Modification Of Earth Research Articles

Episodic evolution of a protracted convergent margin revealed by detrital zircon geochronology in the Greater Caucasus

AbstractConvergent margins play a fundamental role in the construction and modification of Earth's lithosphere and are characterized by poorly understood episodic processes that occur during the progression from subduction to terminal collision. On the northern margin of the active Arabia‐Eurasia collision zone, the Greater Caucasus Mountains provide an opportunity to study a protracted convergent margin that spanned most of the Phanerozoic and culminated in Cenozoic continental collision. However, the main episodes of lithosphere formation and deformation along this margin remain enigmatic. Here, we use detrital zircon U–Pb geochronology from Paleozoic and Mesozoic (meta)sedimentary rocks in the Greater Caucasus, along with select zircon U–Pb and Hf isotopic data from coeval igneous rocks, to link key magmatic and depositional episodes along the Caucasus convergent margin. Devonian to Early Carboniferous rocks were deposited prior to Late Carboniferous accretion of the Greater Caucasus crystalline core onto the Laurussian margin. Permian to Triassic rocks document a period of northward subduction and forearc deposition south of a continental margin volcanic arc in the Northern Caucasus and Scythian Platform. Jurassic rocks record the opening of the Caucasus Basin as a back‐arc rift during southward migration of the arc front into the Lesser Caucasus. Cretaceous rocks have few Jurassic‐Cretaceous zircons, indicating a period of relative magmatic quiescence and minimal exhumation within this basin. Late Cenozoic closure of the Caucasus Basin juxtaposed the Lesser Caucasus arc to the south against the crystalline core of the Greater Caucasus to the north and led to the formation of a hypothesized terminal suture. We expect this suture to be within ~20 km of the southern range front of the Greater Caucasus because all analysed rocks to the north exhibit a provenance affinity with the crystalline core of the Greater Caucasus.

The evolution of the Kaapvaal craton: A multi-isotopic perspective from lithospheric peridotites from Finsch diamond mine

Accurately dating the formation and modification of Earth’s sub-cratonic mantle still faces many challenges, primarily due to the long and complex history of depletion and subsequent metasomatism of this reservoir. In an attempt to improve this, we carried out the first study on peridotites from the Kaapvaal craton (Finsch Mine) that integrates results from Re-Os, Lu-Hf, Sm-Nd and Sr-isotope systems together with analyses of major-, trace- and platinum-group elements. The Finsch peridotites are well-suited for such a study because certain compositional features reflect they were highly depleted residues of shallow melting (1.5 GPa) at ambient Archean mantle temperatures. Yet, many of them have overabundant orthopyroxene, garnet and clinopyroxene compared to expected modal amounts for residues from partial melting. Finsch peridotites exhibit a wide range of rhenium depletion ages (TRD) from present day to 2.7 Ga, with a prominent mode at 2.5 Ga. This age overlaps well with a Lu-Hf isochron of 2.64 Ga (εHf (t) = +26) which records silico-carbonatitic metasomatism of the refractory residues. This late Archean metasomatism is manifested by positive correlations of Pt/Ir and Pd/Ir with 187Os/188Os ratios and good correlations of modal amounts of silicates, especially garnet, with Os isotope ratios. These correlations suggest that the Highly Siderophile Elements (HSE) and incompatible element reenrichment and modal metasomatism result from one single major metasomatic event at late Archean.Our detailed study of Finsch peridotites highlights the importance of using multiple isotopic systems, to constrain the ages of events defining the evolution of lithospheric mantle. The Re-Os isotope system is very effective in documenting the presence of Archean lithosphere, but only the oldest TRD ages may accurately date or closely approach the age of the last major partial melting event. For a meaningful interpretation of the Re-Os isotope systematics the data must be combined with HSE patterns, trace-element compositions and ideally other isotopic systems, e.g. Lu-Hf. This is highlighted by the widespread evidence in Finsch peridotites of Pt, Pd and Re enrichment through significant Base Metal Sulfide (BMS) addition (mainly in the range of 0.002–0.08 wt%) that systematically shifts the mode of TRD model ages to younger ages.

Modification of earth's gravity sphere

The standard radius of the Earth's gravity sphere is 917.000 km. Here we present that the radius is 1.400.000 km.

On the effects observed during modification of the earth’s upper ionosphere by high-power short radio pulses

We report on the results of studies of the evolution of artificial ionospheric turbulence (AIT) excited by short pulses of high-power short-wave O-mode radio emission in the ionospheric F region. On the basis of the obtained experimental data, it is assumed that the streams of thermal and suprathermal electrons generated in the regions of resonant interaction between a high-power radio wave and the plasma and propagating along the geomagnetic field stimulate the development of plasma perturbations far away from the primary-turbulence regions. Specific features of the measurement procedure are considered, an empirical model of the observed phenomena is developed, and possible problems in the further studies are outlined.

ChemInform Abstract: Effect of Rare Earth on the Thermostability and the Surface Area of Auto-Catalyst Washcoats.

In this paper, the influence of rare earth on the thermostability and surface area of auto-catalyst washcoating was studied by XRD and BET analysis. The results showed that the modification of rare earth was positively effective for the thermostability of γ-alumina washcoating. With rare earth, the transformation temperature from γ-alumina to α-alumina was increased from 800°C to 1200°C. Rare earth oxides could improve the thermostability of γ-alumina washcoating better than rare earth nitrates. At the same time, the thermostability was also dependent on the loading amount of rare earth. To make the best thermostability of auto-catalyst washcoating, the additive content into γ-alumina was about CeO2 6%wt, La2O3 8%wt. According to BET measurement, the biggest surface area of γ-alumina washcoating could be reached under the condition of CeO2 10%wt, La2O3 2%wt. To modify auto-catalyst washcoating, the thermostability and surface area should be considered synthetically by adding the most appropriate amount of rare earth.

The relations of environmental history and historical geography

This paper has three parts. The first examines the emergence of environmental history as a distinct subset of the history discipline. Its development is discussed, beginning with its roots in American conservation and intellectual history, its evolving ethical and radical emphasis, and ultimate its more internationalist and interdisciplinary views of humans in nature. The various models (mainly anthropological) and agendas for the study of environmental history are examined. The second part considers the contribution of primarily historical and cultural geographers to the larger human/nature debate raised by environmental history. Attention is focused on four areas of study (1) the transformation and modification of earth, (2) global expansion and the capitalist economy, (3) the place of humans in nature and, (4) the interrelationships between habitat, economy and society. The third part surveys some of the implications, commonalities and challenges of the discourse for both disciplines. It is concluded that both disciplines have much to contribute and learn from each other in "the telling of place stories".

Some studies on the earth's surface conditions relating to the urban heat island

The recent studies of the earth's surface conditions relating to heat islands in Japan are presented from geographical viewpoints as an activity of the Association of Japanese Geographers. Urban climate is defined as the result of urbanization, which is expressed as concentration of population, modification of earth's surface constituent materials, and expansion of living space onto and under the ground. These bring about changes in morphological and physical features of the urban surface, and its energetic conditions, which consequently and unintentionally modify radiation, heat and water balance in urban areas.Some estimations of urban surface conditions are at first explained. Surface conditions treated in this study are morphology of urban surface (mainly building height), roughness, sky view and energy consumption. Next, the relationships were considered between air temperature and surface morphology, heat island intensity and population, population and sky view factor, respectively.Finally the regional differences in heat islands were discussed, and the necessity of urban climate studies to ameliorate human and global conditions.