Gallium, germanium, indium, and iridium in lunar samples

Neutron activation analyses of gallium, germanium, indium, and iridium in eight lunar samples and in meteorites and rocks (including four calciulnrich achondrites and five terrestrial basalts) with similar bulk compositions are reported. Lunar gallium concentrations are remarkably constant at about 5 parts per million, three times higher and four times lower than those in eucritic (calcium-rich) achondrites and terrestrial basalts, respectively. Lunar germanium concentrations range from 相似文献   

Red sea floor origin: rare-Earth evidence

Abundance patterns of rare earths of submarine tholeiitic basalts from the axial trough of the Red Sea resemble those of basalts from mid-ocean ridges but are distinct from shield or plateau basalts of tholeiitic composition. These results imply that à similar magmatic process, related to spreading of sea floors, operates beneath the axial trough of the Red Sea and the crest of mid-ocean ridges.     

Grain size--dependent alteration and the magnetization of oceanic basalts

Unblocking temperatures of natural remanent magnetization were found to extend well above the dominant Curie points in samples of oceanic basalts from the axis of the East Pacific Rise. This phenomenon is attributed to the natural presence in the basalts of three related magnetic phases: an abundant fine-grained and preferentially oxidized titanomagnetite that carries most of the natural remanent magnetism, a few coarser and less oxidized grains of titanomagnetite that account for most of the high-field magnetic properties, and a small contribution to both the natural remanent magnetism and high-field magnetic properties from magnetite that may be due to the disproportionation of the oxidized titanomagnetite under sea-floor conditions. This model is consistent with evidence from the Central Anomaly magnetic high that the original magnetization acquired by oceanic basalts upon cooling is rapidly altered and accounts for the lack of sensitivity of bulk rock magnetic parameters to the degree of alteration of the remanence carrier in oceanic basalts.     

Hotspots, basalts, and the evolution of the mantle

The trace element concentration patterns of continental and ocean island basalts and of mid-ocean ridge basalts are complementary. The relative sizes of the source regions for these fundamentally different basalt types can be estimated from the trace element enrichment-depletion patterns. Their combined volume occupies most of the mantle above the 670 kilometer discontinuity. The source regions separated as a result of early mantle differentiation and crystal fractionation from the resulting melt. The mid-ocean ridge basalts source evolved from an eclogite cumulate that lost its late-stage enriched fluids at various times to the shallower mantle and continental crust. The mid-ocean ridge basalts source is rich in garnet and clinopyroxene, whereas the continental and ocean island basalt source is a garnet peridotite that has experienced secondary enrichment. These relationships are consistent with the evolution of a terrestrial magma ocean.     

Basalts Dredged from the Northeastern Pacific Ocean

Volcanic rocks dredged from seamounts, fault ridges, and other major geological features of the northeast Pacific Ocean include a wide variety of basalts. Most of these are vesicular, porphyritic types with near analogues in the Hawaiian and other oceanic islands. In addition, aluminous basalts and diabasic theoleiites impoverished in potassium also occur. There is no simple correlation of composition, degree of oxidation, vesiculation, or hydration of these basalts with texture, or depth of dredge site. Most samples appear to have been extruded at much shallower depths than those now pertaining at the dredge site. The distribution of these basalts suggests that the andesite line coincides with or lies on the continent side of the foot of the continental slope.     

Production of isotopic variability in continental basalts by cryptic crustal contamination

Regional variations in the Nd, Sr, and Pb isotopic compositions of Neogene basalts from the western United States are commonly interpreted to originate in the subcontinental mantle. In southern California, isotopic variability is restricted to lavas that lack mantle-derived xenoliths; xenolith-bearing basalts have uniform isotopic compositions similar to those of ocean-island basalts (OIBs). Combined with available geochemical data, these observations suggest that isotopic variability at these volcanoes results from subtle crustal contamination, locally by mafic crust, of primitive OIB-like magma. Recognition of such cryptic contamination may help to reconcile local discrepancies between tectonic and isotopic views of the subcontinental mantle.     

The apollo 15 lunar samples: a preliminary description

Samples returned from the Apollo 15 site consist of mare basalts and breccias with a variety of premare igneous rocks. The mare basalts are from at least two different lava flows. The bulk chemical compositions and textures of these rocks confirm the previous conclusion that the lunar maria consist of a series of extrusive volcanic rocks that are rich in iron and poor in sodium. The breccias contain abundant clasts of anorthositic fragments along with clasts of basaltic rocks much richer in plagioclase than the mare basalts. These two rock types also occur as common components in soil samples from this site. The rocks and soils from both the front and mare region exhibit a variety of shock characteristics that can best be ascribed to ray material from the craters Aristillus or Autolycus.     

Primordial radioelements and cosmogenic radionuclides in lunar samples from apollo 15

Two basalts, two breccias, and two soils from Apollo 15 were analyzed by nondestructive gamma-ray spectrometry. The concentrations of potassium, thorium, and uranium in the basalts were similar to those in the Apollo 12 basalts, but the potassium: uranium ratios were somewhat higher. Primordial radioelements were enriched in the soils and breccia, consistent with a two-component mixture of mare basalt and up to 20 percent foreign component (KREEP). The abundance patterns for cosmogenic radionuclides implied surface sampling for all specimens. The galactic cosmic-ray production rate of vanadium-48 was determined as 57 +/- 11 disintegrations per minute per kilogram of iron. Cobalt-56 concentrations were used to estimate the intensity of the solar flare of 25 January 1971.     

Rubidium-strontium and potassium-argon age of lunar sample 15555

The lunar mare basalt 15555 from the edge of Hadley Rille has been dated at 3.3x10(9) years by both rubidium-strontium and potassium-argon techniques. Age and trace element abundances closely resemble those of the Apollo 12 mare basalts. Data from lunar basalts obtained thus far indicate that they cannot be derived by simple fractionation from a homogeneous source.     

The chlorine isotope composition of Earth's mantle

Chlorine stable isotope compositions (delta37Cl) of 22 mid-ocean ridge basalts (MORBs) correlate with Cl content. The high-delta37Cl, Cl-rich basalts are highly contaminated by Cl-rich materials (seawater, brines, or altered rocks). The low-delta37Cl, Cl-poor basalts approach the composition of uncontaminated, mantle-derived magmas. Thus, most or all oceanic lavas are contaminated to some extent during their emplacement. MORB-source mantle has delta37Cl 相似文献   

South american geochronology: radiometric time scale for middle to late tertiary mammal-bearing horizons in patagonia

Radiometric (potassium-argon) age determinations for basalts and tuffs associated with middle to late Tertiary mammal-bearing horizons in Patagonia, southern Argentina, permit refinement of boundaries and hiatuses between beds of Deseadan (early Oligocene) through Friasian (middle to late Miocene) age. At two localities beds of Deseadan age are overlain by basalts, which gave dates of 33.6 and 35.4 million years ago; 34.0 million years ago is tentatively accepted as a terminal date for known Deseadan. At several localities beds of Colhuehuapian age are underlain by basalts, which gave dates ranging from 28.8 to 24.3 million years ago; 25.0 million years is tentatively taken as a basal age for known Colhuehuapian. The paleontological hiatus between known Deseadan and known Colhuehuapian is thus in the order of 9.0 million years. Two tuffs from the Santa Cruz Formation (Santacrucian) gave ages of 21.7 and 18.5 million years. Plagioclase and biotite concentrates of an ignimbrite from the Collón Curá Formation (Friasian) gave ages ranging from 15.4 to 14.0 million years.     

Chemistry, geochronology, and petrogenesis of lunar sample 15555

Lunar sample 15555 is a mare type basalt generally similar in chemical composition to the Apollo 12 basalts. Sample 15555 is older than any Apollo 12 basalt but younger than the Apollo 14 basalts analyzed thus far.     

Argon-40: excess in submarine pillow basalts from kilauea volcano, hawaii

Submarine pillow basalts from Kilauea Volcano contain excess radiogenic argon-40 and give anomalously high potassium-argon ages. Glassy rims of pillows show a systematic increase in radiogenic argon-40 with depth, and a pillow from a depth of 2590 meters shows a decrease in radiogenic argon40 inward from the pillow rim. The data indicate that the amount of excess radiogenic argon-40 is a direct function of both hydrostatic pressure and rate of cooling, and that many submarine basalts are not suitable for potassium-argon dating.     

Formation of magnetic single-domain magnetite in ocean ridge basalts with implications for sea-floor magnetism

Although magnetic data are the primary evidence for ocean floor spreading, the processes by which magnetic phases in ocean floor basalts are formed remain poorly constrained. Scanning transmission electron microscopic observations show that magnetic single-domain magnetite in sheeted dike basalts of Deep Sea Drilling Project hole 504B formed through oxidation-exsolution of ilmenite, exsolution of ulv?spinel lamellae, and recrystallization of end-member magnetite by interaction with convecting fluids. The data suggest that the sheeted dike basalts, with single-domain magnetite as an efficient and stable magnetic carrier, contribute significantly to sea-floor magnetism.     

磷胁迫条件下小麦、蚕豆根系分泌物对红壤磷的活化*

 通过室内盆栽试验研究了磷胁迫下小麦、蚕豆根系分泌物对石灰岩和玄武岩母质上发育的红壤中磷的活化效果。结果表明：在培养至第7 d时,小麦单作、蚕豆单作、小麦蚕豆混作的根系分泌物处理与对照相比,石灰岩母质上发育的红壤有效磷分别提高29.51%,22.16%,23.91%,玄武岩母质发育的红壤有效磷分别比对照提高6.3%,31.19%,31.20%。加入根系分泌物后的2种土壤在培养过程中土壤中的磷酸铝盐（Al-P）和磷酸铁盐（Fe-P）含量有所降低,闭蓄态磷（O-P）和磷酸钙盐（Ca-P）含量变化不大。可能的原因为根系分泌物通过对土壤中无机磷的Al-P和Fe-P的活化从而提高了土壤中磷的有效性。     

Copper systematics in arc magmas and implications for crust-mantle differentiation

Arc magmas are important building blocks of the continental crust. Because many arc lavas are oxidized, continent formation is thought to be associated with oxidizing conditions. On the basis of copper's (Cu's) affinity for reduced sulfur phases, we tracked the redox state of arc magmas from mantle source to emplacement in the crust. Primary arc and mid-ocean ridge basalts have identical Cu contents, indicating that the redox states of primitive arc magmas are indistinguishable from that of mid-ocean ridge basalts. During magmatic differentiation, the Cu content of most arc magmas decreases markedly because of sulfide segregation. Because a similar depletion in Cu characterizes global continental crust, the formation of sulfide-bearing cumulates under reducing conditions may be a critical step in continent formation.     

Highly siderophile element constraints on accretion and differentiation of the Earth-Moon system

A new combined rhenium-osmium- and platinum-group element data set for basalts from the Moon establishes that the basalts have uniformly low abundances of highly siderophile elements. The data set indicates a lunar mantle with long-term, chondritic, highly siderophile element ratios, but with absolute abundances that are over 20 times lower than those in Earth's mantle. The results are consistent with silicate-metal equilibrium during a giant impact and core formation in both bodies, followed by post-core-formation late accretion that replenished their mantles with highly siderophile elements. The lunar mantle experienced late accretion that was similar in composition to that of Earth but volumetrically less than (approximately 0.02% lunar mass) and terminated earlier than for Earth.     

Primitive boron isotope composition of the mantle

Boron isotope ratios are homogeneous in volcanic glasses of oceanic island basalts [-9.9 +/- 1.3 per mil, relative to standard NBS 951 (defined by the National Bureau of Standards)], whereas mid-oceanic ridge basalts (MORBs) and back-arc basin basalts (BABBs) show generally higher and more variable ratios. Melts that have assimilated even small amounts of altered basaltic crust show significant variations in the boron isotope ratios. Assimilation may thus account for the higher boron ratios of MORBs and BABBs. A budget of boron between mantle and crust implies that the primitive mantle had a boron isotope ratio of -10 +/- 2 per mil and that this ratio was not fractionated significantly during the differentiation of the mantle.     

Apollo 17 seismic profiling: probing the lunar crust

Apollo 17 seismic data are interpreted to determine the structure of the lunar crust to a depth of several kilometers. Seismic velocity increases in a marked stepwise manner beneath the Taurus-Littrow region at the Apollo 17 site. A thickness of about 1200 meters is indicated for the infilling mare basalts at Taurus-Littrow. The apparent velocity is high (about 4 kilomleters per second) in the material immediately underlying the basalts.     

Lu-Hf Isotope Systematics of Garnet Pyroxenites from Beni Bousera, Morocco: Implications for Basalt Origin

Six garnet pyroxenites from Beni Bousera, Morocco, yield a mean lutetium-hafnium age of 25 +/- 1 million years ago and show a wide range in hafnium isotope compositions (varepsilonHf = -9 to +42 25 million years ago), which exceeds that of known basalts (0 to +25). Therefore, primary melts of garnet pyroxenites cannot be the source of basalts. The upper mantle may be an aggregate of pyroxenites that were left by the melting of oceanic crust at subduction zones and peridotites that were contaminated by the percolation of melts from these pyroxenites. As a consequence, the concept of geochemical heterogeneities as passive tracers is inadequate. Measured lutetium-hafnium partitioning of natural minerals requires a reassessment of some experimental work relevant to mantle melting in the presence of garnet.