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榍石在各类岩石中普遍存在，其稳定性受全岩成分、氧逸度和水活度以及温度和压力等因素影响。它在岩浆岩中主要存在于高Ca/Al比值的岩石中，在变质岩中常见于绿片岩相、蓝片岩相和角闪岩相岩石，在钙质变质岩中其稳定范围可达榴辉岩相或高压麻粒岩相。一般榍石结构中U含量较高，且具有高达高角闪岩相上限的U Pb同位素体系封闭温度，是理想的U-Pb定年矿物。由于榍石的组成元素均为岩石中的主要元素，很容易与其它矿物、熔体及流体发生反应，所以榍石的U-Pb年龄记录的更可能是结晶年龄，而不是简单的扩散重置年龄；也因为它容易反应，变质榍石复杂的U Pb体系可能记录了岩石的整个变质历史信息。通过与榍石平衡共生的矿物组合或利用榍石Zr温压计可确定岩石的P T条件，结合相关的榍石年龄信息即可建立变质过程的P T t轨迹。利用SHRIMP、LA MC ICP MS以及LA ICP MS方法可对不均一榍石颗粒内部进行原位微区分析得到有意义的U Pb年龄；利用榍石中Zr含量对温度，尤其是对压力比较敏感，可建立榍石Zr含量温压计。 相似文献
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中国东部几个地区新生代玄武岩中单斜辉石—熔体平衡温压—兼论幔源包体的成因 总被引：5，自引：1，他引：4
以中国东部宽甸、汉诺坝和明溪含有幔源包体的新生代玄武岩中的单斜辉石斑（巨）晶为研究对象,采用最新的单斜辉石－熔体平衡温压计对单斜辉石斑（巨）晶－熔体进行了平衡温压计算。结果表明,碱性玄武岩中的单斜辉石斑晶结晶温度和压力高于共生的亚碱性玄武岩中的单斜辉石斑晶,单斜辉石巨晶的结晶温度和压力高于单斜辉石斑晶。这说明碱性玄武岩的形成深度大于亚碱性玄武岩,单斜辉石巨晶是更高压力下的结晶产物,单斜辉石斑晶在岩浆上升的不同深度均有晶出。回归分析表明,尽管携带幔源包体的玄武岩浆上升速度较快,但并不是绝热上升。单斜辉石斑（巨）晶的结晶温压条件与同一地点幔源包体平衡温压条件的对比表明,单斜辉石巨晶和碱性玄武岩中的部分单斜辉石斑（巨）晶的结晶温压大于幔源包体的平衡温压,表明了包体寄主岩浆的来源深度大于包体的深度。因此,幔源包体是寄主岩浆上升途中捕虏的上地幔碎块,而非寄主岩浆形成源区的残留体。 相似文献
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LI Tianfu MA Hongwen . Institute of Geology Chinese Academy of Geological Sciences Beijing . School of Materials Science Engineering China University of Geosciences Beijing 《Continental Dynamics》2001,(1)
1. Introduction The depth of source of Cenozoic basalts and the genesis of mantle xenoliths in eastern China have been widely discussed by many geoscientists. There were basically two main opinions: one was that the relationship of basalts and the peridotite xenoliths are melt and residues (Cong et al, 1982; Liu et al, 1985; Qiu et al, 1986; E et al, 1987; Chi et al, 1988; Deng et al, 1988), and pyroxenite and gabrro enclaves are accumulation of fractional crystallization (Qiu et al, 1986;… 相似文献
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火山岩中玻璃基质或细粒基质在淬火条件下形成,其熔体结构受淬火温压和熔体成分所控制。在已知熔体成分的条件下,淬火温压可根据熔体结构来确定。对于玄武质熔浆有NBO/T=0.098 57+2.77×10~(-4)T+9.13×10~(-10)p;对于粗面安山质熔浆有:NBO/T=-0.465 5+9.10×10~(-4)T+1.14×10~(-9);对于英安质熔浆有:NBO/T=-0.512 3+8.10×10~(-4)T+1.2×10~(-9)p。 相似文献
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Florence Le Hébel Olivier Vidal Jean-Robert Kienast Denis Gapais 《Comptes Rendus Geoscience》2002,334(3):205-211
The so-called ‘Porphyro??des’ Unit of South Brittany is located below units marked by an early HP–LT event (blueschists from the Île de Groix) and above units marked by Upper Carboniferous HT metamorphism. P–T estimates in the Porphyro??des (at Belle-Île-en-Mer), using the phengite–chlorite thermobarometer, indicate pressures around 8 kbar and temperatures of 350–400 °C. These new estimates suggest that the early tectonic history of the ‘Porphyro??des’ should be linked to that of the overlying Blueschists, and imply a much larger areal extension of the HP–LT domain in this part of the Hercynian Belt. To cite this article: F. Le Hébel et al., C. R. Geoscience 334 (2002) 205–211. 相似文献
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The NE to ENE trending Mesozoic Xingcheng-Taili ductile shear zone of the northeastern North China Craton was shaped by three phases of deformation. Deformation phase D1 is characterized by a steep, generally E–W striking gneissosity. It was then overprinted by deformation phase D2 with NE-sinistral shear with K-feldspar porphyroclasts forming a subhorizontal low-angle stretching lineation on a steep foliation. During deformation phase D3, lateral motion accommodated by ENE sinistral strike-slip shear zones dominated. Associated fabrics developed at upper greenschist metamorphic facies conditions and show the deformation characteristics of middle- to shallow crustal levels. In some parts, the older structures have been in turn overprinted by late-stage sinistral D3 shearing. Finite strain and kinematic vorticity in all deformed granitic rocks indicate a prolate ellipsoid (L-S tectonites) near plane strain. Simple shear-dominated general shear during D3 deformation is probably of general significance. The quartz c-axis textures indicate prism-gliding with a dominant rhomb <a> slip and basal <a> slip system formed mainly at low-middle temperatures. Mineral deformation behavior, quartz c-axis textures, quartz grain size and the Kruhl thermometer demonstrate that the ductile shear zone developed under greenschist facies metamorphic conditions at deformation temperatures ranging from 400 to 500 °C. Dislocation creep is the main deformation mechanism at a shallow crustal level. Fractal analysis showed that the boundaries of recrystallized quartz grains had statistically self-similarities. Differential stresses deduced from dynamically recrystallized quartz grain size are at around 20–39 MPa, and strain rates in the order of 10−12 to 10−14 s−1. This indicates deformation of granitic rocks in the Xingcheng-Taili ductile shear zone at low strain rates, which is consistent with most other ductile shear zones. Hornblende-plagioclase thermometer and white mica barometer indicate metamorphic conditions of medium pressures at around ca. 3–5 kbar and temperatures of 400–500 °C within greenschist facies conditions. The main D3 deformation of the ENE-trending sinistral strike-slip ductile shearing is related to the roll-back of the subducting Pacific plate beneath the North China Craton. 相似文献
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