Jiamin Wang

Highly fractionated granites: Recognition and research

Granite is one of the most important components of the continental crust on our Earth; it thus has been an enduring studied subject in geology. According to present knowledge, granite shows a great deal of heterogeneity in terms of its texture, structure, mineral species and geochemical compositions at different scales from small dike to large batholith. However, the reasons for these variations are not well understood although numerous interpretations have been proposed. The key point of this debate is whether granitic magma can be effectively differentiated through fractional crystallization, and, if so, what kind of crystallization occurred during the magmatic evolution. Although granitic magma has high viscosity because of its elevated SiO2 content, we agree that fractional crystallization is effectively processed during its evolution based on the evidence from field investigation, mineral species and its chemical variations, and geochemical compositions. These data indicate that crystal settling by gravitation is not the only mechanism dominating granitic differentiation. On the contrary, flow segregation or dynamic sorting may be more important. Accordingly, granite can be divided into unfractionated, fractionated (including weakly fractionated and highly fractionated) and cumulated types, according to the differentiation degree. Highly fractionated granitic magmas are generally high in primary temperature or high with various volatiles during the later stage, which make the fractional crystallization much easier than the common granitic melts. In addition, effective magmatic differentiation can be also expected when the magma emplaced along a large scale of extensional structure. Highly fractionated granitic magma is easily contaminated by country rocks due to its relatively prolonged crystallization time. Thus, granites do not always reflect the characteristics of the source areas and the physical and chemical conditions of the primary magma. We proposed that highly fractionated granites are an important sign indicating compositional maturity of the continental crust, and they are also closely related to the rare-elemental (metal) mineralization of W, Sn, Nb, Ta, Li, Be, Rb, Cs, REEs, etc.

Experimental study of caesium atom Rydberg state polarizabilities by Doppler-free resonantly enhanced two-photon technique

Using the Doppler-free resonantly enhanced two-photon technique, we have experimentally studied the Stark shift of Cs atom in a weak electric field and obtained the scalar and tensor polarizabilities of (n = 25 - 50) Rydberg states. The experimental results are compared with the calculated ones and the reason for the discrepancy between them is discussed.

U-Pb Dating and Lu-Hf Isotopes of Detrital Zircons From the Southern Sikhote-Alin Orogenic Belt, Russian Far East: Tectonic Implications for the Early Cretaceous Evolution of the Northwest Pacific Margin

The Sikhote-Alin orogenic belt in Russian Far East is comprised of several N-S trending belts, including the Late Jurassic to Early Cretaceous accretionary prisms and turbidite basin which are now separated by thrusts and strike-slip faults. The origin and collage of the belts have been studied for decades. However, the provenance of the belts remains unclear. Six sandstone samples were collected along a 200-km long east-west traverse across the major belts in the southern Sikhote-Alin for U-Pb dating and Lu-Hf isotope analysis to constrain the provenance and evaluate the evolution of the northwest Pacific margin at this time. The result reveals that the sediments from the main Samarka belt was mainly from the adjacent Bureya-Jiamusi-Khanka Block (BJKB); the eastern Samarka belt and the Zhuravlevka turbidite basin were supplied by detritus from both the North China Craton (NCC) and the BJKB; the Taukha belt was mainly fed by sediments from the NCC; whereas the data from the Sergeevka nappes are insufficient to resolve their provenance. In the Late Jurassic to Early Cretaceous, collision and subduction was important in the initial collage of most belts in Sikhote-Alin. However, merely E-W trending collage cannot explain the increasing importance of the NCC provenance from west to east. It is proposed that the main Samarka belt was located adjacent to the BJKB when deposited, whereas the other belts were father south to accept the materials from the NCC. Sinistral strike-slip faulting transported the eastern belts northwards after their initial collage by thrusting.

Midcrustal shearing and doming in a Cenozoic compressive setting along the Ailao Shan-Red River shear zone

The Cenozoic Xuelong Shan antiformal dome is located along the northern segment of the Ailao Shan-Red River shear zone in Yunnan, China. Subhorizontal foliation in the gneiss core is recognized, representing a broad top-to-NE shear initiated under amphibolite facies conditions and propagating into greenschist facies in the mantling schist and strike-slip shear zone. Microfabrics of crystallographic-preferred orientations (CPOs) in quartz suggest that the deformation temperatures increased with increasing structural depth from the upper crust (300–500°C) in the mantling schist to the midcrust (15 km or more, ≥650°C) in the gneissic core. This trend is mirrored by variations in the metamorphic grade of the syn-kinematic mineral assemblages and microstructures, which range from garnet + amphibole + biotite + sillimanite + rutile + feldspar in the core to garnet + staurolite + biotite + epidote + muscovite within the limb units. The dome experienced the following deformation history: (1) a broad top-to-NE shear in the subhorizontal foliation of the gneiss core during the first stage of deformation (D1); (2) opposing reverse-sense shear along the two schist limbs of the dome during contraction-related doming (D2–D3); (3) sinistral strike-slip shearing within the eastern limb (D4); and (4) extensional deformation (D5). The structural-thermal patterns suggest the antiformal dome formation was roughly coeval with top-to-NE ductile shearing in the midcrust of Tibet at 32 Ma or earlier. A major implication is that there was a phase of contractional ductile deformation in the region prior to the initiation of strike-slip deformation.

IONIZATION PROPERTIES IN THE COLLISION OF RYDBERG CS ATOMS WITH CCL4 MOLECULES

The experimental study of ionization in the collision of Rydherg Cs atoms with CCL molecules is conducted using the crossed atomic and molecular beam apparatus. It is found that the relative collision rate constants are not consistent with the prediction of the essentially free electron model in the range ofn=30–50. The possible reason for this discrepancy is discussed.

Stark characteristics of cesium atom studied in a thermionic bulb

MOST of the spectral studies of atomic strong electric effect are carried out by means of atomicbeam and pulse laser. The spectral linewidth is ranged from the order of one to ten GHz. Inrecent years, with the application of CW laser, there appeared the high-resolution work with