland basin turbidites of both mid Ordovician and Early Silurian age, separated by significant environmental changes at the Ordovician-Silurian boundary. After drilling through the main décollement, COSC-2 will penetrate 1-1.5 km into the basement of the Fennoscandian Shield, where prominent seismic reflections indicate the presence of significant crustal shortening of Caledonian or Sveconorwegian age. Study of this internal basement deformation is particularly important for understanding the passage from thin-skinned tectonics in the foreland of the orogen to thick-skinned tectonics in the hinterland, where the underriding Baltica plate experienced deformation and (U)HP metamorphism. ICDP drilling will result in a fully cored borehole that will be further characterised by downhole logging, as well as complemented by VSP and electromagnetic surveys in separate projects. COSC-2 research will span several geoscientific disciplines – geology, geophysics, geochronology, hydrogeology, geothermics and microbiology – performed by various constellations of the COSC science team who will seek funds from national and international funding agencies. Tasks such as Modern analogues – incipient and active orogens, Foreland – hinterland – off-shore connection and others will coordinate the multidisciplinary expertise of the international science team to effectively address the scientific targets. The COSC-2 scientific targets address four out of the five themes identified as the way forward in the ICDP Science Plan 2014: Active Faults and Earthquakes, Global Cycles and Environmental Change, Heat and Mass Transfer and The Ubiquitous Hidden Biosphere.