The permeability structure of oceanic crust controls both the spatial and temporal extent of hydrothermal circulation, but the detailed geometry of fractures in seafloor rocks is not well known. We ...apply an equivalent channel model to veins, joints, faults, and breccias preserved in recovered cores from ODP‐IODP Hole 1256D to calculate paleo‐permeability. In the ~250‐m transition between dikes and lavas, paleo‐permeability is 10−13~10−14 m2 with narrow zones of >10−9 m2 that presumably act as conduits for the largest volume of fluids. Most of these high‐permeability zones are oriented vertically as a result of diking events into a significant thickness of lavas outside of the neovolcanic zone. After an increase in permeability due to off‐axis diking events, fluid temperatures drop, pathways are sealed, and the permeability of the upper oceanic crust drops significantly.
Key Points
Vertical fractures dominate the permeability structure of the transition between dikes and lavas at IODP Hole 1256D
Diking opens new vertical pathways for hydrothermal circulation outside the neovolcanic zone
Crustal permeability is reduced by 1–2 orders of magnitude by vein filling
A subduction complex of the northwestern Alps consists of serpentinites, eclogitic metagabbros, flysch‐like metasediments, meta‐ophicarbonates, and gneissic slices. Unlike other subduction complexes, ...it contains unusual hybridized rocks described here for the first time in the northwestern Alps. They are preserved as patches interstitial in the metagabbro and as layers within metagabbros and serpentinites. The hybridized rocks are made of high modal zoisite/clinozoisite + white mica pseudomorphs of lawsonite, garnet, and amphibole associated with an Alpine eclogite‐facies fabric. While these eclogitic metagabbros are chemically comparable to oceanic oxide gabbros from the ultraslow Southwest Indian Ridge, the layers are extremely enriched in Al2O3 and CaO and depleted in TiO2, MgO, and SiO2 relative to metagabbros. Patches have a geochemical signature that is intermediate between that of layers and metagabbros. Trace element compositions of hybridized rocks suggest a contribution from a fluid derived from a mixed source made of sediments and serpentinites. Except for Ba, Rb, and K, layers are comparable to the global subducting sediments, indicating a sedimentary contribution, whereas the enrichment in Cr indicates a serpentinite contribution. Metasediment dehydration and chemical exchange of Ca and Sr have resulted in significant lawsonite crystallization in the subduction zone, as reflected by the ubiquitous presence of lawsonite pseudomorphs. In light of the unique textures and geochemical signature of the lawsonite pseudomorph‐bearing hybridized rocks, an origin by fluid‐rock interaction and Ca‐metasomatism in the subduction environment is inferred and considered in the Western Alps context.
Key Points
The subduction complex includes serpentinites and metagabbros, flysch‐type metasediments, meta‐ophicarbonates, and gneissic slices
Eclogite‐facies metagabbros are associated to hybridized rocks recording Ca‐metasomatism and hydration/dehydration processes in the subduction environment
Structural characters constrain the timing of metasomatism between the prograde path and the HP peak
Heart failure (HF) has a strong association with the development of lower urinary tract symptoms, especially overactive bladder (OAB); although this condition remains poorly investigated. In this ...study, we assess the aortocaval fistula (ACF) model as a novel experimental model of micturition dysfunction, associated with HF, focused on the molecular and functional studies to evaluate the autonomic nervous system and urinary bladder remodeling. Male rats were submitted to ACF for HF induction. Echocardiography, cystometric, histomorphometry and molecular analysis, as well as concentration-response curves to carbachol and ATP and frequency-response curves to electrical field stimulation (EFS) were evaluated in Sham and HF (4- and 12-weeksendpoint) groups. Compared to SHAM, HF groups exhibited progressive increases in the left ventricle (LV) mass and fractional shortening which indicates cardiac dysfunction, although HF was characterized only after 12 weeks by the reduced ejection fraction. For micturition function, HF groups presented increased non-voiding contractions (NVC) and decreased bladder capacity; however, when comparing HF groups, these urinary parameters were significantly impaired over the weeks (12-weeks). The contractile responses induced by CCh, ATP and EFS were greater in detrusor muscle (DSM) from HF rats. mRNA expression for muscarinic receptors (M2 and M3) was higher in DSM only after 12 weeks of ACF, in addition to MMP9 and TGF-beta. Histomorphometric revealed increased urothelium thickness in both HF groups, whereas DSM thickness occurred only after 12 weeks. Thus, the ACF model induced cardiac dyfunction with progressive micturition dysfunction over the weeks, characterized by increased DSM contractile mechanisms as well as extracellular matrix remodeling in the urinary bladder, representing a useful tool to evaluate the OAB associated with HF.
The ocean crust is formed by the rising of magma from mid‐ocean ridges and voluminous (1–30 km3) flows of lava away from ridge axes. However, our understanding of the emplacement kinematics of ...submarine lava is often limited to plan view geometries of near‐axis lava. Drilled cores provide in situ access to the intact internal structure of submarine lavas. We used neutron diffraction to study off‐axis lava flows drilled into the uppermost crust of ODP/IODP‐Site 1256 (Cocos Plate). We provide quantitative insights into submarine lava microstructures and strong evidence for a secondary lava injection into the interior of a solidifying flow of lava along the NW‐SE direction parallel to the paleo‐ridge axis of the East Pacific Rise. The dynamics of lava inflow are controlled by crystal abundance and the temperature of the lava‐crystal mixture rather than by local seafloor topography. We provide a description of an in situ shear within submarine lavas revealed by composite shape and lattice preferred orientations, accounting for a dominant laminar nonuniform‐type flow.
Key Points
Method to define the direction of subaqueous lava flow
First LPO and SPO analysis conducted on subaqueous basalt
Evidence for inflated lava flows at ODP Site 1256
Laminar flow and evidence of vertical shear supporting inflation of the lava flow by a second episode
The Austroalpine Sesia-Lanzo inlier and upper Austroalpine Dent Blanche, Mt. Mary and Pillonet outliers occur on top of the western-Alpine orogenic wedge and, as a whole, override the structurally ...composite ophiolitic Piemonte zone. Instead, the Mt. Emilius, Glacier-Rafray, Etirol-Levaz and other lower Austroalpine eclogitic outliers are inserted within the Piemonte zone, between its upper (Combin) and lower (Zermatt-Saas) tectonic elements, or within the latter. Rb-Sr dating on phengitic micas show that the eclogitic imprint in the lower Austroalpine outliers, conventionally regarded as Late Cretaceous by comparison with the Sesia-Lanzo inlier, is of Eocene age (49-40 Ma), like the underlying Zermatt-Saas ophiolite (45-42 Ma) between the Aosta valley and Gran Paradiso massif. super(40)Ar- super(39)Ar plateau ages on the same mica concentrates of the ophiolitic Zermatt-Saas nappe (46-43 Ma) are consistent with Rb-Sr dating, whereas that on the Austroalpine Glacier-Rafray klippe (92 Ma) is influenced by argon excess. The lower Austroalpine outliers underwent the subduction metamorphism concurrently with the Zermatt-Saas nappe, 20-25 Ma later than the eclogitic Sesia-Lanzo inlier and blueschist Pillonet klippe. The temporal gap and present intra-ophiolitic position mean that the lower Austroalpine outliers were probably derived from an intraoceanic extensional allochthon (Mt. Emilius domain) stranded inside the Piemonte-Ligurian ocean far from the Dent Blanche-Sesia domain and Adriatic margin.
Textural and petrological data of mantle peridotites sampled in the central and western parts of the Romanche Fracture Zone (Equatorial Atlantic) during the oceanographic expedition PRIMAR-96 ...(Russian R/V Gelendzhik) are presented. The studied rocks are mantle peridotites carrying patches, pockets and veins/dikes of magmatic origin, interpreted to be the product of various extents of magma impregnation on mantle partial melting residues. Estimated partial melting degrees based on clinopyroxene Ti/Zr ratios are in the ranges 5–13% and 18–20%. In highly impregnated samples, refertilization of residual peridotite minerals precludes a correct evaluation of the degree of melting. Magmatic products occur as pl±cpx±opx±ol±sp aggregates with various textural features. Interstitial pl-rich patches and gabbroic pockets are interpreted to derive from magma migration through the upper mantle by diffusive porous flow in the ductile part of the lithosphere and melt–rock reactions. Metasomatism of the host peridotites is testified by Ti and Cr increase in spinel and Ti, Sr, Zr, Y and LREE increase in clinopyroxene. Veins and dikes reflect channeled magma migration focused by brittle failures at shallower lithospheric levels. Minor or no chemical changes occurred in peridotites impregnated along fractures. The compositions of magmatic minerals in impregnated peridotites are consistent with derivation from variably fractionated melts of probably MORB type. Barometric estimates suggest that the Romanche peridotites were impregnated at minimum depths of ca. 9–12 km. Thermometric estimates for the peridotite hosts are in the range 750–1050 °C. The spread in temperature values is partly ascribed to localized heating by migrating melts of relatively cold peridotites. Our data and the occurrence of both fertile and depleted peridotites in a neighbouring area along the western Romanche FZ are in accord with the hypothesis of small-scale (<100 km) mantle heterogeneity along this fracture zone.
We have studied textural relationships and compositions of phyllosilicate minerals in the mafic–ultramafic-hosted massive-sulfide deposit of Ivanovka (Main Uralian Fault Zone, southern Urals). The ...main hydrothermal phyllosilicate minerals are Mg-rich chlorite, variably ferroan talc, (Mg, Si)-rich and (Ca, Na, K)-poor saponite (stevensite), and serpentine. These minerals occur both as alteration products after mafic volcanics and ultramafic protoliths and, except serpentine, as hydrothermal vein and seafloor mound-like precipitates associated with variable amounts of (Ca, Mg, Fe)-carbonates, quartz and Fe and Cu (Co, Ni) sulfides. Brecciated mafic lithologies underwent pervasive chloritization, while interlayered gabbro sills underwent partial alteration to chlorite + illite ± actinolite ± saponite ± talc-bearing assemblages and later localized deeper alteration to chlorite ± saponite. Ultramafic and mixed ultramafic–mafic breccias were altered to talc-rich rocks with variable amounts of chlorite, carbonate and quartz. Chloritization, locally accompanied by formation of disseminated sulfides, required a high contribution of Mg-rich seawater to the hydrothermal fluid, which could be achieved in a highly permeable, breccia-dominated seafloor. More evolved hydrothermal fluids produced addition of silica, carbonates and further sulfides, and led to local development of saponite after chlorite and widespread replacement of serpentine by talc. The Ivanovka deposit shows many similarities with active and fossil hydrothermal sites on some modern oceanic spreading centers characterized by highly permeable upflow zones. However, given the arc signature of the ore host rocks, the most probable setting for the observed alteration–mineralization patterns is in an early-arc or forearc seafloor–subseafloor environment, characterized by the presence of abundant mafic–ultramafic breccias of tectonic and/or sedimentary origin.
Transverse ridges are elongate reliefs running parallel and adjacent to transform/fracture zones offsetting mid-ocean ridges. A major transverse ridge runs adjacent to the Vema transform (Central ...Atlantic), that offsets the Mid-Atlantic Ridge by 320 km. Multibeam morphobathymetric coverage of the entire Vema Transverse ridge shows it is an elongated (300 km), narrow (<30 km at the base) relief that constitutes a topographic anomaly rising up to 4 km above the predicted thermal contraction level. Morphology and lithology suggest that the Vema Transverse ridge is an uplifted sliver of oceanic lithosphere. Topographic and lithological asymmetry indicate that the transverse ridge was formed by flexure of a lithospheric sliver, uncoupled on its northern side by the transform fault. The transverse ridge can be subdivided in segments bound by topographic discontinuities that are probably fault-controlled, suggesting some differential uplift and/or tilting of the different segments. Two of the segments are capped by shallow water carbonate platforms, that formed about 3-4 m.y. ago, at which time the crust of the transverse ridge was close to sea level. Sampling by submersible and dredging indicates that a relatively undisturbed section of oceanic lithosphere is exposed on the northern slope of the transverse ridge. Preliminary studies of mantle-derived ultramafic rocks from this section suggest temporal variations in mantle composition. An inactive fracture zone scarp (Lema fracture zone) was mapped south of the Vema Transverse ridge. Based on morphology, a fossil RTI was identified about 80 km west of the presently active RTI, suggesting that a ridge jump might have occurred about 2.2 m.a. Most probable causes for the formation of the Vema Transverse ridge are vertical motions of lithospheric slivers due to small changes in the direction of spreading of the plates bordering the Vema Fracture Zone.PUBLICATION ABSTRACT
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