北京怀柔云蒙山地区花岗岩风化过程的地球化学基因

地球化学基因是近两年提出的一种新的地球化学示踪技术,本文选择北京怀柔云蒙山地区两个邻近的花岗岩风化剖面(编号为B和C)来分析岩性地球化学基因和金矿化地球化学基因的属性特征.剖面B样品的化学蚀变指数CIA变化为51.3～58.9,WIG的范围为89.4～68.6,属于初始风化程度;剖面C样品的CIA变化为52.4～78....     

青藏高原东南缘次林错岩体晚白垩世—早新生代快速剥蚀

青藏高原东南缘是研究构造、地貌演化和气候变化相互作用的理想场所,前人研究主要揭示了晚始新世—早中新世和晚中新世以来的快速剥蚀事件,缺乏晚白垩世—早新生代时期地貌演化过程的研究。次林错花岗岩已有的低温热年代学数据覆盖了整个新生代时期,为探索该区域新生代早期的剥露演化历史提供了重要资料。该岩体新生代早期冷却事件是岩浆冷却单一作用的结果,还是受快速剥蚀作用的影响,目前仍然存疑,需要定量研究。因此,本文结合已有的岩石地化和年代学数据,对次林错花岗岩开展了锆石饱和温度和一维岩浆冷却模拟研究。锆石饱和温度计算结果表明次林错花岗岩的岩浆结晶温度介于647～705℃之间,属低温花岗岩。一维岩浆冷却模拟结果显示岩体侵位时的最小围岩温度为160～120℃,对应深度约为3.7～5.0 km。结合锆石和磷灰石(U-Th)/He年代学数据,本文认为该岩体在晚白垩世—早新生代时期(67～40 Ma)经历了一期剥蚀量至少为2 km的快速剥蚀事件。已发表成果的综合分析表明,此次快速剥露事件可能是整个青藏高原地区广泛存在的构造剥蚀事件,新特提斯洋的俯冲闭合与印亚板块的初始碰撞可能是触发此次大规模区域剥蚀的主要原因。     

西藏甲玛矿床南坑高分异Ⅰ型花岗斑岩及黑云母矿物学特征

高硅花岗岩对于理解浅部岩浆房的行为具有重要意义.本文对西藏甲玛矿区南坑矿段的花岗斑岩开展了岩相学、岩石地球化学及黑云母矿物学研究.结果显示,该花岗斑岩具有高SiO2(73.39％～77.99％)、高K2O(4.34％～6.45％)和低P2O5(0.03％～0.06％)特征,铝饱和指数为0.97～0.98,富集Rb、Th...     

Single Zircon LA-ICP-MS U-Pb Dating of the Guandimiao and Wawutang Granitic Plutons in Hunan, South China and Its Petrogenetic Significance

1 Introduction The South China Block (SCB), located between the Qinling-Dabie and Songma Indosinian sutures, experienced successively two important tectonic movements during the Mesozoic, i.e. the Indosinian movement (early Mesozoic) and the Yanshanian movement (late Mesozoic). Therefore, the generally accepted viewpoint is that the key geological problems during the Mesozoic are essentially the dynamics and material expression of these two tectonic movements in South China (Chen et al.…     

柴北缘元古宙鹰峰环斑花岗岩及其共生岩石的地球化学特征、成因及地质意义

中元古代鹰峰岩体的主体是环斑花岗岩,与其共生的岩石有石英闪长岩-奥长花岗岩和辉绿岩。环斑花岗岩高碱（Na2O＋K2O=8.49%～9.39%）、富钾（K2O/Na2O=1.12～1.43）,铝近饱和,高铁镁比值[（ΣFeO）/MgO=4.91～7.19];富Rb、Ba、Ga、Th、Zr、Nb、Ta,贫Cr、Ni、V;高ΣREE（392.24×10-6～594.76×10-6）,稀土元素强分异[（La/Lu）N=12.67～17.09],弱铕负异常（δEu=0.58～0.78）,显示碱性花岗岩的特征,与密云环斑花岗岩相似。石英闪长岩-奥长花岗岩具钙碱性系列岩石的特征;与环斑花岗岩相比,其Rb、Ba、Ga、Nb、Ta、Th、Hf、Zr低,而Ni、Cr、V高;ΣREE较低（ΣREE=77.04×10^-6～129.85×10^-6）,轻重稀土分异明显,但（La/Lu）N的比值较小（11.62～14.06）,铕异常更弱（δEu=0.69～0.93）。辉绿岩具低碱、高ΣFeO的特征,属拉斑玄武质,与洋中脊拉斑玄武岩相比,K2O等不相容元素高,具大陆拉斑玄武质的特征。辉绿岩的ISr（1776Ma）为0.7066,εNd（1776Ma）为＋3.6,环斑花岗岩的ISr（1776Ma）为0.7181,εNd（1776Ma）为-5.5,显示辉绿岩起源于年轻的地幔,花岗质岩浆主要源自古老的地壳。综合分析显示,这些侵入岩形成于伸展背景,是北半球中元古代非造山环斑花岗岩的成员之一,在加里东期卷入到柴北缘造山带的古老地壳中。这在世界上提供了一个古老克拉通及环斑花岗岩卷入古生代造山带的一个实例。     

Regional variations in cleavage and fold development in North Wales

The arcuate pattern of the main Caledonian cleavage and associated fold axial plane traces in North Wales is due partly to NW-SE compression with tectonic transport to the southeast against the concealed crop of the Tan y grisiau Microgranite. Low-angle cleavage close to the microgranite is shown to be a local variant of the regional cleavage formed during the main deformation and not an earlier phase as previously supposed. Transcurrent movements along several major fault systems are also related to compression around the microgranite and the Harlech Dome block.     

兴安地块南段晚泥盆世包格德岩体时代的厘定及地质意义

中亚造山带东端兴安地块南段的包格德岩体由石英二长岩、二长花岗岩和花岗斑岩3种岩性组成,岩体锆石LA-ICP-MS U-Pb定年结果分别为368±+1 Ma、364±1 Ma、355±1 Ma,为晚泥盆-早石炭世岩浆活动的产物;岩体的(Na2O+K2O)含量为7.62％～8.82％,K2O/Na2O值为0.93～4.21...     

Geochemistry and Petrogenesis of Late Ediacaran Rare-metalAlbite Granites of the Arabian-Nubian Shield

The Abu Dabbab albite granite(ADAG), in the central Eastern Desert of Egypt, hosts the most significant rare metal ore deposit in the northern part of the Neoproterozoic Arabian-Nubian Shield. Here, we report detailed field,petrographic, mineralogical and geochemical investigation of the ADAG, an isolated stock-like granitic body with sharp intrusive contacts against metamorphic country rocks, probably emplaced at about 600 Ma. The fine-grained porphyritic upper unit is a preserved remnant of the shallowly-emplaced apex of the magma chamber, whereas the medium-grained lower unit crystallized at deeper levels under subvolcanic conditions. The peraluminous leucocratic ADAG shares common geochemical characteristics with post-collisional intraplate A-type magmas. In addition to the conspicuous enrichment in Na2 O, the ADAG is remarkable for its anomalous concentrations of Ta, Nb, Li, Hf, Ga, Sn, Zn and heavy rare-earth elements. Nb-Ta minerals in the ADAG are mixed with Fe-Mn oxides, forming black patches that increase in abundance toward of the base of the intrusion. Columbite-tantalite, cassiterite and wolframite are the most important ore minerals.Pronounced negative Eu anomalies(Eu/Eu* = 0.10–0.24) reflect extreme magmatic fractionation and perhaps the effects of late fluid-rock interaction. The ADAG was most likely generated by partial melting of the juvenile middle crust of the ANS as the geotherm was elevated by erosional uplift following lithospheric delamination and it was emplaced at the intersection of lineations of structural weakness. Although formation of the ADAG and its primary enrichment in rare metals are essentially due to magmatic processes, late-stage metasomatism caused limited redistribution of rare metals. Fluid-driven subsolidus modification was limited to the apex of the magma chamber and drove development of greisen, amazonite, and quartz veins along fracture systems.     

Precipitation‐runoff processes in Shimen hillslope micro‐catchment of Taihang Mountain,north China

Precipitation runoff is a critical hillslope hydrological process for downslope streamflow and piedmont/floodplain recharge. Shimen hillslope micro‐catchment is strategically located in the central foothill region of Taihang Mountains, where runoff is crucial for water availability in the piedmont corridors and floodplains of north China. This study analyzes precipitation‐runoff processes in the Shimen hillslope micro‐catchment for 2006–2008 using locally designed runoff collection systems. The study shows that slope length is a critical factor, next only to precipitation, in terms of runoff yield. Regression analysis also shows that runoff is related positively to precipitation, and negatively to slope length. Soil mantle in the study area is generally thin and is therefore not as critical a runoff factor as slope length. The study shows a significant difference between overland and subsurface runoff. However, that between the 0–10 and 10–20 cm subsurfaces is insignificant. Runoff hardly occurs under light rains (<10 mm), but is clearly noticeable under moderate‐to‐rainstorm events. In the hillslope catchment, vertical infiltration (accounting for 42–84% of the precipitation) dominates runoff processes in subsurface soils and weathered granite gneiss bedrock. A weak lateral flow (at even the soil/bedrock interface) and the generally small runoff suggest strong infiltration loss via deep percolation. This is critical for groundwater recharge in the downslope piedmont corridors and floodplains. This may enhance water availability, ease water shortage, avert further environmental degradation, and reduce the risk of drought/flood in the event of extreme weather conditions in the catchment and the wider north China Plain. Copyright © 2011 John Wiley & Sons, Ltd.     

Sunrise Hill unconformity: A newly discovered regional hiatus between Archaean granites and greenstones in the northeastern Pilbara Craton

Contacts between Archaean granites and greenstones in the northeastern part of the Pilbara Craton have been described as intrusive and tectonic. New field observations in the Shay Gap region demonstrate that greenstones of the Gorge Creek Group unconformably overlie the Muccan and Warrawagine batholiths. Regionally, the unconformity is marked by a persistent but relatively thin basal clastic sequence, locally with a granite boulder conglomerate, overlain by ore‐bearing banded iron‐formation, fine‐grained clastic rocks and chert. The granite basement is dated at 3443 ± 6 Ma. The precise age of the hiatus is unknown but its maximum effect might have been the removal of a substantial thickness of Early to Middle Archaean strata.