华北地块中东部中生代侵入杂岩中角闪石和黑云母的40Ar/39Ar定年:对岩石圈减薄时间的制约

华北地块中东部中生代侵入杂岩存在有富闪侵入岩和花岗闪长岩类两套岩石组合.对其中 8个侵入杂岩体中的角闪石和黑云母进行了 40Ar/39Ar定年研究.山西临汾塔儿山正长闪长斑岩、山西长治西安里岩体和河南安阳东冶岩体富闪侵入岩中角闪石的 40Ar/39Ar坪年龄分别为(124.9± 0.3)Ma,(127.7± 0.3)Ma和(127.1± 0.1)Ma;鲁西临朐铁寨正长闪长岩和枣庄流井花岗闪长斑岩中角闪石的 40Ar/39Ar坪年龄均为(124.9± 0.2)Ma;鲁西莱芜铁铜沟辉石闪长岩和蒙阴虎头崖花岗闪长斑岩中黑云母的 40Ar/39Ar坪年龄分别为(132.8± 0.3)Ma和(124.4± 0.3)Ma;皖北管店花岗闪长斑岩中角闪石的 40Ar/39Ar坪年龄为(126.9± 0.2)Ma.上述结果显示华北地块中生代的岩浆活动主要发生在早白垩世.含有丰富幔源捕虏体的富闪侵入岩类和具有地壳成因的花岗闪长岩类岩石的共存,暗示早白垩世华北地块中生代岩石圈减薄达到了峰期.     

华北地块南缘中段中生代花岗质岩石的40Ar-39Ar年代学研究

对华北地块南缘4个中生代花岗质岩体中的角闪石和黑云母进行了40Ar-39Ar定年研究。结果表明,陕西黑山村岩体黑云母花岗闪长岩中黑云母的40Ar-39Ar坪年龄为126. 6±0. 3Ma,河南马家湾岩体细粒黑云母花岗闪长岩中黑云母的40Ar-39Ar坪年龄为126. 6±0. 2Ma,河南洛宁南八百坡岩体黑云母二长花岗岩中角闪石的40Ar-39Ar坪年龄为128. 3±0. 3Ma,山西蚕坊岩体花岗闪长岩中角闪石的40Ar-39Ar坪年龄为129. 2±0. 2Ma。上述结果显示华北地块南缘中生代的岩浆活动主要发生在早白垩世。该期岩浆的产生应与中国东部早白垩世的伸展环境相联系。     

新疆东昆仑野牛泉石英闪长岩与英安斑岩的^40Ar／^39Ar同位素年龄

对出露在新疆东昆仑落雁山—阿尔喀山一带闪长岩-花岗闪长岩带中的野牛泉石英闪长岩中的角闪石和次火山岩英安斑岩中的黑云母2种单矿物进行40Ar39/Ar同位素定年,分别获得角闪石(219±1.4)Ma坪年龄和(220±11)Ma等时年龄,黑云母(218.59±0.94)Ma坪年龄和(226±11)Ma等时年龄,证实它们形成于晚三叠世。由于它们具有弧侵入体的岩石学和地球化学特征,因此该年龄的确定对于以木孜塔格-鲸鱼湖蛇绿混杂带为标志的南昆仑造山带构造演化研究具有重要意义。     

恩施球粒陨石热历史及原始氩特征

H_s型恩施球粒陨石K-Ar年龄为4503±91Ma,~(40)Ar-~(39)Ar坪年龄为4518±8Ma,总气体年龄为4515±23Ma,等时线年龄为4505±16Ma,年龄的一致性表明该陨石未经受过明显的热扰动,它是我国首次发现的Ar保存年龄高达45亿年以上的陨石。陨石形成早期有过短期的快速冷却。陨石母体在4.66±0.04Ma时破裂。恩施球粒陨石原始捕获(~(40)Ar/~(36)Ar)_t为0.89±0.44,推测4.5Ga前太阳风中~(40)Ar/~(36)Ar近于l。     

大别山北麓的奥陶纪岩浆弧：侵入岩年代学和地球化学证据

采用颗粒级锆石U-Pb和角闪石的~(40)Ar-~(39)Ar定年方法,测得大别山北坡马畈闪长质杂岩体中石英闪长岩的结晶锆石年龄分别为(463.5±3.4)和(458.6±6.7)Ma,角闪石~(40)Ar-~(39)Ar坪年龄为(462.7±1.4)Ma。从镁铁质包体到闪长岩和花岗岩类,ε_(Nd)(t)介于4.3～1.8之间,且随着Mg~#值的减小和SiO_2及Nb含量增高,岩石的ε_(Nd)(t)值降低,结合低Nb/Zr比值和中等-高的Ba/Th比值等特点,认为有关岩石的形成与幔源岩浆受板片流体影响并发生地壳AFC(同化混染与分离结晶同时出现)作用有关,但它们亏损Nb等高场强元素的特征,并不是地壳物质影响所致,而反映了地幔岩浆源区的特点,表明岩浆形成于与俯冲有关的环境。这一研究进一步证明,在大别山北麓的北淮阳地区,曾经发育了奥陶纪岩浆弧,向西与北秦岭岩浆弧相接。从大别山北麓的马畈杂岩体到昆仑山的布青山英云闪长岩体,中央造山带内与俯冲有关的侵入岩侵位年龄有向西变新的趋势,可能意味着原特提斯秦岭洋在向华北地块南缘活动大陆边缘俯冲过程中,是从东向西逐渐关闭的。     

闽西南地区早中生代汤泉岩体同位素年代学、地球化学特征及其构造意义

闽西南大田县境内汤泉花岗闪长岩体呈NE向展布,出露面积约130 km~2,以往被认为是早白垩世岩浆作用的产物。本次研究获得的单颗粒锆石U-Pb年龄为186.8 Ma和179.0 Ma,Rb-Sr等时线年龄为162.02±4.5 Ma,花岗闪长岩中黑云母~(40)Ar/~(39)Ar坪谱年龄为158.1±0.7 Ma,首次确定该岩体应形成于早侏罗世。岩体形成早期(183～162 Ma)处于相对挤压构造环境,冷却速率缓慢(4.76℃/Ma),晚期(162～158 Ma)是在伸展拉张构造环境下较快速冷却(50℃/     

四川西部雀儿山地区两个~(40)Ar/~(39)Ar法年龄测定结果讨论

用~(40)oAr/~(39)Ar法测定了四川西部雀儿山地区的两个样品(黑云母和角闪石)。测定结果,黑云母的坪年龄为247.2±0.3Ma;等时线年龄为245.8±0.3Ma;热事件年龄为86.7Ma。角闪石的坪年龄为157.6±0.2Ma;热事件年龄为38.8Ma。     

山东玲珑和郭家岭岩体的同位素年龄及其地质意义

本文采用~(40)K-Ar/~(39)Ar快中子活化和K-Ar稀释法定年技术对玲珑岩体和郭家岭岩体进行了年龄测定。~(40)Ar/~(39)Ar阶段加热年龄谱表明,玲珑岩体和郭家岭岩体的坪年龄分别为164.2±0.7Ma和134.8±1.7Ma,其形成时代同属燕山期,为同一成因不同阶段的产物。同位素年龄提供的数据支持了两岩体为交代混合岩化的成因观点。~(40)Ar/~(39)At和K-Ar年龄结果还表明:角闪石和黑云母均是~(40)Ar/~(39)Ar理想定年矿物,对K-Ar法而言,角闪石最理想,黑云母次     

云南大坪金矿床赋矿闪长岩锆石SHRIMP U-Pb定年及其地质意义

云南大坪金矿床是哀牢山金矿带中最重要的金矿之一,主要赋存在受到强烈剪切和水-岩反应的闪长岩中,是典型的喜马拉雅期造山型金矿。本文对大坪金矿床赋矿闪长岩中锆石进行了SHRIMP U-Pb定年,得出闪长岩围岩的年龄为773±12Ma,为晚元古代,显示该岩体为华南地区晋宁-澄江期大规模基性到酸性岩浆活动的产物,是Rodinia 超大陆形成、裂解后冈瓦纳大陆形成过程的响应,而不是前人普遍认为的加里东期岩体。该岩体侵入年龄与大坪金矿脉石英流体包裹体⁴⁰Ar-³⁹Ar 年龄测定给出的高温坪年龄(765.5±7.0Ma)基本一致,显示大坪金矿床具有多期成矿的特征,其主体形成于喜马拉雅期碰撞造山运动,但早在晋宁造山运动中就有金的初步富集。在闪长岩中还发现了年龄为33.7±1.1Ma的锆石,其时代与大坪金矿床含金石英脉中热液绢云母的⁴⁰Ar-³⁹Ar定年结果(33.76Ma)基本一致,显示它们很可能为该区强烈的韧性剪切和局部岩浆部分熔融作用的产物。     

福建紫金山矿田深部似斑状花岗闪长岩锆石SHRIMP U-Pb和单矿物~(40)Ar/~(39)Ar年龄及其地质意义

通过对福建紫金山矿田深部与成矿作用有关的主期似斑状花岗闪长岩3组锆石SHRIMP U-Pb和2组角闪石、钾长石~(40)Ar/~(39)Ar测年,获得锆石~(206)Pb/~(238()U加权平均年龄为101.8±1.5 Ma(n=34,MSWD=1.0),代表紫金山矿田深部与成矿作用有关的主期似斑状花岗闪长岩的成岩年龄;同时获得角闪石~(40)Ar/~(39)Ar冷却年龄为100±11 Ma、102.2 Ma,钾长石的~(40)Ar/~(39)Ar冷却年龄为96.3±1.7 Ma、98.5 Ma。依据矿物封闭温度理论,估算紫金山矿田深部与成矿作用有关的主期似斑状花岗闪长岩由锆石结晶至角闪石40Ar/39Ar体系封闭、再到钾长石~(40)Ar/~(39)Ar体系封闭的岩石冷却速率分别是40.7~67.1℃/Ma、116.9~216.3℃/Ma,显示岩石的冷却速率较大;由古地温梯度推算主期似斑状花岗闪长岩结晶(101.8±1.5 Ma)至钾长石~(40)Ar/~(39)Ar体系封闭(96.3±1.7 Ma)期间岩体隆升剥露了约3 km,暗示地壳在这一时期发生了快速隆升剥蚀作用。紫金山矿田深部似斑状花岗闪长岩锆石206Pb/238U年龄佐证了紫金山矿田深部存在一个大岩基,并约束了紫金山矿田斑岩型矿床的成矿时代,单矿物的~(40)Ar/~(39)Ar年龄为矿区的隆升剥露研究提供新资料。     

攀西裂谷内陆盆地自由热对流应力分析及盆地沉降

康滇地区裂谷作用已得到证实,但形成这种地堑地垒的格局有多种解释,以传统的地质力学分析为主。笔者借以热力学的自由热对流原理来加以论述：攀西巨厚的火山岩体在下覆异常地幔热作用下,发生自由热对流,引起热量散失,使地壳沉降与隆起不均衡,生成地堑地垒的格局。自由对流单元的侧向迁移,使盆地形成非对称性。     

The Northwestern (Maghreb) boundary of the Nubia (Africa) Plate

A study of the present compressional deformation of the Northwestern (Maghreb) Nubia (Africa) margin is derived from the analysis of more than 20,000 km of seismic profiles. In the western part the compression is distributed in a large zone with on-land compression in Algeria, mainly strike-slip deformation on the Algerian margin and folds and strike-slip faulting in Eastern Spain. In the middle of the Algerian margin, around Algiers, the evidences of compression become more obvious. In this area a ridge trending N–S that is interpreted as a middle to late Miocene spreading center interacted with the transpressional margin that trends E–W. North of the location of the Boumerdes–Zemmouri earthquake the oceanic crust is deformed by blind thrusts up to 60 km from the coast. These thrusts are south dipping and with the northward dipping thrusts located onshore form a wedge that maybe a positive flower structure at a crustal scale related to the right-lateral transpression of the margin. In the eastern part of the Northwestern (Maghreb) Nubia (Africa) Deformed Belt, off eastern Algeria and Tunisia, the deformation is more intense but limited to the north by the continental slope. Large late Miocene Tortonian folds are cut by the Messinian erosional surface but the present deformation is also evident. It is suggested that the deformation with a double vergence may be followed up to the north of Sicily. After the docking (18 Ma) of the Kabylies to the Africa Plate, the crust has been thinned and the Algerian Basin opened during the middle-late Miocene with an E–W direction. From the late Miocene to the Present the margin has been rethickened by transpression and uplifted.     

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     

Reduction of U(VI) to U(IV) on the surface of magnetite

To increase the understanding of uranium transport in the environment and in the presence of steel corrosion products, the interaction of U(VI) with natural magnetite has been studied. Sorption studies have been carried out using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The XPS results clearly indicate the reduction of U(VI) to U(IV) on the surface of magnetite facilitated by electron transfer between the Fe and U, leading to a coupled oxidation of Fe(II) to Fe(III).     

Site selectivity of the boring Rogerella isp. infesting Cardiaster granulosus (Goldfuss) (Echinoidea) in the type Maastrichtian (Upper Cretaceous,Belgium)

A burrowing spatangoid echinoid (heart urchin), Cardiaster granulosus (Goldfuss), from the type area of the Maastrichtian Stage (Upper Cretaceous) in Belgium, was infested only in the plates of the ambulacral petals by acrothoracian barnacle borings, Rogerella isp. This infestation was after the death and exhumation of the echinoid. The distribution of Rogerella may indicate the azimuth of current flow at the time of exhumation prior to final burial. Copyright © 2015 John Wiley & Sons, Ltd.