We present a new, reliably dated Mesoproterozoic paleopole for Siberia, based on a combined geochronological and paleomagnetic study of mafic rocks within the Mesoproterozoic Sololi Group of the Olenek Uplift in northern Siberia. Ion microprobe (SHRIMP) U–Pb analysis yields crystallisation ages of 2036 ± 11 Ma for zircon from a basement granite and 1473 ± 24 Ma for baddeleyite from a large dolerite sill within the Kyutingde Formation. The baddeleyite result indicates that the lower Sololi Group is significantly older than was suggested by previous K–Ar results. Paleomagnetic analysis of the dolerite sill and related mafic intrusive rocks yields a paleopole at 33.6°N, 253.1°E, A95 = 10.4°. A positive baked-contact test between the Kyutingde sill and sedimentary country rocks shows that the magnetisation is primary. Comparison of this paleopole with coeval results for Laurentia provides a revised reconstruction between Siberia and Laurentia, and implies that these two continents were parts of a single Mesoproterozoic supercontinent since at least 1473 Ma. We argue that Siberia, Laurentia, and Baltica belonged to the same supercontinent between 1473 Ma and mid-Neoproterozoic time. 相似文献
Chronology of Neoproterozoic volcanosedimentary successions remains controversial for many regions of the Arabian–Nubian Shield, including the Dokhan Volcanics of NE Egypt. New U–Pb zircon SHRIMP ages have been obtained for 10 silica-rich ignimbrites and two subvolcanic dacitic bodies, mapped as Dokhan Volcanics, from the North Eastern Desert of Egypt. Crystallization ages range between 592 ± 5 and 630 ± 6 Ma (Early Ediacaran). Apparently, the late consolidation of the Arabian–Nubian Shield was accompanied by the evolution of isolated volcanic centres and basin systems which developed during a period of approx. 40 Ma, independently in space and time and probably under changing tectonic regimes. The obtained age data together with other previously published reliable ages for Dokhan Volcanics suggest two main pulses of volcanic activity: 630–623 Ma and 618–592 Ma. Five samples contain inherited zircons, with ages of 669, 715–746, 847 and 1530 Ma, supporting models that North Eastern Desert crust is mainly juvenile Neoproterozoic crust. 相似文献
ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test general relativity with
an improvement in sensitivity of over three orders of magnitude, improving our understanding of gravity and aiding the development
of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and
our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude
improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an
international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD
missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way,
two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth,
to achieve the ASTROD I goals. A second mission, ASTROD (ASTROD II) is envisaged as a three-spacecraft mission which would
test General Relativity to 1 ppb, enable detection of solar g-modes, measure the solar Lense–Thirring effect to 10 ppm, and
probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger
orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below
the ASTROD II bandwidth.
Based on a comprehensive analysis of kimberlite pipes of Angola, including the near surface structural setting, deep lithospheric structure, pipe morphology and emplacement, mineralogical and petrographic features, diamond characteristics and locations of secondary deposits four geographical regions have been outlined within Angola representing four types of diamond bearing potential. These areas include high diamond bearing potential pipes, possible potential, no potential, and unclear potential areas. It was found that the depth of magmatism and diamond potential of kimberlites increases from the Atlantic coast in southwestern Angola into the continent in the north-easterly direction. Areas prospective for the discovery of new primary diamond deposits have been identified.
The present article is written in response to the recent call of the United Nations for the enhanced international cooperation of different countries on global geodesy to build the Global Geodetic Reference Frame (GGRF). It reviews historical landmarks in the development of the State Geodetic Reference Frame on the territory of Russia over the last two centuries. It discusses major steps in creating the Russian terrestrial reference frame by both the ground-based and space geodesy methods relying upon the satellite observation techniques. Currently the State Geodetic Reference Frame undergoes a radical improvement in order to effectively implement the potential of modern satellite technologies through the use of the Global Navigation Satellite Systems (GNSS). We outline the current status of the National Geodetic Network in Russia, its hierarchical structure and accuracy. We pay a particular attention to the high-precision State Geodetic Coordinate System (GSK-2011), created simultaneously along with the global reference-ellipsoid, and designed for various types of users to conduct the land surveying and mapping in Russia. We also present the geocentric coordinate system (PZ-90.11) used for navigating space missions, solving various problems of global geodesy, and supporting the continuous operation of GLONASS. 相似文献
Rock fragments from the deepest parts of a buried hydrothermal system belonging to the Mesozoic Tethys Ocean entered as xenoliths in a Miocenic diatreme,hence brought to the surface,in the Hyblean Plateau(Sicily).Some xenoliths consist of strongly serpentinized ultramafic rocks bearing blebs of abiotic organic matter,where clusters of amorphous carbon nanoparticles,including nanodiamonds,are immersed.Such an occurrence conjures up established hypotheses that diamond surfaces are suitable catalytic platforms stimulating the assemblage of complex bio-organic molecules relevant to the emergence of life on Earth.The appearance of bio-organic molecules under primitive Earth conditions is one of the major unsolved questions on the origin of life.Here we report new micro-Raman spectra on blebs of abiotic organic matter from a selected xenolith.Diamond bands were related to hydrogenated nanocrystalline diamonds,with size of nearly 1-1.6 nm,formed from organics at low pressures and temperatures.In particular,diamond surfaces can give rise to crystalline interfacial water layers that may have played a fundamental role in the early biosphere evolution as a good medium for rapidly transporting positive charges in the form of hydrated protons.Nowadays,proton gradients in alkaline hydrothermal vents along oceanic ridges are generally viewed as key pre-biotic factors.In general,serpentinites span the entire geological record,including prebiotic times.These hydrous ultramafic rocks often display evidence of abiotic carbon species,both organic and inorganic,including nanodiamonds,being also capable to give rise to chemiosmotic processes and proton gradients necessary to the organisms,such as the"Last Universal Common Ancestor"(LUCA),in the prebiotic Earth. 相似文献
Fourier expansions of elliptic motion functions in multiples of the true, eccentric, elliptic and mean anomalies are computed
numerically by means of the fast Fourier transform. Both Hansen-like coefficients and their derivatives with respect to eccentricity
of the orbit are considered. General behavior of the coefficients and the efficiency (compactness) of the expansions are investigated
for various values of eccentricity of the orbit.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献