Farmland expansion prediction at a pastoral village in northeastern China: a spatially explicit targeting approach

Farmland expansion is one of the main causes of steppe loss in northern China. However, an effective land-use change prediction approach has not been available. A spatially explicit approach designed for identifying the trend of farmland expansion at the village scale was provided here. The first probability estimate model was generated by indicator kriging to predict farmland expansion, and the second was generated using multilevel modeling techniques to identify the causal relationships of farmland expansion. The two models were integrated by using Bayesian inference to eliminate the disadvantages of the two modelings.     

班公湖—怒江俯冲增生杂岩带东段晚古生代辉绿岩锆石U-Pb年龄、Hf同位素特征及其构造意义

嘉玉桥—同卡混杂岩带位于班公湖—怒江俯冲增生杂岩带东段嘉玉桥至邦达地区,1: 250 000区域地质调查将其主体厘定为晚古生代混杂岩,但缺乏准确的同位素年代学与地球化学约束。本文选择该带邦达岩组中的辉绿岩作为研究对象,开展详细的岩相学、地球化学及年代学工作,揭示班公湖—怒江俯冲增生杂岩带的形成时间及构造环境。结果表明,辉绿岩明显具有N-MORB型的地球化学性质,同时富集大离子亲石元素(Rb,Ba),亏损高场强元素(Nb,Zr),其岩浆源区为尖晶石二辉橄榄岩经过约30%的部分熔融,一致指示岩浆源区可能源于受俯冲流体交代影响的亏损地幔源区。辉绿岩的锆石LA-ICP-MS U-Pb年龄为(330.9±1.6) Ma,代表了辉绿岩的结晶年龄,指示邦达辉绿岩形成于早石炭世,进一步揭示班公湖—怒江俯冲增生杂岩带存在古特提斯洋演化残留地质信息。邦达早石炭世N-MORB型辉绿岩的厘定,为进一步认识班公湖—怒江俯冲增生杂岩带早石炭世的构造环境,探讨班公湖—怒江特提斯洋的时空演化提供了重要依据。     

老挝1∶20万孔县幅(B.Khon)区域地质填图主要成果

老挝1∶20万孔县幅是中、老两国政府合作项目,采用区域地质调查、区域地球化学调查等方法手段,查明了区域地层、岩石、构造及矿产的分布及特征,取得了一系列成果与进展: ①系统建立了研究区地层序列及构造格架,新建石炭系—新近系14个组级岩石地层单位和石炭纪—二叠纪4个?化石组合带; ②查明研究区火山岩时代主要为石炭纪、早二叠世和中三叠世,提出莫卡兰扣(Ph.Mokkalangkou)断裂带为难河—程逸缝合带北延部分的认识,所夹超基性岩可能为蛇绿岩残片,对该区及邻区的地层、构造区划具有重要意义; ③查明了研究区构造形迹的特征与分布,划分4个构造层及4个构造单元,总结出构造演化经历了6个阶段; ④新发现铜、铅锌和金13处矿化点,通过水系沉积物测量圈定化探综合异常24处,系统总结了研究区含矿层位、成矿地质背景、成矿时代及成矿规律,划分了4个找矿远景区,对优势矿产资源潜力进行了初步分析。     

基于B超成像的泥沙起动流速测量方法

床面上泥沙颗粒的起动测量一直是泥沙运动规律研究的难题。为此,提出了一种基于B超成像技术的泥沙起动流速测量方法。在模型试验水槽中,该方法利用B超仪获取水下地形及其附近粒子的运行图像,通过图像处理技术分析统计床面附近运动粒子的成像光斑个数,并分析其与流速之间的关系。结果表明,B超成像光斑个数在泥沙起动过程中存在一个突变过程,且该突变过程与泥沙起动运动相对应,可用来判定泥沙起动及其对应的起动流速,并利用该流速下的床面地形变化验证了该方法的正确性。该方法具有无扰动无干扰、适合于清水和浑水、易于实现自动化测量的特点。     

Crustal accretion and metamorphism of Mesoarchean granulites in Palghat-Cauvery Shear Zone,Southern India

This work provides unequivocal evidence of the existence of Mesoarchean granulite facies metamorphic event in the Palghat-Cauvery Shear Zone (PCSZ) of South India. Charnockite samples from two prominent hills at Kollaimalai (KM) and Pachchaimalai (PM) as well as from two quarries within the Bhavani Shear Zone (BSZ) have been analyzed for their Sm-Nd and Rb-Sr ages to investigate the existence or otherwise of the Archean granulite facies events within the PCSZ. The Rb-Sr whole-rock isochron ages for massive charnockites from both the hills appear to be contemporaneous at 2.9 Ga with the initial Sr isotopic ratios of 0.7012 and 0.7014, respectively. However, the Rb-Sr data for whole-rock samples of basic granulites from one of the quarries within the BSZ indicate open system behavior, while the charnockites from the other quarry have insufficient spread in ⁸⁷Rb/⁸⁶Sr ratios and do not yield any isochron. The Sm-Nd data, on the other hand, do not distinguish between the massive charnockite and the lowland charnockite and yield Depleted Mantle model ages in the range 2.98±0.3 Ga for all of them. The ɛ^T _CHUR for all of these rocks are highly positive. Both the Sr isotopic ratios and positive ɛ^T _CHUR values for these rocks strongly suggest a mantle source for all of them. An upper age limit of ∼3.28 Ga may be assigned to the crustal accretion of the protolith of all these rocks on the basis of their Nd model ages. The Rb-Sr isochron ages of 2.9 Ga for the two massifs could be the age of granulite facies metamorphism. Thus, the metamorphism in the KM and PM Hills took place within ∼100 Ma of crustal accretion of these rocks and probably was part of the same geological event of crust formation and metamorphism. The open system behavior with respect to Rb-Sr isotopes in the basic granulite from Bhavani is possibly due to the migration of Sr isotopes, triggered during the later shearing of these rocks.