Neoproterozoic granitic activities in the Xingdi plutons at the Kuluketage block,NW China: Evidence from zircon U–Pb dating,geochemical and Sr–Nd–Hf isotopic analyses

Neoproterozoic igneous rocks are widely distributed in the Kuluketage block along the northern margin of the Tarim Craton. However, the published literature mainly focuses on the ca. 800 Ma adakitic granitoids in the area, with the granites that intrude the 735–760 Ma mafic–ultramafic rocks poorly studied. Here we report the ages, petrography and geochemistry of two granites in the Xingdi mafic–ultramafic rocks, in order to construct a new view of the non-adakitic younger granites. LA-ICP-MS zircon U–Pb dating provided weighted mean ²⁰⁶Pb/²³⁸U ages of 743.0 ± 2.5 Ma for the No.I granite (G1) and 739.0 ± 3.5 Ma for the No.II granite (G2). A clear core-rim texture of similar age and a high zircon saturation temperature of ca. 849 ± 14 °C were observed for the No.I granite; in contrast, G2 has no apparent core-rim texture but rather inherited older zircons and a lower zircon saturation temperature of ca. 763 ± 17 °C. Geochemical analysis revealed that G1 is an alkaline A-type granite and G2 is a high-K calc-alkaline I-type granite. Both granites share similar geochemical characteristics of arc-related magmatic rocks and enriched Sr–Nd–Hf isotopes, likely due to their enriched sources or mixing with enriched magma. Whereas G1 and its host mafic rocks form typical bimodal intrusions of the same age and similar Sr–Nd–Hf isotope compositions, G2 is younger than its host mafic rocks and its Sr–Nd–Hf isotope composition indicates a lower crust origin. Although they exhibit arc-related geochemical features, the two granites likely formed in a rift setting, as inferred from thier petrology, Sr–Nd–Hf isotopes and regional tectonic evolution.     

南海西北次海盆新生代构造 沉积特征及伸展模式 探讨

通过对穿越西北次海盆的3条地震测线以及一条深反射地震剖面的解释,对其新生代的构造 沉积特征进行研究,探讨了伸展模型,并进而对其新生代的构造演化过程和动力学机制进行了分析。结果显示：西北次海盆在30 Ma时开始发育,断层的活动期集中在渐新世,并大致以海盆中部的岩浆岩凸起为轴对称分布,对渐新统的沉积起控制作用。海盆扩张东强西弱,西部显示出更多的陆缘裂谷盆地的特征。25 Ma后扩张轴向南跃迁,西北次海盆的海底扩张运动停止,进入裂后沉降阶段。构造展布方向受到其南侧的中-西沙地块的影响,大致沿其北部边界展布。深反射地震剖面所反映的深部地壳结构也显示出大致沿海盆中轴对称的特征,显示研究区很可能为纯剪的变形模式。     

鄂尔多斯盆地南缘彬县地区铀成矿关键时期的古地貌特征

中侏罗世为直罗组下段沉积期,辫状河道为有利的铀储层砂体,铀矿(化)体主要赋存于辫状河砂体中,受沉积古地貌控制,主要发育在低洼区。晚侏罗世、早白垩世-古新世、始新世-中新世是砂岩型铀成矿期,古地貌控制了地下古水流的流向,控制着氧化还原带的分布和铀矿的富集:晚侏罗世铀预成矿期,古隆起区受到潜水淋滤,含铀物质向斜坡和低洼区迁移;早白垩世-古新世铀主成矿期,古地貌控制了含氧含铀水的水流方向,氧化还原带主要分布在古地貌斜坡区。     

新疆东昆仑西段黄沙河地区托库孜达坂组地质特征及沉积环境分析

黄沙河地区位于新疆东昆仑西段南缘,属于昆南增生杂岩带,研究区内出露大面积下石炭统托库孜达坂组,为了厘定区内托库孜达坂组时代并对其沉积环境进行分析,本文在详细的野外地质调查基础上,通过地层层序学、岩石学及古生物学研究,将新疆东昆仑西段黄沙河地区托库孜达坂组分为下段碎屑岩段和上段碳酸盐岩段,将其时代厘定为早石炭世,结合区内碎屑岩粒度特征及放射虫化石特征,确定该套地层的沉积环境为半深海滨浅海环境。     

柴达木盆地三湖地区第四系沉积相与生物气成藏

柴达木盆地三湖地区第四系蕴藏着巨大的生物气资源,目前已探明加控制天然气储量接近3×1011m3。更新世时期,柴达木盆地的湖相沉积主要分布在三湖(吉乃尔湖、涩聂湖和达布逊湖)地区,自山前至盆地中心依次发育了冲积扇、河流三角洲和湖相沉积,其中湖相沉积分布最为广泛。早更新世湖相沉积开始形成,中更新世湖相沉积扩张并且达到鼎盛,晚更新世湖相沉积开始萎缩并形成盐湖沉积。中、早更新世冰川的出现和青藏高原的崛起使柴达木盆地的古气候变得干旱寒冷,沉积水体温度较低,盐度较高。本区第四纪独特的沉积环境是形成大型生物气藏最重要的地质条件。高盐度的水体环境减缓了有机质的降解速度,长期的低温条件抑制了甲烷菌的活动,避免了沉积有机质在沉积浅埋阶段的过量消耗,推迟了生物产气的高峰期。而三湖地区巨厚的第四系暗色泥岩和频繁发育的砂岩提供了充足的气源条件和构成了良好的生储盖组合。     

基于元素Mn、Co、Cd、Mo的海相沉积岩有机质 富集因素判别指标在四川盆地北缘的应用

基于金属元素Mn、Co、Cd、Mo的海洋富有机质沉积岩沉积环境和有机质富集主控因素判别指标Al—Co·Mn和Co·Mn—Cd/Mo,能够有效地区分促进有机碳埋藏的两种海洋端元沉积环境:大陆边缘开放/上升洋流环境和滞留的边缘海盆环境。利用这种方法研究了四川盆地北缘城口县月亮坪剖面五峰组和龙马溪组页岩沉积时期的水体环境和有机质富集的主控因素。研究表明五峰组Mn、Co富集程度低,Mo富集程度自下而上明显增大;龙马溪组Mn整体亏损,Co富集程度低,Mo富集程度自下而上明显减小。Al—Co·Mn方法的使用发现滞留环境主要出现在五峰组早期和龙马溪组晚期,以及观音桥段附近,而五峰组中晚期和龙马溪组早—中期水体主要处于开放/上升洋流区。剖面[w(Co)/(μg/g)]·[w(Mn)/(%)]值均小于平均页岩值1.615;五峰组Cd/Mo值整体大于正常海水值0.006,全部小于平均页岩值0.308,龙马溪组整体小于正常海水值。Co·Mn—Cd/Mo联合图版的使用发现月亮坪剖面五峰组和龙马溪组有机质富集主要受到保存条件控制,与使用U/Th、V/Cr、P/Ti、Ba/Al与TOC相关性分析得出的结论一致。基于金属元素Mn、Co、Cd、Mo的判别指标对于判断古生代大陆边缘地区富有机质页岩沉积环境及有机质富集主控因素有较好的效果。     

南海东北部冷泉区末次冰期沉积间断及其成因

对南海东沙海域冷泉区DH-CL10和DH-CL5柱状样开展AMS14C年代学、高分辨率底栖有孔虫和沉积物同位素以及沉积学研究。结果表明:DH-CL10柱状样在全新统底部574 cm处出现沉积间断,间断面相邻沉积物AMS14C年龄分别为9 850/(9 680~9 950) cal.aBP和27 610/(27 500~27 700) cal.aBP,相当于MIS2期和部分MIS3期的沉积缺失。底栖有孔虫Uvigerina bifurcata的δ13C值为-0.37‰~-1.91‰,平均值为-1.11‰,沉积物全岩碳同位素值为-22.7‰~-23‰,均为正常的碳同位素值。尽管该柱状样未发现天然气水合物分解释放的地球化学证据,但相邻的DH-CL5柱状样相当于其所缺失的部分沉积中的自生碳酸盐岩和沉积物的δ13C负偏明显,分别为-55.24‰和-25.9‰~-27.9‰,表明与天然气水合物分解有关。推断DH-CL10柱状样沉积间断所缺失的沉积物可能记录了天然气水合物分解的证据,且沉积间断主要出现在末次盛冰期低海平面,与天然气水合物易分解的时间相吻合,因此,沉积间断的形成可能主要与下伏天然气水合物的分解导致沉积物的滑塌有关。     

大兴安岭中北段头道桥一带晚古生代构造沉积环境分析

大兴安岭中北段头道桥一带晚古生代整体为弧后盆地构造环境,发育泥盆系—下石炭统泥鳅河组、大民山组与红水泉组地层.研究区泥鳅河组为浅海沉积,化石发育.在弧后拉张作用下地幔物质上涌,形成大民山组一段细碧岩系,并使地壳下沉,水体加深,在大民山组二段达到最深,为半深海沉积.后期由于陆陆碰撞作用,地壳抬升,红水泉组转为浅海环境,并使该组上部地层抬升出水面遭受剥蚀.     

大兴安岭南部地区林西组油气勘探前景探讨

基于露头资料,利用有机地球化学分析技术,通过研究大兴安岭南部林西组地层及烃源岩发育特征,探讨有利勘探方向.结果表明：大兴安岭南部地区上二叠统林西组广泛发育,其沉积环境主体为三角洲-湖相沉积;林西组暗色泥岩有机质含量以中等为主,有机质类型为Ⅱ2~Ⅲ型,有机质热演化达到高熟-过熟阶段.该区开展油气勘探应远离侵入岩发育区,在有中生界覆盖地区,保存条件及盖层条件更为有利.     

http://www.sciencedirect.com/science/article/pii/S1674987112000266

Major,trace and rare earth element(REE) concentrations of Late Triassic sediments(finegrained sandstones and mudstones) from Hongcan Well 1 in the NE part of the Songpan-Ganzi Basin, western China,are used to reveal weathering,provenance and tectonic setting of inferred source areas. The Chemical Index of Alteration(CIA) reflects a low to moderate degree of chemical weathering in a cool and somewhat dry climate,and an A-CN-K plot suggests an older upper continental crust provenance dominated by felsic to intermediate igneous rocks of average tonalite composition.Based on the various geochemical tectonic setting discrimination diagrams,the Late Triassic sediments are inferred to have been deposited in a back-arc basin situated between an active continental margin(the Kunlun-Qinling Fold Belt) and a continental island arc(the Yidun Island Arc).The Triassic sediments in the study area underwent a rapid erosion and burial in a proximal slope-basin environment by the petrographic data. while the published flow directions of Triassic lurbidites in the Aba-Zoige region was not supported Yidun volcanic arc source.Therefore,we suggest that the Kunlun-Qinling tcrrane is most likely to have supplied source materials to the northeast part of the Songpan-Ganzi Basin during the Late Triassic.