酸性－中酸性火山－侵入杂岩中岩石包体研究的新进展

概括了近几年来酸性－中酸性火山－侵入杂岩中岩石包体研究的新进展，介绍了岩石包体的成因分类，综述了利用岩石包体研究岩浆作用机制及其动力学、研究有关矿床成矿物质来源和成矿机制，以及研究中下地壳物质组成和力学状态等方面的内容。     

南岭东段麻粒岩相变质岩的发现及其地质意义

本文报道了在南岭东段闽西南中元古代桃溪组变质岩中发现的麻粒岩相变质岩。其矿物组合和化学成分显示这些变质岩的原岩是沉积岩。成岩格子和温压计算限定它们的峰期变质作用发生在750-880℃和1．1GPa的高温高压条件下，表明这些表壳岩由于构造作用曾经成为下地壳的物质组成，并经历了麻粒岩相变质作用。等温降压的P-T-t轨迹指示它们很可能是在中生代伸展构造背景下快速抬升到浅部。这些麻粒岩的成分显然与东南沿海地区发现的基性麻粒岩捕虏体的不同，暗示这两地区下地壳的物质组成可能存在差异，也许这就是造成两个地区花岗岩类型不同的最主要原因。     

滇西剑川-大理地区新生代钾玄岩系中深源包体的地质意义

红河-哀牢山大型左旋走滑剪切带剑川-大理段北东侧边缘的早第三纪小型拉张盆地中分布着中性-中酸性的钾玄质浅成侵入岩群（26.3-36.7Ma)，其中有些岩体含有高级或中高级变质的镁铁质包体。依包体的形成温成条件和矿物组合特征可分成三种类型：Ⅰ类包体为石榴透辉石岩，形成于下地壳或壳-幔过渡带部位，变质温度条件为p=10.47-11.51kbar,T=828-901℃；Ⅱ类包体为含石榴透辉角闪岩，形成于中、下地壳部位，变质温压条件为p=6-10kbar,T=760-830℃；Ⅲ类包体为变质辉长岩，形成部位浅于上述两种类型，变质温压条件更低。Ⅰ、Ⅱ类包体经历了由构造抬升机制导致的减压退变质作用，伴随着富硅、钠流体相对岩石的交代作用，抬升后的平衡温度为T=761-778℃。深源包体与寄主岩相似，具有受俯冲带物质影响的EMⅡ源区特征。印度板块和扬子克拉通之间的持续俯冲、挤压以及走滑、剪切作用控制着本地区下部大陆地幔性质、壳-幔相互作用以及钾玄质岩浆的形成和演化。     

Destruction of the Northern Margin of the North China Craton in Mid-Late Triassic: Evidence from Asthenosphere-derived Mafic Enclaves in the Jiefangyingzi Granitic Pluton from the Chifeng Area, Southern Inner Mongolia

The petrology, geochronology and geochemistry of the mafic enclaves in the Mid-Late Triassic Jiefangyingzi pluton from Chifeng area, southern Inner Mongolia, in China are studied to reveal their petrogenetic relationship with the host pluton. Furthermore, the coeval magmatic assemblage and its petrogenesis on the northern margin of the North China craton(NCC) are studied synthetically to elucidate their tectonic setting and the implications for the destruction of the NCC. Zircon U-Pb dating reveals that the mafic enclaves formed at 230.4 ± 2.2 Ma, which is similar to the age of the host pluton. The most basic mafic enclaves belong to weak alkaline rocks, and they display rare earth element(REE) and trace element normalized patterns and trace element compositions similar to those of ocean island basalt(OIB). In addition, they have positive εNd(t) values(+3.84 to +4.94) similar to those of the Cenozoic basalts on the northern margin of the NCC. All of these geochemical characteristics suggest that the basic mafic rocks originated from the asthenosphere. Petrological and geochemical studies suggest that the Jiefangyingzi pluton and the intermediate mafic enclaves were formed by the mixing of the asthenosphere-derived and crust-derived magmas in different degrees. The Mid-Late Triassic magmatic rocks on the northern margin of the NCC could be classified into three assemblages according to their geochemical compositions: alkaline series, weak alkaline–sub-alkaline series and sub-alkaline series rocks. Petrogenetic analyses suggest that the upwelling of the asthenosphere played an important role in the formation of these Mid-Late Triassic magmatic rocks. Basing on an analysis of regional geological data, we suggest that the northern margin of the NCC underwent destruction due to the upwelling of the asthenosphere during the Mid-Late Triassic, which was induced by the delamination of the root of the collisional orogeny between Sino-Korean and Siberian paleoplates in Late Permian.     

河北寿王坟花岗闪长岩中暗色微粒岩石包体的成因

暗色微粒岩石包体可以提供花岗岩浆的起源和演化、壳—幔物质及能量交换、岩浆混合等重要信息。河北兴隆寿王坟闪长质暗色微粒岩石包体及其寄主花岗闪长岩的岩石学、岩石地球化学特征显示了岩浆的混合成因,并具有以下特征:(1)在基性岩浆中丰度大于酸性岩浆中的不相容元素在与SiO2的相关图中呈一向上凸的弧形型式;(2)在基性岩浆中丰度小于酸性岩浆中的不相容元素在与SiO2的相关图中呈正相关的线性趋势;(3)相容元素在与SiO2的相关图中呈一负相关的线性趋势;(4)在w(La) w(La)/w(Sm)图上微粒包体与其寄主花岗闪长岩为一下凹的型式。基性岩浆与酸性岩浆的两端元岩浆的简单混合模型不能解释以上特征,可以用三阶段混合模型来解释,即第一阶段为基性岩浆注入酸性岩浆中,第二阶段为基性岩浆演化并分离结晶形成微粒包体,第三阶段为演化了的基性岩浆与酸性岩浆混合,形成寄主花岗闪长岩。     

Granulitic metamorphism in the Laouni terrane (Central Hoggar, Tuareg Shield, Algeria)

In the Laouni terrane, which belongs to the polycyclic Central Hoggar domain, various areas contain outcrops of formations showing granulite-facies parageneses. This high-temperature metamorphism was accompanied by migmatization and the emplacement of two types of magmatic suite, one of continental affinity (garnet pyroxenites and granulites with orthoferrossilite–fayalite–quartz), and the other of arc affinity (layered metanorites). Paragenetic, thermobarometric and fluid-inclusion studies of the migmatitic metapelites and metabasites make it possible to reconstruct the P–T–aH₂O path undergone by these formations. This path is clockwise in the three studied areas, being characterized by a major decompression (Tamanrasset: 10.5 kbar at 825 °C to 6 kbar at 700 °C; Tidjenouine: 7.5 kbar at 875 °C; to 3.5 kbar at 700 °C; Tin Begane: 13.5 kbar at 850 °C; to 5 kbar at 720 °C), followed by amphibolitization that corresponds to a fall of temperature (from 700 to 600 °C) and an increase in water activity (from 0.2–0.4 to almost 1).The main observed features are in favour of petrogenesis and exhumation related to the Eburnean orogeny. However, the lacks of good-quality dating work and a comparison with juvenile Pan-African formations having undergone high-pressure metamorphism, in some cases reaching the eclogite facies, do not rule out the possibility that high-temperature parageneses are locally due to Pan-African events.     

Geochemical characteristics of Cenozoic high-K igneous rocks from Liuhe-Xiangduo area, eastern Tibet

The major elements, trace elements and Nd-Sr isotopic composition of Cenozoic high-K igneous rocks and mafic deep-derived enclaves from the Liuhe-Xiangduo area, eastern Tibet, indicate the high-K igneous rocks are characterized as being enriched in Ca (CaO= 1.20% - 8.80% ), alkali (Na2O K2O= 3.47% - 10.65% ), especially K (K2O up to 5.96% ) and depleted in Ti (TiO2= 0.27% - 1.50% ). Their REE contents are very high (REE= 91.29 - 231.11 μg/g). Their REE distribution patterns are of the right-inclined type, characterized by intense LREE enrichment [(La/Yb)N= 7.44 - 15.73 ]. The rocks are distinctly enriched in Rb, Sr and Ba ( 46.3 -316 μg/g, 349-1220 μg/g and 386-2394 μg/g, respectively), high in U and Th ( 1.17 - 8.10 μg/g and 2.58 - 27.0 μg/g, respectively), moderate in Zr and Hf ( 87.5 -241 μg/g and 2.83 - 7.52 μg/g, respectively), and depleted in Nb and Ta ( 4.81 - 16.8 μg/g and 0.332 - 1.04 μg/g, respectively). In the primitive mantle-normalized incompatible element spidergram, U, K, Sr and Hf show positive anomalies, whereas Th, Nb, Ta, P, and Ti show negative anomalies. The rocks are strongly depleted in Cr and Ni ( 21.4 -1470 μg/g and 7.79 -562 μg/g, respectively), and their transition element distribution curves are obviously of type-W. The ( 87 Sr/ 86 Sr)i ratios range from 0.704184 to 0.707539 ; ( 143 Nd / 144 Nd)i from 0.512265 to 0.512564 ; and ε Nd (t) from -6.3 to -0.4 . These geochemical features might suggest that the potential source of the high-K igneous rocks in the Liuhe-Xiangduo area is similar to the EM2, which may be similar to the material enriched K that is located under the crust-mantle mixed layer. The mafic deep-derived enclaves in the high-K igneous rocks belong to chance xenoliths. Their ( 87 Sr/ 86 Sr)i ratios range from 0.706314 to 0.707198 ; ( 143 Nd / 144 Nd)i from 0.512947 to 0.513046 ; and ε Nd (t) from 7.0 to 9.0 . These geochemical features might indicate that the enclaves probably came from the depleted mantle. The P-T conditions of the enclaves also showed that the enclaves are middle-lower crust metamorphic rocks, which were accidentally captured at 20-50 km level by rapidly entrained high-K magma, whose source is over 50 km in depth.     

CHANGES IN ETHNIC SOLIDARITY IN CUBAN MIAMI*

ABSTRACT. Many people describe the Cuban community in Miami as a prime example of ethnic solidarity; others see it as internally divided. This study argues that the contradiction can be resolved when ethnic solidarity is seen as encompassing various components and when changes in cohesiveness in response to external and internal influences on the ethnic community are taken into account. These influences include the context of reception in the United States and the relationship between established Cubans and more recent immigrants. We need to refine our understanding of what constitutes ethnic solidarity, how it changes over time, and what role it plays, both within the community in general and within the ethnic‐enclave economy in particular     

安徽女山下地壳麻粒岩包体中的水：红外光谱分析

运用显微傅立叶变换红外光谱技术，对安徽女山新生代玄武岩中的10个麻粒岩包体的主要组成矿物（单斜辉石、斜方辉石、斜长石）进行了观察。结果显示，这些名义上的无水矿物中都普遍含有以OH一形式赋存的结构水，其含量（H10wt．）分别可以高达～2340ppm（单斜辉石）、～1590ppm（斜方辉石）和～910ppm（斜长石）。不同样品间矿物的结构水含量具有明显的不均一性的分布特点，这很可能是对其原岩性质的一种反映。根据单矿物的水含量和各自的体积分数计算出的全岩水含量为125～963ppm。根据二辉石温度计计算的女山麻粒岩包体的平衡温度为～800～900℃，对应于女山最下部地壳（-25～35km），因此本文数据为大陆下地壳含水与否提供了初步的最直接的证据，并且其水含量可能具有不均一性的分布特点。     

东营凹陷王庄地区沙河街组砂砾岩扇体特征

随着东营凹陷北部陡坡带王庄一宁海地区亿吨级稠油藏的发现，稠油成藏类型的砂砾岩扇体隐蔽油气藏勘探已经成为现阶段的油气勘探的重点目标和储量增长点之一。利用现代沉积学、测井学和地震勘探等手段，通过对王庄地区砂砾岩扇体特征研究后认为：王庄地区在早第三纪以形成沙三、沙四段的较高水动力能砂砾岩扇体(冲积扇、扇三角洲、近岸水下扇)沉积体为主，其中扇三角洲砂砾岩体是本区最主要的砂砾岩扇体类型，并具有较好的储集性能，是本区最主要的油气储集体；王庄地区砂砾岩扇体沉积，强烈地受制于边界构造条件；本区的砂砾岩扇体沉积及其形态均受沉积相的控制，并具有复杂多变的特征，从而直接导致了本区油气藏的聚集和分布具有复杂多变的特点。