Based on the observation data of CHAMP satellite from 2006 to 2009, a 2D crustal magnetic anomaly model in China is established to study the distribution characteristics of crustal magnetic anomaly. In this paper, the 2D anomaly model is derived from the Legendre polynomial expansion of harmonic term N =6-50. The result shows that many elaborate structures reflected in magnetic anomaly map well correspond to the geologic structures in China and its adjacent area. The magnetic anomaly at low satellite height behaves complexly, which is mainly caused by the magnetic disturbance of shallow rocks.In contrast, the magnetic field isolines at high satellite height are relatively sparse and only magnetic anomalies of deep crust are reflected. This fact implies that the 2D model of crustal magnetic anomaly provides an important method of the space prolongation of geomagnetic field, and is of theoretical and practice importance in geologic structure analysis and geophysical prospecting.
The water solubility in Al-Fe-Mg orthopyroxene[(Mg,Fe,Al)(Si,Al)O3:XFe=0.1]was investigated as a function of temperature and Al contents.Experiments were performed at 10 kbar with temperatures ranging from 800 to 1200°C under water-saturated conditions.Water contents in the(Mg,Fe)SiO3–H2O–Al2O3system were determined using unpolarized Fourier transform infrared spectroscopy.The present results show that water solubility in Al-bearing orthopyroxene decreases systematically with temperature from approximately 1 weight%at 800°C to 568±58 ppm at 1200°C and increase significantly with increasing Al2O3contents under the same annealing temperature and pressure.Combined with published results on the dependence of hydroxyl solubility on water fugacity and pressure,the present results can be described by the relation20.5OH H O()exp nC A T f1bar solid,R H V P T where A=0.0024±0.0015 ppm/bar0.5,1bar H=103.348±9.768 kJ/mol,andsolid V=9.2±1.1cm3/mol.This equation implies that the incorporation mechanism of water in aluminous orthopyroxene involves the isolated OH groups.Based on the experimentally established solubility model used in this study,it is suggested that water solubility decreases with increasing temperature under typical upper mantle pressure.The predicted temperature dependence of water solubility is in good agreement with the previous experimental observations in Al-bearing orthopyroxene,but the opposite dependence is observed in Al-free systems.Moreover,our estimation of the water solubility in upper-mantle minerals as a function of depth for a typical oceanic geotherm might be of potential importance in interpreting the geophysical observations.
