Geology topics

Jingyuan Wang

Publications and source records attributed to Jingyuan Wang.

6 recordsLinked to original sources

USGS2010

Bleached chondrules: Evidence for widespread aqueous processes on the parent asteroids of ordinary chondrites

We present the first detailed study of a population of texturally distinct chondrules previously described by Kurat (1969), Christophe Michel-Lévy (1976), and Skinner et al. (1989) that are sharply depleted in alkalis and Al in their outer portions. These “bleached” chondrules, which are exclusively radial pyroxene and cryptocrystalline in texture, have porous outer zones where mesostasis has been lost. Bleached chondrules are present in all type 3 ordinary chondrites and are present in lower abundances in types 4–6. They are most abundant in the L and LL groups, apparently less common in H chondrites, and absent in enstatite chondrites. We used x-ray mapping and traditional electron microprobe techniques to characterize bleached chondrules in a cross section of ordinary chondrites. We studied bleached chondrules from Semarkona by ion microprobe for trace elements and H isotopes, and by transmission electron microscopy. Chondrule bleaching was the result of low-temperature alteration by aqueous fluids flowing through finegrained chondrite matrix prior to thermal metamorphism. During aqueous alteration, interstitial glass dissolved and was partially replaced by phyllosilicates, troilite was altered to pentlandite, but pyroxene was completely unaffected. Calcium-rich zones formed at the inner margins of the bleached zones, either as the result of the early stages of metamorphism or because of fluid-chondrule reaction. The mineralogy of bleached chondrules is extremely sensitive to thermal metamorphism in type 3 ordinary chondrites, and bleached zones provide a favorable location for the growth of metamorphic minerals in higher petrologic types. The ubiquitous presence of bleached chondrules in ordinary chondrites implies that they all experienced aqueous alteration early in their asteroidal histories, but there is no relationship between the degree of alteration and metamorphic grade. A correlation between the oxidation state of chondrite groups and their degree of aqueous alteration is consistent with the source of water being either accreted ices or water released during oxidation of organic matter. Ordinary chondrites were probably open systems after accretion, and aqueous fluids may have carried volatile elements with them during dehydration. Individual radial pyroxene and cryptocrystalline chondrules were certainly open systems in all chondrites that experienced aqueous alteration leading to bleaching.

Meteoritics and Planetary Science↗

USGS2010

The lack of potassium-isotopic fractionation in Bishunpur chondrules

In a search for evidence of evaporation during chondrule formation, the mesostases of 11 Bishunpur chondrules and melt inclusions in olivine phenocrysts in 7 of them have been analyzed for their alkali element abundances and K-isotopic compositions. Except for six points, all areas of the chondrules that were analyzed had δ 41 K compositions that were normal within error (typically ±3%, 2s̀). The six “anomalous” points are probably all artifacts. Experiments have shown that free evaporation of K leads to large 41 K enrichments in the evaporation residues, consistent with Rayleigh fractionation. Under Rayleigh conditions, a 3% enrichment in δ 41 K is produced by ∼12% loss of K. The range of L-chondrite-normalized K/Al ratios (a measure of the K-elemental fractionation) in the areas analyzed vary by almost three orders of magnitude. If all chondrules started out with L-chondrite-like K abundances and the K loss occurred via Rayleigh fractionation, the most K-depleted chondrules would have had compositions of up to δ 41 K ≅ 200%. Clearly, K fractionation did not occur by evaporation under Rayleigh conditions. Yet experiments and modeling indicate that K should have been lost during chondrule formation under currently accepted formation conditions (peak temperature, cooling rate, etc.). Invoking precursors with variable alkali abundances to produce the range of K/Al fractionation in chondrules does not explain the K-isotopic data because any K that was present should still have experienced sufficient loss during melting for there to have been a measurable isotopic fractionation. If K loss and isotopic fractionation was inevitable during chondrule formation, the absence of K-isotopic fractionation in Bishunpur chondrules requires that they exchanged K with an isotopically normal reservoir during or after formation. There is evidence for alkali exchange between chondrules and rim-matrix in all unequilibrated ordinary chondrites. However, melt inclusions can have alkali abundances that are much lower than the mesostases of the host chondrules, which suggests that they at least remained closed since formation. If it is correct that some or all melt inclusions remained closed since formation, the absence of K-isotopic fractionation in them requires that the K-isotopic exchange took place during chondrule formation, which would probably require gas-chondrule exchange. Potassium evaporated from fine-grained dust and chondrules during chondrule formation may have produced sufficient K-vapor pressure for gas-chondrule isotopic exchange to be complete on the timescales of chondrule formation. Alternatively, our understanding of chondrule formation conditions based on synthesis experiments needs some reevaluation.

Meteoritics and Planetary Science↗

USGS2008

Mineralogical and compositional characteristics of Late Permian coals from an area of high lung cancer rate in Xuan Wei, Yunnan, China: Occurrence and origin of quartz and chamosite

Some townships in Xuan Wei County, Yunnan Province, have one of the highest lung cancer mortality rates in China and the epidemic disease in the area has generally been attributed to the polycyclic aromatic hydrocarbons (PAHs) released from domestic coal burning. However, the cancer-causing culprit is not settled as Tian [Tian, L., 2005. Coal Combustion Emissions and Lung Cancer in Xuan Wei, China. Ph.D. thesis, University of California, Berkeley.] found nanometer quartz in these coals, soot emissions, and lung cancer tissues. We have conducted mineralogical and geochemical studies of the coals from Xuan Wei for the purpose of shedding light on the minerals which may be related to the epidemic lung cancer. In this paper, abundances, modes of occurrence, and origins of minerals and elements in the coals from two mines in Xuan Wei have been studied using optical microscope, low-temperature ashing, X-ray diffraction analysis, scanning electron microscope equipped with energy-dispersive X-ray spectrometer, and inductively-coupled plasma mass spectrometry. The minerals in the coals are mainly composed of quartz, chamosite, kaolinite, and calcite. The particle size of quartz is rather small, mostly less than 20????m and it is of authigenic origin. Chamosite occurs mainly as cell-fillings. The occurrence of quartz and chamosite indicates that they were derived from the hydrothermal fluids. Epigenetic calcite is derived from calcic fluids. Kaolinite is derived mainly from sediment source region of Kangdian Oldland to the west of coal basin. The composition of Xuan Wei coal is high in SiO2, Fe2O3, TiO2, CaO, MnO, V, Co, Ni, Cu, and Zn. The high SiO2 content is attributed to quartz, and the Fe2O3 content to chamosite. The high Mn and low Mg contents in the coal indicate the inputs of hydrothermal fluids. CaO occurs mainly in epigenetic calcite. Elements Ti, Co, Ni, Cu, Zn, and rare earth elements were derived from the basaltic rocks at sediment source region. ?? 2008 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗

USGS2005

Tidal and seasonal effects on transport of pink shrimp postlarvae

Transport simulations were conducted to investigate a large seasonal peak in postlarvae of the pink shrimp Farfantepenaeus duorarum that occurs every summer on the northwestern border of Florida Bay. Daily vertical migration, a known behavior in pink shrimp postlarvae, was assumed in all scenarios investigated. A Lagrangian trajectory model was developed using a current field derived from a 3 yr ADCP (Acoustic Doppler Current Profiler) time series. To fit the estimated planktonic development time of pink shrimp, the model simulated larvae traveling at night over a 30 d period. We investigated 2 types of effects: (1) the effect of mismatch periodicity between tidal constituents and daily migration, and (2) the effect of seasonal changes in night length. The maximum eastward displacement with the semidiurnal lunar tidal constituent (M2) was 4 km, with periods of enhanced transport in both summer and winter. In contrast, eastward displacement with the semidiurnal solar tidal constituent (S2) and the lunisolar diurnal K1 was 65 km and the period of maximum distance occurred in summer every year. Because the periods of S2 and K1 are so close to the 24 h vertical migration period, and the eastward current (flood) of these constituents matches the diel cycle over extended intervals, they can induce strong horizontal transport during summer. Thus, diel vertical migration can interact with the S2 and the K1 tidal constituents and with the annual cycle of night length to produce a distinct annual cycle that may enhance transport of pink shrimp and other coastal species during summer in shallow areas of the Gulf of Mexico. ?? Inter-Research 2005.

Marine Ecology Progress Series↗

USGS1997

Seasonal Sea-Level Variations in San Francisco Bay in Response to Atmospheric Forcing, 1980

The seasonal response of sea level in San Francisco Bay (SFB) to atmospheric forcing during 1980 is investigated. The relations between sea-level data from the Northern Reach, Central Bay and South Bay, and forcing by local wind stresses, sea level pressure (SLP), runoff and the large scale sea level pressure field are examined in detail. The analyses show that the sea-level elevations and slopes respond to the along-shore wind stress T(V) at most times of the year, and to the cross-shore wind stress T(N) during two transition periods in spring and autumn. River runoff raises the sea-level elevation during winter. It is shown that winter precipitation in the SFB area is mainly attributed to the atmospheric circulation associated with the Alcutian Low, which transports the warm, moist air into the Bay area. A multiple linear regression model is employed to estimate the independent contributions of barometric pressure and wind stress to adjusted sea level. These calculations have a simple dynamical interpretation which confirms the importance of along-shore wind to both sea level and north-south slope within the Bay.

Estuarine, Coastal and Shelf Science↗

USGS1994

A precise 232Th-208Pb chronology of fine-grained monazite: Age of the Bayan Obo REE-Fe-Nb ore deposit, China

We have obtained precise Th-Pb internal isochron ages on monazite and bastnaesite for the world's largest known rare earth elements (REE)-Fe-Nb ore deposit, the Bayan Obo of Inner Mongolia, China. The monazite samples, collected from the carbonate-hosted ore zone, contain extremely small amounts of uranium (less than 10 ppm) but up to 0.7% ThO 2 . Previous estimates of the age of mineralization ranged from 1.8 to 0.255 Ga. Magnetic fractions of monazite and bastnaesite samples (<60-μm size) showed large ranges in 232 Th 204 Pb "> 232 Th 204 Pb values (900–400,000) and provided precise Th-Pb internal isochron ages for paragenetic monazite mineralization ranging from 555 to 398 Ma within a few percent error (0.8% for two samples). These results are the first indication that REE mineralization within the giant Bayan Obo ore deposit occurred over a long period of time. The initial lead isotopic compositions (low 206 Pb 204 Pb "> 206 Pb 204 Pb and high 208 Pb 204 Pb) "> 208 Pb 204 Pb) and large negative ϵ Nd values for Bayan Obo ore minerals indicate that the main source(s) for the ores was the lower crust which was depleted in uranium, but enriched in thorium and light rare earth elements for a long period of time. Zircon from a quartz monzonite, located 50 km south of the ore complex and thought to be related to Caledonian subduction, gave an age of 451 Ma, within the range of monazite ages. Textural relations together with the mineral ages favor an epigenetic rather than a syngenetic origin for the orebodies. REE mineralization started around 555 Ma (disseminated monazite in the West, the Main, and south of the East Orebody), but the main mineralization (banded ores) was related to the Caledonian subduction event ca. 474-400 Ma.

Bayan Obo, Kuanggou Fault↗