The origin of small-scale geochemical and mineralogic variations in a granite intrusion

A post-tectonic unzoned granite intrusion in the Meatiq Dome, a Late Proterozoic metamorphic complex in the Central Eastern Desert of Egypt, shows significant chemical and mineralogic heterogeneity on the scale of sampling (5 kg). Whole rock analyses of 21 samples indicate small variations in SiO₂, Al₂O₃, Na₂O and K₂O, and larger systematic variations in the less abundant major elements such as FeO, TiO₂, CaO, MnO and MgO, and trace elements such as Sc, Cr, Co, Rb, Sr, Zr, La, Ce, Nd, Sm, Tb, Yb, Lu, Ta, Th and U. These variations cannot be accounted for by processes such as marginal accretion, assimilation, alteration by late stage fluids, or multiple intrusion. Instead, we proposed a model involving 35 percent solidification of the granite magma followed by partial solid-liquid segregation during emplacement, resulting in rocks containing 7–71 volume percent early-formed solids. Such randomly distributed local segregation could have been caused by filter pressing, flow differentiation, and possibly gravity segregation, either singly or in combination. Thus, each sample is interpreted as a mixture of two end-members with nearly constant compositions: an early-formed solid assemblage of crystals and a complementary residual liquid. Early formed solids are enriched in TiO₂, FeO, CaO, P₂O₅, Sc, Co, Cr, Sr, La, Ce and depleted in SiO₂, Rb, Yb, Lu, Ta, Th, and U, while the residual liquid has complementary enrichments and depletions. This simple mixing model is consistent with field and petrographic observations, experimental studies pertaining to the crystallization sequence in the system Ab-Or-Qtz-H₂O at 1 Kb, and physical properties of silicic magmas. Furthermore, it is quantitatively supported by trace-element data for minerals, computed endmember compositions at 35% crystallization using mineral analyses and reasonable Kd values, and internal consistency in the percent solid for each sample computed from each of 17 elements in the inferred end-members. We suggest that this model might also apply to other small epizonal granite intrusions that show small-scale chemical heterogeneities.     

Sensitivity of secular trends in precipitation data to observational errors

There has been considerable interest in estimating secular trends in precipitation data in various regions of the world. It is therefore important to ascertain the manner in which errors of observation affect estimated trends. For this purpose we have compared trends at 1219 stations in the contiguous United States for two data sets: (a) original observations, also called raw observations, and (b) the observations, adjusted to compensate for suspected errors. The adjustments were made at the National Climate Data Center, Asheville (Quinlan et al., 1987;karl andWilliams, 1987), In order to focus on the effects of observational errors we attempted to avoid the effects of filling of missing data by limiting the analysis to the period 1940–1984 for which the number of missing values is much smaller than earlier periods. A least-square linear regression was performed on the raw and adjusted data for each station and the slopes of the fitted lines were compared. The comparison was made for monthly, seasonal and annual precipitation values.The results for annual precipitation showed that 23 percent of the stations have trends of opposite signs in the raw and adjusted data. The trends were identical in annual data at only 11 percent of the stations. When monthly data are combined to form seasonal and annual averages the magnitude of the difference between the slopes of the adjusted and the raw observations generally increases, indicating that the errors in the individual monthly observations are correlated. When the station data were averaged to obtain state-wide averages, the effects of the errors became less pronounced in most of the states. These results indicate that obtaining trends in precipitation from station data is a more difficult problem than has been realized.     

Future productivity and phenology changes in European grasslands for different warming levels: implications for grassland management and carbon balance

Background

Europe has warmed more than the global average (land and ocean) since pre-industrial times, and is also projected to continue to warm faster than the global average in the twenty-first century. According to the climate models ensemble projections for various climate scenarios, annual mean temperature of Europe for 2071–2100 is predicted to be 1–5.5 °C higher than that for 1971–2000. Climate change and elevated CO₂ concentration are anticipated to affect grassland management and livestock production in Europe. However, there has been little work done to quantify the European-wide response of grassland to future climate change. Here we applied ORCHIDEE-GM v2.2, a grid-based model for managed grassland, over European grassland to estimate the impacts of future global change.

Results

Increases in grassland productivity are simulated in response to future global change, which are mainly attributed to the simulated fertilization effect of rising CO₂. The results show significant phenology shifts, in particular an earlier winter-spring onset of grass growth over Europe. A longer growing season is projected over southern and southeastern Europe. In other regions, summer drought causes an earlier end to the growing season, overall reducing growing season length. Future global change allows an increase of management intensity with higher than current potential annual grass forage yield, grazing capacity and livestock density, and a shift in seasonal grazing capacity. We found a continual grassland soil carbon sink in Mediterranean, Alpine, North eastern, South eastern and Eastern regions under specific warming level (SWL) of 1.5 and 2 °C relative to pre-industrial climate. However, this carbon sink is found to saturate, and gradually turn to a carbon source at warming level reaching 3.5 °C.

Conclusions

This study provides a European-wide assessment of the future changes in productivity and phenology of grassland, and their consequences for the management intensity and the carbon balance. The simulated productivity increase in response to future global change enables an intensification of grassland management over Europe. However, the simulated increase in the interannual variability of grassland productivity over some regions may reduce the farmers’ ability to take advantage of the increased long-term mean productivity in the face of more frequent, and more severe drops of productivity in the future.

     

Geodynamic Background of Intracontinental Cenozoic Alkaline Volcanic Rocks in Laojiezi, Western Yangtze Craton: Constraints from Sr-Nd-Hf-O Isotopes

The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has been widely studied by geologists because of its porphyry-related Pb-Ag-Au polymetallic deposit and geotectonic location, the material sources of this belt are still debate. Whole-rock analyses show that these rocks have high total alkali contents (3.73–11.08wt%), and their aluminum saturation index (ASI) values widely vary from 0.82 to 3.07, which comprise a metaluminous-peraluminous magma series. These rocks are characterized by high K (K2O/Na2O>1) and low Ti and Mg contents; enrichment in large-ion lithophile elements, such as Rb, Ba, K and light rare earth elements; and depletion in high field strength elements, such as Ta, Nb, P, and Ti. These rocks exhibit moderate Eu (Eu/Eu*=0.86–1.04) and Ce (Ce/Ce*=0.63–0.96) anomalies. Their (87Sr/86Sr)i, εNd(t), zircon εHf(t) and δ18O values range from 0.70839 to 0.71013, from ?10.16 to ?12.45, from ?19.6 to ?5.8, and from 5.69‰ to 8.54‰, respectively, and their Nd and Hf two-stage model ages (TDM2) are 1.67–1.86 Ga and 1.27–2.02 Ga, respectively. These data reflect the primary partial melting of Paleoproterozoic to Mesoproterozoic lower crust with minor residual continental lithospheric mantle and supracrustal metasediments. The lithosphere was likely thickened along the southeastern margin of the Tibetan Plateau following the Indian-Asian continent-continent collision (65–41 Ma). During the post-collision phase (36–16 Ma), the transition from a compressional to extensional setting triggered the convective removal of the over-thickened CLM beneath the Yangtze craton, which led to the upwelling of asthenospheric materials. This process created alkali-rich and high-K magma through the partial melting of the thickened lower crust. Magma that carried Cu-Au-Pb-Ag minerals was emplaced by strike-slip motion along the E- to W- or ENE- to WSW-trending tectonically weak zone, finally forming an alkaline porphyry Cu-Au-Pb-Ag polymetallic deposit.     

Effect of land use land cover changes on land surface temperature during 1984–2020: a case study of Baghdad city using landsat image

Natural Hazards - Urban land surface temperature (LST) is dependent on many factors, including land cover, building materials, urban density, and other human activities. The current study evaluated...     

Derivation of earthquake-induced landslide distribution using aerial photogrammetry: the January 24, 2020, Elazig (Turkey) earthquake

Landslides - On January 24, 2020, an earthquake with the Mw of 6.8 occurred on the East Anatolian Fault Zone in Elazig Province, Turkey, and triggered many landslides. Even though Turkey is in a...     

Delineation of Near-Surface Structure in the Southern Part of 15th of May City, Cairo, Egypt Using Geological, Geophysical and Geotechnical Techniques

The integration of geological, geophysical, and geotechnical interpretation at the southern part of 15th of May City, have been used to evaluate the subsurface stratigraphy, especially the clay layer which may cause serious danger to construction. Those techniques have been used to delineate the subsurface structures as normal faults, which play a critical role on the stability of buildings. Geological setting of the area has been evaluated through the construction of a geological map from different geological sections and samples obtained from more than 30 observation points. Geophysical tools such as vertical electrical soundings (12 VESs), 2-D dipole–dipole array (7 sections), P-wave shallow seismic refraction (31 profiles) and multiple channel analysis of surface waves (31 MASW profiles) have been carried out to image the subsurface situation. Geotechnical evaluation using 26 boreholes, samples, laboratory tests and geotechnical parameters has been done at the area of interest. The geological setting demonstrates that the city had been constructed on the second and third members of Qurn Formation (Upper Eocene) composed of argillaceous limestone, marl and shale. Two normal faults are passing through the area were observed. The resistivity (VES and dipole–dipole) and seismic (P-waves and MASW) results reflect the presence of the two normal faults cross the study area, affecting the obtained section of marl, clayey marl and limestone layers. The geotechnical information indicate the presence of the normal faults and the existence of clay layer with swelling ability reaching 140%, which may cause cracks in the upper layers and/or subsidence.     

On the 3-D inversion of vertical electrical soundings: Application to the South Ismailia area—Cairo desert road, Cairo, Egypt

A code for 3-D resistivity modelling and inversion of vertical electrical soundings has been developed based on the finite-element technique and regularisation method. Synthetic data were used to test the effectiveness of the code and to examine the resolving capability of the Schlumberger array in investigating 3-D resistivity distributions. The code was applied to experimental data set constituted by 35 Schlumberger soundings collected near the Cairo city in order to study the subsurface resistivity distribution. The results have shown that valuable imaging of the subsurface resistivity distribution can be constructed even when the vertical electrical soundings are acquired in a sparse field data set.