Geochemistry and tectonic significance of lherzolites from New Caledonia Ophiolite

The association of rocks with contrasting geodynamic affinities is a quite common feature in ophiolites and it has been documented in several ophiolitic complexes, such as Pindos (Greece), and Lycian and Antalya ophiolites (Turkey) (Saccani & Photiades, 2004; Aldanmaz et al., 2009). New Caledonia hosts one of the World’s largest ultramafic terrane termed “Peridotite Nappe” belonging to an “atypical” ophiolitic sequence of presumed Late Cretaceous- Early Eocene age. It is dominated by mantle lithologies, mostly harzburgite and minor spinel and plagioclase lherzolite, together with some mafic and ultramafic cumulates. Despite their ultra-depleted nature, some efforts were devoted to characterize the mantle rocks from a geochemical point of view. A supra-subduction affinity is generally accepted for harzburgites (Marchesi et al., 2009; Ulrich et al., 2010); in contrast, the origin and evolution of lherzolites still remain a matter of debate. This presentation will focus on the petrological and geochemical characterization of the lherzolitic rocks. Lherzolites are mainly found in northern massifs, where spinel lherzolites extensively crop out in association with minor plagioclase lherzolites. These rocks are low-strain porphyroclastic tectonites, locally grading into protomylonite. They likely record an asthenospheric HT origin followed by sub-solidus re-equilibration, which is also testified by geothermometric estimates (870-1080°C and 830-980°C for porphyroclastic assemblages and recrystallization in the spinel facies, respectively). Spinel lherzolites are relatively undepleted, as attested by the presence of 7-8 vol% of Na and Al-rich clinopyroxene (up to 0.8 wt% Na2O; 3.1-6.7 wt% Al2O3), low Fo in olivine (88.5-90.0 mol%) and Cr# in spinel ([100 • Cr/(Cr+Al)]= 13-17). Major element mineral compositions (e.g. Mg# (Ol) vs Cr# (Spl), Cr# (Spl) vs Mg# (Spl)) coupled with Cpx and whole-rock REE geochemistry show that the lherzolites are akin to abyssal peridotites. In particular, the spinel lherzolites have REE patterns characterized by MREE and HREE enrichment over LREE (NdN/SmN = 0.18-0.27, NdN/YbN = 0.02-0.70) for YbN = 1.0-1.3. The REE patterns of clinopyroxenes have strong LREE depletion (NdN/YbN= 0.001-0.05) and nearly flat HREE segments for YbN = 5.5-5.9. Melting modelling based on REE compositions of Cpx and whole-rock indicate that HREE patterns can be explained by 8-10% fractional melting of a DMM source in the spinel stability field. However, slight MREE/HREE fractionation suggest that melting may have initiated at higher pressure, in the garnet stability field. Whole-rock Nd isotope ratios (Nd = 6.98-11.86) also suggest derivation from a relatively homogenous MORB-type depleted mantle that experienced a recent depletion event, leading to variable 147Sm/144Nd ratios. The aforementioned features point out an origin in a spreading ridge environment, probably related to pre-Early Eocene marginal basin development within the Southeast Gondwana margin

Geochemical and Sr‐Nd Pb isotope investigation of the New Caledonia peridotite nappe: unravelling the history of a poorly known mantle section"

The New Caledonia ophiolite hosts one of the largest and best preserved mantle sections in the world, offering a unique insight into upper mantle processes. Mantle lithologies are dominated by harzburgites, with minor lherzolites, and are locally capped by a mafic-ultramafic intrusive sequence. Although the New Caledonia ophiolite has been the subject of several petrological and geochemical investigations starting from the 1980s (e.g. Prinzhofer et al., 1980; Dupuy et al., 1981), its ultra-depleted nature prevented an adequate geochemical characterisation for long time. However, a renewed phase of interest has recently led to the publication of new works, thereby improving considerably our knowledge on the Peridotite Nappe (Marchesi et al., 2009; Ulrich et al., 2010; Pirard et al., 2013; Secchiari et al., 2016, 2018, submit.). This contribution results from a 5 year lasting collaboration among Montpellier, Parma and New Caledonia Universities. Here we present a comprehensive petrological and geochemical dataset obtained on fresh or little serpentinized peridotites. Spinel lherzolites are slightly depleted rocks, as attested by the presence of 7- 8 vol.% of clinopyroxene, moderate Fo content of olivine (88.5-90.0 mol.%) and low Cr# of spinel (13-17). The harzburgites exhibit a highly refractory character, testified by the notable absence of primary clinopyroxene, high Fo content of olivine (90.9-92.9 mol.%), high Mg# of orthopyroxene (89.8-94.2) and high Cr# of spinel (44-71). Mineral compositional variations and REE geochemistry indicate abyssal-type and supra-subduction zone affinity for lherzolites and harzburgites, respectively. Melting models show that the lherzolites underwent 8-9% degrees of fractional melting of a DMM source, starting in the garnet field. By contrast, the harzburgites record exceedingly high melting degrees (i.e. 15% degree of dry melting and up to 18% degree of hydrous melting). On the other hand, concomitant enrichments in FME, L-MREE and Zr-Hf were likely inherited during interaction with slab-derived silicate-bearing fluids, as supported by the frequent occurrence of secondary interstitial Al2O3, CaO and Cr2O3-poor orthopyroxene and Na2O, Al2O3, TiO2-poor clinopyroxene. Nd isotopes are in the range of the DMM for the lherzolites (+6.98≤εNdi≤+10.97). For the harzburgites, heterogeneous Nd isotopic ratios (-0.80≤εNdi≤+13.32) coupled with Pb isotopes, trending from DMM toward sediment-like compositions, support a derivation from a DMM reservoir variably modified by subduction fluids. The geochemical features of the lherzolites suggest an origin in a MOR setting, i.e. in a marginal basin formed before Eocene subduction. Conversely, the geochemical signature shown by the harzburgites reflects the evolution of a highly depleted fore-arc mantle wedge contaminated by fluid inputs in the subduction zone. Based on our data, a possible genetic link among the peridotites remains difficult to establish

Melt extraction and enrichment processes in the New Caledonia lherzolites: evidence from geochemical and Sr-Nd isotope data

In this study, a comprehensive geochemical data set (major, trace elements and Sr-Nd isotopes) is used to constrain the mantle evolution of the Iherzolites and their relationships with the basalts from the Poya Terrane, which tectonically underlies the mantle rocks. The majority, of the lherzolites are low-strain porphyroclastic tectonites. They likely record an asthenospheric origin followed by re-equilibration at lithospheric conditions, as supported by geothermometric estimates (T = 1100-940 degrees C and 920-890 degrees C for porphyroclastic and neoblastic spinel-facies assemblages, respectively). Olivine composition (Fo = 88.5-90.0 mol%), spinel Cr# ([molar 100 center dot Cr/(Cr + Al)] = 13-17) and relatively high amounts (7-8 vol%) of Al2O3- and Na2O-rich clinopyroxene (up to 0.5 and 6.5 wt.%, respectively) indicate a moderately depleted geochemical signature for the spinel lherzolites. Bulk rock and clinopyroxene rare earth elements (REE) patterns display a typical abyssal-type signature, i.e. steeply plunging LREE accompanied by nearly flat HREE to MREE. Clinopyroxene REE compositions of the spinel lherzolites may be reproduced by small amounts of fractional melting of a garnet lherzolite precursor (similar to 4%), followed by 4%-5% melting in the spinel peridotite field. The plagioclase lherzolites show melt impregnation microstructures, Cr- and Ti-rich spinels and incompatible trace element enrichments (REE, Ti, Y, and Zr) in bulk rocks and clinopyroxenes. Impregnation modelling for these elements suggests that the plagioclase lherzolites originated from residual spinel lherzolites by entrapment of highly depleted (non-aggregated) MORB melt fractions in the shallow oceanic lithosphere. Nd isotope compositions of the investigated peridotites are consistent with derivation from an asthenospheric mantle source that experienced a recent MORB-producing depletion event. This evolution was most likely accomplished in a spreading ridge. However, geochemical trace element modelling and Nd isotopes do not support a genetic mantle-crust link between the lherzolites and enriched-MOR-type basalts from the Poya Terrane

The New Caledonia mantle section: tracking source depletion and contamination processes in a supra-subduction setting

The New Caledonia Ophiolite (NCO) hosts one of the largest obducted mantle sections worldwide, offering a unique opportunity to investigate key mantle processes. The ophiolite includes refractory harzburgites, locally overlain by mafic-ultramafic cumulates, and minor lherzolites. Here we present the results of our recent geochemical and Sr-Nd-Pb isotopic studies on fresh or slightly serpentinized peridotites. The lherzolites display a moderately depleted, abyssal-type signature which may be reproduced by small amounts of fractional melting of a garnet lherzolite precursor (~4%), followed by 4%–5% melting in the spinel peridotite field. Nd isotope compositions are consistent with derivation from an asthenospheric mantle source that experienced a recent MORB-producing depletion event. The harzburgites are Cpxfree highly refractory rocks characterised by remarkably low REE concentrations (<0.1xCh) and "U-shaped" REE profiles. HREE composition can be reproduced by a first phase of melt depletion in dry conditions (15% fractional melting), followed by hydrous melting in a subduction zone setting (up to 15%-18%). Nd isotopic ratios range from unradiogenic to radiogenic and negatively correlate with Sr isotopes. Pb isotopes cover a wide range, trending from DMM toward enriched, sediment-like, compositions. Enrichment in FME, LREE-MREE and Nb, Zr, Hf, coupled with the presence of secondary interstitial phases, may be explained by syn- and post-melting interactions with different subduction-related components. Contamination may have occurred both as result of fluid influx from the subducted slab and through subsequent interaction with subduction-related melts carrying a component of sedimentary origin. A recent HSE and Os isotope study [1] provides additional insights on the evolution of the NCO mantle section

Origin of the spinel-pyroxene symplectites in the harzburgites from the New Caledonia Peridotite

The New Caledonia ophiolite (Peridotite Nappe) hosts one of the largest and best-exposed mantle section worldwide, providing an exceptional insight into upper mantle processes. The Peridotite Nappe is mostly dominated by harzburgites, locally overlain by mafic-ultramafic cumulates, but also includes minor spine! and plagioclase lherzolites, cropping out in the northern part of the island. The New Caledonia harzburgites are low-strain tectonites, showing dominant porphyroclastic textures. The main mantle paragenesis is constituted by olivine (similar to 75-85 vol%), orthopymxene (similar to 15-25 vol%) and spinel (< I vol%), while primary clinopyroxene is notably absent. An important textural feature of these mantle rocks is represented by the common occurrence of spinel-pymxene symplectitic aggregates. In this work, we present a petrographical, textural and major element chemical characterization of the spinel-pyroxene symplectitic intergrowths occurring in the New Caledonia harzburgites (Kopeto, central massif, and Yare, Massif du Sud). Based on textures, size and relationships with the other mineral phases, these spinel-pymxene clusters have been divided into two types, named type-A and type-B. Type-A symplectites occur in the Kopeto harzburgites and are composed of spinel-orthopyroxene clinopyroxene) intergrowths. In type-A symplectites, symplectitic spinel (Sp12) occurs as abundant vermicular shaped grains, ranging in size from similar to 0.5 to 2 mm. By contrast. spinet of the porphyroclastic assemblage (Spl 1) shows smaller size (in the range of few }un) and notably lower abundances (< 1%). Type-A symplectites develop exclusively on porphyroclastic olivine, which in turn displays evidence of chemical disequilibrium and corroded outlines. Bulk major element compositions reconstructed for type-A symplectites rule out a derivation from a pre-existing garnet phase, as the model garnet compositions do not satisfy garnet stoichiometry, being characterized by Si deficiency. By contrast, major element chemical variations of the symplectitic phases, coupled with the high abundance of Sp12 and olivine resorption, suggest an origin from reactive percolation of opx-saturated hydrous melts or slab-derived fluids in a subduction zone setting. Type-B symplectites are found in Yate sample and consist of spinel-orthopyroxene (+/- clinopyroxene). They are characterized by smaller size (few hundreds of gm, i.e. "micro-symplectites") and different shapes compared to type-A symplectites, growing as vermicular, "myrmekite-like" intergrowths at the rims of porphyroclastic orthopyroxene. Major element chemical compositions of type-B symplectites are consistent with an origin as "cooling textures". These structures may derive from unmixing of a high-T, Al-Cr rich, orthopymxene due to the decreased solubility of the Cr-Al component (CrMgTs) during post-melting lithospheric cooling at T < 900 degrees C

Lower Extremity Muscle Strength and Risk of Self-Reported Hip or Knee Osteoarthritis

Purpose: The purpose of this study was to investigate the gender-specific longitudinal association between quadriceps strength and self-reported, physician-diagnosed hip or knee osteoarthritis (OA). Methods: Subjects were 3081 community-dwelling adults who were free of OA, joint symptoms and injuries, completed a maximum treadmill exercise test, had isokinetic knee extension and flexion and isotonic leg press strength measurements taken at baseline and returned at least one written follow-up survey. Multivariate logistic regression was used to estimate odds ratios and 95% confidence intervals. Results: Women with moderate or high isokinetic quadriceps strength had a significantly reduced risk (55% to 64%) of hip or knee OA. A similar, nonsignificant trend was noted among men. Moderate isotonic leg press strength was protective for hip or knee osteoarthritis among men only. Conclusions: These results suggest that quadriceps weakness is an independent and modifiable risk factor for lower extremity OA, particularly among women

The role of bacterial colonization of the suture thread in early identification and targeted antibiotic treatment of surgical site infections: A prospective cohort study

Background: The aim of the present study is to investigate the role of the colonization of suture thread to identify patients at risk of developing a surgical site infection (SSI) after clean surgical procedures. Methods: Patients who underwent elective clean surgery procedures at the Surgery Unit of the AOU-University of Campania Luigi Vanvitelli in a 21-month period were prospectively enrolled. For each patient, a synthetic absorbable thread in Lactomer 9-1 was inserted into the surgical site at the end of surgery and microbiologically evaluated after 48 h. Antibiotic prophylaxis was chosen according to international guidelines. Results: A total of 238 patients were enrolled; 208 (87.4%) of them were subjected to clean procedures without the placement of prosthesis, and 30 (12.6%) with prosthesis. Of the 238 patients, 117 (49.2%) underwent an antimicrobial prophylaxis. Overall, 79 (33.2%) patients showed a bacterial colonization of the thread: among the 208 without the implantation of prosthesis, 19 (21.8%) of the 87 with antibiotic prophylaxis and in 58 (47.9%) of the 121 without it; among the 30 patients with the implantation of prosthesis, only two patients showed a colonized thread. The patients with antibiotic prophylaxis developed a colonization of the thread less frequently than those without it (17.9% vs. 47.9%, p < 0.001). SSI was observed in six (2.5%) patients, all of them showing a colonized thread (7.6% vs. 0%, p < 0.001). The bacteria identified in colonized threads were the same as those found in SSIs. Conclusions: Our study presents a new method that is able to precociously assess patients who have undergone clean procedures who may develop SSI, and identify the microorganism involved

Prevalence of Physical Activity in the United States: Behavioral Risk Factor Surveillance System, 2001

INTRODUCTION: The health benefits of regular cardiovascular exercise are well-known. Such exercise, however, has traditionally been defined as vigorous physical activity, such as jogging, swimming, or aerobic dance. Exercise of moderate intensity also promotes health, and many U.S. adults may be experiencing the health benefits of exercise through lifestyle activities of moderate intensity, such as yard work, housework, or walking for transportation. Until recently, public health surveillance systems have not included assessments of this type of physical activity, focusing on exercise of vigorous intensity. We used an enhanced surveillance tool to describe the prevalence and amount of both moderate-intensity and vigorous-intensity physical activity among U.S. adults. METHODS: We analyzed data from the 2001 Behavioral Risk Factor Surveillance System, a state-based, random-digit–dialed telephone survey administered to U.S. adults aged 18 years and older (n = 82,834 men and 120,286 women). Physical activity behavior was assessed using questions designed to quantify the frequency of participation in moderate- or vigorous-intensity physical activities performed during leisure time or for household chores and transportation. RESULTS: Overall, 45% of adults (48% of men and 43% of women) were active at recommended levels during nonworking hours (at least 30 minutes five or more days per week in moderate-intensity activities, equivalent to brisk walking, or at least 20 minutes three or more days per week in vigorous activities, equivalent to running, heavy yard work, or aerobic dance). Less than 16% of adults (15% of men and 17% of women) reported no moderate or vigorous activity in a usual week. CONCLUSION: Integrating surveillance of lifestyle activities into national systems is possible, and doing so may provide a more accurate representation of the prevalence of recommended levels of physical activity. These results, however, suggest that the majority of U.S. adults are not active at levels associated with the promotion and maintenance of health