Spider capture silk is a natural material that outperforms almost any synthetic material in its combination of strength and elasticity. The structure of this remarkable material is still largely unknown, because spider-silk proteins have not been crystallized. Capture silk is the sticky spiral in the webs of orb-weaving spiders. Here we are investigating specifically the capture spiral threads from Araneus, an ecribellate orb-weaving spider. The major protein of these threads is flagelliform protein, a variety of silk fibroin. We present models for molecular and supramolecular structures of flagelliform protein, derived from amino acid sequences, force spectroscopy (molecular pulling) and stretching of bulk capture web. Pulling on molecules in capture-silk fibres from Araneus has revealed rupture peaks due to sacrificial bonds, characteristic of other self-healing biomaterials. The overall force changes are exponential for both capture-silk molecules and intact strands of capture silk.

Abstract. Despite slow opening rates generally inferred for the Mariana Trough, the southernmost part of the basin has "fast spreading" geophysical and morphologic characteristics that are unlike the features of the basin to the north. A side-scan sonar and geophysical survey maps the eastern part of the basin and the seafloor spreading center between 11 ø50'N and 13ø40'N and identifies the following characteristics: the ridge across-axis profile forms a triangular to rounded high with relief of 100 to 500 m and cross-sectional area variations of 1 to 7 km2; the along-axis mantle Bouguer gravity gradient is 0.2 mGal/km; axial segmentation occurs as overlapping axes and small deviation in trend; no transform fault offsets exist despite significant changes in the trend of the spreading center. Characteristics of the surrounding basin include shallower overall depth than in the north; no well-developed frontal arc high in the southernmost trough; the close proximity of submarine arc-type volcanoes to the spreading center; and tectonic fabric that is at a high angle to the trend of the spreading center on the eastern flank but is concordant on the western flank. These characteristics imply different tectonic and magmatic conditions in the southern trough from the rest of the basin. We propose that these effects are related to (1) the geometry of trench rollback in the southern trough leading to trench-parallel extension generating inward radiating extensional faults; (2) decoupling of the trench-parallel extensional strain by the spreading center so that it primarily affects the eastern flank of the basin; and (3) augmentation of the spreading center's magmatic budget by arc magmatic sources contributing to its fast spreading character. Although these effects may be accentuated in the southern Mariana Trough by the geometry of trench rollback and position of the slab, which here underlies the spreading center, they reflect distinct volcanic and tectonic processes which are varyingly expressed in back arc systems but are not normally found at mid-ocean ridges.

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Serpentinites are distinctive components of on-land exposures of former convergent-margin terranes throughout the world, commonly mingled with high-pressure, low-temperature blueschist-facies metamorphic rocks in complex mélange assemblages that have long perplexed geologists. Serpentinite blocks within these mélanges commonly retain vestiges of original igneous textures and were once widely considered to be igneous intrusive rocks, altered in situ. These chaotic assemblages never show contact-metamorphic aureoles, but usually do show extensive internal shearing and are commonly found along fault zones; thus an alternative explanation was that they formed as tectonically intrusive (i.e., protrusive) bodies. Early workers suggested that these serpentinites were emplaced during or after deformation and metamorphism. Particularly puzzling were occurrences of sedimentary serpentinite, masses of originally unconsolidated serpentine enclosing clasts of serpentinized peridotite and metabasites (some reaching blueschist-grade metamorphism), showing evidence of sedimentary structures and occasionally incorporating cherts and marine fossils.Recent discoveries of large submarine serpentine mud volcanoes containing blueschist materials in the forearc of the active Mariana convergent plate margin show that serpentine mud, crystals, and clasts can be emplaced directly on the seafloor by protrusive processes. Mudflows from these serpentine seamounts are incorporated in the forearc strata before subsequent emplacement on land and before the deformation and associated metamorphism of the materials enclosing them. The Mariana forearc mud volcanism is episodic and brings up materials derived both from the descending plate and from the mantle and crustal sections of the overriding plate. These materials rise along deep-seated faults above the subduction zone and probably represent fault gouge mobilized by seismicity and rising fluids released during dehydration of materials on the downgoing plate. The serpentine mud volcanoes of the Mariana forearc are the only ones known to be currently active and to be venting slab-derived fluids. These mud volcanoes contain a wide variety of metamorphosed rocks either as clasts or as disaggregated crystals disseminated throughout the muds. Blueschist materials discovered in these seamounts indicate depths of origin of Յ30 km. Probably these materials derive from the top of the descending Pacific plate. Other, unmetamorphosed rocks of plate origin have also been recovered from several of these seamounts. Many examples of sedimentary serpentinite exist throughout the world in ancient convergent-margin settings; thus the phenomenon of serpentine mud volcanism is likely a more important agent of recycling of subducted constituents than previously thought.Fryer, P., et al., 2000, Significance of serpentine mud volcanism in convergent margins, in Dilek, Y., Moores, E.M., Elthon, D., and Nicolas, A., eds., Ophiolites and

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