Almandine megacrysts from Yingfengling Cenozoic basalt in Leizhou Peninsula and their parental magma origin

The garnet megacrysts from Yingfengling basalts are characterlzed by high FeO (】20%), CaO (7.02% -8.16%) and low MgO (5.88%-10.87%). Significant composition variations are observed in these megacrysts, of which Ni, V, Sc, Co, and HREE are positively correlated with their Mg# and Zr, Hf, Ga, Y, Sr, Nb, Zn and LREE-MREE are negatively correlated with Mg#. Megacryst parent magma is a highly evolved residual melt with strongl depletion in Ti, Sr, Hf, Nb and HREE. This parental magma was generated by more than 60% of crystallization fractionation of clinopyroxene, garnet, plagioclase and ilmenite from quartz tholeiitic magma. It has not erupted to the surface, but stayed at the upper mantle and formed the megacrystic cumulate. Megacrysts and their host basalt are in disequilibrium.

Petrography and Mineral Chemistry of the Almanden Garnet, and Implication for Kelyphite Texture in the Miocene Alkaline Basaltic Rocks North East Jordan

The Miocene alkali basaltic rocks cover the northeastern part of Jordan, within Harrat Al-Shaam plateau. The volcanic concentrated along the Dead Sea boundary and spread around the north east of Jordan area, and was considered as interplat volcanic field in Jordan. The volcanic basalt is associated with xenoliths fragmental rocks or xenocryst minerals. Nine samples were collected from the study area and analyzed for XRD, XRF and SEM. These samples presented the xenoliths rocks and minerals existing in the study area. This study is focused on the garnet and pyroxene xenoliths minerals in Tulayl Al-Hasna area within Ufayhim Formation. Hand samples are characterized by coarse aggregates of garnets up to (2 cm in diameter) with dark brown to red color, and highly fresh fractures. Also, the pyroxene (<1.5 cm) with gray to dark green color, and the olivine (range 3 - 4 mm) are pale green to dark green and pale yellowish color. In thin sections, plagioclase phenocryst in the garnet presented corona texture. In addition, garnet surrounded by orthopyroxene refers to kelyphite texture. There are two types of kelyphite texture fibers and radial as shown in Scanning Electron Microscope photomicrograph. The mineralogical analyses of garnet for X-Ray Diffraction are composed of almandine, pyrope and majorite. The existence of minerals reflects the high pressure and temperature of the upper mantle origin. The chemical analysis showed the average composition of garnet as follow (Alm 42.78, Pyro 41.04, Gross 16.18), pyroxene (Wo 16.90, Fs 20.37, En 62.73). This referred to presentation of the following elements Mg, Fe and Ca in the garnet. As a result, the basaltic garnet xenoliths were from shallow lithosphere mantle origin.

Electrical Conductivity of Multiphase Garnet under High-Temperature and High-Pressure Conditions

Mineral mixing,a fundamental process during mantle convection,alters the chemical composition of mantle minerals.However,the impact of this process on the electrical conductivity of mineral assemblages remains poorly understood.We measured the electrical conductivity of three single-phase garnets and their corresponding mixtures at 1.5 GPa and varying temperatures using the impedance spectroscopy within frequency from 10^(-1)to 10^(6)Hz.The electrical conductivity of dehydrated garnets is primarily controlled by their iron content,exhibiting an activation energy about 1.0 eV,indicative of small polaron conduction.The garnet mixture displays lower electrical conductivities and higher activation energies compared to their single-phase counterparts.This discrepancy of conductivity can be half order of magnitude at high temperatures(>1073 K),suggesting formation of resistive grain boundaries during the mixing process.In the mantle transition zones,grain boundary conductivity could exert a limited impact on the bulk conductivity of the interface between the stagnant slab and ambient mantle.