ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

Hits per page

hits 1 - 4 | 4 hits

Sorting

Unknown

Crustal Melting and Flow beneath Northern Tibet: Evidence from Mid-Miocene to Quaternary Strongly Peraluminous Rhyolites in the Southern Kunlun Range (2012)

Wang, Q., Chung, S.-L., Li, X.-H., Wyman, D., Li, Z.-X., Sun, W.-D., Qiu, H.-N., Liu, Y.-S., Zhu, Y.-T.

Oxford University Press

In: Journal of Petrology

add to mindlist on the mindlist

Details

Publication Date: 2012-11-21

Description: One of the major geophysical discoveries concerning the Tibetan Plateau is the existence of unusually weak layers in the mid- to lower crust, a characteristic widely interpreted as the result of crustal melting. This interpretation, however, remains highly contentious, particularly when applied to northern Tibet where crustally derived magmatic rocks are scarce. Here we report the finding of tourmaline-bearing mica and biotite rhyolites in the Bukadaban–Malanshan area, southern Kunlun Range, near the northern margin of the Tibetan Plateau. Zircon U–Pb and whole-rock or mineral 40 Ar– 39 Ar analyses suggest that these rocks erupted between 9·0 and 1·5 Ma. These rocks are geochemically similar to Himalayan leucogranites (interpreted as crustal melts), with strongly peraluminous compositions, high SiO 2 contents (69·0–76·0 wt %), and clear negative Eu, Ba and Sr anomalies. They have low Nd (–5·8 to –8·6) and high 87 Sr/ 86 Sr (0·7125–0·7178), 206 Pb/ 204 Pb (18·59–18·70), 207 Pb/ 204 Pb (15·49–15·63) and 208 Pb/ 204 Pb (38·31–38·74) isotopic compositions as well as magmatic zircon Hf (–0·7 to –5·0) compositions similar to those of global marine sediments and Proterozoic–Triassic sedimentary rocks in northern Tibet. We suggest that the Bukadaban–Malanshan rhyolites were generated by dehydration melting of metasedimentary rocks at 0·5–1·2 GPa and 740–863°C. Our data not only confirm the occurrence of a partially molten zone in the mid- to lower crust beneath northern Tibet but also constrain the crustal melting to have existed from middle Miocene to Quaternary times. Adopting the crustal flow model, we further argue the importance of outward flowing of the melt-weakened crust in the formation of crustal inflation, surface uplift, and earthquakes along the northern margin of the Tibetan Plateau.

Print ISSN: 0022-3530

Electronic ISSN: 1460-2415

Topics: Geosciences

Published by Oxford University Press

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

PAPER CURRENT

S·F·X

Fulltext

Unknown

Improved Application of Bomb Carbon in Teeth for Forensic Investigation (2010)

Wang, N ; Shen, C D ; Ding, P ; [et al.]

Cambridge University Press

In: Radiocarbon. 2010; 52(2): 706-716. Published 2010 Jan 01. doi: 10.1017/s0033822200045720.

add to mindlist on the mindlist

Details

Publication Date: 2010-01-01

Description: While radiocarbon is widely applied in dating ancient samples, recent studies reveal that 14C concentrations in modern samples can also yield precise ages due to the atmospheric testing of thermonuclear devices between 1950 and 1963. 14C concentrations in both enamel and organic matter of 13 teeth from 2 areas in China were examined to evaluate and improve this method of forensic investigation. Choosing enamel near the cervix of the tooth can reduce the error caused by the difference between the sample formation time and whole enamel formation time because tooth enamel formations take a long time to complete. A proper regional data set will be helpful to get an accurate result when calculating the age of the sample (T1) by the CALIBomb program. By subtracting the enamel formation time (t), the birth date of an individual (T2) can be confirmed by enamel F14C from 2 teeth formed at different ages. Calculated enamel formation dates by 14C concentration are basically consistent with corresponding actual values, with a mean error of 1.9 yr for all results and 0.2 yr for the samples formed after AD 1960. This method is more effective for dating samples completed after AD 1960. We also found that 14C concentrations in organic matter of tooth roots are much lower than atmospheric concentrations in root formation years, suggesting that the organic material keeps turning over even after tooth formation is complete. This might be a potential tool for identification of death age to extract a proper component for 14C dating. We also observed that δ13C values between hydroxyapatite and organic matter indicate that isotopic fractionation during the biomineralization is 8–9%‰ more positive in mineral fractions than in organic matter.

Print ISSN: 0033-8222

Electronic ISSN: 1945-5755

Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences

Published by Cambridge University Press

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

PAPER CURRENT

S·F·X

Fulltext

Unknown

Effects of water discharge and sediment load on evolution of modern Yellow River Delta, China, over the period from 1976 to 2009 (2011)

Yu, J. B. ; Fu, Y. Q. ; Li, Y. Z. ; [et al.]

Copernicus

In: Biogeosciences Discussions. 2011; 8(2): 4107-4130. Published 2011 Apr 26. doi: 10.5194/bgd-8-4107-2011.

add to mindlist on the mindlist

Details

Publication Date: 2011-04-26

Description: The Yellow River, which is the second largest river in China, is regarded as the world's largest contributor of fluvial sediment load to the ocean. In recent decades, the dramatic reduction in water discharge and sediment load due to climate change and human activities in the drainage basin has greatly constrained the evolution process of Yellow River delta. We highlight how runoff and sediment load discharged into sea affected extension of shoreline length and area of modern Yellow River delta during 1976–2009 based on remote sensing interpretation and long-term monitoring data in hydrological station. Average runoff of 207.47 × 108 m3 year−1 and average sediment load of 4.63 × 108 m3 year−1 were discharged into the sea from 1976 to 2008. The annual runoff reduced by ~59.7% in 1990–2002 and annual sediment load reduction up to ~72.1% in 2003–2008. Both shoreline length and area of Yellow River Delta extended overall in the studied period, but with decreasing rates in accordance with changes of runoff and sediment load. High increasing rate of shoreline length of ~3.63 km year−1 and quick area extension of ~16.26 km2 year−1 were observed in 1976–1985. Since 1996 however, the average increase rate of shoreline length and area decreased to ~0.80 km year−1 and ~3.94 km2 year−1, respectively. In addition, the fluctuated changes of shoreline and area were great and the net negative increase of land area was occurred during this period. There exist significant exponential relationships between the accumulated sediment load and extensions of shoreline length and the area during the evolution of the modern Yellow River Delta. Our results indicate that the evolution of shoreline and change of area of the Yellow River Delta are directly affected by the dramatic reduction of runoff and sediment load, which are much close related human being activities in Yellow River drainage basin in recent decades.

Print ISSN: 1810-6277

Electronic ISSN: 1810-6285

Topics: Biology , Geosciences

Published by Copernicus on behalf of European Geosciences Union.

Permalink