MORB

Center for Disease Control and Prevention (1999) Outbreak of Escherichia coli 0157 H7 and Camylobacter among attendees of the Washington County Fair - New York. Morb Mortal Wkly Rep 48 803-805... 

Centers for Disease Control and Prevention Gamma hydroxy butyrate use—New York and Texas, 1995-96. JAMA 277 1511, 1997 Centers for Disease Control and Prevention Adverse events associated with ingestion of gamma-butyrolactone—Minnesota, New Mexico, and Texas, 1998-1999. MMRW Morb Mortal Wkly Rep 48 137-140, 1999 Chatlos JC Recent trends and a developmental approach to substance abuse in adolescents. Child Adolesc Psychiatr Clin N Am 5 1-27, 1996... 

Centers for Disease Control and Prevention (CDC). Fatalities associated with ingestion of diethylene glycol-contaminated glycerin used to manufacture acetaminophen syrup—Haiti, November 1995-June 1996 MMWR Morb Mortal Wkly Rep 1996 45 649-50. 

Breese K, M Boll, J Alt-Morbe, H Schaggrer, G Fuchs (1998) Genes encoding the benzoyl-CoA pathways of anaerobic aromatic metabolism in the bacterium Thauera aromatica. Eur J Biochem 256 148-154. 

Honma et al. (1991) have shown that the Okinawa Trough basalts have significantly high K, Rb and Sr contents and D/H, 0/ 0 and Sr/ Sr ratios than N-Morb have and these are due to generation of magma from normal-type mantle peridotite modified by component from the subducted slab and crustal contamination. 

Fiji Transform Fault Extensional Relay Zone A (16°10 S, 177°25 E) 1869-2335 Short spreading ridge axis which displaces Fiji transform fault as interpreted by Jarvis et al. (1994). Hydrothermal sulfide impregnation in MORB-like ba.salt dredged from axial valley. M etite, pyrrhotite, chalcopyrite and opal on fracture surface. 

The flK-f of plagioclase from MORB is generally lower than that of back-arc basin igneous rocks. Therefore, the higher m +/mY + of midoceanic ridge fluids compared with back-arc basin fluids could be explained in terms of Na-feldspar/K-feldspar/hydro-thermal fluids equilibrium. 

Chemical composition of Kuroko ore and MORB (midoceanic ridge basalt) (logarithmic unit in wt%) (Shikazono, 1988)... 

Elements enriched into Ktrroko Elements enriched into MORB... 

Fig. 2.46. Frequency histogram for MgO/FeO ratios (in wt%) of chlorite from the Kuroko basalt (A) and MORE (B). Data sources are Shikazono et al. (1995), Humphris and Thompson (1978) (M Mid-Atlantic Ridge) and Kawahata (1984) (C Costa Rica Rift, Galapagos Spreading Centre). The data on chlorite from MORB are taken from typical metabasalt and not from quartz-chlorite breccia and veins which formed in a hydrothermal upflow zone(Shikazont) et al., 1995).

It is shown in Fig. 2.57 that the lead isotopic variation of the Besshi-subtype is similar to that of midoceanic ridge basalt, suggesting the lead in the Besshi-subtype was derived from mantle. The data from the Shimokawa, and Yanahara deposits (Group B) are slightly more radiogenic than Group A, suggesting that crustal lead was involved in the formation of the Shimokawa deposit, and lead isotopic values for the Shimokawa and Yanahara plot between MORB and Cretaceous-Tertiary deposits in Japan (Kuroko, skarn, vein-type deposits). 

Fig. 2.58. Relationships between esr and Nd the pillowed basalts. MORB and OIB indicate midoceanic...

Watanabe et al. (1993) indicated Nd and sr for the pillowed basalt plot within the OIB region, but very close to the MORB region (Fig. 2.58), assuming 130 Ma is the age of the original basalt lavas (Isozaki and Itaya, 1990). 

CDC (2008). Norovirus outbreak in an elementary school—District of Columbia, February 2007. MMWR Morb. Mortal. Wkly. Rep. 56,1340-1343. 

The same method was also applied to a few MORB from the Juan de Fuca - Gorda ridges on the EPR (Volpe and Goldstein 1993). 

OBSERVED U-SERIES DISEQUILIBRIA IN MORB 2.1. Analysis of U-series nuclides... 

Measurement of U-series disequilibria in MORB presents a considerable analytical challenge. Typical concentrations of normal MORB (NMORB) are variable but are generally in the 50-150 ppb U range and 100-400 ppb Th range. Some depleted MORB have concentrations as low as 8-20 ppb U and Th. The concentrations of °Th, Pa, and Ra in secular equilibrium with these U contents are exceedingly low. For instance, the atomic ratio of U to Ra in secular equilibrium is 2.5 x 10 with a quick rule of thumb being that 50 ng of U corresponds to 20 fg of Ra and 15 fg of Pa. Thus, dissolution of a gram of MORB still requires measurement of fg quantities of these nuclides by any mass spectrometric techniques. 

Other early alpha spectrometry studies examined U-series disequilibria in East Pacific Rise (EPR) samples. Newman et al. (1983) measured samples from the RISE study area (21°N EPR) finding significant variations in Th/U and ( °Th)/( U) (Fig. 2B). Rubin and Macdougall (1988) measured ( °Th)/( U) and ( Ra)/( °Th) for samples from both the northern ( 10-12°isn and southern (-20-25°) EPR (Fig. 2C,D). This study was first to document large disequilibria in young MORB and interpreted the... 

Applications dating of MORB nsing U-series diseqnilibria... 

Cl and Ba consistently argue that the U-series disequilibria in MORB do not reflect secondary contamination. One important check that all U-series studies of MORB routinely perform is analysis of ( " U)/( U). Since of seawater is well... 

Boron concentrations and isotopes are also useful geochemical tracers of contamination in MORB. Boron concentrations are low (<2 ppm) in unaltered ocean floor basalt but high in altered basalts (>8 ppm B) (Spivack and Edmond 1987 Ryan and Langmuir 1993). Goldstein et al. (1989) measured B concentrations in their samples and found them to be less than 1.6 ppm, inconsistent with contamination. More recently, B isotopes have been used to assess contamination since large differences in 5 B are known to exist between seawater, sediments, and unaltered MORB. Sims et al. (2002) reported that 6 B for their 9°N EPR samples were inconsistent with incorporation of any seawater or seawater-derived material. 

Because the concentration difference between MORB and hydrothermal chimney materials for both Ba and Ra is greater than lO , incorporation of small amounts of barite from hydrothermal systems could create the high ( Ra)/( °Th) observed in MORB. However, if Ra excess results from this process, then Ba concentrations (and Ba/Th) should be equally raised by such contamination. However, Ba/Th in highly depleted glasses from the Siquieros Transform that have ( Ra)/( °Th) greater than 3 are typical for MORB and do not have anomalously high Ba contents (Lundstrom et al. 1999). 

Although U-series disequilibria have been observed in MORB for over 20 years, consensus about how the disequilibria are generated by the melting process does not yet... 

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