Ca. 1.7 Ga Magmatism on Southwestern Margin of the Yangtze Block: Response to the Breakup of Columbia

This paper presents some data of the Jiaopingdu gabbro and Caiyuanzi granite at the southwestern margin of the Yangtze Block, on the geochemical compositions, zircon LA–ICP–MS U–Pb ages and Hf isotopic data. The Jiaopingdu gabbro gives the age of 1721 ± 5 Ma, the Caiyuanzi granite 1732 ± 6 Ma and 1735 ± 4 Ma, and the Wenjiacun porphyry granite 1713 ± 4 Ma, suggesting nearly contemporaneous formation time of the gabbro and granite. The bimodal feature is demonstrated by the gabbro SiO2 content of 44.64–46.87 wt% and granite 73.81–77.03 wt%. In addition, the granite has high content of SiO2 and Na2O + K2O, low content of Al2O3 and CaO, enriched in REEs (except Eu) and Zr, Nb, Ga and Y, depleted in Sr, implying it belongs to A-type granite geochemistry and origin of within-plate environment. The zircon εHf(t) of the granite and gabbro is at the range of 2–6, which is near the 2.0 Ga evolution line of the crust, implying the parent magma of the gabbro being derived from the depleted mantle and a small amount of crustal material, and the parent magma of the granite from partial melting of the juvenile crust and some ancient crustal material at the same time. Compared with 1.8–1.7 Ga magmatism during breakup of other cratons in the world, we can deduce that the Columbia has initially broken since ca. 1.8 Ga, and some continental marginal or intra-continental rifts occurred at ca. 1.73 Ga.     

Research and exploration progress on lithium deposits in China

Since 2012, some advances have been made through the resource investigation, metallogenesis research, and comprehensive utilizing of lithium deposits in China. Firstly, the progress of lithium exploration has been made in Sichuan, Xinjiang, Qinghai and Jiangxi provinces (autonomous region). Li deposits are not only found within the pegmatite rocks but also within the granitic rocks and sedimentary rocks. Secondly, the methods of geological survey, geochemical and geophysical exploration, remote sensing technology and even drilling technology have been improved, which can be delineating orebodies quickly. Thirdly, the mechanisms of Li mineralization were summarized by analyzing the relationship between the Li contents and kinds of geological phenomena. Based on practice, a new understanding of “multi-cycle, deep circulation, integration of internal and external” metallogenic mechanism or “MDIE” metallogenic mechanism for short has been put forwarded further in this paper, and the “five levels + basement” exploration model has been successfully expanded to guide the prospecting work both in the Jiajika and Keeryin pegmatite ore fields in western Sichuan Province. Besides, new progress has been made in the aspect of amblygonite deposits of granite-type and hydrothermal type in the Mufushan-Jiuling ore district, which points out a new direction for prospecting new types of lithium deposits in China.     

Geological characteristics and co-exploration and co-production methods of Upper Permian Longtan coal measure gas in Yangmeishu Syncline,Western Guizhou Province,China

Coal measure gas (also known as coal-bearing unconventional gas) is the key field and development direction of unconventional natural gas in recent years. The exploration and evaluation of coal measure gas (coalbed methane, coal shale gas and coal measure tight sandstone gas) from single coalbed methane has greatly expanded the field and space of resource evaluation, which is of positive significance for realizing the comprehensive utilization of coal resources, maximizing the benefits and promoting the innovation of oil and gas geological theory and technological advances in exploration and development. For the first time, in Yangmeishu Syncline of Western Guizhou Province, the public welfare coalbed methane geological survey project of China Geological Survey has been carried out a systematic geological survey of coal measure gas for the Upper Permian Longtan Formation, identified the geological conditions of coal measure gas and found high quality resources. The total geological resource quantity of coalbed methane and coal shale gas is 51.423×10⁹ m³ and the geological resource abundance is up to 566×10⁹ m³/km². In this area, the coal measures are characterized by many layers of minable coal seams, large total thickness, thin to the medium thickness of the single layer, good gas-bearing property of coal seams and coal measure mudstone and sandstone, good reservoir physical property and high-pressure coefficient. According to the principle of combination of high quality and similarity of key parameters of the coal reservoir, the most favorable intervals are No.5⁻², No.7 and No.13⁻² coal seam in Well YMC1. And the pilot tests are carried out on coal seams and roof silty mudstone, such as staged perforation, increasing hydraulic fracturing scale and “three gas” production. The high and stable industrial gas flow with a daily gas output of more than 4000 m³ has been obtained, which has realized the breakthrough in the geological survey of coal measure gas in Southwest China. Based on the above investigation results, the geological characteristics of coal measure gas in the multi-thin-coal-seam-developed area and the co-exploration and co-production methods, such as the optimization method of favorable intervals, the high-efficiency fracturing and reservoir reconstruction method of coal measures, and the “three gas” drainage and production system, are systematically summarized in this paper. It will provide a reference for efficient exploration and development of coal measure gas in similar geological conditions in China.     

“泛西南”地区加卸载响应比异常及大震活动预测与追踪

21世纪初, 在中国西南及周边地区(本文称为“泛西南”)开始出现大面积的加卸载响应比(以下简称LURR)异常, 根据LURR异常演化, 我们于2008年首次提出该地区正在孕育着“超大地震”。 追踪研究结果显示, 孕震积分I_t于2012年7月达到峰值。 根据LURR与量纲分析方法结合得到的预测地震时空强的新方法, 我们预测: 2015年7月前后(±25月), 在“泛西南”地区将发生8级左右“超大地震”。 我们在2014年参加的两次会议上交流了这一预测结果, 2015年4月25日尼泊尔M_S8.1强震发生在预测范围内。 尼泊尔M_S8.1地震后, “泛西南”地区的加卸载响应比大尺度异常不仅没有消退, 反而更加增强。 I_t于2015年7月达到新峰值, 超过了尼泊尔地震前的水平, 因此, “泛西南”地区可能仍面临非常严重的地震灾害。     

张量CSAMT有效观测区域模拟对比分析

根据标量CSAMT、垂直双偶极源CSAMT、三偶极源CSAMT等多分量响应式设计程序,通过数值模拟给出其十字型场源的X方向和Y方向电偶极子电磁场各分量的场值分布图,发现十字型观测区域中存在着分布零散且较广的弱区,有效观测区域较小,且对地形条件要求苛刻,不利于在山区等地形起伏复杂地区施工.在旋转三偶极装置的原理基础上提出了多偶极子源矢量合成测量方式,相比较十字型场源的施工方式而言,通过矢量合成多组的电偶极子,有利于实现全区无弱区观测,同时场源铺设简便对各种地形有着较强的适用性.研究结果为张量可控源进一步的测量工作提供技术依据.     

福建福安留洋盆地早白垩世安山岩的特征及成因探讨

福安留洋盆地早白垩世安山岩广泛分布于黄坑组中,与流纹质岩石组成双峰式火山岩,且晚期伴有潜正长斑岩、晶洞碱长花岗岩等偏碱性岩石产出。通过福安地区1∶5万区调研究,认为该区安山岩可能是基性—酸性岩浆演化系列中的过渡性岩石,并有地壳物质的混染,进而得出基性岩浆与酸性岩浆可能是同源的新认识,这对当前“区域基性和酸性岩浆不同源”这一主流观点提出新的研究思路。