We compared the morphology of gully sedimentary fans on Svalbard as possible analogs to gullies on Mars in order to constrain whether fluvial and/or debris-flow processes are predominantly responsible for the formation of Martian gullies. Our analysis is based on high-resolution imagery (High Resolution Stereo Camera [HRSC-AX], ~20 cm/pixel) acquired through a flight campaign in summer 2008 and ground truth during two expeditions in the summers of 2008 and 2009 in Svalbard, compared to high-resolution satellite imagery (High Resolution Imaging Science Experiment [HiRISE], ~25 cm/pixel) from Mars. On Svalbard, fluvial and debris-flow processes are evident in the formation of gullies, but the morphological characteristics clearly show that the transport and sedimentation of eroded material are predominated by debris flows. Most investigated gullies on Mars lack clear evidence for debris-flow processes. The Martian gully fan morphology is more consistent with the deposition of small overlapping fans by multiple fluvial flow events. Clear evidence for debris flows on Mars was only found in one new location, in addition to a few previously published examples. The occurrence of debris-flow processes in the formation of Martian gullies seems to be rare and locally limited. If predominantly fluvial processes caused the formation of gullies on Mars, then large amounts of water would have been required for their formation because of the relatively low sediment supply in stream and/or hyperconcentrated flows. Repeated seasonal or episodic snow deposition and melting during periods of higher obliquity in the recent past on Mars can best explain the formation of the gullies.

We present landforms on Svalbard (Norway) as terrestrial analogs for possible Martian periglacial surface features. While there are closer climatic analogs for Mars, e.g., the Antarctic Dry Valleys, Svalbard has unique advantages that make it a very useful study area. Svalbard is easily accessible and offers a periglacial landscape where many different landforms can be encountered in close spatial proximity. These landforms include thermal contraction cracks, slope stripes, rock glaciers, protalus ramparts, and pingos, all of which have close morphological analogs on Mars. The combination of remote-sensing data, in particular images and digital elevation models, with field work is a promising approach in analog studies and facilitates acquisition of first-hand experience with permafrost environments. Based on the morphological ambiguity of certain landforms such as pingos, we recommend that Martian cold-climate landforms should not be investigated in isolation, but as part of a landscape system in a geological context.

Abstract Periglacial landforms on Spitsbergen (Svalbard, Norway) are morphologically similar to landforms on Mars that are probably related to the past and/or present existence of ice at or near the surface. Many of these landforms, such as gullies, debris-flow fans, polygonal terrain, fractured mounds and rock-glacier-like features, are observed in close spatial proximity in mid-latitude craters on Mars. On Svalbard, analogous landforms occur in strikingly similar proximity, which makes them useful study cases to infer the spatial and chronological evolution of Martian cold-climate surface processes. The analysis of the morphological inventory of analogous landforms on Svalbard and Mars allows the processes operating on Mars to be constrained. Different qualitative scenarios of landscape evolution on Mars help to better understand the action of periglacial processes on Mars in the recent past.

Abstract Permo-Carboniferous rifting in Europe was accompanied by the widespread emplacement of mantle-derived magmas forming regional dyke swarms and sills in northern England, Scotland, Norway and southern Sweden during the late Stephanian and early Autunian. The trends of the dyke swarms intersect at a focal point in the Kattegat south of the Oslo Graben, and are probably all related to a single magmatic centre that could be plume-related. The WNW- to NW-trending dyke swarm at the SW margin of the Fennoscandian Shield in southern Sweden is composed mainly of tholeiitic dolerites, with lesser amounts of alkaline mafic rocks (camptonites, alkali basalts and spessartites) and trachytes. The alkaline mafic rocks are enriched in Ba, Sr, Nb, P and CO 2 , implying a metasomatic enrichment of their upper-mantle source prior to melting. After generation of alkaline melts by relatively small degrees of partial melting, increased extension was accompanied by the formation of subalkaline tholeiitic magmas. Whole-rock compositions (Mg-numbers between 55 and 30) and mineral chemistry (olivine Fo 60 -Fo 40 ; clinopyroxene approximately Wo 30 En 45 Fs 15 ; plagioclase An 70 -An 50 ) indicate relatively evolved melts that have undergone crystal fractionation of olivine and clinopyroxene. Two groups of dolerites can be distinguished on the basis of bivariate element plots, e.g. Zr-TiO 2 and La-Sm. Although both groups show enrichment in the whole range of incompatible trace elements, slight differences in mantle-normalized trace-element patterns and different Nb/La ratios suggest that they were generated from two different sources. Group I dolerites were formed from a (re-)enriched, but isotopically mildly depleted, sublithospheric garnet-bearing mantle source (Nb/La mostly > 0.9, εNd i = +4 to +3, where εNd i is the initial Nd isotope ratio), whereas group II dolerites seem to indicate mixing of the asthenospheric-derived magmas with lithospheric mantle melts (Nb/La mostly <0.9, εNd i = 0 to −1). Increasing Th/Ta ratios together with decreasing U/Nb ratios from group I towards group II dolerites further reflect progressive crustal contamination.