青藏及邻区新生代火山活动及构造演化

青藏高原是现今地球动力学和地质演化研究的一个热点。该区火山活动受中 -新生代以来高原深部地球物理 -化学反应的控制 ,是多种因素相互作用所表现的形式和结果。本区既有富钾质的 (主导 ) ,也有富钠质的火山岩 (次要 ) ;既有喷发熔岩流 (主导 ) ,也有一些浅源上侵的次火山岩体 ;火山活动发育在古近纪、新近纪与第四纪 ,而最强烈的发生在中新世期间。本区钠质和钾质两类火山岩在形成环境和时代上有很大的差异 :前者一般发育在古新世—始新世 (6 0～ 4 0MaBP) ,而后者主要形成在渐新世—中新世 (30～ 10MaBP) ;存在着钠质—钾质—酸性次火山岩的演化过程 ;大体上可划分为西羌塘、北羌塘、可可西里、中昆仑、西昆仑等 5个火山岩省。本文对比了青藏高原及邻区甘肃礼县和云南三岩区 (金沙江北段、腾冲和滇东南地区 )新生代火山岩的岩石组合、同位素年代学以及地球化学特征 ,大量的证据表明 ,这些火山岩形成在原始地幔、或“壳 -幔过渡带”或陆壳基底等源区。在实际考察和综合研究的基础上 ,探讨了岩石圈的区域构造特征及其与高原隆升的关系等     

Computerized database on salt affected soils in western and central India using GIS

Salt affected soils occupy significant areas in western and central India manifested by the arid and semiarid climate, sandy/clayey soil texture, absence of natural drainage, and inadequate infrastructure and irrigation development. These soils are productive following reclamation and appropriate management. The National Remote Sensing Agency, Hyderabad (India) published state-wise maps of salt affected soils in India on 1:250,000 scale using a legend that includes physiography, soil characteristics, and the aerial extent of the mapping units. In the analogue form, voluminous data contained in such maps were difficult to handle by users of varied backgrounds. An attempt was made to prepare a computerized database of salt affected soils for easy access, retrieval, and manipulation of spatial and attribute data useful for management of salt affected soils. The salt affected soils maps were prepared, for Rajasthan, Gujarat, Madhya Pradesh, and Maharashtra states, overlaying digitized layers of SAS polygons and the Survey of India basemap using the ILWIS (Integrated Land and Water Information System) software. GIS was used to prepare a composite (master) database of western and central India that showed the extent and distribution of salt affected soils. A relational database was prepared combining the digitized polygons with soil characteristics such as nature and degree of salinity (presence of higher concentration of neutral salts and neutral soil reaction), sodicity (presence of higher concentration of basic salts and alkaline reaction) and ground coverage. The regional and zonal databases of salt affected soils were prepared at a suitable scale overlaying agro-climatic regions agro-climatic zones. Spatial relation of salt affected soils with physiography, climate, geology, and agro-eco-sub-regions were evaluated employing map calculations in GIS. Saline soils were prevalent in Gujarat, and Rajasthan while sodic soils were dominant in Maharashtra and Madhya Pradesh. These were distributed primarily in the arid (B) plain of Rajasthan, alluvial (A) and coastal (D) plains of Gujarat, and peninsular plain (F) of Maharashtra and Madhya Pradesh. It occupied 2,596,942 ha (78%) in the western (Rajasthan and Gujarat) and 733,608 ha (22%) in the central (Madhya Pradesh and Maharashtra) regions. The SAS occupied 3.3 million ha in the western and central region constituting 50% of the total salt affected soils in India. The saline and sodic soils occupied 2,069,285 ha (62%) and 1,261,266 ha (38%), respectively.     

FORMATION OF GOLD-BEARING HYDROFRACTURING BRECCIA BODIES IN TECTONIC LENSES： A CASE STUDY ON SHUANGWANG GOLD DEPOSIT, SHAANXI, CHINA

1 Introduction Hydrofracturing is possibly an important fracture behavior within the whole lithospheric crust, many geologists have noticed and carried out study on hydrofracturing in the fluid-rock systems (e.g., Phillips, 1972; Sibson, 1986; Fyfe, 1987; Svyatoslav and Kirill, 1993; Cox, 1995; Nakashima and Toriumi, 1996; James et al., 2000; Agust et al., 2002). Hydrofracturing phenomena are universally existent in the active structural belts, nonlinear tension vein systems in metamorphi…     

Effects of water quality on infiltration,runoff and interrill erosion processes during simulated rainfall

This paper discusses the effects of water quality on the hydrological and erosion response of non‐saline, non‐sodic soils during simulated rain experiments. It is well known that rain water quality affects the behaviour of saline soils. In particular, rain simulation experiments cannot be run using tap water if realistic values of infiltration rates and soil erosion are to be found. This paper reports on similar effects for non‐saline, non‐sodic soils. Two soils – a well‐aggregated clay‐rich soil developed on marine silty clay deposits and a soil developed on silt loam – were selected and subjected to a series of simulated rainstorms using demineralized water and tap water. The experiments were conducted in two different laboratories in order to obtain results independent of the tap water quality or the rainfall simulator characteristics. The results indicate that time‐to‐ponding is largely delayed by solute‐rich water (tap water). When tap water is used, infiltration rates are significantly overestimated, i.e. by more than 100 per cent. Interrill erosion rates increase by a factor of 2·5–3 when demineralized water is used. The silty clay soil was more affected by the water quality than the silt loam soil, with respect to infiltration and runoff production. Regarding interrill erosion rates, the two tested soils were similarly affected by the water quality. Therefore, it can be concluded that rainfall simulation experiments with non‐dispersive soils (e.g. non‐saline, non‐sodic) must also be conducted using water with very low electrical conductivity (i.e. less than 30–50 µS cm⁻¹), close to that of distilled water. The use of tap water certainly hampers comparisons and the relative ranking of the hydrological and erosion response of different soils, while parameter values, such as final infiltration rate or time‐to‐ponding, cannot be extrapolated and extended to natural situations. Therefore, the majority of hydrological and erosion models and parameter values measured during rainfall simulations in the past should be used with caution for all types of soils. Copyright © 2001 John Wiley & Sons, Ltd.     

615铀矿床蚀变和矿石特征

提出615铀矿床侧缘蚀变的双层交代蚀变结构,即碱性流体交代之后叠加的酸性流体交代蚀变;强调在蚀变带中元素变化与蚀变岩石中矿物之间的相互关系;论述该矿床铀成矿是酸性流体叠加的结果;总结矿床经历了3次不同性质的热流体作用过程：即前期为富硫氢酸期,铀矿化期为氟化物、硫化物、磷酸盐、碳酸盐期和矿后富氧的简单流体作用期。     

Assessment of salt affected soils in India using GIS

Salt affected soils are characterized by variable distribution and dynamic nature. Based on Landsat data from 1986/1987 supported by ground truth, salt affected soil maps were prepared at 1:250,000 scale for 14 states and a union territory (UT). A map legend was evolved that described the nature, degree and extent of salt affected soils suitable for varied physiographic and agroclimatic regions of the country. Fifteen categories of salt affected soil were identified for the entire country. These were merged to two categories – saline and sodic – for management purposes. Digitized maps were developed in a geographical information system (GIS) depicting salt affected areas of the country. An area of 6.73 million ha of salt affected soils was estimated for the entire country. State-wise estimates showed that this extensive area is distributed over the Gangetic plain of Uttar Pradesh; the arid and semiarid regions of Gujarat and the peninsular plains of Maharashtra state. A significant area is also located in the coastal region covering seven states. The salt affected soils are primarily saline in deltaic (C), coastal (D) and mud flats/mangrove swamps (G) and sodic in alluvial (A), aeofluvial/aeolian/arid (B) and peninsular (F) plains. The distribution of salt affected soils in agroclimatic zones (ACZs) showed occurrence in Gujarat plain, East Coast plains, Upper-Gangetic plain, Trans-Gangetic plain, Central Plateau, Lower-Gangetic plain and Southern Plateau of the country.     

苏打碱化土壤区地下水质的模糊综合评价

运用模糊数学方法,从农业灌溉角度,分别对该地区旱季、雨季的地下水质进行模糊综合评价。结果表明,无论是旱季还是雨季,该区30m深度以内的浅层地下水质均普遍较差,利用其灌溉会产生中等及较高程度的盐碱化危害;而60m深度以下地下水质较优,作为灌溉水源产生盐碱化的程度较低。浅层地下水受地表盐碱性水体和苏打碱化土壤影响,致使水质盐碱性较强;深层地下水由于埋藏较深,不受地表土壤和水体影响,因而水质稳定。     

山东郯城神泉钠质火山岩的年代学与地球化学——对源区地幔性状与岩石成因的启示

山东神泉钠质火山岩出露于郯城李庄东侧,构造上位于沂沭断裂带南段,构成一盾状火山机构,主体岩性为粗安岩。锆石LA-ICP-MS U-Pb定年结果显示,其成岩年龄为96.5±1.4 Ma,较之区内广泛分布的钾质火山岩形成年龄晚,指示沂沭断裂带及邻区中生代火山岩总体上具有由钾质向钠质演变的趋势。在化学组成上,神泉火山岩具有富碱(Na2O+K2O=10.34%~11.95%)和明显富钠(Na2O/K2O=1.76~3.92)的特征,按多种方法判别均可归为典型的钠质火山岩。该火山岩稀土元素总量较高(ΣREE=411.3×10-6~456.3×10-6),富集轻稀土元素,LREE/HREE=19.53~21.10,(La/Yb)N=29.69~33.26,缺乏明显的铕异常(δEu=0.77~0.82),稀土元素配分型式呈明显的右倾型。岩石富Rb、Ba、Th等大离子亲石元素,亏损Ti、Nb、Ta等高场强元素,在微量元素蛛网图上显示一定的Pb负异常。神泉火山岩具有富集的Sr-Nd同位素特征,ISr=0.706 8~0.707 7,εNd(t)=-16.66~-16.82,与山东中生代镁铁质岩石的Sr-Nd同位素组成类似,表明其应起源于富集的岩石圈地幔。综合分析表明,神泉火山岩源区极可能遭受了因扬子板块深俯冲和华北克拉通岩石圈拆沉等多次富集事件的影响,至晚白垩世,随着郯庐断裂引张的加剧,诱发了软流圈地幔上涌,并对先期形成的富集地幔进一步改造,同时在断裂减压作用的影响下,促使了这一经叠次改造的富集地幔的部分熔融,由此产生的岩浆经进一步分异演化,最终导致了神泉钠质火山岩的形成。     

新疆阿尔泰南缘康布铁堡组钾-钠质流纹岩锆石U-Pb年龄和地球化学

阿尔泰南缘分布着大量的晚古生代康布铁堡组火山岩系,是许多铁矿、铜矿以及铅锌矿的赋矿围岩。阿尔泰南缘麦兹和克朗火山-沉积盆地内的钾-钠质流纹岩的年龄分别为396.7±1.4Ma和394.0±6.0Ma,结合近期研究成果,进一步表明阿尔泰南缘火山岩主要形成于晚古生代早期,锆石U-Pb年龄峰期在400Ma左右。钾-钠质流纹岩具有高硅(SiO₂的含量范围为73%~82%)、高碱(总碱含量介于4%~7%)和过铝质(高A/CNK值>1)的特征,并见有白云母和黑云母的矿物组合,属于高硅高碱过铝质的钙碱性火山岩。此外,它们的Sr和Nd同位素分别为⁸⁷Sr/⁸⁶Sr=0.7074~0.7144,¹⁴³Nd/¹⁴⁴Nd=0.512072~0.512252,具有上地壳来源的特征,说明其岩石成因与初生地壳的部分熔融作用有着密切关系。结合区域地质背景分析,它们都产在与俯冲消减作用有关的陆缘岛弧的地质环境中。因此,我们推断本区钾-钠质流纹岩的原始岩浆为高硅高碱的花岗质岩浆,是由进入陆壳的高侵位玄武岩浆的底侵作用导致其上部地壳近固相线的低程度部分熔融的产物。     

Calculated stabilities of sodic phases in the Sambagawa metapelites and their implications

Pressure (P)–temperature (T) pseudosection analyses were carried out on metapelites from Sambagawa belt by using Perple_X 07 so as to determine mineral equilibria and the stability of sodic phases, in the model system MnO–Na₂O–K₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–(CO₂) under high‐pressure (HP) conditions (0.5–2.5 GPa/400–600 °C). A pressure–X_NA [=Na/(Na+Al–2K–1.5Ca)] pseudosection at 500 °C is also calculated to examine the effect of Na/Al value of the bulk‐rock composition on the stabilities of sodic minerals. The bulk‐rock compositions of Sambagawa metapelite are variable in X_NA values. The calculation results of stable assemblages in metapelites under the blueschist and eclogite facies conditions indicate that: (i) paragonite and glaucophane are stable throughout the wide X_NA range of bulk‐rock compositions of host rocks; (ii) stable P–T conditions of sodic pyroxene enlarge with increasing X_NA value; and (iii) the stability field of paragonite enlarges with the presence of CO₂ in the metamorphic fluid. The suggested wide stability of paragonite in metapelites and the relationships between the stability of sodic pyroxene and the bulk‐rock compositions explain the reasons why (i) the occurrence of omphacite in metapelites from several subduction‐related terranes is rare; and (ii) paragonite commonly occurs as inclusions in garnet of metapelites from the Besshi region of the Sambagawa belt. Paragonite is an important sodic phase of HP metapelites, and a combination of paragonite and quartz with high residual pressure included in garnet may be a useful indicator to verify the evidence for the eclogite facies metamorphism recorded in metapelites.