新疆喀拉通克铜镍硫化矿区二、三号矿床特征及成因

喀拉通克铜镍硫化矿区二、三号矿床的两个岩体为隐伏的中－基性岩体，受北西向断裂的控制，侵位于石炭统南明水组上段之下部地层中，为岩浆熔离型铜镍硫化矿床。矿物成分以磁黄铁矿、镍黄铁矿、黄铜矿为主。有用元素除铜、镍外，尚伴生有金、银、铂、色、钴、硫可综合利用。它国内外同类型矿床相比，具有成岩、成矿时代新，岩体基性程度低、铜大于镍等特点，因而又具有新的地质找矿意义。     

Chronology of the high-pressure metamorphism of Norwegian garnet peridotites/pyroxenites

Eclogite facies mineral assemblages are variably preserved in mafic and ultramafic rocks within the Western Gneiss Region (WGR) of Norway. Mineralogical and microstructural data indicate that some Mg–Cr-rich, Alpine-type peridotites have had a complex metamorphic history. The metamorphic evolution of these rocks has been described in terms of a seven-stage evolutionary model; each stage is characterized by a specific mineral assemblage. Stages II and III both comprise garnet-bearing mineral assemblages. Garnet-bearing assemblages are also present in Fe–Ti-rich peridotites which commonly occur as layers in mafic complexes. Sm–Nd isotopic results are reported for mineral and whole rock samples from both of these types of peridotites and related rocks. The partitioning of Sm and Nd between coexisting garnet and clinopyroxene is used to assess chemical equilibrium. One sample of Mg–Cr-type peridotite shows non-disturbed partitioning of Sm and Nd between Stage II garnet and clinopyroxene pairs and yields a garnet–clinopyroxene–whole-rock date of 1703 ± 29 Ma (I= 0.51069, MSWD = 0.04). This is the best estimate for the age of the Stage II high-P assemblage. Other Stage II garnet–clinopyroxene pairs reflect later disturbance of the Sm–Nd system and yield dates in the range 1303 to 1040 Ma. These dates may not have any geological significance. Stage III garnet–clinopyroxene pairs typically have equilibrated Sm–Nd partitioning and two samples yield dates of 437 ± 58 and 511 ± 18 Ma. This suggests that equilibration of the Stage III high-P assemblage is related to the Caledonian orogeny and is more or less contemporaneous with high-P metamorphism of ‘country-rock’eclogites in the surrounding gneisses. The Sm–Nd mineral data for the Fe–Ti-rich garnet peridotites and for a superferrian eclogite, which occurs as a dyke within the Gurskebotn Mg–Cr-type peridotite, are consistent with a Palaeozoic high-P metamorphism. Finally a synoptic P–T–t path is proposed for the Mg–Cr-type peridotites which is consistent with the petrological and geochronological data.     

A white mica crystallinity study of the Berwyn Hills, North Wales

Abstract White mica crystallinity studies have been carried out on 90 samples of mudrocks, six of spotted slate, and five of accretionary lapilli tuff from the area around the Berwyn Hills, North Wales. Strain was measured for some of the spotted slate and tuff samples. The metamorphic grade increases from southeast to northwest, with values of the Kübler index varying from 0.64 to 0.20Δ2θ. Metamorphic zonal boundaries follow the strike of bedding and cleavage, but crystallinity values increase into stratigraphically younger rocks on the northwest side of the Berwyn Dome. This effect is attributed mainly to a rapid increase in the thickness of synmetamorphic overburden to the northwest, comprising exposed Silurian turbidites and inferred Lower Devonian non-marine sediments. Strain variations have a more local influence on crystallinity, and lateral variations in the contemporary geothermal gradient cannot be ruled out. However, only with unrealistically high gradients would the need for a thick Lower Devonian component to the overburden be removed. This reasoning implies that the metamorphic peak was coeval with the Acadian (late Caledonian) event, rather than with an early diastathermal event.     

天目山火山岩的反序现象及其成因

浙江天目山地区的中生代火山岩由流纹岩、英安岩、安山岩组成,其喷发存在反序现象。笔者用带状岩浆房的模式解释了该区火山岩的特点,应用各种物理化学方法建立了岩浆房中存在的温度、密度和粘度梯度。主要元素及微量元素的行为及其定量模拟表明,分离结晶是导致岩浆成分变化的主要机理。然而,各种矿物在岩浆房中的沉降速度计算表明,尤其是酸性岩浆中,晶体的重力沉降是不可能的。因此,岩浆房中存在的分离结晶现象主要是通过对分离作用进行的。     

湘东北长沙—平江断裂动力变质带的构造及地球化学特征

长沙—平江动力变质带是组成湘东北中生代地洼型拉伸构造型式的剥离断层带,其中的糜棱岩是大型韧性滑脱剪切作用的产物。文中重点阐述了糜棱岩的构造及地球化学特征及其成因意义,表明该断裂带的动力变质作用与大规模的地洼岩浆活动有着密切的生成联系,这可能是地洼构造演化的一个重要特征。     

新疆巴楚瓦吉里塔格金伯利岩矿物中岩浆包裹体研究

笔者在代表金伯利质熔浆结晶演化产物的橄榄石巨斑、金云母斑晶和磷灰石精晶中首次发现了岩浆包裹体。捕晶角闪石、单斜辉石及橄榄石中岩浆包裹体研宄证实,其源于基性-超基性杂岩。依据充填物相态和成分,将本区岩浆包裹体划分为两类:A,硅酸盐熔融包裹体;B,流体熔融包裹体,前者又细分出一个亚炎(A′),即晶体-玻璃包裹体。经岩浆包裹体均一化温度值的测定和压力估算,原始金伯利质熔浆晶出巨斑橄榄石的温度略高于1116℃,压力约4.5GPa。     

K-Ar dating of ring complexes and fault systems in Northern Kordofan,Sudan: evidence for independent magmatic and tectonic activity

From an area of brittle shearing and ring complexes in Northern Kordofan, Sudan 28 K-Ar ages were calculated to determine the geochronology of tectonic and magmatic events. The age results for deformational episodes are 560, 340 and 255 Ma, whereas alkaline magma was intruded at 280, 220 and 165 Ma. The incompatibility of age marks leads to the conclusion that magmatic and tectonic activity in this area have to be regarded as independent events. This holds true even when all dated intrusions from the entire region are compared with post-Pan-African continental tectonic features.     

下庄矿田基底的控矿作用及其有关地质问题

本文提出武夷及其邻区存在两个裂陷槽及一裂隆，鹰潭－南城－安远－河源韧性断裂带为东部的火山岩型与西部的花岗岩型铀矿床的地质分界线，指出了加里东运动在本区的突出作用是使裂隆基底岩石发生混合花岗岩化作用。根据下庄矿田及其外围发现较深变质的岩石和较大规模韧性剪切糜棱岩带，得出下庄矿田是古老基底加里东热穹隆区多次构造、岩浆活动的产物。由于铀成矿作用赋存于初、脆性两种构造中，建议重新划分矿化类型以指导勘查工作。     

Multiple intrusions and low-pressure metamorphism in the central Old Woman Mountains, south-eastern California: constraints from thermal modelling

The Old Woman Mountains in south-eastern California are a Late Cretaceous low-pressure metamorphic terrane where multiple magmatic intrusions generated broad regions of elevated metamorphic temperatures. In the Scanlon Gulch area, two sheet-like, Late Cretaceous granitoid plutons are in contact with the Scanlon shear zone, a 1-km-thick sheet of isoclinally folded and transposed metamorphic rocks. The metaluminous Old Woman granodiorite underlies the shear zone and the peraluminous Sweetwater Wash granite overlies it. Both plutons record emplacement ages of ∼74 Ma. Thermobarometry and phase relations in the shear zone suggest that peak metamorphism was at 650 ± 50† C and 4.3 ± 0.5 kbar. Late Cretaceous metamorphic temperatures were less elsewhere in the Old Woman Mountains, away from the intrusions.
One-dimensional thermal models are used to investigate how differences in the time between the emplacement of plutons would affect the thermal evolution of the central Old Woman Mountains. The prediction of a thermal history inferred from petrological and thermochronological data requires the rapid emplacement of the two plutons around the shear zone; simulations with delays of more than 1 Myr in the emplacement of the second pluton failed to predict peak metamorphic temperatures. Calculations which consider only the emplacement of a single pluton yield metamorphic temperatures that are too low. The time separating the intrusions is by far the most sensitive parameter in the calculations; assumptions concerning the treatment of the initial geothermal gradient and the latent heat of crystallization have relatively small effects on the predicted thermal histories. Our results suggest that for certain geometries, relatively short-lived magmatic events involving rapid emplacement of multiple intrusions can produce low-pressure metamorphism.