Jerzy S. Blusztajn

The fingerprint of seawater circulation in a 500-meter section of ocean crust gabbros

A novel strip-sampling technique has been applied to the 500-m gabbroic section drilled at site 735 during Leg 118. Twenty-two continuous strips of 1.1- to 4.5-m length were cut longitudinally from the core, allowing for a more representative sampling of this section of the deep ocean crust. A full suite of trace element and isotopic (Sr, Nd, Pb, Os, δ18O) analyses were conducted on these strip samples; for comparison, analyses were conducted on a small suite of protolith samples, selected for their fresh and unaltered appearance. Amphibole, diopside, and plagioclase from 18 vein samples were also analyzed for Sr and Nd isotopes. Although the evidence for a seawater component in these gabbros is clear (87/86 Sr up to 0.70316; 206/204 Pb up to 19.3; δ18O down to 2.0‰; 187/188 Os up to 0.44), the trace element signatures are dominated by magmatic effects (infiltration and impregnation by late-stage melts derived locally or from deeper levels of the crust). The average upper 500 m 735B gabbro section is somewhat lower than average N-MORB in trace elements such as Ba (30%), Nb (50%), U (40%), and heavy REE (Yb and Lu, 30%), but somewhat enriched in others such as La (23%), Ce (24%), Pb (23%), and Sr (40%). Although the section is largely comprised of cumulate gabbros (Natland et al., 1991), and many of the strip samples show marked Sr and Eu anomalies (plagioclase cumulation), the average composition of the total 500 m section shows no Sr or Eu anomalies (<1%). This implies that there has been local separation of melt and solids, but no large scale removal of melts from this 500-m gabbro section.

The return of subducted continental crust in Samoan lavas

Substantial quantities of terrigenous sediments are known to enter the mantle at subduction zones, but little is known about their fate in the mantle. Subducted sediment may be entrained in buoyantly upwelling plumes and returned to the Earth’s surface at hotspots, but the proportion of recycled sediment in the mantle is small, and clear examples of recycled sediment in hotspot lavas are rare. Here we report remarkably enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures in Samoan lavas from three dredge locations on the underwater flanks of Savai’i island, Western Samoa. The submarine Savai’i lavas represent the most extreme 87Sr/86Sr isotope compositions reported for ocean island basalts to date. The data are consistent with the presence of a recycled sediment component (with a composition similar to the upper continental crust) in the Samoan mantle. Trace-element data show affinities similar to those of the upper continental crust—including exceptionally low Ce/Pb and Nb/U ratios—that complement the enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures. The geochemical evidence from these Samoan lavas significantly redefines the composition of the EM2 (enriched mantle 2; ref. 9) mantle endmember, and points to the presence of an ancient recycled upper continental crust component in the Samoan mantle plume.

Erosional response of South China to arc rifting and monsoonal strengthening; a record from the South China Sea

Abstract Ocean Drilling Program sampling of the distal passive margin of South China at Sites 1147 and 1148 has yielded clay-rich hemipelagic sediments dating to 32 Ma (Oligocene), just prior to the onset of seafloor spreading in the South China Sea. The location of the drill sites offshore the Pearl River suggests that this river, or its predecessor, may have been the source of the sediment in the basin, which accounts for only ∼1.8% of the total Neogene sediment in the Asian marginal seas. A mean erosion depth of ∼1 km over the current Pearl River drainage basin is sufficient to account for the sediment volume on the margin. Two-dimensional backstripping of across-margin seismic profiles shows that sedimentation rates peaked during the middle Miocene (11–16 Ma) and the Pleistocene (since 1.8 Ma). Nd isotopic analysis of clays yielded ϵNd values of −7.7 to −11.0, consistent with the South China Block being the major source of sediment. More positive ϵNd values during and shortly after rifting compared to later sedimentation reflect preferential erosion at that time of more juvenile continental arc rocks exposed along the margin. As the drainage basin developed and erosion shifted from within the rift to the continental interior ϵNd values became more negative. A rapid change in the clay mineralogy from smectite-dominated to illite-dominated at ∼15.5 Ma, synchronous with middle Miocene rapid sedimentation, mostly reflects a change to a wetter, more erosive climate. Evidence that the elevation of the Tibetan Plateau and erosion in the western Himalaya both peaked close to this time supports the suggestion that the Asian monsoon became much more intense at that time, much earlier than the 8.5 Ma age commonly accepted.

Large‐scale drainage capture and surface uplift in eastern Tibet–SW China before 24 Ma inferred from sediments of the Hanoi Basin, Vietnam

Current models of drainage evolution suggest that the non-dendritic patterns seen in rivers in SE Asia reflect progressive capture of headwaters away from the Red River during and as a result of surface uplift of Eastern Asia. Mass balancing of eroded and deposited rock volumes demonstrates that the Red River catchment must have been much larger in the past. In addition, the Nd isotope composition of sediments from the Hanoi Basin, Vietnam, interpreted as paleo-Red River sediments, shows rapid change during the Oligocene, before similar to 24 Ma. We interpret this change to reflect large-scale drainage capture away from the Red River, possibly involving loss of the middle Yangtze River. Reorganization was triggered by regional tilting of the region towards the east. This study constrains initial surface uplift in eastern Tibet and southwestern China to be no later than 24 Ma, well before major surface uplift and gorge incision after 13 Ma.

Evidence for the survival of the oldest terrestrial mantle reservoir

Helium is a powerful tracer of primitive material in Earth’s mantle. Extremely high 3He/4He ratios in some ocean-island basalts suggest the presence of relatively undegassed and undifferentiated material preserved in Earth’s mantle. However, terrestrial lavas with high 3He/4He ratios have never been observed to host the primitive lead-isotopic compositions that are required for an early (roughly 4.5 Gyr ago) formation age. Here we show that Cenozoic-era Baffin Island and West Greenland lavas, previously found to host the highest terrestrial-mantle 3He/4He ratios, exhibit primitive lead-isotope ratios that are consistent with an ancient mantle source age of 4.55–4.45 Gyr. The Baffin Island and West Greenland lavas also exhibit 143Nd/144Nd ratios similar to values recently proposed for an early-formed (roughly 4.5 Gyr ago) terrestrial mantle reservoir. The combined helium-, lead- and Nd-isotopic compositions in Baffin Island and West Greenland lavas therefore suggest that their source is the most ancient accessible reservoir in the Earth’s mantle, and it may be parental to all mantle reservoirs that give rise to modern volcanism.

Osmium–oxygen isotopic evidence for a recycled and strongly depleted component in the Iceland mantle plume

Abstract Highly magnesian lavas characterised by strong light rare earth element depletion are a feature of Theistareykir and the Reykjanes Peninsula of Iceland, which are marginal to the proposed axis of the mantle plume. These lavas define positive covariations between whole rock osmium and olivine oxygen isotope ratios ( 187 Os/ 188 Os=0.1269–0.1369; δ 18 O olivine =4.2–5.7‰) that extend the array defined by Hawaiian samples to more unradiogenic Os isotope ratios and lower δ 18 O. The Os–O variation is difficult to explain in terms of high level crustal assimilation of Icelandic crust, with the possible exception of a subset of large volume lava flows from Theistareykir. The strong coupling of Os and O isotopic compositions of the lavas in addition to large excesses in large ion lithophile elements (Rb, Ba, Sr), positive Eu anomalies, and deficiencies in Hf and Zr relative to the rare earth elements clearly distinguishes these recent picrites from mid-ocean ridge basalts. The Reykjanes and Theistareykir lavas appear to represent melting of a very ancient (Archaean) mantle source which has isotopic and elemental characteristics suggestive of recycled oceanic lithosphere. We suggest that tapping of the refractory and depleted part of such a mantle plume (i.e. low 187 Os/ 188 Os and δ 18 O) is only possible due to the fortuitous location of the Iceland plume beneath a spreading ridge, which permits more extensive melting than would occur in an intraplate setting (e.g. Hawaii).

Reorganization of the western Himalayan river system after five million years ago

Uplift of mountains driven by tectonic forces can influence regional climate as well as regional drainage patterns, which in turn control the discharge of eroded sediment to the ocean. But the nature of the interactions between tectonic forces, climate and drainage evolution remains contested. Here we reconstruct the erosional discharge from the Indus river over the past 30 million years using seismic reflection data obtained from drill core samples from the Arabian Sea and neodymium isotope data. We find that the source of the Indus sediments was dominated by erosion within and north of the Indus suture zone until five million years ago; after that, the river began to receive more erosional products from Himalayan sources. We propose that this change in the erosional pattern is caused by a rerouting of the major rivers of the Punjab into the Indus, which flowed east into the Ganges river before that time. Seismic reflection profiles from the Indus fan suggest high mass accumulation rates during the Pleistocene epoch partly driven by increased drainage to the Indus river after five million years ago and partly by faster erosion linked to a stronger monsoon over the past four million years. Our isotope stratigraphy for the Indus fan provides strong evidence for a significant change in the geometry of western Himalayan river systems in the recent geologic past.

Testosterone administration inhibits hepcidin transcription and is associated with increased iron incorporation into red blood cells

Testosterone administration increases hemoglobin levels and has been used to treat anemia of chronic disease. Erythrocytosis is the most frequent adverse event associated with testosterone therapy of hypogonadal men, especially older men. However, the mechanisms by which testosterone increases hemoglobin remain unknown. Testosterone administration in male and female mice was associated with a greater increase in hemoglobin and hematocrit, reticulocyte count, reticulocyte hemoglobin concentration, and serum iron and transferrin saturation than placebo. Testosterone downregulated hepatic hepcidin mRNA expression, upregulated renal erythropoietin mRNA expression, and increased erythropoietin levels. Testosterone‐induced suppression of hepcidin expression was independent of its effects on erythropoietin or hypoxia‐sensing mechanisms. Transgenic mice with liver‐specific constitutive hepcidin over‐expression failed to exhibit the expected increase in hemoglobin in response to testosterone administration. Testosterone upregulated splenic ferroportin expression and reduced iron retention in spleen. After intravenous administration of transferrin‐bound 58Fe, the amount of 58Fe incorporated into red blood cells was significantly greater in testosterone‐treated mice than in placebo‐treated mice. Serum from testosterone‐treated mice stimulated hemoglobin synthesis in K562 erythroleukemia cells more than that from vehicle‐treated mice. Testosterone administration promoted the association of androgen receptor (AR) with Smad1 and Smad4 to reduce their binding to bone morphogenetic protein (BMP)‐response elements in hepcidin promoter in the liver. Ectopic expression of AR in hepatocytes suppressed hepcidin transcription; this effect was blocked dose‐dependently by AR antagonist flutamide. Testosterone did not affect hepcidin mRNA stability. In conclusion, testosterone inhibits hepcidin transcription through its interaction with BMP/Smad signaling. Testosterone administration is associated with increased iron incorporation into red blood cells.

Hobbs Coast Cenozoic volcanism: Implications for the West Antarctic rift system

Abstract Basaltic lavas were erupted from a 40-km-long lineament near the Hobbs Coast of Marie Byrd Land, Antarctica, over the period from 11.7 m.y. to 2.3 m.y. ago. The lavas from the southernmost locality, Coleman Nunatak, are virtually constant in major, trace element and isotopic composition over this entire age span. Their high FeO-low Al203 character indicates melting of garnet peridotite at about 140 km depth. There is no evidence for the involvement of ancient continental lithosphere or MORB asthenosphere in the magmatism. Isotopically, the lavas show the highest 206 Pb/ 204Pb ratios (up to 20.7) of any of the Cenozoic volcanism associated with the West Antarctic rift system (WARS). This HIMU isotopic signature is also clear in the trace element patterns, which closely mimic end-member HIMU basalts from the oceanic islands of Tubuai and Mangaia. From the other localities along the Hobbs Lineament, the earliest volcanism, which is coeval with that at Coleman Nunatak, is of shallower derivation (∼ 110 km), and isotopically like the oceanic FOZO end-member (206Pb/204Pb ∼19.5). The trace-element patterns are similar to those at Coleman, but less enriched in the most incompatible elements by a factor of two. Modeling of the trace element data is consistent with a uniform mantle source composition, depleted in major elements, but hydrous and mildly enriched in the incompatible and LREE. Inversion for the bulk distribution coefficients of the source mantle reveals a spidergram with a marked negative Ti anomaly and marked positive anomalies for K, Sr, Zr and HE From this modeling, the extent of melting at Coleman is inferred to be ∼ 1.6%, as compared to ∼ 3.2% during the earliest volcanism elsewhere on the lineament. With time, the volcanism from these other localities progresses to greater depth, becomes more HIMU in character, and lower in extent of melting (i.e., approaches the character of basalts from the Coleman locality). The FOZO component is prevalent as a mixing end-member in WARS volcanism from numerous other Marie Byrd Land (MBL) and Northern Victoria Land (NVL) localities. It is also the main constituent of the three nearby oceanic plumes (Balleny, Scott, Peter I islands). The HIMU component is at best a minor constituent of these oceanic plumes, but is present at several other MBL and NVL localities, as well as in pieces of Zealandia which were adjacent to this coast of Antarctica prior to fragmentation of Gondwana. We propose that this HIMU mantle source was emplaced under Gondwana lithosphere prior to breakup, as a large weak plume head, with little or no accompanying volcanism. This ‘fossil-plume’ proto-lithosphere is now being sampled during WARS extension. Likely mechanisms for the volcanism relate either to small-scale convection associated with strong basal topography of the lithosphere (such as that recorded by the Hobbs Lineament volcanism), or to emplacement of a new plume, which may in part be driving the extension.

Nd and Pb isotope variability in the Indus River System: implications for sediment provenance and crustal heterogeneity in the Western Himalaya

Abstract The Indus River system is the only major drainage system in the western Himalaya, and erodes not only the High Himalaya, but also topographically high regions within and north of the Indus Suture Zone, most notably the Karakoram. Ion microprobe analysis of Pb isotopes in detrital K-feldspar grains taken from the tributaries of the Indus, together with bulk Nd isotope analysis of those same sediments, is here used to identify distinct sediment source regions. These span the very radiogenic Nanga Parbat and associated Lesser Himalaya, the relatively radiogenic-intermediate High Himalaya, the unradiogenic Ladakh and Kohistan Batholiths and intermediate values in the Hindu Kush, Karakoram and Lhasa Block. The range of compositions reflects differing degrees of recycling of older continental crust during petrogenesis. K-feldspars from the Ladakh and Kohistan Batholiths are less radiogenic than the laterally equivalent Gangdese granite of Tibet, interpreted to reflect the preferential recycling of accreted oceanic arc units within the western Transhimalaya prior to India–Asia collision. Similarly the Zanskar High Himalaya are less radiogenic than their equivalents in Nepal. Isotope values from Pleistocene Indus Fan sediment are compatible with a dominant source in the Karakoram, with additional important contributions from the arc batholiths and High Himalaya, reflecting both the area and modern rates of tectonic uplift within the drainage basin. In contrast, radiogenic grains are common in the lower reaches of the modern Indus River, possibly as a result of the damming of the main river channel where it reaches the foreland.