Thermal equations of state of dioctahedral micas on the join muscovite–paragonite

 Powder diffraction measurements at simultaneous high pressure and temperature on samples of 2M1 polytype of muscovite (Ms) and paragonite (Pg) were performed at the beamline ID30 of ESRF (Grenoble), using the Paris-Edinburgh cell. The bulk moduli of Ms, calculated from the least-squares fitting of V–P data on each isotherm using a second-order Birch–Murnaghan EoS, were: 57.0(6), 55.1(7), 51.1(7) and 48.9(5) GPa on the isotherms at 298, 573, 723 and 873 K, respectively. The value of (∂K _T /∂T) was −0.0146(2) GPa K⁻¹. The thermal expansion coefficient α varied from 35.7(3) × 10⁻⁶ K⁻¹ at P ambient to 20.1(3) × 10⁻⁶ K⁻¹ at P = 4 GPa [(∂α/∂P) _T = −3.9(1) × 10⁻⁶ GPa⁻¹ K⁻¹]. The corresponding values for Pg on the isotherms at 298, 723 and 823 K were: bulk moduli 59.9(5), 55.7(6) and 53.8(7) GPa, (∂K _T /∂T) −0.0109(1) GPa K⁻¹. The thermal expansion coefficient α varied from 44.1(2) × 10⁻⁶ K⁻¹ at P ambient to 32.5(2) × 10⁻⁶ K⁻¹ at P = 4 GPa [(∂α/∂P) _T = −2.9(1) × 10⁻⁶ GPa⁻¹ K⁻¹]. Thermoelastic coefficients showed that Pg is stiffer than Ms; Ms softens more rapidly than Pg upon heating; thermal expansion is greater and its variation with pressure is smaller in Pg than in Ms. Received: 28 January 2002 / Accepted: 5 April 2002     

湘南红旗岭锡多金属矿床地质特征及Ar-Ar同位素年代学研究

红旗岭锡多金属矿床是湖南东坡矿田代表性的脉状矿床,亦是湖南省最大的脉状锡矿,并与同一断裂带上相邻的枞树板和南风坳等脉状铅锌银矿构成了一套Sn-W-Pb-Zn-Ag矿床组合。在已有研究的基础上,我们对该矿床进行了高精度白云母Ar-Ar测年,获得坪年龄为153.3±1.0Ma,相应的等时线年龄为153.6±1.5Ma(MSWD=0.55),反等时线年龄为153.5±1.5Ma(MSWD=2.1)。这些年龄数据明显早于相同矿石类型石英流体包裹体的Rb-Sr等时线年龄(143.1±8.7Ma)及相伴产出的花岗斑岩钾长石40Ar-39Ar年龄(144±3Ma),而与千里山岩体主体相锆石SHRIMPU-Pb年龄(155～151Ma)及与之相关的柿竹园矿床(151.0±3.5Ma)和金船塘矿床(158.8±6.6Ma)矽卡岩型矿床的Re-Os等时线年龄在误差范围内相一致,指示区内脉状矿床亦与千里山岩体存在密切的时空关系。综合已有的研究认为,高热花岗岩浆的高分异演化是区内多金属元素巨量堆积成矿的物质基础,不同的围岩性质及构造条件则可能制约了不同的矿化过程,从而形成不同的矿床组合。当围岩为泥盆系碳酸盐岩时,形成一套接触带矽卡岩-云英岩-大理岩型钨锡钼铋铅锌矿和远端脉状铅锌银矿床组合,而当围岩为震旦系碎屑岩时,沿构造通道(断裂带)发育一套脉状钨锡多金属矿和远端脉状铅锌银矿床组合。