Study on the potential of cultivated land quality improvement based on a geological detector

The restrictive factors of cultivated land are key to the improvement of cultivated land quality, scientific implementation of the land consolidation projects, and the efficiency of remediation. On the basis of the provincial plots of cultivated land quality in Shaanxi Province, this paper analysed the improvement potential of cultivated land quality from the perspective of restrictive factors. First, the potential exponential model was used to determine the distribution of various combinations of restrictive factors at the provincial scale. Second, a geological detector was used to determine the influences of different combinations of restrictive factors on cultivated land quality. Finally, through the investigation of cultivated land consolidation projects that have been implemented in the study area, the improvement potential level of different combinations of restrictive factors was determined. The degree of influence of the single restrictive factor or combinations of restrictive factors on the quality of cultivated land was improved, and the difference of the quality of cultivated land in different index areas could be revealed as well. The results showed that there were 12 single-factor restrictions and 34 double-factor restrictions. The area under single-factor restrictions reached 76.77% of the total land. The quality of cultivated land in the southern and central areas of Shaanxi Province was relatively good. The quality of cultivated land in the northern region was under significant influence of restrictive factors whereas that in southern and middle areas was less affected. From the perspective of improvement potential of restrictive factors, Shaanxi was relatively low with huge internal diversity, whereas the improvement potential in northern Shaanxi had huge advantage.

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Garnet zoning in kyanite-bearing eclogite from Golfo Aranci: New data on the early prograde P–T evolution in NE Sardinia, Italy

Kyanite-bearing eclogites from the Migmatite Complex of Golfo Aranci area, NE Sardinia, have been investigated using microstructural analyses and thermodynamic modelling in order to define their early metamorphic evolution and P–T path. The eclogites underwent a clockwise P–T path recorded by the different composition of garnet core, mantle, and rim. P–T pseudosection modelling allowed to estimate P–T conditions in the range T = 580–630 °C and P = 1.5–2.00 GPa for the formation of garnet core, between T = 620–690 °C and P = 2.0–2.3 GPa for garnet mantle, and within T = 650–700 °C and P = 1.4–2.1 GPa for garnet rim. The first part of the P–T path is characterized by a prograde increase in P and T in the eclogite facies that occurred between the growth of the garnet core and mantle. After the peak pressure, recorded by the garnet mantle composition, the rocks underwent moderate temperature increase and significant pressure decrease until they reach the peak temperature near to the eclogite/upper granulite-facies transition, recorded by the garnet rim composition. The P–T trajectory proposed for the early stage of the metamorphic evolution of the kyanite-bearing eclogites is similar to already existing observations from the Sardinian Low- to Medium-Grade Metamorphic Complex and introduce new constraints on their prograde eclogite-facies evolution. The role of the new prograde path is then discussed in the light of the Variscan orogen.

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Geochemistry and a metallogenic model for Nb–Ta-bearing granitic pegmatites from the northern Qaidam Basin

The Palaeoproterozoic Dakendaba Group and the Cambrian–Ordovician Tanjianshan Group occur on the northern margin of the Qaidam Basin. Their fracture structure is well developed, and intermediate-acid rocks are widely distributed, providing an ideal setting for pegmatite mineralization. Field investigation has identified 200 pegmatite veins, of which more than 40 have various degrees of Nb and Ta mineralization. These pegmatites can be classified into four types, based on distribution, mineral assemblages, and a genesis sequence of ① microcline, ② microcline–albite, ③ albite, and ④ muscovite–albite. Pegmatite types ③ and ④ are typically mineralized, with Nb and Ta occurring as niobite and columbite–tantalite. These pegmatites have high silica and alkali content and are Al-rich. The aluminium saturation index (A/CNK) is 1.36–1.60, and (A/NK) is 1.45–1.93. Their ∑REE values are 2.61–23.95 × 10−6. Other REE ratios have values of (La/Yb)N = 2.02–8.04, (La/Sm)N = 0.47–3.20, and (Gd/Yb)N = 1.34–4.93. Their REE distribution pattern is right-inclined, with slight LREE enrichment. Negative Eu anomalies are apparent in types ① and ④ but not in types ② and ③. High field strength elements, such as Nb, Ta, Zr, and Hf, have low contents, with Y depletion. Concentrations of REE are generally low, although Sr and Ba are slightly enriched. Thus, pegmatites of this area have low Ca, K, and Al but high Na and Si and are rich in rare metal elements and poor in REEs. This suggests liquid immiscibility was involved in their metallogenic evolution process.

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Petrogenesis of rhyolite at Kalatage in the Eastern Tianshan, Northwest China: Evidences from geochemistry, zircon U–Pb geochronology, and Hf isotopes

The Central Asian Orogenic Belt was one of the most important sites for juvenile crustal growth during the Phanerozoic worldwide, and Eastern Tianshan, Northwest China, located in southern Central Asian Orogenic Belt, is one of the key areas for unravelling the accretionary processes and continental growth. Zircon U–Pb geochronological, Hf isotopic, and whole-rock geochemical analyses are reported for the Upper Carboniferous Qishan Formation rhyolites from the Kalatage area in the middle of the Harlik–Dananhu arc, Eastern Tianshan, to investigate its petrogenesis and geodynamic setting. Zircon U–Pb ages obtained by laser-ablation inductively coupled mass spectrometry (LA-ICP-MS) indicated that zircon crystallization age of the rhyolite was 299.1 ± 2.1 Ma. The rhyolites are classified as subalkaline and high-K calc-alkaline series with A/CNK values mainly lower than 1.10. The REE patterns exhibit right inclined curves with negative Eu anomalies, and the trace element spider diagrams show depletions in Nb, Ta, and Eu, which is consistent with the geochemical characteristics of the island arc calc-alkaline magma suffered fractional crystallization. In situ zircons Hf isotopic analyses yielded positive initial εHf(t) values ranging from 8.0 to 11.9 and the two-stage Hf isotope crustal model ages (TDMC) of 554 to 807 Ma. It indicated that the rhyolite was derived from remelting of juvenile crust. The geochemical data for the rhyolites indicate that they were probably generated in a suprasubduction zone setting. It is proposed that the North Tianshan oceanic crust subducted northward beneath the Harlik–Dananhu arc during the Late Upper Carboniferous, and the rhyolites were derived from remelting of juvenile crust and generated in a suprasubduction zone setting.

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Magnetic field traces gas and dust swirling around supermassive black hole

Astronomers reveal a new high resolution map of the magnetic field lines in gas and dust swirling around the supermassive black hole at the centre of our Galaxy, published in a new paper in Monthly Notices of the Royal Astronomical Society. The team, led by Professor Pat Roche of the University of Oxford, created the map, which is the first of its kind, using the CanariCam infrared camera attached to the Gran Telescopio Canarias sited on the island of La Palma.

 

Black holes are objects with gravitational fields so strong that not even light can escape their grasp. The centre of almost every galaxy appears to host a black hole, and the one we live in, the Milky Way, is no exception. Stars move around the black hole at speeds of up to 30 million kilometres an hour, indicating that it has a mass of more than a million times our Sun.

 

thumbThe colour scale in the image shows the amount of infrared (heat) radiation coming from warm dust particles in the filaments and luminous stars within a light year of the Galactic centre. The position of the black hole is indicated by an asterisk. The lines trace the magnetic field directions and reveal the complex interactions between the stars and the dusty filaments, and the impact that they and the gravitational force has on them. Credit: E. Lopez-Rodriguez / NASA Ames / University of Texas at San Antonio. Click for a larger image

Visible light from sources in the centre of the Milky Way is blocked by clouds of gas and dust. Infrared light, as well as X-rays and radio waves, passes through this obscuring material, so astronomers use this to see the region more clearly. CanariCam combines infrared imaging with a polarising device, which preferentially filters light with the particular characteristics associated with magnetic fields.

 

The new infrared map covers a region about 1 light year on each side of the supermassive black hole. The map shows the intensity of infrared light, and traces magnetic field lines within filaments of warm dust grains and hot gas, which appear as thin lines reminiscent of brush strokes in a painting.

 

The filaments, several light years long, appear to meet close to the black hole (at a point below centre in the map), and may indicate where orbits of streams of gas and dust converge. One prominent feature links some of the brightest stars in the centre of the Galaxy. Despite the strong winds flowing from these stars, the filaments remain in place, bound by the magnetic field within them. Elsewhere the magnetic field is less clearly aligned with the filaments. Depending on how the material flows, some of it may eventually be captured and engulfed by the black hole.

 

The new observations give astronomers more detailed information on the relationship between the bright stars and the dusty filaments. The origin of the magnetic field in this region is not understood, but it is likely that a smaller magnetic field is stretched out as the filaments are elongated by the gravitational influence of the black hole and stars in the galactic centre.

 

Roche praises the new technique and the result: “Big telescopes like GTC, and instruments like CanariCam, deliver real results. We’re now able to watch material race around a black hole 25,000 light years away, and for the first time see magnetic fields there in detail.”

 

The team are using CanariCam to probe magnetic fields in dusty regions in our galaxy. They hope to obtain further observations of the Galactic Centre to investigate the larger scale magnetic field and how it links to the clouds of gas and dust orbiting the black hole further out at distances of several light years.

 
 

Media contacts

 

Dr Robert Massey

Royal Astronomical Society

Tel: +44 (0)20 7292 3979

Mob: +44 (0)7802 877699

rmassey@ras.ac.uk

 

Dr Helen Klus

Royal Astronomical Society

Tel: +44 (0)20 7292 3976

hklus@ras.ac.uk

 
 

Science contact

 

Professor Pat Roche

University of Oxford

pat.roche@physics.ox.ac.uk

 
 

Image and caption

 

The colour scale in the image shows the amount of infrared (heat) radiation coming from warm dust particles in the filaments and luminous stars within a light year of the Galactic centre. The position of the black hole is indicated by an asterisk. The lines trace the magnetic field directions and reveal the complex interactions between the stars and the dusty filaments, and the impact that they and the gravitational force has on them. The observations were made with the largest telescope in Europe, which allowed details of the fine structure in the magnetic fields to be revealed for the first time. 

Credit: E. Lopez-Rodriguez / NASA Ames / University of Texas at San Antonio

 
 

Further information

 

The new work appears in: “The Magnetic Field in the central parsec of the Galaxy”, P.F. Roche, E. Lopez-Rodriguez, C.M. Telesco, R. Schödel, C. Packham, Monthly Notices of the Royal Astronomical Society (2018), in press (DOI: 10.1093/mnras/sty129).

A copy of the paper is available from: https://doi.org/10.1093/mnras/sty129

 

The magnetic field directions are indicated by the polarisation produced in infrared light emitted from billions of tiny spinning elongated dust particles. These become aligned to the weak magnetic field that threads through the gas in which they are embedded.

Polarised light in this instance is produced because the emitting grains are elongated and aligned so that the emission along the long axis of the grains is greater than along the short axis, and when the spin is aligned to a magnetic field, the direction of the field threading through the emitting material can be traced.

Here polarisation is measured with the CanariCam instrument mounted on the Gran Telescopio Canarias (GTC). With a main mirror 10.4 metres in diameter, the GTC provides greater resolution than was possible with previous instruments, and reveals the fine details of the polarised structures for the first time. CanariCam was developed at the University of Florida by a team led by Prof Charles Telesco. It has unique capabilities for measuring polarisation at infrared wavelengths.

 
 

Notes for editors

 

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

 

The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.

 

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