Abstract:

An intense focus has been put on collecting geoscientific data to understand the ongoing volcanic processes at Reykjanes Peninsula. Less attention has, however, been to connect this into the long time geological history of the region observed in the boreholes. This presentation summarizes the wealth of geological data available from boreholes from Svartsengi to Reykjanes high-T areas with comparison with other areas such as Hengill.

More than half of the volcanic succession at Svartsengi-Eldvörp consist of sub-areal lavas and the remainder subglacial hyaloclastites.  This ratio of lava/hyaloclastite accumulation is in stark contrast with the time lengths of glacials and interglacials and clearly indicates a much lower eruption rate during the former. This might in turn imply variations in magma production in the mantle. Intrusions intersected by the boreholes become notable below about 600 m and reach over 30% below about 2 km depth. For comparison 100% intrusions are reached below 2 km depth in Hengill central volcano and same below 1 km depth in Krafla. These intrusions are both dykes as well as sills and tend to become coarser grained with depth.

The volcanic succession at Reykjanes high temperature field is fundamentally different from that of Eldvörp and Svartsengi, as it accumulated sub-aqueously and is assumed to present a recent addition to the Reykjanes Peninsula. A topographic map of the Reykjanes Ridge nearest to the peninsula shows the rift zone consisting of “microplates” separated by a NNW striking transform structures. Such a structure may underlie and separate Reykjanes and Svartsengi thermal anomalies.

The Svartsengi reservoir is aligned near E-W for more than 6 km extending from Svartsengisfell to west of Eldvörp. It has an anomalously high permeability and near constant temperature reaching down to at least 2 km depth. It is believed that the high permeability is controlled by a segment of the transform fault.

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