北秦岭瓦穴子—乔端断裂带的构造特征及形成温度—压力条件探讨

瓦乔(瓦穴子—乔端)断裂带是北秦岭尤为重要的断裂带之一,该带经历了长期的变质变形作用,记录了二郎坪弧后盆地向华北板块南缘俯冲消亡的信息。本文运用多种方法,对瓦乔断裂带几何学、运动学及形成温压条件进行研究和探讨,得出以下几点认识:①瓦乔断裂带产状基本倾向NNE,带内线理发育,表现为由N向S逆冲的运动学特征,且存在左旋剪切的分量;②瓦乔断裂带变形岩石显微构造特征明显,反映了挤压应力下塑性流变的特征;③运用角闪石全铝压力计,得到瓦乔断裂带形成压力为0.64GPa。越靠近瓦乔断裂带中心,压力逐渐变大,位于断裂带中心压力达到0.68GPa,已达到中压相系环境;④运用角闪石—斜长石地质温压计算得瓦乔断裂带形成温度范围500～550℃,属中温环境。     

Differential uplift between Beihuaiyang and Dabie orogenic belt

Isotope dating, hornblende geobarometer, fission-track analysis and fluid inclusion homogeneous temperature analysis have been applied to Caledonian, Variscan and Yenshan plutons in Bei Huaiyang (BHY) and Dabie orogenic belt (DOB), and the emplaced depths and ages of these plutons have been obtained in order to obtain differential uplift time and uplift heights between BHY and DOB since late Paleozoic era. BHY had experienced three stages of uplift (C1-C2, T-J2, J3-K1) and its total uplift height is about 10 km, but, DOB had only experienced two stages of uplift (T-J2, J3-K1) and its maximum uplift height is more than 15 km. BHY uplift occurred mainly before the mid-Jurassic (about 150 Ma), but DOB uplift took place after the mid-Jurassic (about 150 Ma).     

Seismic,petrologic, and geodetic analyses of the 1999 dome-forming eruption of Guagua Pichincha volcano,Ecuador

Guagua Pichincha, located 14 km west of Quito, Ecuador, is a stratovolcano bisected by a horseshoe-shaped caldera. In 1999, after some months of phreatic activity, Guagua Pichincha entered into an eruptive period characterized by the extrusion of several dacitic domes, vulcanian eruptions, and pyroclastic flows. We estimated the three-dimensional (3-D) P-wave velocity structure beneath Guagua Pichincha using a tomographic inversion method based on finite-difference calculations of first-arrival times. Hypocenters of volcano-tectonic (VT) earthquakes and long-period (LP) events were relocated using the 3-D P-wave velocity model. A low-velocity anomaly exists beneath the caldera and may represent an active volcanic conduit. Petrologic analysis of eruptive products indicates a magma storage region beneath the caldera, having a vertical extent of 7–8 km with the upper boundary at about sea level. This zone coincides with the source region of deeper VT earthquakes, indicating that a primary magma body exists in this region. LP swarms occurred in a cyclic pattern synchronous with ground deformation during magma extrusions. The correlation between seismicity and ground deformation suggests that both respond to pressure changes caused by the cyclic eruptive behavior of lava domes.     

新疆尾亚—天湖地区花岗岩类剥蚀程度估算及对区域找矿的启示

尾亚—天湖地区位于新疆中亚造山带东南部的中天山地块内,晚古生代—中生代岩浆活动强烈,产出了战略性关键矿产尾亚钒铁磁铁矿.在详细岩相学观察的基础上,对尾亚、天湖和沙泉子南岩体中的角闪石和黑云母进行了电子探针(EMPA)测试分析,限定了 3个岩体结晶的温压条件、氧逸度、含水量和含铁指数等要素,为解析中天山地块的岩浆-成矿物...     

Recalibration of the Garnet-Muscovite (GM) Geothermometer and the Garnet-Muscovite-Plagioclase-Quartz (GMPQ) Geobarometer for Metapelitic Assemblages

The garnet–muscovite (GM) geothermometer and the garnet–muscovite–plagioclase–quartz(GMPQ) geobarometer have been simultaneously calibrated underconditions of T = 450–760°C and P = 0·8–11·1kbar, using a large number of metapelitic samples in the compositionalranges = 0·53–0·81, = 0·05–0·24, = 0·03–0·23 in garnet, = 0·17–0·74 in plagioclase, and Fe = 0·04–0·16, Mg =0·04–0·13, Al^VI = 1·74–1·96in muscovite on the basis of 11 oxygens. The resulting GM thermometeryielded similar temperature estimates (mostly within ±50°C)to that of the garnet–biotite thermometer, and successfullydiscerned the expected systematic temperature change of progradesequences, thermal contact zones and an inverted metamorphiczone. The resulting GMPQ barometer yielded similar pressureestimates (mostly within ±1·0 kbar) to the garnet–aluminumsilicate–plagioclase–quartz (GASP) barometer andplaced the aluminosilicate-bearing samples in the appropriatealuminosilicate stability fields. Application of the GMPQ barometerto thermal contact aureoles or rocks within limited geographicalareas confirmed the expected constant pressures that shouldexist in these settings. The random errors of the GM thermometerand the GMPQ barometer are estimated to be ±16°Cand ±1·5 kbar, respectively. When biotite or aluminosilicateis absent in metapelites, metamorphic P–T conditions maybe determined by simultaneously applying the GM thermometerand the GMPQ barometer. KEY WORDS: application; calibration; geobarometer; geothermometer; metapelite     

Petrography and uplift history of the Quaternary Takidani Granodiorite: could it have hosted a supercritical (HDR) geothermal reservoir?

The Quaternary Takidani Granodiorite (Japan Alps) is analogous to the type of deep-seated (3–5 km deep) intrusive-hosted fracture network system that might support (supercritical) hot dry/wet rock (HDR/HWR) energy extraction. The I-type Takidani Granodiorite comprises: porphyritic granodiorite, porphyritic granite, biotite-hornblende granodiorite, hornblende-biotite granodiorite, biotite-hornblende granite and biotite granite facies; the intrusion has a reverse chemical zonation, characterized by >70 wt% SiO₂ at its inferred margin and <67 wt% SiO₂ at the core. Fluid inclusion evidence indicates that fractured Takidani Granodiorite at one time hosted a liquid-dominated, convective hydrothermal system, with <380°C, low-salinity reservoir fluids at hydrostatic (mesothermal) pressure conditions. ‘Healed’ microfractures also trapped >600°C, hypersaline (35 wt% NaCl_eq) fluids of magmatic origin, with inferred minimum pressures of formation being 600–750 bar, which corresponds to fluid entrapment at 2.4–3.0 km depth. Al-in-hornblende geobarometry indicates that hornblende crystallization occurred at about 1.45 Ma (7.7–9.4 km depth) in the (marginal) eastern Takidani Granodiorite, but later (at 1.25 Ma) and shallower (6.5–7.0 km) near the core of the intrusion. The average rate of uplift across the Takidani Granodiorite from the time of hornblende crystallization has been 5.1–5.9 mm/yr (although uplift was about 7.5 mm/yr prior to 1.2 Ma), which is faster than average uplift rates in the Japan Alps (3 mm/yr during the last 2 million years). A temperature–depth–time window, when the Takidani Granodiorite had potential to host an HDR system, would have been when the internal temperature of the intrusive was cooling from 500°C to 400°C. Taking into account the initial (7.5 mm/yr) rate of uplift and effects of erosion, an optimal temperature–time–depth window is proposed: for 500°C at 1.54–1.57 Ma and 5.2±0.9 km (drilling) depth; and 400°C at 1.36–1.38 Ma and 3.3±0.8 km (drilling) depth, which is within the capabilities of modern drilling technologies, and similar to measured temperature–depth profiles in other active hydrothermal systems (e.g. at Kakkonda, Japan).     

甘肃金川Ⅱ号岩体辉石化学特征及其地质意义

金川Ⅱ号岩体主要由二辉橄榄岩和硫化物橄榄岩构成,单斜辉石和斜方辉石为岩相中主要造岩矿物,单斜辉石含量一般高于斜方辉石.矿物间的结构关系表明主要造岩矿物的结晶顺序为:橄榄石-斜方辉石-单斜辉石-斜长石.单斜辉石的TiO2,Al2O3,Cr2O3和Na2O质量分数依次为:0.29%～1.26%、3.17%～3.59%、0.86%～1.14%、0.29%～0.57%,斜方辉石的TiO2,Al2O3,Cr2O3和Na2O质量分数普遍低于单斜辉石,依次为:0.16%～0.40%、1.85%～2.38%、0.48%～0.68%、0.03%～0.10%.元素间的相关关系显示辉石的类质同像置换方式为:M1Fe2 2 Si=M1Ti 2IV Al,M1Fe2 Si=M1Fe3 IVAl,Fe3 和Ti进入矿物晶格置换Fe2 来平衡Al置换Si产生的正电价差.两种辉石较低的TiO2,Al2O3和Na2O质量分数显示出母岩浆为拉斑玄武岩浆的特征.二辉石温度计和单辉石温度计算表明斜方辉石的结晶温度下限和单斜辉石结晶温度上限大致在1146℃～1166℃之间,单斜辉石的结晶一直持续到1032℃或者更低.金川Ⅱ号岩体单斜辉石演化明显表现出向透辉石端员偏离,暗示岩浆在结晶分异过程中,可能与富钙质围岩发生了同化混染作用.     

多硅白云母地质压力计的研究进展

白云母是变质岩中分布最广泛的矿物之一,在大多数矿物组合中白云母的Si含量随着变质作用压力的增加而增加,可作为地质压力计。对KMASH体系3个有限组合中多硅白云母的Si含量与温压条件关系的实验研究结果表明,多硅白云母Si含量地质压力计明显与矿物组合有关。因此,不能把这些实验结果简单地外延到矿物组合不同的天然岩石中。在KMASH体系的温压视剖面图上模拟白云母的Si含量等值线与质量较好的实验结果非常接近,由此可以把这种方法推广到KFMASH或更复杂的体系中。在利用多硅白云母Si的含量确定天然矿物组合的变质作用压力时,最好利用视剖面图的方法。     

赞皇前寒武纪变质杂岩区变质反应结构与变质作用P-T-t轨迹

赞皇变质杂岩位于华北克拉通中部造山带中南段、太行山东麓低山区。出露于该变质杂岩区中南部的含石榴石的斜长角闪片麻岩、泥质片麻岩,均保存了三期矿物组合:进变质、峰期变质和退变质矿物组合。这两大类变质岩石中,进变质阶段矿物组合(M₁)以石榴石变斑晶核部的包裹体矿物组合为代表,变质高峰期矿物组合(M₂)由石榴石变斑晶"边部"和基质矿物组成,退变质阶段矿物组合(M₃)主要是环绕石榴石边部发育的"白眼圈"状后成合晶矿物组合。泥质片麻岩中的石榴石变斑晶均保存了明显的成分环带,且在边部很窄的范围内X_Mn有所增加、Mg/(Mg+Fe)有所降低,指示存在变质高峰期后的退变质过程。温度与压力计算结果表明,赞皇斜长角闪片麻岩所经历的进变质阶段(M₁)温度约为640~710℃、 压力约为8.2~8.6kbar;高峰期(M₂)变质温度超过810℃,压力大于12.1kbar;退变质阶段(M₃)的温压范围为590~670℃和3.2~5.6kbar。此前的研究已说明泥质片麻岩的进变质阶段(M₁)变质温度为660~690℃,压力为9.0~9.2kbar;高峰期(M₂)变质温度超过780℃,压力大于12.5kbar。变质高峰属于中压相系的顶部至高压相系的底部。斜长角闪片麻岩、泥质片麻岩均记录了典型的顺时针P-T轨迹,并显示近等温减压(ITD)的退变质片段。对泥质片麻岩中多颗锆石的变质增生边的SHRIMP U-Pb定年表明,变质高峰期时代为1821±17Ma。变质作用历史说明赞皇变质岩区卷入了华北克拉通东部陆块和西部陆块之间的俯冲-碰撞、随后的快速隆升过程,为华北克拉通中部造山带早元古代末期(~1850Ma)存在的造山事件提供了新的证据 。     

石榴子石—斜方辉石—堇青石—石英—一种新的地质压力计

根据反应：2石榴子石（Gt）＋3石英（Q2）=2斜方辉石（Opx）＋堇青石（Cord），采用最新热力学资料，在平衡热力学原理的基础上，建立该反应Mg、Fe端员组分压力计表达式：经世界典型孔兹岩系地区的验证以及与其它石榴子石一墓青石压力计对比，计算结果基本合理，表明这一新的压力计具有较好的应用价值。