ABSTRACT The Scandinavian Caledonides formed during the continental collision between Baltica and Laurentia. During the collision, a complex nappe stack was thrust over the Baltican continental margin. The orogen can be subdivided into segments based on architectural differences within the Scandian nappes. The southern and central segments of the orogen link up in the Gudbrandsdalen area in south-central Norway. Alpine-type metaperidotite-bearing metasedimentary complexes occur in the southern and central segments and can be traced continuously along the strike of the orogen from one into the other segment. Traditionally, these units have been assigned to different tectono-stratigraphic levels, one below the Middle Allochthon and one above the Middle Allochthon. Here, we trace the Alpine-type metaperidotite-bearing units from Bergen to Esandsjøen and show that these units exhibit a common geologic and metamorphic history, consistent with the metaperidotite-bearing units representing a single tectonic unit. We suggest that the metaperidotite-bearing units can be used as a “marker level” to revise the tectono-stratigraphy of the Gudbrandsdalen and adjacent areas. The tectono-stratigraphic revisions imply that the Scandian nappe stack consists of seven tectono-stratigraphic levels that can be traced throughout the southern and central segments of the Scandinavian Caledonides. Moreover, the revision of the tectono-stratigraphy and new U-Pb geochronology data also suggest a revision of the timing of the succession of tectonic events leading up to the Scandian continental collision. The available evidence indicates that Baltica-derived tectonic units collided with the Iapetan/Laurentian subduction complexes as early as ca. 450 Ma. The initial collision was followed by in-sequence nappe formation of Baltican-derived units, which occurred contemporaneously with the opening of a marginal basin in the upper plate. After the arrival of thick, buoyant, unthinned Baltican crust at the trench, the main zone of convergence stepped outboard, the marginal basins closed, and those basins were thrust out-of-sequence over the previously assembled nappe stack.

ABSTRACT A high concentration of hydrogen gas occurs in fracture zones of active faults that are associated with historical earthquakes. To explain the described phenomenon, we propose the piezoelectrochemical (PZEC) effect as a mechanism for the direct conversion of mechanical energy to chemical energy. When applied to natural piezoelectric crystals including quartz and serpentine, hydrogen and oxygen are generated via direct water decomposition. Laboratory experiments show H 2 gas is generated from strained piezoelectric material due to the extremely low solubility of H 2 , suggesting that the deformed or strained mineral surfaces can catalyze water decomposition. If the strain-induced H 2 production is significant, hydrogen measurements at monitoring sites can offer information on deformation of rocks operating at depth prior to earthquakes. Oxygen can be measured in water due to its high solubility compared to hydrogen. Our experimental results demonstrate that dissolved oxygen generated from the PZEC effect can oxidize dissolved organic dye and ferrous iron in an aqueous Fe(II)–silicate metal complex. The hydrogen and oxygen formed through stoichiometric decomposition of water in the presence of strained or deformed minerals in fault zones (including subduction zones and transform faults) may be referred to as tectonic hydrogen and tectonic oxygen. Tectonic hydrogen could be a potential energy source for deep subsurface and glacier-bedrock interface microbial communities that rely on molecular hydrogen for metabolism. Tectonic oxygen may have been an important oxidizing agent when dissolved in water during times in early Earth history when atmospheric oxygen levels were extremely low. Reported “whiffs” of dissolved oxygen before the Great Oxidation Event might have been related to tectonic activity.

ABSTRACT In 1935, Krynine postulated that first-cycle arkose in the humid tropical setting of southern Mexico can be rapidly eroded with minimal chemical weathering and redeposited as second-cycle arkose. Modern quantitative data confirm this hypothesis and highlight exceptions where first-cycle arkosic sediments have been diagenetically altered by intense weathering to yield second-cycle quartz arenites. In this study, extensive sampling of upland source rocks and their derived sediments provided a robust data set with which to quantitatively evaluate the composition and provenance of Holocene sediments. Three upland source terrains were identified: Paleozoic crystalline basement of the Chiapas Massif; Mesozoic to Cenozoic siliciclastic and carbonate rocks of the Chiapas fold belt; and Cenozoic sedimentary rocks in the foothills of the fold belt. Holocene sediments from these source terrains are grouped into seven facies (A–G) based on their provenance and geographic location. Facies A consists of feldspathic sediments from the Mezcalapa-Grijalva River that are sourced from the Chiapas Massif. Facies B consists of lithic-rich sediments from the same area that are derived from the Chiapas fold belt. Facies A and B consist predominantly of first-cycle sand capable of yielding arkosic deposits. Facies C represents a mixture of Facies A and B sands deposited along the course of the Mezcalapa-Grijalva River. Facies D (from Rio Sierra) and Facies E (from Rio Pedregal) represent second-cycle feldspathic sands of the coastal-plain delta and were derived from Cenozoic sedimentary rocks of the foothills. Mild chemical weathering due to rapid mechanical erosion enabled the creation of these arkosic deposits. They are less feldspathic than their parents and have limited occurrence due to mixing with less feldspathic first-cycle sands downstream from their sources. Facies F (from Rio Zanapa) and Facies G (from Lagunas Rosario and Enmedio) represent second-cycle quartzose sands of the low-lying savanna that were also derived from Cenozoic sedimentary rocks in the foothills of the fold belt. Intense, long-term (>10,000 yr) chemical weathering of these sands has precluded the formation of arkoses, instead yielding quartz arenites. They are more weathered than the delta sands (Facies D, E) with a greater loss of feldspar and carbonate detritus. They are enriched in silica and depleted in alumina, CaO, Na 2 O, and K 2 O relative to Facies A arkoses due to loss of feldspars and mafic minerals. Second-cycle sediments eroded from Tertiary sedimentary rocks in the foothills (Facies D–G) contain detrital serpentine and chromite with high abundances of Cr and Ni, suggesting an ultramafic component in their provenance. Cr and Ni are effective tracers for second-cycle components in sands of mixed provenance.