Distribution of Fe and Mg between coexisting garnet and hornblende in synthetic and natural systems: an empirical calibration of the garnet–hornblende Fe–Mg geothermometer

Multiple regression analysis of a compilation of the Fe²⁺–Mg distribution between garnet and hornblende from experimental runs on basaltic to intermediate compositions (n=22) and coexisting garnet–clinopyroxene–hornblende from natural (intermediate to basaltic) rocks (n=43) has been performed to define ln K_{D(Fe²⁺/Mg)}^Grt–Hbl as a function of temperature and garnet composition. The regression of data covering a large span in pressure (5–16 kbar), temperature (515–1025°C) and composition yields the ln K_{D(Fe²⁺/Mg)}^Grt–Hbl–P–T compositional relationship (r²=0.93):

where

Application of this expression to natural garnet–hornblende pairs in intermediate to basaltic and semipelitic rock types from various settings gives temperatures that are consistent with other methods.     

响山碱性花岗岩晶洞中的蓝色石棉

响山碱性花岗岩晶洞中生长着一种罕见的蓝色石棉,该矿物系铁-亚铁蓝透闪石。微区组成研究揭示了该闪石是由铁-红闪石—铁-亚铁冻蓝闪石生长演化而来,对它进行了红外吸收谱,X射线结构分析和差热性质的研究,并确定了岩石中还存在另外三种闪石,即铁-浅闪石、亚铁钠闪石和铁-阳起石。上述所有矿物都以铁含量高为特征。     

燕山中段走滑断裂中辉绿岩脉的SHRIMP U-Pb年龄和Ar-Ar年龄

燕山中段东西向走滑断裂的活动时代一直存在争议,对侵入断层中的辉绿岩脉的直接测年可以给出一个年龄上限。侵入密云-喜峰口断裂中的辉绿岩脉的锆石SHRIMP U-Pb和角闪石Ar-Ar测年发现,锆石U-Pb年龄为290~125Ma,没有一个谐和年龄;角闪石Ar-Ar坪年龄为123.5Ma±1.5Ma。Ar-Ar年龄与最年轻的锆石U-Pb年龄一致,代表了辉绿岩脉的冷却年龄,是断裂活动时代的上限。分散的锆石U-Pb年龄,均为继承年龄,与燕山造山带5次岩浆活动的时代对应。     

Determination and Significance of the Bluemull Blastomylonite Zone in the Northeast——East of Yell,Shetland

There is a zone of blastomylonites containing hornblende gneisses of Lewisian Inliertype in the northeast-east of Yell,Shetland.This zone with a north—northwesterlytrend consists of blastomylonised hornblende-banded gneiss,hornblende-feldspar gneissand mica-felsie-gneiss with lenses of hornblende gneiss.It is indicated that theblastomylonite zone is actually a ductile shear zone and the sense of shear is dextral.This contributes to understanding the details of tectonic evolution in this area,and thiszone is probably a part of tectonic system of the British Caledonides.     

崂山花岗岩中角闪石成分的变化及其意义

报道了崂山钙碱性岩套和碱性岩套花岗岩中角闪石的矿物成分及其变化特征,在此基础上,追索其物理化学条件的演变与成岩意义。指出,角闪石的成分及其变化特征在两个岩套中的差异,指示两个岩套岩浆可能有其独立的岩浆起源,同时也经历了不同的岩浆演化路径,分别受不同的物理化学条件制约。     

钙碱性火成岩的角闪石全铝压力计 ——回顾、评价和应用实例

定量地获得岩体结晶时的压力,对于探讨其剥蚀深度及了解造山带的构造热演化史等方面有重要意义。对于钙碱性侵入岩而言,可以应用角闪石全铝压力计对钙碱性火成岩结晶压力进行估计。对于不同角闪石压力计公式的选择,前提是满足它们各自的适用条件,否则所得结果没有意义。角闪石全铝压力计不能用于估算A型花岗岩的结晶压力,更不能用于计算变质岩的变质压力。对于结晶温度低于750℃的钙碱性中酸性岩体而言,Anderson和Smith(1995)的温度校正意义不大。Ridolfi等(2010)提出的指数关系角闪石压力计公式适用于钙碱性火山岩中角闪石斑晶的结晶压力估算。Uchida等(2007)的黑云母全铝压力计缺乏理论和实验基础,不建议使用。应用角闪石全铝压力计所得到薛家石梁—黑山寨复式岩体侵位深度的区域变化,指示了云蒙山变质核杂岩下盘的掀斜;低角度正断层(拆离断层)可以通过高角度正断层的掀斜旋转而形成。     

福建同安角闪辉长岩的矿物化学、40Ar-39Ar年龄及地质意义

福建同安角闪辉长岩的岩石化学成分具有低MgO高铝玄武岩的特征,其中的角闪石是富钙钙镁闪石,斜长石是An=91～95的钙长石.在基性的弧岩浆中,低MgO高铝玄武岩浆富水是导致结晶出高钙斜长石的关键因素.钙镁闪石的40Ar-39Ar年龄为129.62±0.15 Ma,说明同安角闪辉长岩是东南沿海早白垩世"初始引张阶段"岩浆活动的产物.     

Intercalibration of the Hb3gr Ar/Ar dating standard

The ⁴⁰Ar/³⁹Ar dating technique is based on the knowledge of the age of neutron fluence monitors (standards). Recent investigations have improved the accuracy and precision of the ages of most of the Phanerozoic-aged standards (e.g. Fish Canyon Tuff sanidine (FCs), Alder Creek sanidine, GA1550 biotite and LP-6 biotite); however, no specific study has been undertaken on the older standards (i.e. Hb3gr hornblende and NL-25 hornblende) generally used to date Precambrian, high Ca/K, and/or meteoritic rocks.In this study, we show that Hb3gr hornblende is relatively homogenous in age, composition (Ca/K) and atmospheric contamination at the single grain level. The mean standard deviation of the ⁴⁰Ar^?/³⁹Ar_K (F-value) derived from this study is 0.49%, comparable to the most homogeneous standards. The intercalibration factor (which allows direct comparison between standards) between Hb3gr and FCs is R_FCs^Hb3gr = 51.945 ± 0.167. Using an age of 28.02 Ma for FCs, the age of Hb3gr derived from the R-value is 1073.6 ± 5.3 Ma (1σ; internal error only) and ± 8.8 Ma (including all sources of error). This age is indistinguishable within uncertainty from the K/Ar age previously reported at 1072 ± 11 Ma [Turner G., Huneke, J.C., Podosek, F.A., Wasserburg, G.J., 1971. ⁴⁰Ar-³⁹Ar ages and cosmic ray exposure ages of Apollo 14 samples. Earth Planet. Sci. Lett. 12, 19-35].The R-value determined in this study can also be used to intercalibrate FCs if we consider the K/Ar date of 1072 Ma as a reference age for Hb3gr. We derive an age of 27.95 ± 0.19 Ma (1σ; internal error only) for FCs which is in agreement with the previous determinations. Altogether, this shows that Hb3gr is a suitable standard for ⁴⁰Ar/³⁹Ar geochronology.     

角闪斜长片麻岩流变力学特性研究

为了解小湾水电站枢纽区角闪斜长片麻岩的流变力学特性,采用岩石全自动三轴流变伺服仪对角闪斜长片麻岩进行三轴流变力学试验。试验结果表明,强度较高的角闪斜长片麻岩会发生流变现象,尤其在高应力水平条件下,其流变特性明显;外荷载超过岩样的长期强度时,随着时间的逐渐增加试样变形经历典型流变3个阶段,并最终加速流变破裂。依据岩样稳态流变阶段的流变速率与应力水平的关系,提出了一种确定长期强度的方法。在Burgers流变模型中加入统计损伤,并用Mohr-Coulomb准则确定的岩石长期强度作为开始进入非线性加速流变阶段的阀值,得到相应的非线性损伤流变模型。利用岩石全程三轴流变试验结果,采用优化后的算法,对非线性损伤流变模型相应的参数进行了辨识,结果表明,建立的岩石统计损伤非线性流变变模型与流变试验结果吻合较为理想,可以较为准确地反映角闪斜长片麻岩的流变力学特征     

黑龙江省伊春市牛奶沟钼矿地质特征及找矿标志

通过对伊春市牛奶沟钼矿地质特征及其矿体产出规律的分析,总结了侵入岩、构造对成矿的控制作用,为本矿区及周边地区进一步找矿提供了依据。