西天山特克斯达坂一带晚古生代花岗岩类的地球化学特征及其构造意义

依据地质学、岩石学和年代学特征,西天山特克斯达坂一带花岗岩类被解体为早石炭世库勒萨依序列和早二叠世其那尔萨依序列,其同位素年龄分别为347Ma、291～292Ma。通过对该花岗岩类地球化学特征的研究得出,库勒萨依序列A/CNK平均值为1,K2O/Na2O平均值为0.96,（Na2O+K2O）/Al2O3平均值为0.66,里特曼指数δ平均值为3.2,为准铝质钙碱性花岗岩;其那尔萨依序列A/CNK平均值为1.05,K2O/Na2O平均值为1.17,富钾,为过铝质碱性花岗岩。库勒萨依序列为形成于岛弧环境的钙碱性花岗岩,是古亚洲洋向北俯冲的产物;其那尔萨依序列为形成于后造山期松弛阶段的碱性花岗岩。     

反倾层状岩质边坡内开挖隧道引发边坡失稳与隧道塌方的机制和治理研究

在反倾层状边坡内,开挖边坡并修筑隧道洞口后,出现岩体从隧道掌子面整体挤出和洞顶塌方现象,并导致边坡出现后缘拉裂、坡体内出现多处裂缝和岩块崩塌等坡体失稳迹象。通过对该边坡失稳和隧道塌方的勘察和机制分析,确定该坡体的变形破坏模式,提出针对性治理方案。     

Petrogenesis of extension-related alkaline volcanism in Karaburhan (Sivrihisar–Eskisehir), NW Anatolia, Turkey

Alkaline lavas were erupted as phonolites and trachytes around Karaburhan (Sivrihisar–Eskisehir, NW Anatolia) within the Izmir–Ankara–Erzincan suture zone. These volcanic rocks were emplaced as domes, close and parallel to the ophiolite thrust line. According to ⁴⁰Ar/³⁹Ar geochronological analyses of sanidine crystals from the phonolites, the age of the alkaline volcanics is 25 Ma (Late Oligocene–Early Miocene).The flow-textured phonolites are porphyritic and consist mainly of sanidine, clinopyroxene, and feldspathoid crystals. The clinopyroxenes show compositional zoning, with aegirine (Na_0.82–0.96Fe⁺³_0.68–0.83) rims and aegirine–augite cores (containing calcium, magnesium, and Fe⁺²). Some aegirine–augites are replaced with sodium-, calcium-, and magnesium-rich amphibole (hastingsite). Feldspathoid (hauyne) crystals enriched with elemental Na and Ca have been almost completely altered to zeolite and carbonate minerals. The fine-grained trachytes with a trachytic texture consist of feldspar (oligoclase and sanidine) phenocrystals and clinopyroxene microphenocrystals within a groundmass made up largely of alkali feldspar microlites.Although there are some differences in their element patterns, the phonolites and trachytes exhibit enrichment in LILEs (Sr, K, Rb, Ba, Th) and LREEs (La, Ce, Pr, Nd) and negative anomalies in Nb and Ta. These geochemical characteristics indicate a lithospheric mantle enriched by fluids extracted from the subduction component. In addition, the high ⁸⁷Sr/⁸⁶Sr (0.706358–0.708052) and low ¹⁴³Nd/¹⁴⁴Nd (0.512546–0.512646) isotope concentrations of the alkaline lavas reflect a mantle source that has undergone metasomatism by subduction-derived fluids. Petrogenetic modeling indicates that the alkaline lavas generated from the subduction-modified lithospheric mantle have undergone assimilation, fractional crystallization, and crustal contamination, acquiring high Pb, Ba, Rb, and Sr contents and Pb isotopic compositions during their ascent through the thickened crust in an extensional setting.     

中东地区鲁卜哈利盆地古生界地震反射构型特征与储层预测

根据中东地区鲁卜哈利盆地古生界不同沉积相储集砂体的地震反射构型不同,运用地震资料精细解释与地震沉积学、层序地层学相结合的方法,对盆地东部已钻井区辫状河道和三角洲前缘砂体的沉积特征与地震反射构型特征进行了识别分析;并由此类比到西部地区进行储层预测,在沉积环境相同的T构造区古生界志留系三级基准面旋回TS3下降期,识别出与东部反射特征相似的两套地震反射体,分别预测为辫状河道和三角洲前缘砂体;以此为依据提交的井位建议得到采纳,实钻后证实预测砂体存在。     

The influence of volcanism on paleoclimate in the northeast of China： Insights from Jinchuan peat, Jilin Province, China

Just like contemporary sediments, peat itself is a good repository of information about climate change, the effects of volcanic activity on climate change have been truly recorded in peat, since it is a major archive of volcanic eruption incidents. A section of sand was identified as tephra from the Jinchuan peat, Jilin Province, China, for the grains look like slag with surface bubbles and pits, characterized by high porosity, and loose structure with irregular edges and corners. According to the peat characteristics of uniform deposition, the tephra was dated at 2002–1976 a B.P. by way of linear interpolation, so the time of volcanic eruption was 15 B.C.–26 A.D. (the calibrated age). While the geochemical characteristics of tephra in this study are quite the same as those of tephra from the Jinlongdingzi volcano at Longgang and from alkaline basaltic magma, with the contents of SiO₂<55%, and the similar contents to Al₂O₃ and Fe, but the contents of Na₂O>K₂O. We speculated that the tephra in this study came from the Longgang volcano group. Compared with 11 recorded volcanic eruption events as shown on the carbon and oxygen isotope curves of the Jinchuan peat cellulose, it is obviously seen that adjacent or large-scale volcanic eruptions are precisely corresponding to the minimum temperature and humidity. It seems that these volcanic eruptions indeed affected the local climate, leading to the drop of regional temperature and humidity. As a result, there was prevailing a cold and dry climate there, and all these changes can be well recorded in peat. So the comparison of volcanic eruption events with information about climate change developed from peat, can provide strong evidence for the impact of volcanism on climate change.     

Early Paleozoic tectonic evolution of the Chinese South Tianshan Orogen: constraints from SHRIMP zircon U–Pb geochronology and geochemistry of basaltic and dioritic rocks from Xiate,NW China

Traditionally the Chinese South Tianshan has been regarded as a late Paleozoic orogenic belt. However, little is known about the early Paleozoic tectonic architecture of the region. This paper presents the first evidence of Cambrian–Ordovician MORB-type basalts and adakitic diorites on the southern margin of the Yili plate in China. Basalts from Xiate in southwestern Tianshan show a typical transitional (T-) MORB and ferrobasalt composition, which indicate a formation at a propagating spreading ridge. The basalts give a weighted mean ²⁰⁶Pb/²³⁸U crystallization age of 516.3 ± 7.4 Ma by SHRIMP U–Pb zircon dating and have experienced contact metamorphism due to the intrusion of a dioritic pluton. The dioritic pluton has a weighted mean ²⁰⁶Pb/²³⁸U crystallization age of 470 ± 12 Ma and geochemical characteristics resembling that of adakitic rocks. The pluton is considered to have been formed by partial melting of garnet amphibolites from thickened lower crust in arc or continental collision settings. The basalts and diorites are considered to outline the eastern extension of the early Paleozoic suture zone, the Nikolaev Line, which stretches east–west for hundreds of kilometers between the Northern Tianshan and Central Tianshan terranes of Kyrgyzstan. Our findings substantiate that the Yili and Central Tianshan plates were separated by the early Paleozoic Terskey ocean. The Terskey ocean probably closed during the early stage of the late Ordovician (Lomize et al. in Geotectonics 31(6):463–482, 1997), resulting in the final amalgamation of the Yili and Central Tianshan plates. Consequently, an early Paleozoic suture zone is documented in the Chinese Tianshan region, which is most likely represented by the North Nalati fault.     

Paleomagnetic constraints on Miocene rotation in the central Japan Arc

We present new Middle Miocene paleomagnetic data for the central Japan Arc, and discuss their implications for Miocene rotation. To obtain a refined paleodirection, we made magnetic measurements on basaltic to andesitic lavas and intrusive rocks from 12 sites in the Tsugu volcanic rocks (ca 15 Ma) in the northern part of the Shitara area, Japan. Significant secondary magnetizations in samples with strong magnetic intensities are interpreted as lightning‐induced components. Mean directions carried by magnetite and/or titanomagnetite were determined for all sites. An overall mean direction with a northerly declination was obtained from dual‐polarity site means for nine sites. This direction is indistinguishable from the mean direction for coeval parallel dikes in the northern part of the Shitara area, and also indistinguishable from the Miocene reference direction derived from the paleopole for the North China Block in the Asian continent. These comparisons suggest little or no rotation or latitudinal motion in the study area with respect to the North China Block since 15 Ma. We obtained a refined early Middle Miocene paleodirection (D = 9.7°, I = 52.5°, α₉₅ = 4.8°; 30 sites) and paleopole (82.0°N, 230.8°E, A₉₅ = 5.6°) for Shitara by combining data from the Tsugu volcanic rocks and a coeval dike swarm. An anomalous direction found at three sites could be a record of an extraordinary field during a geomagnetic polarity transition or excursion. Paleomagnetic data from Shitara suggest that: (i) the western wing of the Kanto Syntaxis, a prominent cuspate geologic structure in central Honshu, underwent a counterclockwise rotation with respect to the main part of the southwestern Japan Arc between ca 17.5 Ma and 15 Ma; (ii) collision between the Japan and Izu–Bonin (Ogasawara) Arcs began prior to 15 Ma; and (iii) clockwise rotation of the entire southwestern part of the Japan Arc had ceased by 15 Ma.     

碳酸盐岩裂缝型储层最小二乘偏移成像方法研究

碳酸盐岩裂缝型储层是海相油气储层以及西部探区的重要储层类型之一,多表现为缝洞储集体形态,埋藏深度大,地震反射波信号复杂,波场特征分析困难,因而对其进行高分辨成像具有一定的难度.本文推导并实现了基于最小二乘理论的偏移成像(LSM)方法,并将LSM用于西部探区碳酸盐岩裂缝型储层等效地震地质模型的偏移成像工作,成像结果表明:在理论上,LSM方法能够较好地分辨出埋藏深度在3000 m以下的中深部20 m尺度碳酸盐岩裂缝型储层,在西部碳酸盐岩裂缝型储集体地震勘探中,具有较好的适应性.     

腾冲地区地壳速度结构的有限差分成像

利用流动台网和固定台站的地震观测数据,采用有限差分层析成像方法反演了腾冲及邻近地区的地壳P波速度结构,分析了腾冲火山区的岩浆活动和龙陵七级地震的深部构造成因.研究结果表明,腾冲火山区的地壳结构具有明显的非均匀性,浅表层偏低的速度主要为盆地内部的松散沉积层、新生代火山堆积及断裂附近的流体裂隙和热泉活动所致;5～15 km之间的高速体可能代表了早期火山通道内冷却固结的岩浆侵入体或难挥发的超铁镁质残留体;地壳深部的低速体则反映了熔融或半熔融的岩浆体,推断火山区下方的岩浆活动与龙陵七级地震震源区地壳深部的岩浆侵入来自同一源区--现今壳内岩浆活动的主要区域.龙陵震源区的地壳速度结构横向变化较大,怒江断裂东侧和龙陵断裂西侧为高速特征,介质应变强度较大,为应力积累的主要载体;两断裂之间的低速区向下延伸至下地壳,可能与地壳深部的岩浆侵入有关;龙陵断裂和怒江断裂明显控制了这一区域的岩浆活动,七级地震正是发生在断裂下方的速度边界附近.地壳介质强度的横向变化导致了震源区应力积累的不均一性,深部岩浆的聚集和动力作用是龙陵地区发生强震的主要原因.     

河南省舞阳铁矿田基底岩系归属

舞阳铁矿田地处河南舞阳-新蔡地区铁矿集区的重要区段上,找矿潜力巨大。通过对该矿集区基底岩系归属的研究,为该区及区带的地质找矿工作提供指导和理论依据。