Gravity anomaly and crustal density structure in Jilantai rift zone and its adjacent region

This paper deals with the interpretation of Bouguer gravity anomalies measured along a 250 km long Suhaitu-Etuokeqi gravity profile located at the transitional zone of the Alxa and Ordos blocks where geophysical characteristics are very complex. The analysis is carried out in terms of the ratio of elevation and Bouguer gravity anomaly, the normalized full gradient of a section of the Bouguer gravity anomaly (G ^h ) and the crustal density structure reveal that (1) the ratio of highs and lows of elevation and Bouguer gravity anomaly is large between Zhengyiguan fault (F4) and Helandonglu fault (F6), which can be explained due to crustal inhomogeneities related to the uplift of the Qinghai-Tibet block in the northeast; (2) the main active faults correspond to the G ^h contour strip or cut the local region, and generally show strong deformation characteristics, for example the Bayanwulashan mountain front fault (F1) or the southeast boundary of Alxa block is in accord with the western change belt of G ^h , a belt about 10 km wide that extends to about 30 km; (3) Yinchuan-Pingluo fault (F8) is the seismogenic structure of the Pingluo M earthquake, and its focal depth is about 15 km; (4) the Moho depth trend and Bouguer gravity anomaly variation indicates that the regional gravity field is strongly correlated with the Moho discontinuity.     

Three-dimensional admittance analysis of lithospheric elastic thickness over the Louisville Ridge

Using bathymetry and altimetric gravity anomalies, a 1° 9 1° lithospheric effective elastic thickness(Te) model over the Louisville Ridge and its adjacent regions is calculated using the moving window admittance technique. For comparison, three bathymetry models are used: general bathymetric charts of the oceans, SIO V15.1,and BAT_VGG. The results show that BAT_VGG is more suitable for calculating T e than the other two models. T e along the Louisville Ridge was re-evaluated. The southeast of the ridge has a medium Te of 10–20 km, while Te increases dramatically seaward of the Tonga-Kermadec trench as a result of the collision of the Pacific and IndoAustralian plates.     

福建海坛岛青峰老红砂旋回沉积的粒度特征及其古环境意义

福建海坛岛青峰老红砂剖面以棕红色砂层和黄橙色砂层的交替旋回变化为显著特征。通过野外考察、采样和测定分析,对青峰老红砂剖面的粒度特征及其古气候意义进行深入研究。结果表明：（1）青峰剖面棕红色砂层以细砂为主,黄橙色砂层以中砂为主,细砂-中砂在剖面上呈现明显的交替旋回变化;（2）棕红色砂层和黄橙色砂层的粒度频率曲线均以单峰加一细尾为主,含有一定量的粉砂、黏土;概率累积曲线以滚-跳-悬三段式为主,但两种砂层在组分含量、斜率等方面存在差异;（3）粒度参数呈现明显的波动旋回变化,可能指示沉积时期区域风力、搬运动力、化学风化强度方面发生了周期性变化,即棕红色砂层显示了暖湿气候条件下的红壤化过程,黄橙色砂层则显示凉干气候条件下的黄壤化过程。因此,青峰老红砂旋回沉积表明第四纪晚期以来,福建东部沿海的古气候古土壤可能经历了南亚热带（赤红壤）和暖温带（黄壤）的交替变迁。     

吉林东部大蒲柴河adakites锆石U-Pb年龄、Hf同位素特征及其意义

地球化学研究表明,大蒲柴河岩体具有典型的埃达克岩特征,来自加厚下地壳的部分熔融作用.本文采用激光等离子质谱对该岩体进行了U-Pb同位素定年,结果表明该岩体为晚侏罗世(165Ma)岩浆活动的产物.锆石的LA-MC-ICPMS Hf同位素研究结果显示,ε_(Hf)(165Ma)范围为-5.02～5.43,二阶段Hf模式年龄(t_(DM2))范围为965～1622Ma,暗示原始母岩浆为两种不同源区岩浆的混合.另外,Hf同位素研究表明,研究区在中-新元古代时(965～1304Ma)曾经历了一次重要的地壳增生事件.     

中国可供性煤炭资源潜力分析

以全国第三次煤田预测数据为基础,通过对查明煤炭资源量和未查明煤炭资源量的分布、埋藏深度和煤类的系统分析,指出中国查明尚未占用的煤炭储量2282.97亿t,经济可采储量仅684.89亿t。未查明的预测煤炭资源量45521.04亿t,潜力巨大,但在近期可供找煤普查的埋深小于1000m的预测可靠级煤炭资源量只有9169.10亿t。因此,必须科学地、客观地再认识中国煤炭资源优势,合理地制定国家能源政策,以确保中国能源安全。     

埋藏岩溶洞穴垮塌深度定量图版及其在碳酸盐岩缝洞型储层地质评价预测中的意义

通过对岩溶洞穴垮塌的岩石力学原理及塔里木盆地奥陶系实钻资料的分析,基本明确了洞穴埋藏垮塌的控制因素是岩石抗弯强度、洞穴尺度、洞穴距风化暴露面的距离等,并得到了洞穴垮塌深度的定量图版。该图版对于钻前预测现今埋藏于地下的碳酸盐岩洞穴是否已经垮塌、洞穴埋藏演化史精确恢复以及对裂缝—洞穴型储层的评价预测具有较强的实践意义。     

礁滩体与建设性成岩作用

礁、礁丘、丘同属碳酸盐建隆,礁、滩是重要勘探目的层。但各自在沉积组分、组构、环境和时空分布,以及油气地质条件上迥然不同,因而无论从理论还是勘探实践上,都有必要将其各成体系划分开来。礁滩自身为好储集岩,当建设性成岩作用叠加后可形成好的储层。碳酸盐岩优质储层形成,主要受沉积微相与建设性成岩作用两大因素控制。前者是基础,并以高能的礁滩相带为最好;后者主要包括破裂、白云石化和溶蚀三大类,并以白云石化或溶蚀为最优,其中的溶蚀分布最广泛、影响最深刻而对优质储层形成起决定性作用。礁滩储层中的古岩溶类型最为丰富多彩,包括同生期、准同生期、表生期和埋藏期热流体岩溶的所有类型,白云岩化礁滩体也不例外。其中,同生-准同生期岩溶的形成机制与礁滩沉积时高频层序旋回向上变浅序列的短暂暴露淋溶有关,表生期岩溶则受控于礁滩沉积后三级层序旋回Ⅰ型界面的暴露淋溶。由此,导致礁滩储层中除了可以也是(碳酸盐岩中)唯一保存原生孔隙外,还发育了次生溶蚀孔洞缝和大型溶洞。礁丘、灰泥丘尤其是丘间洼地中发育高有机质丰度烃源岩;它们自身没有有效的原生孔隙,但岩溶作用可以形成次生孔隙。