Denudation and cooling of the Lake Teletskoye Region in the Altai Mountains (South Siberia) as revealed by apatite fission-track thermochronology

Lake Teletskoye occupies a narrow graben located in the northwestern sector of the Altai fold belt in South Siberia. The lake basin is thought to have formed during the Pleistocene as a distant result of the Cenozoic collision of India and Eurasia that caused a tectonic reactivation of the Palaeozoic Gorny–Altai (GA) and West Sayan (WS) blocks.The present work reports of a pilot fission-track study performed on 13 apatite separates collected from rocks that were sampled along two profiles in close proximity of the lake. The age–length data and AFT thermochronological modelling reveal two important phases of cooling in the Altai Mountains, a first one during the Late Jurassic–Early Cretaceous and a second one that started in the Miocene–Pliocene and that persists until today. The first event is interpreted to result from uplift-induced denudation probably related to the closure of the Mongol–Okhotsk Ocean; the second event can be linked to the young Cenozoic movements that lie at the origin of the formation of the Lake Teletskoye basin.     

Internal deformation of Sikhote Alin volcanic belt, far eastern Russia: Paleocene paleomagnetic results

We present paleomagnetic results of Paleocene welded tuffs of the 53–50 Ma Bogopol Group from the northern region (46°N, 137°E) of the Sikhote Alin volcanic belt. Characteristic paleomagnetic directions with high unblocking temperature components above 560 °C were isolated from all the sites. A tilt-corrected mean paleomagnetic direction from the northern region is D=345.8°, I=49.9°, α₉₅=14.6° (N=9). The reliability of the magnetization is ascertained through the presence of normal and reversed polarities. The mean paleomagnetic direction from the northern region of the Sikhote Alin volcanic belt reflects a counterclockwise rotation of 29° from the Paleocene mean paleomagnetic direction expected from its southern region. The counterclockwise rotation of 25° is suggested from the paleomagnetic data of the Kisin Group that underlies the Bogopol Group. These results establish that internal tectonic deformation occurred within the Sikhote Alin volcanic belt over the past 50 Ma. The northern region from 44.6° to 46.0°N in the Sikhote Alin volcanic belt was subjected to counterclockwise rotational motion through 29±17° with respect to the southern region. The tectonic rotation of the northern region is ascribable to relative motion between the Zhuravlevka terrane and the Olginsk–Taukhinsk terranes that compose the basements of the Sikhote Alin volcanic belt.     

Cenozoic tectonic events at the border of the Paraná Basin, São Paulo, Brazil

In the last decade, even in areas that had been considered tectonically stable, a great amount of Cenozoic, including the Quaternary period, structural data have been collected throughout Brazil. The main goal of this study is to describe the Cenozoic structures and tectonic evolution of an area that is located at the border of the Paraná Basin in the state of São Paulo.The research methods consisted of the analysis of: (1) brittle structure data, mainly conjugate fractures and fault slip data; (2) lineaments traced on air photos and TM Landsat and radar images; and (3) a second-order base surface map.The study area, during the Cenozoic, has been affected by five strike–slip tectonic events, which generated mainly strike–slip faults, and secondarily normal and reverse ones. The events were named, from the oldest to the youngest, E1-NE, E2-EW, E3-NW, E4-NS, and E5-NNE; and the maximum principal stresses σ1 strike approximately NE–SW, E–W, NW–SE, N–S, and NNE–SSW, respectively. Event E2-EW seems to have been contemporaneous with the deposition of the Rio Claro Formation, the most important Cenozoic deposit of probable Neogenic age, and also to have controlled the distribution of its deposits. Event E3-NW was the strongest one in the area, as is pointed out by structural data, and the maximum principal stress σ1 of event E5-NNE is partially concordant with the orientation of σH-max of well break-out data in the Paraná Basin, suggesting a Neotectonic activity for this event. Finally, discontinuities parallel and correlated to the directions of strike–slip faults of the Cenozoic events seem to have actively controlled the sculpturing of the relief in the study area.     

雄关漫道真如铁——论中国油气二次创业

半个多世纪以来，中国经历了油气资源的第一次创业，在祖国大陆和近海大陆架地区的新生代陆相碎屑岩沉积盆地中，发现了一批油气田，使原油年产量达1．67亿吨，位居世界第五，天然气疸这241亿立方米，居世界第十五位，成绩是巨大的，但是，1993年开始进口原油3000万吨，2000年进口原油7200万吨，严重影响国家经济建设，而且这种趋势还在不断发展，预测2010年将进口原油1亿吨，天然气200亿立方米，那么，中国油气资源的出路何在？作者指出，从中国大地构造演化来看，前新生代海相残留盆地还有巨大的油气潜力，尽管其勘探的难度是世界级的，但是，只要我们切实地依靠科学技术，进行油气资源的二次创业，困难上，在实践中克服困难，就可以发现更多的石油天然气，支持国家经济建设的持续发展。     

藏北新生代两套钾玄质火山岩系列地球化学特征

岩石学和元素地球化学特征研究表明，藏北新生代自南向北沿可可西里岩带和喀喇昆仑—玉门岩带出露有两套钾玄质系列火山岩。它们富集大离子亲石元素(LILE)和轻稀土(LREE)及明显亏损Nb—Ta—Ti，同时具有板内和岛弧(陆弧)的双重特征。源区来源于可能与俯冲带流体有关的相似交代富集地幔，成岩过程主要经历了低度(＜10％)辉石分离结晶作用，同时，源区伴有地壳物质的混染作用。     

合肥盆地中、新生代沉积相初步研究

合肥盆地是与大别山造山带有密切关系的山前前陆盆地，盆地中、新生界沉积物主要来自南面大别山区以及盆地东部、北部剥蚀区。通过野外实际踏勘、室内岩石薄片显微分析，认为合肥盆地中、新生界发育的沉积相主要有冲积扇相、河流相和湖泊相，其中以河流相最为发育。该盆地中、新生界油气源条件比较丰富，储盖条件良好，生储盖组合形式多样，存在多种油气圈闭类型，是一个油气勘探潜力较大的陆相沉积盆地。     

长江口海域新生代地层与断裂活动性初探

长江口海域通过浅层人工地震勘察查明，新生代地层可分为5个地震层。分别为第四系、上新统、中新统上段、中新统下段及始新统。第三纪地层自东北向西南依次超覆、减薄尖灭，上部被第四纪地层不整合覆盖。沉积基底主要由晚侏罗世火山岩系及燕山晚期酸性小岩体构成，未发现早第三纪及晚白垩世断陷盆地。断裂构造很发育，按展布方向大体可归为北东、北西及近东西向3组，皆为正断层。前两者数量多、延伸长、断距大，与同区的航磁异常构架吻合。北东向断裂分段明显，西南段为第四纪断裂，中段为晚第三纪断裂，东北段为早第三纪断裂；而北西向断裂分段不很清晰。两者的垂直位移速率平均在0．015mm/a。本文对该海域有关的几个地质问题进行了讨论。     

Cenozoic Plate interaction of the Australia and Philippine Sea Plates: “hit-and-run” tectonics

Recent studies in northwest New Guinea have shown the presence of at least two marginal basins of different age, both of which formed in back-arc settings. The older basin opened between the Middle Jurassic and Early Cretaceous, a remnant of which is now preserved as the New Guinea Ophiolite. Its obduction started at 40 Ma and it was finally emplaced on the Australian margin at 30 Ma. The younger basin was active during the Oligocene to Middle Miocene and was obducted in the Early Pliocene. Studies of the western edge of the Philippine Sea also reveal an important deformation of the Philippine arc in the Oligocene, which hitherto has remained unexplained. Using information from these systems, paleomagnetic results, kinematic reconstructions and geochemistry of the supra-subduction ophiolite, we present a plate model to explain the region's Eo–Oligocene development. We suggest that an extensive portion of oceanic crust extended the Australian Plate a considerable distance north of the Australian Craton. As Australia began its steady 7–8 cm/year northward drift in the Early Eocene, this lithosphere was subducted. Thus, the portion of the Philippine Sea Plate carrying the Taiwan–Philippine Arc to its present site may have actually been in contact with the ophiolite now in New Guinea and obduction led to deformation of the Philippine Sea Plate itself. Neogene Plate kinematics transported the deformed belt in contact with the Sunda block in the Late Miocene and Pliocene. This interpretation has implications for the origin for the Philippine Sea Plate and the potential incorporation of continental fragments against its boundaries.