Sr, Nd and O Isotopic Studies on the Genesis of the Huashan Granite Complex

Systematical Sr, Nd and O isotopic studies were made on the Huashan granite complex in Guangxi. Incombination with the studies of geological, petrological and geochemical data, it is believed that the complexconsists of granites of three stages. with different geneses and different source materials. They are not the prod-ucts of differentiation and evolution of one single consanguineous magma. Granites of the 1st stage are of theIndosinian syntectic type or I type, also derived from a mixed mantle-crustal source. Those of the 2nd stage areof the early Yanshanian syntectic type or I type. also derived from a mixed mantle-crustal source, and those ofthe 3rd stage are of the late Yanshanian transformed type or S type. derived from a crustal source.

Geochemical Characteristics and Genesis of the Metallogenic Rocks in the Chagande'ersi Molybdenum Deposit in Wulatehouqi,Inner Mongolia

Geochemical characteristics of the Chagande＇ersi molybdenum deposit in Inner Mongolia and its genesis were analyzed in this study using rock mineralography and rock geochemical testing. The mineralized country rocks of the Chagande＇ersi molybdenum deposit consist mainly of medium- to fine-grained monzogranite, medium-to fine-grained rich-K granite, with minor fine-grained K- feldspar granite veins and quartz veins. The rocks are characterized by high silica, rich alkali, high potassium, which are favorable factors for molybdenum mineralization. The rocks have the Rittmann index ranging from 1.329 to 1.961, an average Na20＋K20 value of 7.41, and AI2Oa/（CaO＋Na20＋K^O） 〉1, suggesting that the rocks belong to the high-K calc-alkaline peraluminous granite. The typical rock samples are enriched in Rb, Th, K and light rare earth elements, depleted in Sr, Ba, Nb, P and Ti, and these features are similar to that of the melt granite resulting from collision of plate margins. The JEu of the rocks falls the zone between the crust granite and crust-mantle granite, and are close to that of the crust granite; （La/LU）N indicates the formation environment of granite is a continental margin setting. The Nb/Ta ratios are close to that of the average crust （10）; the Zr/Hf ratios of monzogranite are partly below the mean mantle （34-60）, while the Zr/Hf ratio of K-feldspar granite are close to the mean value in the crust. Comprehensive analyses show that the granite in this area formed during the transition period between tectonic collision and post-collision. During the plate collision and orogeny, the crust and mantle material were mixed physically, remelting into lava and then crystal fractionation, finally gave rise to the formation of the rock body in this area. This has close spatial and temporal relation with the molybdenum mineralization.

On the genesis of granite pits on top of the Shigujian Peak of the Dayangshan Mountain in Jinyun County,Zhejiang Province

On top of Shigujian Peak(1477 m a.s.l.) of the Dayangshan Mountain in Jinyun County, Zhejiang Province, large amounts of granite pits with diameters ranging from several dozens of centimeters to around one meter and depth from 10 cm to 45 cm are found on rock surface.These pits mainly appear on the NE and SE sides, and their drainage mouths are in the same direction.The identification results through micropolariscope and X-ray fluorescence spectrometer reveal that bedrock of pits is from middle to fine-grained moyite being apt to be weathered and modified.In Dayangshan region the annual mean temperature is 9.2℃ and annual precipitation is over 1700 mm.On the one hand, there always experiences a period of periglacial action with temperature oscillating near 0℃ for 4 months, i.e., from December to March next year.As a consequence, the freezing-thawing cycles may be remarkable to disintegrate the bedrock.On the other hand, the windward slope of Shigujian Peak meets typhoon of over force 10 on the Beaufort scale in summer, therefore, the blowing makes suspending sands or pebbles grind in swirling form.Based on field investigation and periglacial geomorphic theory, the pits on top of Shigujian Peak are attributed to freez-ing-thawing of periglacial action.Meanwhile, storm and strong wind accelerate the process.Observation shows that both the actions are still undergoing and variant directions of wind are the main cause for making different shapes of the pits.Because the top of Shigujian is 1500 m lower than the present snow line, some scholars considered that"glacial pothole"formed in the Quaternary is hard to work, even though in the Last Glacial Maximum(LGM).

Chronology and Genesis of S-type Granites in Hetai District, Guangdong Province: Constraints from LA-ICP-MS Zircon U-Pb Dating and Tourmaline Boron Isotope In-situ Analyses

1 Introduction Hetai district,which is a mountainous area,situated on Guangning and Zhaoqing city,west Guangdong Province.Hetai district is generally located on southwest of South China Caledonian fold belt,east margin of Yunkai post-Caledonian uplift.Multiple type granites are widely distributed in Hetai district,including Caledonian,Indosinian and Yanshanian granites.Based on different