东准噶尔和尔赛斑岩铜矿成岩成矿时代与形成的构造背景

东准噶尔和尔赛铜矿是近年来新发现的斑岩型铜矿,位于野马泉-琼河坝古生代岛弧带东段。成矿岩体为侵位于花岗闪长岩中的花岗闪长斑岩,花岗闪岩中包含有钾长花岗岩体。锆石CAMECA U-Pb测年结果显示,钾长花岗岩年龄为429Ma,并含有405Ma的锆石;花岗闪长岩年龄为411Ma,并含432Ma的碎屑锆石;花岗闪长斑岩主体年龄为410.5Ma。研究区经历了3期岩浆与热液活动,且至少在早志留世就已开始,琼河坝岛弧是开始于早古生代的岛弧。辉钼矿Re-Os等时线年龄为409Ma,与花岗闪长斑岩年龄一致。和尔赛斑岩铜矿的主成岩成矿时代为早泥盆世,年龄约为410Ma。和尔赛铜矿的花岗闪长岩和花岗闪长斑岩具有埃达克岩与岛弧岩浆岩的地球化学特征,包括63.79%～68.86%SiO2、14.91%～17.48%Al2O3、0.68%～2.35%MgO、高Sr(383×10-6～971×10-6)与Sr/Y比值(48.3～111)、低Y(7.92×10-6～9.69×10-6)与Yb(0.76×10-6～0.98×10-6),Ba、U、K、Sr等大离子元素富集,Th、Nb、Ta、Ti等高场强元素亏损,较低的(87Sr/86Sr)i值(0.703852～0.704565)、正的εNd(t)值(6.1～7.4)、与亏损地幔接近的较低的初始铅同位素比值((206Pb/204Pb)i=17.58～17.91,(207Pb/204Pb)i=15.40～15.48,(208Pb/204Pb)i=37.25～37.47)。这些地球化学特征说明其形成于岛弧环境,可能为古俯冲洋壳部分熔融的产物。琼河坝地区以花岗闪长岩和花岗闪长斑岩为代表的岩浆岩带是形成和寻找斑岩铜矿的有利地区。     

661铀矿床矿石U-Pb等时线年龄及其成矿构造背景

661铀矿床位于赣杭构造火山岩铀成矿带东段大洲铀矿田内,矿体赋存于磨石山群九里坪组流纹岩之中,矿床定位于岩石圈伸展断陷盆地附近,明显受断裂带的控制.利用矿石U-Pb等时线法确定了该矿床两个矿体的成矿时代,分别为(107.0±2.3)Ma和(110.0±3.5)Ma.这些年龄值与断陷红盆底部发育的玄武岩的成岩年龄一致,也与东南沿海地区明显存在的110 Ma基性脉岩拉张活动的时间一致,表明岩石圈伸展与铀成矿之间具有良好的对应关系,为岩石圈伸展期与铀成矿关系研究提供了年代学证据.岩石圈伸展控制着富CO2热液形成的时间,因而也大致控制了铀成矿的时代.     

东准卡拉麦里地区苏吉泉一带黑山头组的厘定

分布于卡拉麦里大断裂之北苏吉泉一带的一套以陆源碎屑岩为主,夹有少量火山碎屑岩和火山熔岩的地层,前人将其划归中泥盆世平顶山组(蕴都喀拉组),作者等新获得该地层中火山岩夹层的全岩Rb-Sr等时年龄(339±4)Ma,依据岩石组合并与区内同时代地层对比分析,将其厘定为早石炭世黑山头组.黑山头组的厘定为确立卡拉麦里大断裂之北地层总体为一单斜构造提供了重要佐证,也为东准噶尔地区的地层正确划分与对比,建立区域地层格架和重建中亚地区晚古生代地质历史有重要意义.     

Rb - Sr Whole Rock-Mineral Isochron Ages of Plutonic Rocks from the Wanni Complex, Sri Lanka

Granitoid plutons in different East Gondwana fragments give evidence for vigorous felsic magmatism during the Pan-African period (800 to 500 Ma). The Sri Lankan basement, which is mainly composed of Proterozoic high-grade metamorphic rocks, was intruded by a few late- to post-tectonic syenitic and granitic plutons. Reliable geochronological data for these plutons are few, and some of the available data are inconsistent with the ages of the surrounding metamorphic country rocks.This report presents five Rb-Sr whole-rock-mineral isochron (WRMI) ages and initial Sr isotope ratios of three granitoid plutons from the Wanni Complex, Sri Lanka, namely the Ambagaspitiya, Tonigala and Kotadeniya Granites. Two samples from the Ambagaspitiya Granite yielded ages of 520±5 and 502±15 Ma, with initial Sr ratios of 0.7103±0.0003 and 0.7125±0.0009 respectively, whereas ages of 467±27 and 497±11 Ma and initial Sr ratios of 0.7070±0.0004 and 0.7085±0.0008 were determined for two Tonigala Granite plutons. A single sample from the Kotadeniya Granite gave an age of 533±19 Ma and an initial Sr ratio of 0.7202±0.0018.These ages are consistent with the geological relations between the granitoids and their country rocks, which underwent granulite facies metamorphism between 650 and 550 Ma, and also with available U-Pb zircon ages (550 Ma). The present study gives improved chronological correlation of the felsic magmatism in East Gondwana fragments in Sri Lanka, India, Madagascar, Antarctica and Western Australia. Each of the Sri Lankan plutons exhibits different initial Sr isotope ratios, indicating that their magmas were derived from distinct source materials.     

花岗岩浆晶出锆石U Pb体系的封闭温度≥850℃”质疑

根据实验条件及元素扩散作用理论分析,本文认为Lee等(1997)和Chemiak等(2000)进行花岗岩锆石中U和Pb扩散系数实验得出的“锆石U-Pb同位素体系封闭温度＞900C”结论只适用于解释源区岩石升温产生部分熔融形成花岗岩浆过程中存在残留锆石的情况,而不表明从花岗岩浆晶出锆石的U-Pb同位素体系封闭温度≥850℃.对花岗岩体的523对锆石U-Pb年龄(tz,)与全岩Rb-Sr等时线年龄(tRb)差值△t(△t=tzr-tRb)进行的频数统计分析表明:①△t既有正值又有负值,△t直方图呈正态分布(偏度系数CSK:-0.205;峰度系数CKU=5.093);②花岗岩体△t值的分布不存在系统正(或负)偏差,而受偶然因素(实验误差)支配.这些锆石U-Pb年龄和全岩Rb-Sr等时线年龄进行的相关分析拟合出相关系数很高(R =0.997),回归系数接近1的线性方程(tzr=0.999775×tRb+0.06898Ma).这表明花岗岩锆石U-Pb定年结果与全岩Rb-Sr等时线定年结果在误差范围内一致,不存在花岗岩锆石U-Pb同位素年龄大于花岗岩全岩Rb-Sr等时线年龄的规律.     

北祁连西段石鸡河地区火山岩地球化学特征及其动力学意义

石鸡河一带是近年新发现的北祁连山多金属成矿带, 气侯和自然条件恶劣, 研究程度很低.该区地层岩性为阳起石岩、角岩和细碧岩; 岩石地球化学和Nd同位素数据显示岩石来源于亏损地幔, 具有N-MORB洋脊玄武岩特征; Sr同位素特征显示地层Sr同位素组成的改变是蚀变引起, 而不是由地壳物质加入引起的.Sm-Nd等时线年龄为481±20 Ma.提出了石鸡河地区地层形成于早奥陶世, 成岩环境为北祁连洋扩张环境, 而非区域资料上显示的残留海盆封闭、大陆碰撞造山环境.      

花岗岩体高温热年代学研究的新思路、方法及计算实例

对国内外花岗岩体723 对锆石U-Pb 年龄（t _Zr）和全岩Rb-Sr 等时线年龄（t _Rb）进行的相关分析, 拟合出相关系数很高
（Ｒ =0.997）, 回归系数接近l 的线性回归方程（t _Zr=1.0005×t _Rb+0.493041）。 Δt _Zr-Rb（t _Zr-t _Rb）频数统计分析表明: Δt _Zr-Rb呈对
称正态分布（偏度系数C _SK=0.193; 峰度系数C _KU=6.722）, 其均值为0.624 Ma, 众数值为1.0 Ma。这表明花岗岩体锆石U-Pb 定
年的测定结果与全岩Rb-Sr 等时线定年测定结果在允许的误差范围内是一致的。不存在花岗岩体锆石U-Pb 年龄必定大于全
岩Rb-Sr 等时线年龄的规律表明,同位素热年代学方法只适用于研究花岗岩结晶固结后的低温热演化史。 前人根据锆石U-Pb
年龄和全岩Rb-Sr 等时线年龄差值及相应同位素体系封闭温度研究的10 个花岗岩体的冷却速率（CR Zr-Rb）表明,它们与岩
体体积尺度不相关,这有悖于“热物体的体积（质量）愈大,则在相同热物理条件下其冷却速率愈小”的热物理学基本定律。
根据热传导理论及本文作者（2010）提出的侵位结晶时差概念我们得出“在相同热物理学条件下,体积尺度是决定花岗岩
体冷却速率最主要因素”的结论。以上述10 个花岗岩体为例,本文计算得出它们在结晶固结前高温阶段的冷却速率（CR _ECTD）
并拟合出冷却速率与岩体体积尺度呈幂函数关系：CR _ECTD=7544.7×D -2.1686, 计算结果符合热物理学基本定律。     

Metallogenic Chronology of Boron Deposits in the Eastern Liaoning Paleoproterozoic Rift Zone

1 Introduction Metallogenic chronology is one of the keys in the research of mineral deposits. Determination of metallogenetic epoch is very important for understanding the relationships between mineralization and regional tectonomagmatic events, in studying the origin of mineral deposits, and for summarizing regional mineralization and instructing regional prospecting. The eastern Liaoning region hosts the main concentration of boron resources in China. The boron reserve in eastern Liaoning…     

Sm-Nd ISOTOPIC AGE OF LAMPROPHYRES IN THE GEZHEN GOLD-BEARING SHEAR ZONE ON HAINAN ISLAND AND ITS GEOLOGICAL IMPLICATIONS

Sm-Nd isotopic compositions of eight lamprophyre samples, which come from the Gezhen gold-bearing shear zone on western Hainan Island, are measured. The Sm-Nd isochron age is 495.98±13.14 Ma, (143Nd/144Nd) 0=0.512094, εNd(t) ranges from +1.80 to +2.00 and TDM from 982 Ma to 1196 Ma (average: 1060 Ma). The authors point out that the whole-rock Sm-Nd isochron age (495.98 ± 13.14 Ma) really represents the petrogenetic age of lamprophyre and the time of magmatism during subsequent subduction.