Expedition 376 summary

Volcanic arcs are the surface expression of magmatic systems that result from subduction of mostly oceanic lithosphere at convergent plate boundaries. Arcs with a submarine component include intraoceanic arcs and island arcs that span almost 22,000 km on Earth’s surface, and the vast majority of them are located in the Pacific region. Hydrothermal systems hosted by submarine arc volcanoes commonly contain a large component of magmatic fluid. This magmatic-hydrothermal signature, coupled with the shallow water depths of arc volcanoes and their high volatile contents, strongly influences the chemistry of the fluids and resulting mineralization and likely has important consequences for the biota associated with these systems. The high metal content and very acidic fluids in these hydrothermal systems are thought to be important analogs to numerous porphyry copper and epithermal gold deposits mined today on land. During International Ocean Discovery Program (IODP) Expedition 376 (5 May–5 July 2018), a series of five sites was drilled on Brothers volcano in the Kermadec arc. The expedition was designed to provide the missing link (i.e., the third dimension) in our understanding of hydrothermal activity and mineral deposit formation at submarine arc volcanoes and the relationship between the discharge of magmatic fluids and the deep biosphere. Brothers volcano hosts two active and distinct hydrothermal systems: one is seawater influenced and the other is affected by magmatic fluids (largely gases). In total, 222.4 m of volcaniclastics and lavas were recovered from the five sites drilled, which include Sites U1527 and U1530 in the Northwest (NW) Caldera seawater-influenced hydrothermal field; Sites U1528 and U1531 in the magmatic fluid-influenced hydrothermal fields of the Upper and Lower Cones, respectively; and Site U1529, located within an area of low crustal magnetization that marks the West (W) Caldera upflow zone on the caldera floor. Downhole logging and borehole fluid sampling were completed at two sites, and two tests of a prototype turbine-driven coring system (designed by the Center for Deep Earth Exploration [CDEX] at Japan Agency for Marine-Earth Science and Technology [JAMSTEC]) for drilling and coring hard rocks were conducted. Core recovered from all five sites consists of dacitic volcaniclastics and lava flows with only limited chemical variability relative to the overall range in composition of dacites in the Kermadec arc. Pervasive alteration with complex and variable mineral assemblages attest to a highly dynamic hydrothermal system. The upper parts of several drill holes at the NW Caldera hydrothermal field are characterized by secondary mineral assemblages of goethite + opal + zeolites that result from low-temperature (<150°C) reaction of rock with seawater. At depth, NW Caldera Site U1527 exhibits a higher temperature (~250°C) secondary mineral assemblage dominated by chlorite + quartz + illite + pyrite. An older mineral assemblage dominated by diaspore + quartz + pyrophyllite + rutile at the bottom of Hole U1530A is indicative of acidic fluids with temperatures of ~230°–320°C. In contrast, the alteration assemblage at Site U1528 on the Upper Cone is dominated by illite + natroalunite + pyrophyllite + quartz + opal + pyrite, which attests to high-temperature reaction of rocks with acid-sulfate fluids derived from degassed magmatic volatiles and the disproportionation of magmatic SO2. These intensely altered rocks exhibit extreme depletion of major cation oxides, such as MgO, K2O, CaO, MnO, and Na2O. Furthermore, very acidic (as low as pH 1.8), relatively hot (≤236°C) fluids collected at 160, 279, and 313 meters below seafloor in Hole U1528D have chemical compositions indicative of magmatic gas input. In addition, preliminary fluid inclusion data provide evidence for involvement of two distinct fluids: phase-separated (modified) seawater and a ~360°C hypersaline brine, which alters the volcanic rock and potentially transports metals in the system. The material and data recovered during Expedition 376 provide new stratigraphic, lithologic, and geochemical constraints on the development and evolution of Brothers volcano and its hydrothermal systems. Insights into the consequences of the different types of fluid–rock reactions for the microbiological ecosystem elucidated by drilling at Brothers volcano await shore-based studies

Semi-groupe de Lie associé à un cône symétrique

Volcanic arcs are the surface expression of magmatic systems that result from the subduction of mostly oceanic lithosphere at convergent plate boundaries. Arcs with a submarine component include intraoceanic arcs and island arcs that span almost 22,000 km on Earth\u27s surface, the vast majority of which are located in the Pacific region. Hydrothermal systems hosted by submarine arc volcanoes commonly contain a large component of magmatic fluid. This magmatic-hydrothermal signature, coupled with the shallow water depths of arc volcanoes and their high volatile contents, strongly influences the chemistry of the fluids and resulting mineralization and likely has important consequences for the biota associated with these systems. The high metal contents and very acidic fluids in these hydrothermal systems are thought to be important analogs to numerous porphyry copper and epithermal gold deposits mined today on land

STUDIES ON 2,122 CASES WITH HIGH BLOOD PRESSURE AMONG 14,102 PATIENTS TREATED IN TEACHING HOSPITALS ON ISFAHAN UNIVERSITY

Among 14,102 patients admitted in teaching hospitals of the Isfahan Medical School, whose records were studied, 2,122 or 15.4% of patients had high blood pressure. The most common reason for blood pressure in this group was diseases of the kidney and for those, glomerolonephritis and pilonephrititis were important causes. Among patients under 30 years old, high blood pressure was twice as common in men as in women, but no great difference was found among patients over 30 years old. The incidence of blood pressure had a direct relation with age. Illnesses encountered among patients with high blood pressure were, Diabetes in 12.9%, Hypercholesterolemia in 8.5%, Hyperuresemy in 11.0%, heritage factors in 10.7% use of alcohol in 5.1% and smoking in 61%. These conditions are more severe among younger patients and patients with higher diastolic blood pressure

Measurement of Volume Change and Mass Transfer During Serpentinization: Insights From the Oman Drilling Project

International audienceSerpentinization plays a key role on the evolution of the physicochemical properties of the mantle lithosphere. The rate of serpentinization reactions is controlled by the transport of fluid, which itself depends on volume change during reaction. Element transfer can strongly modify the magnitude and sign of volume change. Here, we measure solid volume change and element transport perpendicular to a serpentine vein in a serpentinized dunite collected at depth during the Oman Drilling Project. The sample is extensively replaced (extent of reaction > 80%) by a serpentine/brucite mixture parallel to a main serpentine vein network. The Mg content of serpentine and brucite indicates reaction with a small amount of fluid at temperatures below 100°C. Concentrations of fluid‐mobile trace elements (Na, Ca, Sr, Rb, and Ba) decrease perpendicular to the main vein. Primary olivine contains parallel platelets of a clinopyroxene/magnetite symplectite. Tomography at the nanoscale reveals that these inclusions do not react during serpentinization but are cracked and displaced. We use these inert markers to measure a 59% to 74% positive volume change that is close to the 52% expected for reaction in a closed system. Chemical data indicate no change in major element composition during reaction except for the addition of water. The initial olivine zoning in Al, Ti, V, Sc, and Cr is still preserved in serpentine and brucite. Serpentinization can thus be a local replacement process during which the solid volume homogeneously increases at the micrometer scale and the transport of aqueous species is limited