Release of mineral-bound water prior to subduction tied to shallow seismogenic slip off Sumatra

Plate-boundary fault rupture during the 2004 Sumatra-Andaman subduction earthquake extended closer to the trench than expected, increasing earthquake and tsunami size. International Ocean Discovery Program Expedition 362 sampled incoming sediments offshore northern Sumatra, revealing recent release of fresh water within the deep sediments. Thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial-induced temperature increases in the past 9 million years. Complete dehydration of silicates is expected before plate subduction, contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction. Shallow slip offshore Sumatra appears driven by diagenetic strengthening of deeply buried fault-forming sediments, contrasting with weakening proposed for the shallow Tohoku-Oki 2011 rupture, but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records

Significance of radiolarian biostratigraphy of the southern New England Orogen, New South Wales

Diverse and well-preserved radiolarian faunas are rare in the Early Paleozoic, but the importance of the result of the ages should suggest some idea on the provenance linkage and terrane amalgamation in the NEO. A moderately well-preserved radiolarian fauna consisting of 12 Devonian taxa was recovered from siliceous strata in both the Djungati and Gamilaroi terrane, in the southern New England Orogen, New South Wales. Fauna includes; Trilonche davidi(Hinde), Tr. hindea (Hinde), Tr. echinata (Hinde), Tr. minax (Hinde), Tr. vetusta (Hinde), Tr. elegan (Hinde), Tr. palimbola (Foreman), Tr. tanheensis (Luo, Aitchison & Wang), Palaeoscenidium cladophorus(Deflandre), Stigmosphaerostylus sp., Helenifore laticlavium (Nazarov) and Protoholoeciscus hindea (Aitchison) Results of radiolarian studies on each site provide reliable age constraints on the timing of sedimentation of each terrane. The Birpai sub-terrane recovered well radiolarian faunas that contained Helenifore laticlavium (Nazarov), which dates the terrane to a lower Famennian (Cheng, 1986) the upper Frasnian age. Protoholoeciscus hindea (Aitchison), recovered from the Djungati cherts at the Barnard River dated an age of Lower (Emsian) to Middle (Eifelian) Devonian age. The needle-like spines and spumellarians with three -bladed spines, from the Woolomin beds at Chaffey Dam, are indicative of Middle Devonian and younger radiolarians (Jones and Murchey, 1986). Indicative of fossils are scarce even though there was a thick exposure of cherts reflecting the extensive deformation at this site. The red ribbon-bedded cherts of the Djungati terrane were accreted in a sediment starved trench probably associated with an intra-oceanic island arc, but there is no evidence linking the red-ribbon cherts as an accretionary complex of the Gamilaroi terrane. The rarity of zircons and SHRIMP ages of the two zircons obtained from the coarse sandstones from the Upper Barnard River reflects events of much older origins than the sedimentary rocks themselves, and further support the distal environment for formation. These Devonian lithologies have inherited structural patterns as a result of processes of accretion and orogenesis throughout the Carboniferous. Three different types of structures are distinguished: (i) conjugate arrays of en echelon, quartz-filled tension gashes, showing extensional shear offsets. (ii) Fining directions on tuffs and overlay sequences, showing younging directions. (iii) Fold vergence. From these results geological model of the Chaffey Dam, Yarras district have been established in relation to the NEO. The structural data from this report supports the theory proposed by Aitchison (1992), about the collision of the Gamilaroi terrane giving rise to a subduction flip, causing another subduction zone developed east of accreted Gamilaroi terrane rocks in association with the east-dipping subduction

Micro-CT videos of Paleozoic radiolarians

Micro-CT study of Middle Ordovician Spumellaria (radiolarians) from western Newfoundland, Canad

Micro-CT study of Middle Ordovician Spumellaria (radiolarians) from western Newfoundland, Canada

A new, previously undescribed Middle Ordovician (middle Darriwilian: Dw2) radiolarian assemblage has been recovered from the Table Cove Formation at Piccadilly Quarry, western Newfoundland. Constituents of the fauna described herein are both distinctive and exceptionally well preserved. Three-dimensional X-ray micro-computed tomography (μ-CT) is used to make a detailed examination of four key spumellarian specimens. This technology enables visualization of hitherto ambiguous details of the internal morphologies of key lower Paleozoic taxonomic groups, among which a lack of knowledge has impeded resolution of higher taxonomic rankings

Silurian radiolarians from the Jenolan Caves region, New South Wales, Australia

Moderately-preserved Silurian radiolarians have been recovered from the Jenolan Caves region, eastern NSW, Australia. Radiolarians were first reported from this area in the late 19th\ua0Century by T.W. Edgeworth David, but were not described in detail, neither were they illustrated. Nearly 120\ua0years later, the first images of these fossils are presented. The radiolarians reported include: ?Futobari cf. solidus Furutani, ?Zadrappolus sp., Haplentactiniid gen. and sp. indet, Borisella sp., ?Palaeoephippium sp., ?Insolitignum vivanima MacDonald and ?Helenifore speciosus (Furutani). The fauna is similar to others described from Upper Silurian strata in Japan

Micro-CT 3D models and videos of two middle Cambrian spicular radiolarians recovered from the Georgina Basin, Australia

This dataset includes the micro-CT 3D models of two Archeoentactinia incaensis and A. tetractinia radiolarians of the Miaolingian Series (middle Cambrian) recovered from the Georgina Basin, Australia. Two videos of the rotating models showing their skeletal architecture are also included

Adding a new dimension to investigations of early radiolarian evolution

Knowledge of the detailed architecture of the earliest radiolarian microfossils is key to resolving the evolution and systematics of this important group of marine protozoans. Non-destructive methods for observing the complexity within the internal structures of their siliceous skeletons have long eluded paleontologists. By developing methodologies that overcome some limitations of existing micro-computed tomography (micro-CT) we demonstrate a technique with potential to provide new insight into their evolution. Using 3D micro-CT data to generate models for six well-preserved siliceous radiolarian skeletons from the Middle Cambrian Inca Formation in far north Queensland, Australia and the Middle Ordovician Piccadilly Formation, in western Newfoundland, Canada, we can reconstruct phylogenetic relationships amongst some of the earliest radiolarians. Better knowledge of early radiolarian morphologies clarifies the vital function of internal structures and hierarchical diagnosis across a range of taxonomic affiliations

Skeletal architecture of middle Cambrian spicular radiolarians revealed using micro-CT

X-ray micro-computed tomography (micro-CT) is used to resolve the detailed internal architecture of the siliceous skeletons of two well-preserved middle Cambrian (Miaolingian Series) radiolarians from the Inca Formation of the Georgina Basin, Australia. Digital dissections of specimens of Archeoentactinia incaensis and A. tetractinia reveal for the first time that both are exclusively composed of tetractine spicules. A basal layer consisting of robust spicules together with an interwoven meshwork of smaller spicules is observed in both micro-CT models. Detailed structural analysis with the aid of a digitally inserted artificial sphere shows that the framework spicules are likely to have been added one by one as the radiolarian cell enlarged. The timing of spicule genesis may be an important factor controlling the morphology of different groups of spicular radiolarians. Observation of these fundamental skeletal structures suggests that the type genus of Archeoentactiniidae Archeoentactinia belongs to Echidninidae; thus, Archeoentactiniidae is a junior synonym of Echidninidae

The Spongtang Massif in Ladakh, NW Himalaya: An Early Cretaceous record of spontaneous, intra-oceanic subduction initiation in the Neotethys

The Spongtang Massif is a remnant of Neotethyan ocean crust emplaced onto the Indian passive margin along the Indus-Yarlung-Tsangpo Suture in the NW Himalayan region of Ladakh. The age, tectonic evolution and timing of ophiolite obduction are critical to our understanding of the mechanisms via which entire oceans are formed, consumed and partly preserved before the onset of terminal continent-continent collisions. Geochemistry of the gabbro and basaltic units suggest the presence of both MORB-type and primitive arc-related mafic rocks. Zircons extracted from the Spongtang Massif gabbros yield U-Pb (SHRIMP) ages of 136-133 Ma with initial εHfvalues of +14 to +16, indicating Early Cretaceous juvenile, depleted mantle sources devoid of contamination by older continental crust. Previously, Middle Jurassic (~177 Ma) zircon ages were obtained from gabbro and we suggest these represent MORB-type Neotethyan oceanic crust through which a younger intra-oceanic island-arc (Spong arc) developed in response to subduction initiation during the Early Cretaceous (~136 Ma). Our zircon ages are consistent with Early Cretaceous ages obtained for radiolarian cherts within the Spong Arc complex. Subduction beneath the Spong Arc continued until its collision with the northern Indian continental margin during the early Eocene. We suggest that the Spongtang Massif is equivalent to the nearby Dras island arc terrane. Intra-oceanic subduction beneath this system was possibly initiated along NNE-SSW trending transform faults in the Neotethyan Ocean, along which different ages of ocean crust was juxtaposed, thereby development of the Early Cretaceous Spong Arc is superimposed on the older Jurassic Spongtang N-MORB crust. The juvenile ɛHfsignature indicates the subduction system that spawned the Spong island arc was not related to the coeval Trans-Himalayan (Ladakh-Gangdese) arc that developed along the southern margin of Eurasia. The age, composition and nature of geological relationships with the underlying Indian rocks indicate the Spong Arc was a juvenile, intra-oceanic terrane that first collided with India before the onset of final continent-continent collision. Therefore, final late Eocene Neotethys closure was between the Kohistan-Ladakh (Eurasian) continental arc and the already inactive Indian + Spongtang margin