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481.
江西吉泰盆地碱性玄武岩的地球化学特征及其构造意义 总被引:6,自引:0,他引:6
吉泰盆地位于赣中地区, 目前尚无在该盆地中发现玄武岩的报道。新发现的玄武岩产于吉泰盆地南部泰和附近的南溪镇。玄武岩露头新鲜, 蚀变微弱, 属碱性玄武岩, 形成于板内快速拉张环境; 锆石U Pb年龄为 ( 139±0 7 ) ~(143±1 1)Ma, 表明岩石形成于早白垩世早期。玄武岩无明显的Nb、Ta负异常, Rb Sr、Sm Nd同位素组成分析结果显示[N(87Sr) /N(86Sr) ]i=0 704 1~0 704 8, εNd(t) = +3 78~+4 38, 反映玄武岩浆起源于亏损地幔, 未经地壳物质混染。结合吉泰盆地边部存在中侏罗世 (168Ma) 玄武岩的事实, 表明赣中地区在早白垩世已经处于拉张背景, 吉泰盆地的碱性玄武岩可能是在板内岩石圈伸展减薄作用下, 由北东向的赣江断裂带拉张形成的。 相似文献
482.
变质核杂岩研究的新进展 总被引:6,自引:0,他引:6
从三个方面综述了变质核杂岩研究的新进展:(1)通过研究基底滑脱带与兽层脆性断层的产状变化,认为递进变形中基底滑脱带原始产状可能是水平的,而上盘盖层中脆性产状从高角度开始变化;(2)变质核姆岩的形成与热异常和岩浆活动及由此引起的伸展作用具有密切的成因关系;(3)变质核杂岩可以形成于不同的区域构造背景下。 相似文献
483.
In the late Precambrian history of the Wadi Kid area in the Sinai, Egypt, two deformation phases are clearly recognized. The first phase, D1 (pre-620 Ma), produced a steep regional foliation, axial planar to upright F1 folds, in rocks of a lower-greenschist grade. This compressional phase of deformation is interpreted in terms of subduction in an island-arc setting. The second phase, D1 (post-620 Ma), is mainly expressed by the widespread development of sub-horizontal mylonitic zones with a total thickness of 1.5 km. Shear sense indicators give a consistent regional transport direction to the northwest, with local indications of reversal to the southeast. This event is associated with regional LP/HT metamorphism, indicative of high thermal gradients. Because of the LP/HT metamorphism, the change in geochemical nature of the granitoids, and the orientation of the dykes, we interpret the mylonitic zones as low-angle normal shear zones related to core-complex development during an extensional event with the transport reversal being induced by doming. We postulate that orogenic collapse was responsible for the transition from the D1 compressional phase to the D1 extensional phase. 相似文献
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486.
Low-Pressure Metamorphism of Granulite Facies in an Early Proterozoic Orogenic Event in Central Inner Mongolia 总被引:4,自引:0,他引:4
Liu Xishan Jin Wei Li Shuxun Changchun University of Earth Sciences Changchun Jilin Sun Sheping 《《地质学报》英文版》1993,67(1)
According to the kinds of feldspar and rock associations in the Ai-rich gneisses, the low-pressure metamorphic crust of the Early Proterozoic granulite facies in central Inner Mongolia can be divided into southern and northern belts which are composed of six rock associations. They represent the relevant rock sequences of the layered metamorphic rock series formed under specific metamorphic temperature and pressure conditions as well as tectonic environments. Mineral inclusions and reaction texture have recorded that the medium-temperature high-pressure mineral assemblages are replaced by the high-temperature low-pressure mineral assemblages, thus, giving rise to: garnet+quartz→ hypersthene+plagioclase; kyanite→sillimanite and garnet+kyanite/sillimanite+quartz→cordierite. The deformation fabrics of the rocks, the change of mineral assemblages and the PTt path of metamorphism indicate that the contempranceous high-temperature normal-slip ductile shearing is the main cause of the formation of the low-pressure metamorphic crust of granulite facies. In the orogenic event, the co-action of thrusting and extension resulted in the change of a medium-temperature high-pressure metamorphic environment into the high-temperature low-pressure metamorphic conditions. 相似文献
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489.
Devana Chasma is a rift system on Venus formed in association with the Beta Regio and Phoebe Regio volcanic highlands, which are interpreted as mantle plumes. We present a new analysis of a 2500-km-long segment of Devana. Based on the rift topography, the horizontal extension across the rift boundary faults is 3–9 km. This is a lower bound on the total rift extension because the altimetry does not resolve the topographic relief across the numerous faults that are visible in radar images of the rift floor. The total extension across Devana is approximately 20 km, similar in magnitude to continental rift systems on Earth. Rift flank elevations are up to 3.1 km in the regions nearest the mantle plumes and decay strongly with increasing distance from the plumes, indicating a strong thermal component to the rift flank topography, unlike the situation usually reported for terrestrial rifts. As on Earth, there is also a flexural uplift component to the flank topography. Rift depths are up to 2.5 km below the surrounding plains, with considerable along-strike variability. There is a 600 km lateral offset along Devana Chasma near the mid-point between the two mantle plumes. Devana most likely formed as two distinct rifts due to the horizontal stresses created by outflow from the upwelling plumes. The offset zone formed as a result of the interaction between the two rift tips, which requires that upwelling at the two mantle plumes overlapped in time. 相似文献
490.
江汉盆地早第三纪玄武质岩石^39Ar/^40Ar年代学和地球化学特征及其成因意义 总被引:1,自引:0,他引:1
江汉盆地早第三纪火山岩主、微量元素和Sr-Nd同位素以及精确的40 Ar/39 Ar年代学研究表明该火山岩形成于57.3±0.4Ma,由亚碱性的玄武岩和玄武质安山岩组成,富集LILE和HFSE,(La/Yb)cn=3.5~10.4,Eu/Eu*=0.99~1.08,具有与洋岛玄武岩(OIB)相似的地球化学特征.微量元素比值和Sr-Nd同位素组成上表明,其地球化学特征与源于EMⅡ型富集岩石圈-软流圈相互作用而形成的华北南缘早第三纪火山岩以及东南沿海新生代玄武质岩石相似.结合长江中下游地区中生代玄武岩Pb同位素的资料,暗示扬子北缘新生代岩石圈地幔属性可能是其中生代属性的继承.江汉盆地早第三纪玄武质岩石是在陆内的岩石圈伸展拉张构造背景下,对流软流圈上涌导致EMⅡ型岩石圈地幔部分熔融的结果. 相似文献