‘WHY FAMILIES MOVE’: A RE-EXAMINATION

Abstract

This study examines the role of surface geomorphic features in tree establishment at the alpine treeline in Glacier National Park, Montana, through the presentation of a multiscale, conceptual model of biogeomorphic relationships at alpine treeline. Empirical observations gathered through a multiscale field methodology over three summers serve as a base for the model. The model highlights the importance of surface geomorphic features, specifically boulders and terrace risers, in creating favorable local site conditions, largely by protecting seedlings from wind. The sheltering effect of surface features enables initial seedling establishment, and in some cases survival, above current treeline locations, thereby initiating a positive feedback effect that encourages subsequent tree establishment. Geomorphic features are therefore important in linking scales of pattern and process at the alpine treeline ecotone.     

基于DEM的中国山地空间范围定量界定

目前为止,中国的山地空间范围尚没有一致的划定和界线.在众多影响山地和非山地划分的因素中,山地的界定标准和地形起伏度计算尺度最为重要.山地是一个令许多科学工作者难于严密定义的科学对象和学术用语,到目前为止,仍然没有统一的山地定义出现.该文对前人研究成果进行了总结和分析,提出4种关于我国山地的定量界定标准,结合作者关于地形起伏度计算尺度的研究,分别得出4种定义下的我国山地的范围和面积.通过与现有资料(《中国地貌类型图》)的对比和分析,确定适合于我国的山地定量界定标准,并最终计算出我国山地面积为658.81万km2,占国土面积的68.2％.     

Precambrian geotectonic units of the Río de La Plata craton

The main Precambrian tectonic units of Uruguay include the Piedra Alta tectonostratigraphic terrane (PATT) and Nico Pérez tectonostratigraphic terrane (NPTT), separated by the Sarandí del Yí high-strain zone. Both terranes are well exposed in the Río de La Plata craton (RPC). Although these tectonic units are geographically small, they record a wide span of geologic time. Therefore improved geological knowledge of this area provides a fuller understanding of the evolution of the core of South America. The PATT is constituted by low- to medium-grade metamorphic belts (ca. 2.1 Ga); its petrotectonic associations such as metavolcanic units, conglomerates, banded iron formations, and turbiditic deposits suggest a back-arc or a trench-basin setting. Also in the PATT, a late to post-orogenic, arc-related layered mafic complex (2.3–1.9 Ga), followed by A-type granites (2.08 Ga), and finally a taphrogenic mafic dike swarm (1.78 Ga) occur. The less thoroughly studied NPTT consists of Palaeoproterozoic high-grade metamorphic sequences (ca. 2.2 Ga), mylonites and postorogenic and rapakivi granites (1.75 Ga). The Brasiliano-Pan African orogeny affected this terrane. Neoproterozoic cover occurs in both tectonostratigraphic terranes, but is more developed in the NPTT. Over the past 15 years, new isotopic studies have improved our recognition of different tectonic events and associated processes, such as reactivation of shear zones and fluids circulation. Transamazonian and Statherian tectonic events were recognized in the RPC. Based on magmatism, deformation, basin development and metamorphism, we propose a scheme for the Precambrian tectonic evolution of Uruguay, which is summarized in the first Palaeoproterozoic tectonic map of the Río de La Plata craton.     

Metallogeny of Cretaceous carbonate-hosted Zn–Pb deposits of Iran: geotectonic setting and data integration for future mineral exploration

More than 285 carbonate-hosted Zn–Pb deposits occur in Iran, including world-class deposits such as Mehdiabad and Irankuh. Cretaceous carbonates are the most common host rock for these deposits, which are largely concentrated in the Malayer-Esfahan metallogenic belt (MEMB) and the Yazd-Anarak metallogenic belt (YAMB) and, to a lesser extent, in the Central Iranian geological and structural gradual zone and in the Central Alborz metallogenic belt. To erect a broad metallogenic framework for Cretaceous-hosted Zn–Pb resources in Iran, we integrated a geographic information system data base, including all reported deposits and occurrences of this affinity. A significant correspondence between the distribution of these deposits and the main suture zones in the Iran plate is clearly indicated. In addition, stratiform laminated sulphides are common features in most of the Early Cretaceous deposits (e.g. Irankuh, Ravanj, and Anjireh-Tiran), indicating a synsedimentary origin of these deposits. Most of the Cretaceous-hosted orebodies cluster around the Nain-Baft and Sabzevar Cretaceous suture zones and are associated with two major tectonic events: (1) extensive Early Cretaceous back-arc basin formation, producing, for instance, the Nain-Baft mineralized basin and (2) compressive Late Cretaceous closure of the back-arc basins, reflecting the Laramide orogenesis, for example, around the Nain-Baft and Sabzevar sutures in the west and north of the Central Iranian Microcontinent. Related to the back-arc basin formation and evolution, stratiform sedimentary exhalative (SEDEX)-like (e.g. Irankuh, Vejin, Robat, Takiyeh, and stratiform Ravanj) and Irish-type (e.g. Mehdiabad) Zn–Pb ± Ba deposits formed, whereas basin closure and plate collision triggered basinal fluid flow from the suture towards both sides of the MEMB and the YAMB, thus causing the formation of Late Cretaceous-hosted Mississippi Valley-type provinces (e.g. Nakhlak, stratabound Ravanj, Khanjar-e-Reshm, Chahriseh, and Lapalang deposits) on both sides of the Nain-Baft suture zone. These two different geotectonic scenarios and their evolution explain the distribution pattern of most of the Zn–Pb deposits hosted by Cretaceous sedimentary rocks in Iran. On the other hand, the formation of these deposits is not related to the collision between the Arabian and Iran plates (including the Sanandaj-Sirjan zone), inasmuch as no spatial relationship exists between this tectonic event and the distribution pattern of the deposits, which occurs far away from the collision front. The occurrence of SEDEX-like deposits in continental back-arc basins of the Iran plate confirms that an extensional setting favourable for regional Zn–Pb metallogenesis prevailed during the Early Cretaceous. In addition, Irish-type Zn–Pb mineralization took place in carbonate platforms developed on the passive margins that surrounded the Nain-Baft back-arc oceanic basin (e.g. Mehdiabad deposit).     

Meso–Neoarchaean crustal evolution of the Bundelkhand Craton,Indian Shield: new data from greenstone belts

ABSTRACT

The Mauranipur and Babina greenstone belts of the Bundelkhand Craton are formed of the Central Bundelkhand greenstone complex (CBGC). This complex represents tectonic collage which has not been previously studied in depth. The purpose of this study is to contribute to the understanding of the main features of the Archaean crustal evolution of the Bundelkhand Craton. The CBGC consists of two assemblages: (1) the early assemblage, which is composed of basic-ultramafic, rhyolitic–dacitic, and banded iron formation units, and (2) the late assemblage, which is a felsic volcanic unit. The units and assemblages are tectonically unified with epidote–quartz–plagioclase metasomatic rocks formed locally in these tectonic zones.

The early assemblage of the Mauranipur greenstone belt is estimated at 2810 ± 13 Ma, from the U–Pb dating (SHRIMP, zircon) of the felsic volcanics. Also, there are inherited 3242 ± 65 Ma zircons in this rock. It is deduced that this assemblage is related to early felsic subduction volcanism during the Mesoarchaean that occurred in the Bundelkhand Craton.

Zircons extracted from metasomatic rocks in the early assemblage’s high-Mg basalts show a concordant age of 2687 ± 11 Ma. This age is interpreted as a time of metamorphism that occurred simultaneously with an early accretion stage in the evolution of the Mauranipur greenstone belt.

The felsic volcanism, appearing as subvolcanic bodies in the late assemblage of the Mauranipur greenstone belt, is estimated to be 2557 ± 33 Ma from the U–Pb dating (SHRIMP, zircon) of the felsic volcanic rocks. This rock also contains inherited 2864 ± 46 Ma zircons. The late assemblage of the Mauranipur greenstone belt corresponds with a geodynamic setting of active subduction along the continental margin during Neoarchaean.

The late assemblage Neoarchaean felsic volcanic rocks from the Mauranipur and Babina greenstone belts are comparable in age and geochemical characteristics. The Neoarchaean rocks are more enriched in Sr and Ba and are more depleted in Cr and Ni than the Mesoarchaean felsic volcanic rocks of the early assemblage.

Through isotopic dating and the geochemical analysis of the volcanic and metasomatic rocks of the CBGC, this study has revealed two subduction–accretion events, the Meso–Neoarchaean (2.81–2.7 Ga) and Neoarchaean (2.56–2.53 Ga), during the crustal evolution of the Bundelkhand Craton (Indian Shield).     

A study on resonance Rayleigh scattering spectra of Humic Acid (HA)

This paper deals with the influences of pH, acidity and ionic intensity of the solutions on the resonance Rayleigh scattering spectra and fluorescence spectra of humic acid. When the pH value is low and the acidity and ionic intensity are high, the resonance Rayleigh spectra and fluorescence spectra both show a tendency of increasing, though the former’s intensity is much higher. In combination with the transmission electron microscope data, the factors leading to the occurrence and enhancement of the resonance Rayleigh scattering spectra of humic acid were explored. It is considered that particle enlargement caused by aggregation, the increase of heterogeneity, the increase of hydrophobility, the formation of interface, etc., are the factors leading to the occurrence and enhancement of the resonance Rayleigh scattering spectra of humic acid. As the intensity of the resonance Rayleigh scattering spectra of humic acid is much higher, resonance Rayleigh scattering spectroscopy can be used as a newly developed spectrum technology, which is more sensitive and simpler, to study humic acid and its complicated behaviors.     

GIS集成技术在天山公路地质灾害评价与决策中的应用研究

天山公路由于其特殊的复杂地形、地质条件及降雨等因素,严重影响其正常通行.因此,借助于GIS新技术手段优势,建立一套适合于天山公路特殊区域的评价决策支持系统,就显得尤其重要.天山公路地质灾害评价与决策支持信息系统的建立,首先在详细分析天山公路地质病害原理的基础上,收集公路沿线已有的基础地理、地学等资料,对照实地工作成果和遥感成果,结合数据库及遥感图像处理技术,按数据库规则进行相应的综合、整理、筛选、归纳及转换,建立以ArcGIS为数据平台的多源信息数据库.然后基于ArcEngine平台,开发一套集基础数据的采集、存储、管理、检索、图形编辑、空间模型分析、线路区域稳定性评价、公路地质选线,以及三维可视化飞行成果图形生成及输出为一体的地质灾害评价与决策支持信息系统操作应用平台.系统整合不同类型的数据资料和多媒体信息,实现了基于三维的空间信息查询和分析功能,势必为国土资源和交通建设管理部门提供一种可靠的决策管理应用平台.     

米仓山构造带的应变与涡度分析

米仓山构造带东西向的断裂逆冲兼左旋走滑,西段的韧性变形较强,东段脆性为主。北东向三个主断裂带由北而南逆冲兼左行剪切,早期可能发生脆韧性变形,后期叠加了脆性变形。前震旦系基底岩系变形特征主要表现为透入性流变,碎斑结构和糜棱结构发育,镶嵌构造、S-C组构、带状构造、眼球构造为主,局部偶见"δ"和"σ"旋转碎斑以及矿物鱼。石英颗粒以亚颗粒旋转动态重结晶为主。显微特征反映岩石变形温度相当于绿片岩相。利用Fry法测定石英颗粒三维应变应变强度集中在1.35～1.60之间,显示出从北到南逐渐增强的趋势。Flinn指数K和Nadei-Hossack图解均表明应变类型为近似平面应变的拉长型。运动学涡度分析表明米仓山应变以简单剪切变形作用为主,具有由南向北递增趋势。     

江苏省地质环境综合区划研究

提要：城市化、工业化进程的加快不可避免地对地质环境产生巨大影响,从而影响到地质环境作为人居环境的功能。因此,合理划定地质环境保护区域,对有效保护地质环境、履行地质环境保护管理职能具有重要意义。本文以江苏地质环境调查成果为基础,基于地质环境的自然属性和社会属性,建立了包含地质灾害、矿山地质环境、山体资源保护、地质遗迹保护、地下水污染防治和土壤污染防治等6个专题区划的地质环境综合区划。具体划分的地质环境专题区划包括,地质灾害划分为重点防治区和一般防治区、矿山地质环境划分为重点治理(防治)和一般治理(防治)区、地下水(土壤)划分为修复治理区、重点防护区、一般防护区、自然防护区、山体资源划分为特殊保护区和适宜开发区、地质遗迹划分为重点保护(开发)区和一般保护(开发)区、地质环境综合区划划分为保护区、控制开发区、修复治理区和适宜开发区。