Jong Ik Lee

Chelyabinsk airburst, damage assessment, meteorite recovery, and characterization

Deep Impact? On 15 February 2013, the Russian district of Chelyabinsk, with a population of more than 1 million, suffered the impact and atmospheric explosion of a 20-meter-wide asteroid—the largest impact on Earth by an asteroid since 1908. Popova et al. (p. 1069, published online 7 November; see the Perspective by Chapman) provide a comprehensive description of this event and of the body that caused it, including detailed information on the asteroid orbit and atmospheric trajectory, damage assessment, and meteorite recovery and characterization. A detailed study of a recent asteroid impact provides an opportunity to calibrate the damage caused by these rare events. [Also see Perspective by Chapman] The asteroid impact near the Russian city of Chelyabinsk on 15 February 2013 was the largest airburst on Earth since the 1908 Tunguska event, causing a natural disaster in an area with a population exceeding one million. Because it occurred in an era with modern consumer electronics, field sensors, and laboratory techniques, unprecedented measurements were made of the impact event and the meteoroid that caused it. Here, we document the account of what happened, as understood now, using comprehensive data obtained from astronomy, planetary science, geophysics, meteorology, meteoritics, and cosmochemistry and from social science surveys. A good understanding of the Chelyabinsk incident provides an opportunity to calibrate the event, with implications for the study of near-Earth objects and developing hazard mitigation strategies for planetary protection.

Oxygen isotope measurements of terrestrial silicates using a CO2-laser BrF5 fluorination technique and the slope of terrestrial fractionation line

Here we report oxygen isotopic compositions (both δ18O and δ17O) of San Carlos olivine, Juan de Fuca basalt glass, garnet standard at University of Wisconsin (UWG-2 garnet), National Bureau of standard #28 quartz (NBS-28 quartz), a hydrothermal quartz from China (CQ4 quartz), chert flint standard and a serpentine measured with a CO2-laser BrF5 fluorination system installed at Korea Polar Research Institute. In addition we measured VSMOW (Vienna standard mean ocean water) and SLAP (standard light Antarctic precipitation) with the same line; a scaling factor of 1.056 was obtained to fit the measured SLAP data to the recommended value of δ18OSMOW = −55.5‰. All the other data were corrected using the VSMOW-SLAP scaling factor. Majority of the samples in this work have been measured by several laboratories; our data in general agree very well with previous data. We report data using the delta prime notation, since linearity of a mass-dependent fractionation line holds in δ′17O vs. δ′18O diagram for wide range of oxygen isotopic compositions. Average δ′18O values and 2σ standard error of means are 5.27 ± 0.04‰ for San Carlos olivine, 5.49 ± 0.02‰ for Juan de Fuca basalt glass, 5.73 ± 0.05‰ for UWG-2 garnet, 9.18 ± 0.08‰ for NBS-28 quartz, 23.14 ± 0.36‰ for CQ4 quartz, 33.97 ± 0.16‰ for chert flint standard and 0.78 ± 0.07‰ for the serpentine. Slope of terrestrial fractionation was obtained using these data, which is 0.5248 ± 0.0003 (R2 = 0.99992).

Origin of E-MORB in a fossil spreading center: the Antarctic-Phoenix Ridge, Drake Passage, Antarctica

The fossilized Antarctic-Phoenix Ridge (APR) with three segments (P1, P2, and P3), Drake Passage, is distant from the known hotspots, and consists of older N-MORB formed prior to the extinction of spreading and younger E-MORB after extinction. The older N-MORB (3.5–6.4 Ma) occur in the southeastern flank of the P3 segment (PR3) and the younger E-MORB (1.4–3.1 Ma) comprise a huge seamount at the former ridge axis of the P3 segment (SPR) and a big volcanic edifice at the northwestern flank of the P2 segment (PR2). The PR3 basalts have higher Mg#, K/Ba, and CaO/Al2O3 and lower Zr/Y, Sr, and Na80 (fractionation-corrected Na2O to 8.0% MgO) with slight enrichment in incompatible elements and almost flat REE patterns. The SPR and PR2 basalts are highly enriched in incompatible elements and LREE. The extinction of spreading at 3.3 Ma seems to have led to a temporary magma oversupply with E-MORB signatures. Geochemical signatures such as Ba/TiO2, Ba/La, and Sm/La suggest the heterogeneity of upper mantle and formation of E-MORB by higher contribution of enriched materials (e.g., metasomatized veins) to mantle melting than the N-MORB environment. E-MORB magmas beneath the APR seen to have been produced by low-degree melting at deeper regime, where enriched materials have preferentially participated in the melting. The occurrence of E-MORB at the APR is a good example to better understand what kinds of magmatism would occur in association with extinction of the ridge spreading.

Geochemistry of volcanic rocks in Barton and Weaver peninsulas, King George Island, Antarctica: Implications for arc maturity and correlation with fossilized volcanic centers

We investigated geochemical characteristics of the Paleocene-Eocene volcanic rocks in Barton and Weaver peninsulas, King George Island, Antarctica. Volcanic rocks are predominantly tholeiitic, and show geochemical properties typical for island arc volcanism. The volcanic rocks can be subdivided into three groups based on the differences of geochemistry and regional distribution. The group 1 rocks are distributed in Weaver Peninsula and in the central part of Barton Peninsula. They show relatively mafic compositions (basalts to basaltic andesites) with the lowest level of total REEs. The group 2 rocks are widely distributed in Barton Peninsula, and show intermediate compositions (basaltic andesites to andesites) with the highest LILE/HFSE and LREE/HREE ratios. The group 3 rocks occur as intermediate dikes or plugs along the southern coast of Barton Peninsula. They generally show similar compositions to those of the group 2, but have smaller LREE/HREE ratios. The parental magma of the group 1 seems to be most depleted among three groups, whereas that of the group 2 rocks enriched in LILEs and LREEs. Predominance of tholeiite series rocks, general absence of the basement complex, and difficulty of identifying dual volcanic chains suggest that the Early Tertiary volcanism in King George Island occurred in an immature island arc without thickened continental-type crust. Geochemical correlations between volcanic rocks and fossilized volcanic vents suggest that volcanic groups can be linked with vents: the group 1 with Weaver Nunatak, and the group 2 with Three Brothers Hill, Florence Nunatak and/or Czajkowski Needle. However, the group 3 seems to be correlative with the Chottaebawi plug (the Narebski Point), or represent distinct dike swarms.

Geochronologic evidence for Early Cretaceous volcanic activity on Barton Peninsula, King George Island, Antarctica

Ages of six volcanic and plutonic rocks on Barton Peninsula, King George Island, were determined using 40 Ar/ 39 Ar and K-Ar isotopic systems. The 40 Ar/39 Ar and K-Ar ages of basaltic andesite and diorite range from 48 My to 74 My and systematically decrease toward the upper stratigraphic section. Two specimens of basaltic andesite which occur in the lowermost sequence of the peninsula, however, apparently define two distinct plateau ages of 52-53 My and 119-120 My. The latter is interpreted to represent the primary cooling age of basaltic andesite, whereas the former is interpreted as the thermally-reset age caused by the intrusion of Tertiary granitic pluton. The isochron ages calculated from the isotope correlation diagram corroborate our interpretation based on the apparent plateau ages. It is therefore likely that volcanism was active during the Early Cretaceous on Barton Peninsula. When the K-Ar ages of previous studies are taken into account with our result, the ages of basaltic andesite in the northern part of the Barton Peninsula are significantly older than those in the southern part. Across the north-west-south-east trending Barton fault bounding the two parts, there are significant differences in geochronologic and geologic aspects.

Phlogopite and tetraferriphlogopite from phoscorite and carbonatite associations in the Sokli massif, Northern Finland

The phoscorite—carbonatite complex (PCC) in the Sokli massif, northern Finland, is divided into 5 stages according to mineral assemblages and occurrences. The earlier three stages comprise phoscorites and calcite carbonatites (P1 to P3 and C1 to C3, respectively), and they usually occur as pairs with the same mineral assemblage (calcite, apatite, megnatite, olivine, and mica). The latter two stages consist of only dolomite carbonatites called D4 and D5. All micas investigated from the Sokli PCC fall in the range of the phlogopite-tetraferriphlogopite series. Tetraferriphlogopite begins to crystallize from late stage 2 and becomes a dominant silicate in the P3C3 rocks and D4-D5 dolomite carbonatites. Although tetraferriphlogopites occur as primary or secondary products, discrete and euhedral (magmatic) tetraferriphlogopites are considered to have crystallized from a melt strongly depleted in aluminum and saturated in Ti-bearing phases under low temperature condition. The chemical variation of phlogopites shows that Fe and F contents increase, whereas Al, Ba, Ti and Mg contents decrease from stage 1 to stage 5. The progressive depletion in aluminum and the enrichment in fluorine towards the later stages seem to be a specific feature of the Sokli phlogopite. The difference of phlogopite rim compositions between phoscorites and paired carbonatites indicates that there was a slight difference of elemental partitioning into the interstial melts during the segregation of the rocks from a parental magma.

Petrology and geochemistry of the Youngju and Andong granites in the northeastern Yeongnam Massif, Korea

Two late Paleozoic, partly deformed granitic batholiths, the Youngju and Andong granites, regionally occur in the northeastern Yeongnam Massif. The deformed granites generally occur along the shear zone trending northeast in the central part of the study area, and their foliations are subparallel to the trend of shear zone, indicating post-emplacement deformation. Both granites belong to tonalite-granodiorite-granite association, but have dominantly granodiorite composition. They have similar chemical features, corresponding to metaluminous, calc-alkaline, I-type, and volcanic arc granites. Most chemical variation trends suggest that mineral fractionation patterns in the two granites should be similar except for the plagioclase fractionation. Relative to the Andong granites, the Youngju granites contain significantly higher FeO, MnO, MgO, K2O, Rb, Th, U, Sc, and Pb, and lower Al2O3, Na2O, P2O5, TiO2, Sr, Zr, and Ga. The Youngju granites also have higher K2O/Na2O, Rb/Sr, and Th/Y ratios, and a lower K/Rb ratio than the Andong granites. The geochemical differences between the two granites are prominent, particularly, in mafic facies. The more incompatible nature of the Youngju granites may be attributed to higher degree of mixing or assimilation with old crustal materials during ascent or emplacement of magma. Taking into account that the tonalitic compositions are the most mafic facies of the two granites, the protoliths seem to have been mafic igneous rocks or their metamorphic equivalents distributed in the lowermost crust.

Noble gas and stable isotope geochemistry of thermal fluids from Deception Island, Antarctica

Abstract New stable isotope and noble gas data obtained from fumarolic and bubbling gases and hot spring waters sampled from Deception Island, Antarctica, were analysed to constrain the geochemical features of the islands active hydrothermal system and magmatism in the Bransfield back-arc basin. The 3He/4He ratios of the gases (< 9.8 × 10-6), which are slightly lower than typical MORB values, suggest that the Deception Island magma was generated in the mantle wedge of a MORB-type source but the signature was influenced by the addition of radiogenic 4He derived from subducted components in the former Phoenix Plate. The N2/He ratios of fumarolic gas are higher than those of typical mantle-derived gases suggesting that N2 was added during decomposition of sediments in the subducting slab. The δ13C values of -5 to -6‰ for CO2 also indicate degassing from a MORB-type mantle source. The H2/Ar- and SiO2 geothermometers indicate that the temperatures in the hydrothermal system below Deception Island range from ~150°C to ~300°C. The δD and δ18O values measured from fumarolic gas and hot spring waters do not indicate any contribution of magmatic water to the samples. The major ionic components and δD-δ18O-δ34S values indicate that hot spring waters are a mixture of local meteoric water and seawater. Mn and SiO2 in spring waters were enriched relative to seawater reflecting water-rock interaction at depth.

The A-type Pirrit Hills Granite, West Antarctica: an example of magmatism associated with the Mesozoic break-up of the Gondwana supercontinent

The Mesozoic geology of West Antarctica is largely related with the break-up of the Gondwana supercontinent and offers a good example for understanding magmatism associated with the continental break-up process. West Antarctica can be divided into five crustal blocks with relatively thin crust. The blocks are separated by deep rift zones and have moved during the Mesozoic break-up of Gondwana. The Pirrit Hills granite occurs as an isolated pluton in the Ellsworth-Whitmore Mountains block, which is the center of five blocks in the present configuration. The granite consists of quartz, perthitic alkali feldspar, and plagioclase with minor amounts of interstitial biotite and muscovite. The granite is a highly homogeneous, strongly fractionated, and mildly peraluminous granite and belongs to A-type granites with A2-type characteristics, suggesting its generation in an anorogenic environment. The strong enrichment of HREE and significant negative Eu anomalies suggest that the granitic magma was produced by a small degree of partial melting of a garnet granulitic source in the unusually hot lower crust. A weighted mean 206Pb/238U age of zircons is 164.5 ± 2.3 Ma (MSWD = 1.3), which is 8 to 9 Mys younger than a former Rb-Sr whole rock age (173 ± 3 Ma), and corresponds to the first rifting stage of the break-up of Gondwana (at 165 Ma). We suggest this age to be the emplacement age of the Pirrit Hills granite. The A-type Pirrit Hills granite was emplaced in the Middle Jurassic accompanying crustal thinning due to the break-up of Gondwana.

Oxygen isotopic fractionation of O₂ during adsorption and desorption processes using molecular sieve at low temperatures.

RATIONALE Cryogenic trapping using molecular sieves is commonly used to collect O2 extracted from silicates for (17)O/(16)O and (18)O/(16)O analyses. However, gases which interfere with (17)O/(16)O analysis, notably NF3, are also trapped and their removal is essential for accurate direct measurement of the (17)O/(16)O ratio. It is also necessary to identify and quantify any isotopic fractionation associated with the use of cryogenic trapping using molecular sieves. METHODS The oxygen isotopic compositions of O2 before and after desorption from, and adsorption onto, 13X and 5A molecular sieves (MS13X and MS5A) at 0°C, -78°C, -114°C, and -130°C were measured in order to determine the oxygen isotopic fractionation at these temperatures. We also investigated whether isotopic fractionation occurred when O2 gas was transferred sequentially into a second cold finger, also containing molecular sieve. RESULTS It was confirmed that significant oxygen isotopic fractionation occurs between the gaseous O2 and that adsorbed onto molecular sieve, if desorption and adsorption are incomplete. As the fraction of released or untrapped O2 becomes smaller with decreasing trapping temperature (from 0 to -130°C), the isotopic fractionation becomes larger. Approximately half of the total adsorbed O2 is released from the molecular sieve during desorption at -114°C, which is the temperature recommended for separation from NF3 (retained on the molecular sieve), and this will interfere with (17)O/(16)O measurements. CONCLUSIONS The use of a single cold finger should be avoided, because partial desorption is accompanied by oxygen isotopic fractionation, thereby resulting in inaccurate isotopic data. The use of a dual cold finger arrangement is recommended because, as we have confirmed, the transfer of O2 from the first trap to the second is almost 100%. However, even under these conditions, a small isotopic fractionation (0.18 ± 0.05‰ in δ(17)O values and 0.26 ± 0.06‰ in δ(18)O values) occurred, with O2 in the second trap being isotopically enriched in the heavier isotopes.