江西修水地区震旦纪前后沉积岩的Nd同位素组成和物质来源

本文报导了江西修水地区前震旦系与震旦—寒武系沉积岩的Nd同位素组成。前震旦系浅变质沉积岩:~(143)Nd/~(144)Nd=0.512000～0.512214,ε_(Nd)(t)=-2.57～3.91,t_(DM)=1563～1859Ma;震旦—寒武系沉积岩:~(143)Nd/~(144)Nd=0.511710～0.511902,ε_(Nd)(t)=-8.04～-9.99,t_(DM)=1833～2426Ma。两者之间的显著差异反映了震旦纪前后沉积岩物质来源的不同及沉积构造环境的改变,前震旦纪地壳活动性     

粤北热水岩体SHRIMP锆石U-Pb年龄及地球化学特征研究

热水岩体位于贵东岩体中部南侧,SHRIMP锆石U-Pb定年结果为162.8±5.8 Ma(MSWD=4.2),属于燕山早期岩浆活动产物。该岩体具有富硅(SiO2平均为76.32%)、富铝(A/CNK值平均为1.14)、钾大于钠(K2O/Na2O值平均为1.32)和高的P2O5含量(平均为0.41%);大离子元素富集,Ba、Sr、Ti、Nb、Ta亏损,具有高的Rb/Sr(平均为28.5)和Rb/Nb值(平均为19.8);轻、重稀土之间分馏不明显,配分模式呈水平型,Eu亏损明显(δEu值平均为0.14);εNd(t)值低(平均为-10.2),Nd模式年龄古老(平均为1777 Ma);岩浆源区物质由泥质岩组成。这些特征表明,热水岩体属于典型的S型或壳源型花岗岩。热水岩体可能是在燕山早期太平洋板块俯冲导致先存的东西向大东山-贵东断裂带重新复活的构造背景下,由古—中元古代泥质变质岩低程度部分熔融的方式形成。     

江西相山铀矿田燕山期岩浆活动的多阶段性及其意义

相山铀矿田是我国最大的火山岩型铀矿田,区域内主要出露有碎斑熔岩、流纹英安岩、花岗斑岩等火山岩—潜火山岩。前人对这三种岩浆岩进行了较为详尽的年代学研究。近年来随着相山西部深部钻探的开展,发现钻孔中由上至下出现‘碎斑熔岩—流纹英安岩—碎斑熔岩’的现象,现有的年代学结果还不能给予合理的解释。为此,我们对相山西部典型钻孔中的上下两层碎斑熔岩及其间的流纹英安岩,以及相山北部和西部钻孔中的三个花岗斑岩样品进行了详细的年代学研究,结果显示,流纹英安岩的锆石206Pb/238 U加权平均年龄为139.7±1.0Ma,碎斑熔岩（上层）的加权平均年龄为135.3±0.9Ma,碎斑熔岩（下层）的加权平均年龄为129.9±0.9Ma,不同地点的三个花岗斑岩样品的加权平均年龄分别为125.4±1.0Ma, 134.4±1.3Ma,148.8±2.3Ma,结合上下两层碎斑熔岩的镜下特征,认为下层碎斑熔岩是在上层碎斑熔岩形成后沿流纹英安岩之下的凝灰岩接触面超浅层侵入形成,从而在剖面上显示出“上老下新”的特征。这些结果表明相山燕山期岩浆活动持续时间较长（长达约24Ma）,为成矿有利因素,而不是前人认为的相山燕山期岩浆活动是一次短暂而集中的活动。对相山火山—侵入杂岩锆石的Hf同位素研究表明,各岩石样品的锆石εHf(t)值相近,分布在-10.6~-4.9之间,锆石的Hf模式年龄TDM2介于1478~1844Ma之间,本研究认为相山火山—侵入杂岩体可能起源于相山深部中元古代岩地壳所衍生的基底副变质岩部分熔融。     

Geochemical Charactristics and Genesis of Topaz—Bearing Porphyries in Yangbin Area of Taishun County,Zhejiang Province

The host rocks of the porphyry tin deposits in the Yangbin area are principally topaz-bearing porphyry dikes about 2 km long and 2–20m wide. Three lithologie types are identified for the dikes: topaz-bearing potassium feldspar granitic porphyry, topaz-bearing monzonitic granitic porphyry and topaz-bearing quartz porphyry. The content of topaz in the rocks ranges from 10 to 20 vol.%. Porphyritic texture is characteristic, with quartz, potassium feldspar and albite as main phenocryst minerals. The phenocryst occupies 10–20 vol% of the rocks. The rock groundmass consists of subhedral topaz, quartz and protolithionite. Topaz has a unit-cell parameter b=8.797 (Å), and F:OH=1.92:0.18, indicating a F-rich variety formed at high temperature. The topaz-bearing porphyries occurring in this area are strongly peraluminous (A/NKC=1.574–12.94), with high ratios of F/Cl (146–303) and Rb/Sr (5–122). They are rich in incompatible elements (Sn, 313 × 10^?6–1042 × 10^?6; W, 6 × 10^?6–218 × 10^?6; Nb, 27 × 10^?6–54 × 10^?6), but poor in compatible elements (Sr, 10 × 10^?6–28 × 10^?6; Ba, 58 × 10^?6–73 × 10^?6; V, 3 × 10^?6–12 × 10^?6, Cl, 150 × 10^?6–226 × 10^?6). The rocks are also characterized by high total REE amount (281.69 × 10^?6–319.76 × 10^?6), with strong Eu depletion (δEu=0.01–0.03) and low ratio of LREE/HREE (0.78–0.84). In summary, the authors propose an idea of S-type genesis for the topaz-bearing porphyries with tin mineralization, instead of I-type.     

丹巴地区变质沉积岩Sm-Nd同位素研究

对丹巴地区广泛分布的志留系、泥盆系和三叠系地层进行了较系统的Sm-Nd同位素研究。这些变质沉积岩的地壳存留年龄为2284-1977Ma,它介于扬子板块核部晚太古代地壳(2900-2600Ma)和板块边缘中-新元古代地壳(1180-812Ma)之间,表明丹巴地区的古生代地层可能主要是这两个物源区按一定比例均匀混合的产物。     

Xinjiangoxylon Gen.Nov., a New Gymnosperm from the Latest Permian of China

Following the greatest known end-Permian mass extinction plants have low diversity. Lycopsids and conifers dominated on land. A new gymnosperm Xinjiangoxylon gen. nov. is proposed based on a woody stem specimen collected from the Upper Permian （latest, Changhsingian） Upper Guodikeng Formation of the Taoshuyuan section, Turpan, Xinjiang Uygur Autonomous Region, Northwest China. The decorticated stem is characterized by a complex pith, endarch primary xylem and a thick secondary xylem cylinder. Numerous petrified woods were found in the Changhsingian at this section. However, there are rare wood fossils in the Early Triassic. The abrupt decrease of fossil woods worldwide relates to the crisis at the end of the Permian. Xinjiangoxylon turpanense gen et. sp. nov. appears to represents one gymnosperm that existed in the latest Permian.     

粤北桃村坝花岗岩锆石U-Pb年代学、地球化学及成因研究

桃村坝花岗岩体位于粤北贵东复式花岗岩体中部。锆石U-Pb年龄为161.5±1.8 Ma (MSWD=1.7),属于燕山早期岩浆 活动产物。该岩体具有稍低的硅、富铝、富碱、钾大于钠、贫钙镁和高FeO*/MgO等特征。富集Rb,Th,U而亏损Ba, Sr,Ti和Nb;LREE富集(LREE/HREE=7.39~16.4, (La/Yb)N=8.79~25.5),Eu亏损较为明显(δEu=0.44~0.59);Ga/Al比值较高(平 均值为2.99),Zr+Nb+Ce+Y含量(平均为518×10-6)大于350×10-6,可归属于A2型花岗岩;εNd(t)值低,为-9.7~-8.95,Nd模式 年龄为1.66~1.76 Ga;锆石的εHf(t)值为-20.0~-14.6,相应的Hf模式年龄为2.12~2.46 Ga。综合以上特征表明桃村坝花岗岩是 在地壳伸展-减薄的构造背景下、由古元古代地壳组分部分熔融的方式形成。     

拉萨地体东南部整体地壳成分及其成因分析

造山带地壳结构和成分的基本特征对于认识大陆地壳成分演化和区域成矿背景具有重要意义.综合青藏高原拉萨地体东南部地球物理、高温高压岩石物性和岩浆岩地球化学资料,分析该地区地壳整体成分特征,并探讨其可能成因.该地区平均地壳波速显著低于全球大陆和造山带地壳的平均值,表明地壳整体具有中酸性成分,下地壳特征也可由中性岩石(残余体性质的中性含石榴石麻粒岩)解释.拉萨地体东南部整体地壳成分特征应与多阶段长英质化有关,包括碰撞前大陆弧演化阶段(以堆晶或残余体下地壳拆沉为主)和碰撞后高原垮塌阶段(以加厚下地壳拆沉为主,伴随印度古老长英质陆壳物质的俯冲回返/构造底侵).拉萨地体是研究大陆地壳成分演化的绝佳区域,亟待进一步开展多学科综合研究.     

Investigation of Lushan earthquake ionosphere VTEC anomalies based on GPS data

Vertical total electron content （VTEC） time series were obtained from 22 GPS stations near the epicenter of the Lushan earthquake. In this paper, we have adopted a sliding average method to detect and analyze anomalous VTEC associated with the earthquake. The results show that signif- icant, negative ionosphere VTEC anomalies appeared over the 5 days before the earthquake, and on the day when earthquake occurred. The maximum value of VTEC anoma- lies that exceeded the lower bound reached 20 TECU. The spatial distribution of VTEC anomalies showed a conjugate structure, which shifted to the magnetic equator, and subse- quently moved westwards.     

扬子地块南缘中—晚寒武世浅海多次短暂增氧及其诱因：来自碳酸盐岩铈异常及碳- 锶同位素证据

中—晚寒武世(509～485 Ma)是地球历史上的一个动荡时期,期间发生了多次碳同位素漂移和生物灭绝事件,表明地球表层环境可能发生了剧烈变动。本文以湖南省永顺县王村剖面的清虚洞组、敖溪组和花桥组的碳酸盐岩地层为研究对象,通过碳、锶同位素地层学对比和稀土Ce异常的分析,揭示出扬子地块南缘在中晚寒武世发生了四次短暂的浅海短暂增氧(Ce_N/Ce_N^*<0.8),分别位于乌溜期(约509～504.5 Ma)、早鼓山期(约505 Ma)、古丈期(约500.5～497 Ma)和早排碧期(约497～496 Ma),其中排碧期早期和乌溜期内发生的增氧可能指示了全球表层海水的广泛增氧,而鼓山期早期和古丈期内发生的增氧可能仅局限于扬子地块南部边缘海。根据最新的生物地层学研究成果,浅海短暂增氧发生的时间与华南地区三叶虫和总体的生物多样性高峰基本对应,指示浅海氧气含量的上升可能促进了生物多样性的发展。海水δ¹³C和⁸⁷Sr/⁸⁶Sr值的变化趋势指示大陆风化增强向海洋输入大量营...