Volcanic and geochemical evolution of the Teno massif, Tenerife, Canary Islands: some repercussions of giant landslides on ocean island magmatism

Large-scale, catastrophic mass wasting is a major process contributing to the dismantling of oceanic intraplate volcanoes. Recent studies, however, have highlighted a possible feedback relationship between flank collapse, or incipient instability, and subsequent episodes of structural rearrangement and/or renewed volcano growth. The Teno massif, located in northwestern Tenerife (Canary Islands), is a deeply eroded Miocene shield volcano that was built in four major eruptive phases punctuated by two lateral collapses, each removing >20–25 km3 of the volcano's north flank. In this paper, we use detailed field observations and petrological and geochemical data to evaluate possible links between large-scale landslides and subsequent volcanism/magmatism during Teno's evolution. Inspection of key stratigraphic sequences reveals that steep angular unconformities, relics of paleolandslide scars, are marked by polymict breccias. Near their base, these deposits typically include abundant juvenile pyroclastic material, otherwise scarce in the region. While some of Teno's most evolved, low-density magmas were produced just before flank collapses, early postlandslide lava sequences are characterized by anomalously high proportions of dense ankaramite flows, extremely rich in clinopyroxene and olivine crystals. A detailed sampling profile shows transitions from low-Mg # lavas relatively rich in SiO2 to lavas with low silica content and comparatively high Mg # after both landslides. Long-term variations in Zr/Nb, normative nepheline, and La/Lu are coupled but do not show a systematic correlation with stratigraphic boundaries. We propose that whereas loading of the growing precollapse volcano promoted magma stagnation and differentiation, the successive giant landslides modified the shallow volcano-tectonic stress field at Teno, resulting in widespread pyroclastic eruptions and shallow magma reservoir drainage. This rapid unloading of several tens of km3 of near-surface rocks appears to have upset magma differentiation processes, while facilitating the remobilization and tapping of denser ankaramite magmas that were stored in the uppermost mantle. Degrees of mantle melting coincidently reached a maximum in the short time interval between the two landslides and declined shortly after, probably reflecting intrinsic plume processes rather than a collapse-induced influence on mantle melting. Our study of Teno volcano bears implications for other oceanic volcanoes where short-term compositional variations may also directly relate to major flank collapse events

Prodigious submarine landslides during the inception and early growth of volcanic islands

Volcanic island inception applies large stresses as the ocean crust domes in response to magma ascension and is loaded by eruption of lavas. There is currently limited information on when volcanic islands are initiated on the seafloor, and no information regarding the seafloor instabilities island inception may cause. The deep sea Madeira Abyssal Plain contains a 43 million year history of turbidites among which many originate from mass movements in the Canary Islands. Here, we investigate the composition and timing of a distinctive group of turbidites that we suggest represent a new unique record of large-volume submarine landslides triggered during the inception, submarine shield growth, and final subaerial emergence of the Canary Islands. These slides are predominantly multi-stage and yet represent among the largest mass movements on the Earth’s surface up to three or more-times larger than subaerial Canary Islands flank collapses. Thus whilst these deposits provide invaluable information on ocean island geodynamics they also represent a significant, and as yet unaccounted, marine geohazard

Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

Aeromagnetic anomalies reveal the link between magmatism and tectonics during the early formation of the Canary Islands

The 3-D inverse modelling of a magnetic anomaly measured over the NW submarine edifice of the volcanic island of Gran Canaria revealed a large, reversely-magnetized, elongated structure following an ENE-WSW direction, which we interpreted as a sill-like magmatic intrusion emplaced during the submarine growth of this volcanic island, with a volume that could represent up to about 20% of the whole island. The elongated shape of this body suggests the existence of a major crustal fracture in the central part of the Canary Archipelago which would have favoured the rapid ascent and emplacement of magmas during a time span from 0.5 to 1.9 My during a reverse polarity chron of the Earth’s magnetic field prior to 16 Ma. The agreement of our results with those of previous gravimetric, seismological and geodynamical studies strongly supports the idea that the genesis of the Canary Islands was conditioned by a strike-slip tectonic framework probably related to Atlas tectonic features in Africa. These results do not contradict the hotspot theory for the origin of the Canary magmatism, but they do introduce the essential role of regional crustal tectonics to explain where and how those magmas both reached the surface and built the volcanic edifices.Project CGL2015-63799-P of the Spanish Ministry of Economy and Competitivenes

Enzymic Unwinding of DNA 1. Purification and Characterization of a DNA‐Dependent ATPase from Escherichia coli

Evidence from various sources in the literature suggests that, in connection with DNA, ATP dephosphorylation can be used to provide energy for mechanical effects. Starting from this concept we have studied a novel DNA‐dependent ATPase purified to 90% homogeneity from Escherichia coli. The enzyme has a peptide weight near 180000 and, in high salt, is a monomeric, probably highly anisometric molecule. In salt‐free buffer, where the ATPase activity is highest, the enzyme forms aggregates. ATP is the preferred substrate (Km 0.27 mM) and dephosphorylated at the γ‐position at a maximal rate near 104 molecules per enzyme monomer per min at 35 °C. A requirement for divalent cation is best satisfied by Mg2+ or Ca2+ and the requirement for DNA best by the single‐stranded, circular DNA of phages øX174 (Km 62 nM nucleotide) and fd indicating that the enzyme recognizes internal DNA regions. When saturated with E. coli DNA unwinding protein, øX DNA is not accepted but, once in contact with the DNA, the enzyme is little inhibited by unwinding protein. Apparently the unwinding protein interferes preferentially with the recognition of DNA. The enzyme does not detectably cleave DNA, and for this and genetic reasons is not identical with the recBC ATPase or the K12 restriction ATPase of the extracted cells. The enzyme is probably not identical either with the dnaB‐product‐associated ATPase or the ATPase activity found in DNA polymerise III holoenzyme under appropriate conditions, and it is certainly not identical with a DNA‐dependent ATPase of molecular weight 69000 from E. coli which has recently been purified. Attempts to ascribe the enzyme to other genes, including recA, lex and rep, have failed

Enzymic Unwinding of DNA 2. Chain Separation by an ATP‐Dependent DNA Unwinding Enzyme

The DNA‐stimulated ATPase characterized in the accompanying paper is shown to be a DNA unwinding enzyme. Substrates employed were DNA · RNA hybrid duplexes and DNA · DNA partial duplexes prepared by polymerization on fd phage single‐stranded DNA template. The enzyme was found to denature these duplexes in an ATP‐dependent reaction, without delectably degrading. EDTA, an inhibitor of the Mg2+ ‐requiring ATPase, was found to prevent denaturation suggesting that dephosphorylation of the ATP and not only its presence is required. These results together with those from enzyme‐DNA binding studies lead to ideas regarding the mode of enzymic action. It is proposed that the enzyme binds, in an initial step, to a single‐stranded part of the DNA substrate molecule and that from here, energetically supported by ATP dephosphorylation, it invades double‐stranded parts separating base‐paired strands by processive, zipper‐like action. It is further proposed that chain separation results from the combined action of several enzyme molecules and that a tendency of the enzyme to aggregate with itself reflects a tendency of the molecules to cooperate. Various functions are conceivable for the enzyme

DNA unwinding enzymes

DNA unwinding enzymes use the energy released by ATP hydrolysis for separating the strands of a DNA. They are representatives of a large group of chemomechanically active DNA enzymes

DNA Unwinding Enzyme II of Escherichia coli 2. Characterization of the DNA Unwinding Activity

The DNA‐stimulated 75000‐Mr ATPase described in the preceding paper is shown to be a further catalytic DNA unwinding principle (DNA unwinding enzyme II) made in Escherichia coli cells (the first being the 180000‐Mr ATPase of the cells: DNA unwinding enzyme I). Unwinding depends, strictly, on the supply of ATP. It occurs only under conditions permitting ATP dephosphorylation and it proceeds as long as enzyme molecules are permitted to enter the enzyme. DNA complex. The enzyme binds specifically to single‐stranded DNA yielding a complex of only limited stability. These results are interpreted in terms of a distributive mode of action of the enzyme. It is argued that chain separation starts near a single‐stranded DNA region and that, forced by continued adsorption of enzyme molecules to the DNA, it develops along the duplex. This mechanism is different from that deduced previously for DNA unwinding enzyme I. Complicated results were obtained using ATPase prepared from rep3 mutant cells