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    20 September 2011, Volume 17 Issue 3
    Magmatism and Evolution of the Tibetan Plateau
    MO Xuan-Xue
    2011, 17(3):  351. 
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    The Tibetan Plateau  is one of  the regions  in China where  igneous rocks are very widely developed. Various  types of
    volcanic and plutonic rocks are distributed over 300,000 km2 in area and take 10% area of the entire Plateau. These igneous rocks
    and carried deep-seated nodules play  important  roles  in understanding geodynamic evolution of  the Tibetan Plateau, as either
    lithoprobes/windows or  tectonic  records, and are closely  related  to mineralization as well. This paper discusses some  important
    scientific  topics via studying  igneous  rocks.  (1) The  timing of  Indo-Asia collision: This  is a very  important scientific problem.
    There  is, however, a wide  range of discrepancy about  the  timing of  initiation of  the collision  (from earlier  than 70 Ma,  to even
    later than 34 Ma). According to multiple lines of evidences from the 1500 km-extending main collision zone in southern Tibet, we
    deduced a conclusion that Indo-Asia collision likely started from 65/70 Ma and completed in c. 40 Ma (syn-collisional stage), and
    then transformed into post-collisional stage after 40 Ma. (2) Underplating and magma mixing, an event of mantle-crust interaction
    during  syn-collisional  stage: There are abundant evidences  for underplating and magma mixing  in  southern Gangdese. An

    important process of continental growth and evolution took place in the Tibetan Plateau. (3) The origin of formation of extremely
    thick crust of  the Tibetan Plateau: A deduction of “Two  types of crust and  two  types of mechanism”  is suggested based on  the
    studies of collisional and post-collisional  igneous  rocks. There are  two  types of crust,  juvenile crust and  recycled crust,  in  the
    Plateau. Crustal  thickening of  the Plateau was caused by  two  types of mechanism,  i.e., both structural compression and  input of
    mantle materials via magmatism. (4) The composition, structure and evolution of the lithosphere of the Tibetan Plateau: There are
    three geochemical reservoirs in the lithospheric mantle, and three types of lithospheric structure underneath the Tibetan Plateau.
    Nodules and outcrops of mantle/lower crust-seated rocks are found in several locations of the Plateau. (5) Possible lateral flow of
    lower crust and upper mantle: Migration of collisional and post-collisional volcanism with time shows a highly distinctive pattern,
    which can be interpreted to reflect lateral flow of the lower crust and asthenospheric mantle induced by the approach and ensuing
    collision of relatively thick (India and Eurasia) continental plates.

    Titanite as an Indicator Mineral of Tin Mineralizing Potential of Granites in the Middle Nanling Range
    WANG Ru-Cheng, XIE Lei, CHEN Jun, YU A-Peng, WANG Lu-Bin, LIU Jian-Jun, ZHU Jin-Chu
    2011, 17(3):  368. 
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         Titanite  is a common accessory mineral  in calc-alkailine granites, and may contain  tin  to various extents owing  to similar crystal-chemical  features between Ti4+and Sn4+.  It  thus may be considered as a useful mineral  in studying  tin granites (particularly oxidized tin granites). This paper deals with a systematic study on titanite from three granites with known extensive tin mineralization  (Qitianling, Huashan and Guposhan)   and other  three granites currently unknown  for important  tin mineralization (Lianyang, Dadongshan and Jiufeng). Titanite  from all  these granites can  form both at early-magmatic stage and during biotite chloritization at hydrothermal stage; late-magmatitc titanite is also found in Qitianling, Huashan and Jiufeng. Electron-microprobe results  reveal distinct compositions among  three  types of  titanite. Early-magmatic  titanite contains  trace of  tin  (generally < 1%  SnO2), whereas  late-magmatic  titanite with 3  to 26 % SnO2 can be  found  in Qitianling, Huashan and Jiufeng. Hydrothermal titanite is typified by high Al and F contents. Comparison of SnO2 contents for titanite from six granites shows that titanite, either magmatic or hydrothermal,  from  three  tin granites  (Qitianling, Huashan and Guposhan)  is  rich  in SnO2 with averages > 0.4 %,revealing  their strong  tin mineralizing potential;  titanite of Lianyang and Dadongshan granites  is very poor  in SnO2  (< 0.1 %), consistent with their barren feature. However, similar to Huashan titanite, the magmatic titanite from Jiufeng granite contains up to 3 % SnO2, and hydrothermal one up to 2 % SnO2. Such tin enrichment in titanite might imply higher tin potential of the Jiufeng granite, possibly favorable for further tin exploration. The present results demonstrate that titanite may act as a simple, but useful mineral criterion of tin mineralizing potential in granites.

    Fractionation, Evolution, Petrogenesis and Mineralization of Laiziling Granite Pluton, Southern Hunan Province
    ZHU Jin-Chu, WANG Ru-Cheng, LIU Jian-Jun, ZHANG Hui, ZHANG Wen-Lan, XIE Lei, ZHANG Rong-Qing
    2011, 17(3):  381. 
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           The Laiziling granite stock was emplaced in the Early Yanshanian period. Its zircon U-Pb age is dated at (154-155)
    Ma. This granite pluton is characterized by enrichment in Li, Rb, Sn, W, Nb, Ta etc. rare metal elements, Pb, Zn etc. base metal elements and H2O, F etc. volatiles. A vertical zonation  is well developed within a vertical distance of  (450~500) m. From  the deeper  level upwards  to  the  top of  the Laiziling Mountain peak,  the  following zones are successively observed: protolithionite granite zone, leucogranite (two-mica granite and Li-muscovite granite) zone, albite granite zone, greisen zone, massive quartz and pegmatoid stockscheider. Along this direction, the major and trace elements concentrations of rocks are regularly changed. Well developed magmatic fractionation and magmatic-hydrothermal evolution are responsible for high-degree enrichment of rare-metal elements, base metal elements and volatiles in the rocks and further mineralization. 
        Although most samples of the Laiziling granite stock exhibit peraluminous feature, the protolithionite granite at deeper level has high contents of Zr, REE, Y, Nb, Th, U etc. high field strength elements. Furthermore, relatively higher ε Hf values (from -5.9 to -1.9, averaging -4.2) and relatively lower Hf model ages (  tDM values from 1.32 Ga to 1.58 Ga, averaging 1.47 Ga) indicate an evident involvement of mantle materials. We propose that the primary magma source of the Laiziling granite might be derived from the A-type Qitianling batholith, or a fractionated deeper magmatic chamber similar to the Qitianling granite.

    Geological and Geochemical Characteristics and Petrogenesis of the Mafic Rocks from Zhangyuan, Northern Jiangnan Orogen
    ZHANG Yan-Jie, ZHOU Xiao-Hua, LIAO Sheng-Bing, TU Ming-Gang, JIANG Ren, JIANG Yang
    2011, 17(3):  393. 
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              Zhangyuan mafic rocks of NE-SW trend are distributed along the Yaoli-Zhangyuan-Jiangtan line in the northern slope of Zhanggong Mountain, between Anhui and Jiangxi provinces. They occur as structural shivers and  fragments  in  flysch matrix textured by Neoproterozoic volcano-fine clastic rocks of continental margin, and overall display characteristics of tectonic melange belt. Mafic  fragments  include altered pillow-block basic  lava, gabbro, dolerite, etc, which were concomitant  in space since  the Neoproterozoic. By analyzing geological and geochemical characteristics of the Zhangyuan mafic rocks, their origin is considered to be  in a  small,  slow expansion oceanic basin  spreading  ridge of  the continental margin environment, with  the  features of primitive oceanic crust mafic rocks. It is proposed that Zhangyuan mafic rocks belong to westward extension of Fuchuan ophiolite in Southern Anhui province.

    Recognizing the TTG Rock Types: Discussion and Suggestion
    FENG Yan-Fang, DENG Jin-Fu, XIAO Qing-Hui, XING Guang-Fu, SU Shang-Guo, CUI Xian-Yue, GONG Fan-Ying
    2011, 17(3):  406. 
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            This paper briefly describes and compares  two  international classifications of  the  rock  types of TTG series:the Le Maitre’s QAP modal classification based on accurate mineral modes, and  the O’Connor's An-Ab-Or normative classification when the Q-norm is>10%. Both modal and normative classifications are generally consistent with each other. The field 5 of the QAP is called tonalite as the root name. It includes trondhjemite and plagiogranite (adopted by part of the USSR geologists). The latter may be called as    light-coloured  (M≤10)  tonalite. However,  the  tonalite and  trondhjemite can be directly determined by using  the An-Ab-Or normative classification. Based on  the comparison between  the Le Maitre’s QAP modal classification and some Chinese modified QAP modal classifications, and paying attention  to some examples  for  recognizing  the TTG  rock  types using O’Connor’s An-Ab-Or normative classification by  the authors, several suggestions are proposed here as  follows:  (1) The Le Maitre’s QAP modal classification may be used for recognition of the TTG rock types, when the accurate mineral modes are available, and then the procedure is necessary to be determined whether these rock types are tonalite or trondhjemite using the M indexes. When the chemical data are available but the accurate modes are lacking, the O’Connor’s normative classification may be used. When both the accurate mineral modes and the chemical data are available, both classifications may be used for a better recognition of  the TTG  rock  types;  (2)  In  terms of widespread utilization of  the O’Connor’s classification  for  the Archean grey gneiss and granite-greenstone belt, and for some Phanerozoic magmatic arcs, a suggestion of using the O’Connor’s classification for  the orogenic belts  in China may be helpful  for  recognizing  the TTG  rock  types;  (3) A unified classification  is needed  for regional  igneous petrological  investigations, particularly  in China, because of  large available chemical data rather  than accurate mineral modes, then the O’Connor’s normative classification may be suggested; (4) The O’Connor’s classification  is actually a chemical classification, which is good for a comparison between the intrusive and volcanic rocks, as well as between the igneous rocks and  the experimental melts. Finally, a  two-step  recognition procedure  is suggested: Firstly, use  the TAS classification by Middlemost to discriminate the felsic rocks; and second, use the O’Connor’s An-Ab-Or normative classification for recognition of TTG rock types.

    Review on Application of Geobarometry for Granitic Rocks
    LI Xiao-Wei, HUANG Xiong-Fei, HUANG Dan-Feng
    2011, 17(3):  415. 
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           This paper briefly and critically discusses several common geobarometers applied  to granitic systems, especially
    the specific  rock  types, and  their  limitation and error analysis. The Al-in-hornblende barometer can be applied  to calc-alkaline granites and  is  suitable  for  low-pressure mineralized granitic pluton. The Fe-rich orthopyroxene-fayalite-quartz assemblage barometer can be used  to calculate  the crystallization pressure condition of  rapakivi granites, and  the crystallization pressure of coexisting alkali  feldspar, plagioclase and quartz can be obtained via projecting onto  the Q-Ab-Or-H2O phase diagram  for granites. The hydrostatic pressure of  fluid  inclusion  in granites can be acquired by  thermodynamic state equations or    raman spectroscopy. Some  indicative minerals  like magmatic epidote  sometimes can constrain  the  lower pressure  limit. Moreover, the pseudosection calculated by THERMOCALC   eventually can define  the pressure scope  for a specific coexisting mineral assemblage and specific pressure and temperature.

    Accessory Minerals of Lisong Granite and Mafic Microgranular Enclaves in the Guposhan Area as Indicators of Magma Mixing
    WANG Lu-Bn, WANG Ru-Cheng, ZHU Jin-Chu
    2011, 17(3):  423. 
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           In the middle part of Nanling Range there is an early Yanshanian (Jurassic) A-type granite belt. The Guposhan granite
    batholith  is well known by  its mafic microgranular enclaves  (MME).  In order  to study  the mineralogical evidence of magma
    mixing and the relationship between basic magma and tin-mineralization, we studied and compared the compositions of accessory minerals  in  the granite and MME by using elecron microprobe. We  firstly confirmed  the appearance of subhedral cassiterite of magmatic origin  in cleavages of mafic minerals  in MME. We also  found  that  the zircon and  titanite  in MME show a  rapid crystallization evidence after  the basic magma emplacement. Particularly,   consistent with  the  tin enrichment during  the granite evolution, the late-stage titanite from the granite has higher tin contents than the early-stage one. However, the MME titanite has just the opposite evolution trend in the aspect of tin contents, which is the result of rapid crystallization.

    Origin of the Early Cretaceous Trachyte in Northern Guangdong Province Constraints of Sr-Nd-Pb Isotopes
    XIANG Yuan-Xin, Wu-Jian-Hua
    2011, 17(3):  436. 
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     The trachyte in the Dachangsha basin of the northern Guangdong province was formed in the Early Cretaceous (SHRIMP
    zircon U-Pb dating shows an age of  trachyte as 135.3±1.5 Ma). The Sr-Nd-Pb  isotopic composition cnaracteristics of  trachyte are as  follows: enriched  in  radiogenic  lead,(206Pb/204Pb)i=18.23~18.39,(207Pb/204Pb)i = 15.78~15.88,(
    208Pb/204Pb)i=38.83~39.14; moderate initial Nd isotopic ratios, εNd( t )=-3.35~-3.21; and higher initial Sr isotopic rations, (
    87Sr/86Sr)i= 0.706871~0.709074. On the Pb-Pb diagrams, the trachyte is plotted above NHRL line and △Sr = 99.1~247.0  (140.5 in average), which indicates that the trachyte has obvious Dupal anomaly. The Sr-Nd, Sr-Pb, Nd-Pb and Pb-Pb relationship of the trachyte suggests that the trachyte should be originated from partial melting of the young lower crust, while the lower crust should be influenced by metasomatism of fluids from dehydration of subducted upper crust,and there was no upper crust contamination in the process of magma rising.

    Aluminic Ester Modified Tourmaline Powder and Characterization
    HU Ying-Mo, XIONG Pei, YANG Xue, BIAN Jing, ZHU Jian-Hua, WANG Qing-Ling
    2011, 17(3):  447. 
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          The surface modification of  the  tourmaline powder with an aluminic ester was discussed. The experimental  results
    showed that the activation index of aluminic ester modified tourmaline powder reached to 97% when 1.5 % aluminic ester reacted with tourmaline powder at 70 ℃ for 0.5 h in benzene; and the aluminic ester modified tourmaline had an excellent hydrophobic property, but with no change in crystal configuration of tourmaline.

    Assessing Precambrian Stratigraphic Sequence of Dongchuan Area:  Evidence from Zircon SHRIMP and LA-ICP-MS Dating
    ZHU Hua-Beng, FAN Wen-Yu, ZHOU Bang-Guo, WANG Sheng-Wei, LUO Mao-Jin, LIAO Zhen-Wen, GUO Yang
    2011, 17(3):  452. 
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              The authors got a  series of  zircon U-Pb ages  for 3  samples  in Dongchuan area, Yunnan province:  the diabase
    (TW1) cutting Yinming Formation,  the  ignimbrite  (TW2) of Sahaiguo Formation, and  the sedimentary conglomerate  (TW3) of
    Pingdingshan Formation. The SHRIMP zircon U-Pb dating for TW1 yielded an upper intersection age of (1667±13) Ma, which
    indicates  the  timing of diabase  intrusion activity  in Mesoproterozoic. The SHRIMP zircon U-Pb dating  for TW2 showed  two
    ages: an everage weighted age of (2285±11) Ma can be considered as  the eruption  timing of  lava  in Paleoproterozoic, and  the
    upper intersection age of (2742±48) Ma indicates that a series of older rocks might exist in the Dongchuan area. The LA-ICP-
    MS dating  for sample TW3 yielded an youngest concordant age of  (1838±10) Ma, which constrained  the oldest sedimentation
    age of the Pingdingshan Formation. Based on these dating results, the Precambrian stratigraphic sequence fitting the Dongchuan
    area from the older rocks upwards is as follows: Sahaiguo Formation, Wangchang Formation, Caiyuanwan Formation, Pingdishan
    Formation, Yinming Foramation, Luoxue Formation, Heisan Formation, Qinglongsan Formation and Dayingpang Formation.

    Layer Thickness Controls on Surface Density and Fractal Dimension of  Structural Fractures in Carbonate Strata
    MENG Qing-Feng, HOU Gui-Ting, BAN Wen-Qiang, JU Yan, ZHANG Qing-Lian, LI Le, SHU Wu-Lin
    2011, 17(3):  462. 
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           Layer  thickness  is  fairly  important  for  the development of  structural  fractures  in carbonate  strata. According  to
    statistical analys  is, of  the profile measuring  results of Dawangou, Qingsong and Penglaiba of Keping, Xinjiang,  the surface
    densities of structural  fractures  in carbonate strata  is negatively correlated  to  layer  thicknesses. The  thicker  the  layer  is,  the
    smaller  the  fracture densityis. But  the  scale of  fractures  is  relatively bigger; when  the  layer  thickness becoming  thinner,
    the  fracture density  is  linearly  increasing, meanwhile,  the scale of  fractures  is getting  relatively smaller. Structural  fractures  in
    carbonate strata own good  fractal characteristics. Statistics shows  that  there  is a negative correlation between  fracture  fractal
    dimension and  layer  thickness. Fracture  fractal dimension becomes bigger when  layer  thickness gets smaller, which  indicates
    a better  fracture development. Certain  linkage exists between  fractal dimension and density of  fractures, which can  together
    quantitatively describe development  level of  fractures. Generally,  fracture  fractal dimension  increases wiih  increasing  fracture
    density.  If  fractures have  the same density,  the bigger  fractal dimension  is,  the more uniform  the distribution of  fractures  is.
    Meanwhile, permeability of the carbonate layers is poorer.

    Seismic Properties of Typical Rocks in South China
    HU Hai, WANG Qi, MA Zhong-Gao, ZHOU Feng, WANG Liang-Shu 
    2011, 17(3):  469. 
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              Because  the  interpretation of seismic data  is not unique, seismic properties of  typical rock samples  from Jiangxi and
    Fujian Provinces were studied  to better explain seismic data  in South China  in  terms of  the crustal structure and composition.
    The P- and S-wave velocities of 5 rock samples were measured using MTS-815 Rock and Concrete Mechanics Test System. The
    results indicate that seismic velocities of the samples increase with increasing pressure, but decrease with increasing temperature.
    At  the  same pressure and  room  temperature,  the P- and S-wave velocities gradually decrease  from marbleized  limestones,
    through granodiorites, K-feldspar granites  to siltstones. Because  the highest confining pressure  in  the experiments  is 140 MPa,
    the measured velocities are only comparable with seismic observations  in  the upper crust. To constrain  interpretation of seismic
    data at greater depths, we calculated  the seismic velocities of 39 samples based on modal compositions, elastic constants of
    minerals and generalized mixing rules. The Vp/Vs and Poisson,s ratios of the samples increase with decreasing contents of quartz.
    Compared with felsic rocks, the limestones, dolomites and marbles are characterized by high P-wave velocities, and high Vp/VS
    and poisson,s ratios, which provides a way to search carbonate basins beneath the granite regions in South China.