Late Mesozoic Exhumation of the Huangling Massif:Constraints on the Evolution of the Middle Yangtze River

Plate subduction leads to complex exhumation processes on continents.The Huangling Massif lies at the northern margin of the South China Block.Whether the Huangling Massif was exhumed as a watershed of the middle reaches of the Paleo-Yangtze River during the Mesozoic remains under debate.We examined the exhumation history of the Huangling Massif based on six granite bedrock samples,using apatite fission track(AFT)and apatite and zircon(U-Th)/He(AHe and ZHe)thermochronology.These samples yielded ages of 157–132 Ma(ZHe),119–106 Ma(AFT),and 114–72 Ma(AHe),respectively.Thermal modeling revealed that three phases of rapid cooling occurred during the Late Jurassic–Early Cretaceous,late Early Cretaceous,and Late Cretaceous.These exhumation processes led to the high topographic relief responsible for the emergence of the Huangling Massif.The integrated of our new data with published sedimentological records suggests that the Huangling Massif might have been the watershed of the middle reaches of the Paleo-Yangtze River since the Cretaceous.At that time,the rivers flowed westward into the Sichuan Basin and eastward into the Jianghan Basin.The subduction of the Pacific Plate beneath the Asian continent in the Mesozoic deeply influenced the geomorphic evolution of the South China Block.

Exploratory and Descriptive Study of the Kimberlite Massif of Boya-02 at Eastern Kasai in the Democratic Republic of Congo

The Boya-02 kimberlite was identified at depth by geophysical survey work (a single-probe AM survey in 1997 and a gravity survey in 2006) that De Beers DRC Exploration carried out around anomaly 193/172/0019. This anomaly located approximately 50 km southwest of the town of Mbuji-Mayi in the Kasaï-Oriental Province in the DRC should therefore be the subject of detailed exploration with the aim of better identifying and describing this kimberlite. Thus, through exploratory work and cross-checking of geophysical and geological data, the discovery of this Massif was made by drilling on the aeromagnetic anomaly 193/172/X298. Based on drilling, sampling and laboratory petrographic analysis reports, the Boya-02 kimberlite was classified among highly diluted re-sedimented volcaniclastic kimberlites (KVR), rich in olivine and incidentally in quartz and poor in juvenile substances. This kimberlite represents a deposit of very low economic interest following extremely high dilution. The Boya-02 kimberlite was modeled using ground magnetism data. It is a complex anomaly comprising 2 components with variable amplitude appearing on a subtly magnetized linear detail. The modeled dimensions of two components of this anomaly are 0.32 Ha and 0.2 Ha at depths of 32 m & 14 m for the deposits to the West and the East respectively. Garnet data for the Boya-02 occurrence reports a maximum Pmin value of 49.7 kbar (207 garnets). These data demonstrate the high diamond potential which assumes a conductive cratonic geotherm of 40 mWm2.

Rare-Element Pegmatites Rocks Rich and Li of the Aïr Massif of the Tchirozerine: Mineralogy and Chemical Composition Agadez Region-Northem Niger

The lithium potential in the Aïr massif is represented by mineral index of spodumene pegmatites and, lepidolite pegmatites. The mineral deposits of lithium occur in cluster or veins that cut the host rock or are located near the contact between the greenstone belt and granitic massif. The evidence of lithium is in the form of clusters or disseminated and stockwerk. Mineralogical characteristics show similarities between the Air Massif pegmatites and indicate the same homogenous source during the magma-generation process. The pegmatite rocks attracted the attention due to their wide exposure and composition, well appearance, and economically hosting of significant rare earth metals such as Sn and W. The mineralogical and petrographical investigations on the eight pegmatites rocks samples observed have a relative similarity, while a little difference in the shapes attributed to the ratio in the pegmatite rocks of the minerals. The occurrence of the kink band indicates the influence of the tectonic processes which affected the Aïr massif after the emplacement of late magmatic or post-magmatic pegmatites by injection into fractured rocks in the upper part of the crust. The Air Massif pegmatite has higher concentrations Li and of all trace elements except Hf and occasionally Zr, Ti, Sn and Mg of for the economic exploration.

Neoarchean Magmatic Events in the Western Songnen Massif,Central Asian Orogenic Belt:Timing and Tectonic Significance

Whether a Neoarchean basement existing in the Songnen massif is currently debated.Identification of Archean magmatism from the Songnen Massif is helpful to resolve this issue.Here,we report newly discovered Neoarchean Shanquan pluton in the Western Songnen Massif.These Neoarchean Shanquan pluton are mainly composed of granites that are exposed near the town of Shanquan in Heilongjiang Province.LA-ICP-MS zircon U-Pb dating reveals that the sample 2015TW1 has an upper intercept age of 2801±69 Ma and a weighted mean age of 2708±18 Ma,while samples LJ27QY1 and LJ27QY2 have upper intercept ages of 2677±57 Ma and 2653±18 Ma,and weighted mean ages of 2649±10 Ma and 2653±15 Ma,respectively.This indicates that these granites were formed at~2.7 Ga.Most of the~2.7 Ga zircons have older TDM2 ages of 2762–3326 Ma with positiveεHf(t)values ranging from 0 to 6.4,while a few of the zircons have negativeεHf(t)values ranging from-8.1 to-11.5 and older TDM2 ages varying from 3158 to 3264 Ma.The zircon Hf isotopes indicate that Paleo-Mesoarchean crusts might once existed in the Songnen Massif,and the studied Neoarchean magmas were principally derived from partial melting of these Paleo-Mesoarchean ancient crust.Based on the geochronological spectrum of magmatic and detrital zircons,the Songnen,Erguna,Jiamusi,Bureya massifs may have a common basement prior to the Neoproterozoic and may even be linked with the Triam Craton.

贵东复式岩体中东部晚期花岗质小岩体的SHRIMP锆石U-Pb年龄及其地质意义

贵东复式岩体由多期次、多类型的岩体组成,且东部盛产铀矿床,因此精确厘定该复式岩体的时代及其时序,查明复式岩体东部与中西部岩浆活动的差异性及其与铀成矿的关系,不仅有利于深入研究区域岩浆活动,而且有利于深刻认识铀的成矿规律。现有研究认为,以龟尾山断裂带为界,贵东复式岩体中西部岩基属燕山早期、东部岩基属印支早期,东部广泛发育的燕山期中基性脉岩与铀成矿关系密切。但对复式岩体中东部呈岩枝、岩株广泛出露的晚期花岗质小岩体的成岩地质时代及其分布规律尚存在争议,也有待进一步查明花岗质小岩体与铀矿床的时空关系。文章选择贵东复式岩体中东部晚期花岗质小岩体为研究对象,采用SHRIMP锆石U-Pb法厘定其成岩时代,并分析它们的时空分布及其与铀成矿的关系。测试结果显示,贵东复式岩体中东部晚期花岗质小岩体普遍存在高铀锆石,这可能是对同一岩体不同学者所获得的^(206)Pb/^(238)U加权平均年龄差别较大的主要原因。剔除高铀锆石的年龄数据,龟尾山断裂带以西的隘子、司前、陈洞岩体锆石^(206)Pb/^(238)U加权平均年龄分别为163.0±1.6 Ma、163.1±1.6 Ma、160.7±1.9 Ma,属燕山早期岩浆活动的产物;而以东的帽峰、分水坳、龟尾山岩体锆石^(206)Pb/^(238)U加权平均年龄分别为230.0±2.7 Ma、225.9±2.9 Ma和232.6±3.1 Ma,属印支期岩浆活动的产物。所以,龟尾山断裂以西和以东晚期花岗质小岩体的时代不同。且龟尾山断裂带以东的印支期花岗质小岩体空间上与铀矿化、尤其是与燕山早期的绢英岩化型等中高温热液铀矿化关系密切,是主要的储矿围岩;结合元素地球化学研究结果,该区产出的印支期花岗质小岩体也可为铀成矿提供铀源。

拉萨地块东部石炭——二叠系地层碎屑锆石年代学研究及启示

拉萨地块东部连续出露石炭—二叠系海相地层,研究其物源对揭示松多古特提斯洋演化过程具有重要意义。文章对工布江达娘蒲和林芝龙得地区石炭—二叠系地层开展碎屑锆石年代学研究,定年结果表明该套地层最年轻的年龄簇为314 Ma~322 Ma,指示其沉积时代不早于晚石炭世。综合对比前人报道的澳大利亚Canning和Perth盆地石炭—二叠系地层碎屑锆石年龄谱、拉萨地块内松多古特提斯洋演化岩浆作用记录和增生杂岩碎屑锆石年龄谱,笔者认为该套地层中石炭纪年龄的碎屑锆石主要来源于松多古特提斯洋演化过程中岩浆作用;工布江达娘蒲松多群(AnOs)地层与直孔—松多地区的松多组(C2P1s)为同一套地层,是松多古特提斯洋增生杂岩的一部分;林芝龙得地区诺错组(C1n)地层与当雄来姑组(C2P1I)地层类似,是松多古特提斯洋边缘稳定沉积。

大兴安岭北段盘古河上游早古生代中基性杂岩体U-Pb年龄、地球化学特征及其地质意义

额尔古纳地块出露的早古生代岩浆岩的成因、源区特征及动力学背景对于揭示恢复额尔古纳地块及其周缘地区的构造演化历史具有重要意义。笔者等选取大兴安岭北段盘古河上游地区早古生代中基性杂岩体进行了岩石学研究和锆石U-Pb年代学及岩石地球化学分析。野外调查及室内研究表明杂岩体的岩石类型以角闪辉长岩和辉长岩为主,少见石英闪长岩、闪长岩、辉石岩、橄榄辉长岩等中性岩和超基性岩。测年结果显示,角闪辉长岩的成岩年龄为479.2±2.1 Ma,表明该杂岩体形成时代为早奥陶世。地球化学组成上,盘古河上游早古生代中基性杂岩体SiO_(2)含量介于40.74%~54.95%,Fe_(2)O_(3)^(T)含量为3.99%~14.66%,MgO含量介于3.36%~17.78%,Mg^(#)值为47~79,为(高钾)钙碱性系列岩石,相对富集轻稀土元素,亏损重稀土元素,δEu=0.77~2.06,相对富集Rb、Ba、U、K、Pb和Sr等大离子亲石元素及放射性元素,亏损Nb、Ta、Ti等高场强元素,与俯冲带弧岩浆岩地球化学特征类似。岩浆来源于以俯冲流体交代为主、沉积物熔体交代为辅的岩石圈地幔部分熔融。源区以含尖晶石的石榴二辉橄榄岩为主,少量为尖晶石二辉橄榄岩,并在上升过程中经历了不同程度的结晶分异作用。结合区域岩石地层资料,综合分析表明盘古河上游早古生代中基性杂岩体形成于大陆拉张带(或初始裂谷)的构造环境,很可能与西伯利亚板块和额尔古纳地块碰撞后岩石圈伸展背景有关。

Permian Tectonic Evolution in Southwestern Khanka Massif:Evidence from Zircon U-Pb Chronology,Hf isotope and Geochemistry of Gabbro and Diorite

Laser ablation-inductively coupled plasma mass spectrometry （LA-ICP-MS） zircon U-Pb dating and geochemical data for the Permian gabbros and diorites in the Hunchun area are presented to constrain the regional tectonic evolution in the study area. Zircons from gabbro and diorite are euhedral-subhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios （0.26-1.22）, implying their magmatic origin. The dating results indicate that the gabbro and diorite formed in the Early Permian （282-2 Ma） and in the Late Permian （255-3 Ma）, respectively. In addition, the captured zircons with the weighted mean age of 279-4 Ma are also found in the diorite, consistent with the formation age of the gabbro within uncertainty. The gabbros belong chemically to low-K tholeiitic series, and are characterized by low rare earth element （REE） abundances, fiat REE pattern, weak positive Eu anomalies （JEu）, and depletion in high field strength elements （HFSEs, Nb, Ta, and Ti）, similar to the high-aluminum basalts from island arc setting. Initial Hf isotopic ratios of zircons from the gabbro range from ＋7.63 to ＋14.6, suggesting that its primary magma could be mainly derived from partial melting of a depleted lithospheric mantle. The diorites belong to middle K calc-alkaline series. Compared with the gabbros, the diorites have higher REE abundance, weak negative Eu anomalies, and more depletion in HFSEs （Nb, Ta, and Ti）, similar chemically to the volcanic rocks from an active continental margin setting. Initial Hf isotopic ratios and Hf two-stage model ages of zircons from the diorite range from ＋11.22 to ＋14.17 and from 424 to 692 Ma, respectively, suggesting that its primary magma could be mainly derived from partial melting of the Early Paleozoic and/or Neoproterozoic accretted lower crust. Taken together, it is suggested that geochemical variations from the Early Permian gabbros to the Late Permian diorites reveal that the subduction of the Paleo-Asian oceanic plate beneath the Khanka Massif and collision between the arc and continent （Khanka Massif） happened in the late stage of the Late Paleozoic.

2.7 Ga Monzogranite on the Songnen Massif and Its Geological Implications

Objective The formation and evolution of Songnen massif has always been a hot topic,and the presence of Precambrian basement on the Songnen massif is still controversial:(1)Lacking of Pre-Paleozoic dating results,the Precambrian basement on Songnen massif does not extend largely according to the isotopic dating results of core from basement,(2)the existence of gneiss from deep drill holes

Paleoproterozoic Nb-enriched meta-gabbros in the Quanji Massif,NW China:Implications for assembly of the Columbia supercontinent

Diverse models have been proposed for the role of the Tarim Craton within the Paleoproterozoic Columbia supercontinent assembly. Here we report a suite of-1.71 Ga Nb-enriched meta-gabbro lenses in the eastern Quanji Massif, within the Tarim Craton in NW China. The meta-gabbroic rocks have Nb contents of 11.5-16.4 ppm with Nb/La ratios varying from 0.84 to 1.02((Nb/La)_N = 0.81-0.98) and Nb/U ratios from 38.0 to 47.2. They show low SiO_2(45.1-48.5 wt.%) and MgO(5.96-6.81 wt.%) and Mg#(Mg# = Mg/(Mg + Fe) = 43.5-47.7), high FeO^t(13.0-15.7 wt.%) and moderate Ti02(1.70-2.51 wt.%).with tholeiitic affinities. These rocks possess low fractionated REE patterns without obvious Eu anomalies(Eu/Eu~* = 0.87-1.02). Their primitive mantle-normalized elements patterns display significant Zr-Hf troughs, positive Nb anomalies, weak negative Ti and P anomalies, and high contents of Rb and Ba,resembling Nb-enriched basalts generated in arc-related tectonic settings. Their arc-like geochemical signatures together with whole rock εNd(t) values of 0.4-2.1 and corresponding old T_(DM)(2.22-2.37 Ga)as well as(^(143)Nd/^(144)Nd)_t and(^(87)Sr/^(86)Sr)t(t = 1712 Ma) values of 0.5104-0.5105 and 0.7030-0.7058,respectively, suggest that their precursor magma originated from mantle wedge peridotite metasomatised by subduction-derived melts. The results from our study reveal subduction along the eastern periphery of the Tarim Craton and marginal outgrowth continuing to ~1.7 Ga within the Columbia supercontinent.

New Zircon U-Pb Geochronology of the Post-kinematic Granitic Plutons in the Diancang Shan Metamorphic Massif along the Ailao Shan-Red River Shear Zone and Its Geological Implications

The Ailao Shan-Red River fault zone is the boundary between the Yangtze block to the northeast and the Indochina block to the southwest.It is an important tectonic zone due to its role in the southeastward extrusion of the Indochina block during and subsequent to the Indian-Eurasian collision.Diancang Shan（DCS） high-grade metamorphic complex,located at the northwest extension along the Ailao Shan-Red River（ASRR） shear zone,is a representative metamorphic complex of the ASRR tectonic belt.Structural and microstructural analysis of sheared rocks in the high-grade metamorphic rocks reveals that they are coherent with solid-state high-temperature ductile deformation,which is attributed to left-lateral shearing along the ASRR shear zone.New LA-ICP-MS zircon U-Pb geochronological and microstructural studies of the post-kinematic granitic plutons provide a straightforward time constraint on the termination ductile left-lateral shearing and exhumation of the metamorphic massif in the ASRR shear zone.It is suggested that the left-lateral shearing along the ASRR shear zone ended at ca.21 Ma at relative lower-temperature or decreasing temperature conditions.During or after the emplacement of the young dikes at ca.21 Ma,rapid brittle deformation event occurred,which makes the DCS massif start fast uplift/exhumation and cooling to a shallow crustal level.

ANISOTROPIC FEATURE OF QIANGTANG MASSIF TEXTURE

Qiangtang Massif is located in the hinterland of Qinghai—Tibet plateau, which belong to the mid\|east section of Tethys Tectonic Domain.1 Features of the whole texture and structure of Qiangtang massif By synthetic analysis of gravity,magnetic field,MT,seismic surveying,etc. Geophysical data, the massif, lied in the tectonic setting and geodynamic setting mingled by the south,north tectonic belts, have the features of massif,basin and tectonic belt three forming an organic whole,multi\|degree coupling in plane and section with division of region in south\|north trend,division of block\|fault in east\|west trend,division of sphere\|layer in vertical direction. (1) Belting in south\|north trend: Qiangtang massif could be divided into four units from north to south, that is north edge doming zone, west part doming area,Qiangtang Basin and south edge doming zone. Qiangtang Basin also can be divided into four tectonic units—north Qiangtang down\|warping region, middle downing zone, south Qiangtang down\|warping and east part slope region. The near east\|west trend tectonic zones are well developed. There is aero\|magnetic anomaly distributed in belting with east\|west trend but also concentrated in section. Gravity anomaly is high in the south\|west part and low in the northeast part. Inter\|crust low resistance layer alternately distributed with high and low belting of sou th\|north trend in plane.

Sequence of Ductile Shear Zones in UHP Metamorphic Province with in Dabie Massif,China

Structural studies in the Dabie massif show that distribution of strain is extremely heterogeneous and illustrates the pattern of deformation partitioning in the ultra high pressure (UHP) metamorphic province on all scales. Based on the field structural analysis along with microstructural observation, at least five widespread episodes of ductile shear zone systems are identified by using geometric, kinematic and rheological indicators and they constitute a shear zone sequence in the UHP metamorphic province within the Dabie massif (DM), China. Each shear zone system, for example, the UHP eclogite facies shear zone system in the sequence, exhibits its own features including geometric styles, mineral assemblages, metamorphic pt conditions and deformation regimes during the formation of such shear zone system. Detailed macro and micro scopical features of different episodes of the shear zones are given with respect to mechanism of strain localization and deformation partitioning. The tectonic significance during the creation and exhumation of the UHP metamorphic rocks is evaluated briefly, as well. It is argued that the ductile shear zones in the UHP metamorphic province play an important role in the Dabie mountain building geodynamic process.

The Puesto Piris Formation: Evidence of basin-development in the North Patagonian Massif during crustal extension associated with Gondwana breakup

The Marifil Volcanic Complex, exposed in the eastern North Patagonian Massif, Argentina, includes up to 550 m of red conglomerates, sandstones, black siltstones, limestones, and reworked tuff of the Puesto Piris Formation. The basal part of this unit, which was deposited in high-gradient topographic relief, is composed of conglomerates and sandstones with thin layers of reworked tuffs. The lithofacies associations of the basal part indicate that the depositional mechanisms were mantled and gravitational flows.The middle part of the unit consists of fine sandstones, limestones, and black siltstones that were deposited in low-energy fluvial and lacustrine environments. The outcrops are located along the NEe SW direction and the major thickest units represented by limestones and siltstones, occur near the southeastern border of this NEeS W depocenter. Since the rhyolitic and trachytic lava flows and tuffs of the Marifil Volcanic Complex are interbedded with the sedimentary sequences of the Puesto Piris Formation,both units are coeval. Zircon Ue Pb age was obtained for a trachytic lava flow(193.4 ±3.1 Ma) suggesting that sedimentation and volcanism are Sinemurian. This extensional episode was recorded in the eastern,western, and southwestern sectors of the North Patagonian Massif, and is possibly associated with the Gondwana supercontinent breakup.

Control of Interior Sources on Time-Bound Characteristics of Mineralization in Southwest Yangtze Massif

Strata bound ore deposits of Au, Ag, Hg, Sb, As, Sn, Pb and Zn in southwest Yangtze massif are concentrated in Cambrian, Devonian, Upper Permian to Lower Triassic and rarely in other horizons, showing a strong time bound feature. The metallogenic elements are highly enriched in these host strata and limited in other horizons. Isotope researches indicate that the metallogenic elements in the ore deposits mainly come from the host strata. The studies of trace elements in the host mudstone show lower w (Th)/ w (Sc), w (Th)/ w (U) ratios, higher mafic elements (such as Cr, Ni, Co) mass fractions than the average values of the same kind of rocks in the upper crust and the research area. The chondrite normalized REE patterns of mudstone in the host strata are quite different from the common mudstones and shales with relatively steep HREE slopes (relatively high w (Tb) n/ w (Yb) n ratios, between 1.48 and 2.00) and no or slightly negative Eu anomalies (high δ (Eu) ratios, between 0.79 and 0.89). The NASC normalized REE patterns of siliceous rocks in the host strata show the HREE enrichment (the w (La) n/ w (Yb) n ratios are less than 1), a little Eu positive anomalies and Ce depletion with high abundances of As, Se, Sb and Ba elements, which shows the hydrothermal deposit features. The NASC normalized REE patterns of the mudstone in the host strata are very similar to those of the hydrothermal siliceous rocks and to those of the tuffs and basalts except the higher total REE mass fractions. All of these geochemical characteristics suggest the existence of interior sources pouring into basin when the host strata were deposited. The research of basin evolution also indicates that the host strata were deposited in the pulling apart periods. It can be realized from these facts that the degree of enrichment and deficiency of the elements in the normal depositional strata is very limited, and it is only the particular horizons corresponding to the particular periods of the earth ’s evolution that can be the significant source beds because only in these unusual horizons can be highly enriched metallogenic elements. The interior sources corresponding to the pulling apart of basin evolution may be the main cause to make the mineralization of the strata bound ore deposits in southwest Yangtze massif take on time bound characteristics.

Age and geochemistry of the Neoproterozoic granitoids in the the Songnen–Zhangguangcai Range Massif, NE China: Petrogenesis and tectonic implications

1 Introduction The Songnen–Zhangguangcai Range Massif(SZRM)crops out over an extensive part of NE China and was thought to contain Precambrian crystalline basement material,as evidenced by the presence of what appears to bePaleoproterozoicbasementmaterialwithin exploration drillholes(Pei et al.,2007).An alternative view is that the basement within the SZRM is

Speleological Investigation of the Largest Limestone Massif in Georgia (Caucasus)

Georgia is home to multiple, widespread limestone massifs with well-developed karst areas and their associated landscape features found throughout the country. Due to geological, geomorphological, and speleological characteristics of the limestone massifs in Georgia, there are developments in classical karst processes and landforms, which contain very impressive karst features, such as dolines, caves, calcite depositions and others. For example, in Georgia, the world’s deepest caves are found, such as: Krubera-2197 m;Sarma-1830 m;Pantyukhina-1508;Ilyukhina-1275 m;Kuibyshev-1110 m, and others. Of these, Krubera Cave is currently the deepest in the world. The goal of this work is to present speleological investigation of Muradi Cave, which is developed in Racha limestone massif. Muradi Cave is unique as the fact that it contains almost all types and subtypes of speleothems and sediments recorded nowadays in the caves of the Caucasus region, and the mineral aggregates found in Muradi Cave are rare for the caves of the Caucasus region. Unlike many of the hypogene caves in the region, Murdai Cave is formed from a more traditional mechanism of speleogenesis, but the influence of tectonic activity and complex hydrologic regimes led to the development of speleothems and passage morphology less common in the region and likely from hypogenic overprinting. The primary objectives of this study of Muradi Cave included undertaking important investigation in this country, to better understand the speleogenetic processes.

Geoecological Monitoring of Karst Water in Georgia, Caucasus (Case Study of Racha Limestone Massif)

Karst groundwater is the major natural resource of drinking water for many countries in the world. Especially in karstic regions, karst water requirements for settlements are provided from karst aquifers. Also, we should consider, that karst groundwater is becoming more and more valuable for drinking water supply. Thus, karst groundwater quality and permanent ecological monitoring are very important for populations. Moreover, if we consider that the karst landscape is the extremely sensitive system towards anthropogenic activities, since exaclty the anthropogenic activities largely identify the karst water pollution-turbidity causing factors. This paper presents a new study regarding the quality of the karst groundwater of the study area, which contains important resource of drinking water. In the mentioned study, 12 water samples were collected from different locations of the 4 main karst springs (Krikhula, Dolabistavi, Kidobana and Sakishore) during the spring and summer of 2014 and 2015 years. The main aim was to identify chemical compositions (Ni, Ag, Co, Cd, Zn, Pb, Al, Mg, Fe, F, Cu), and also, it was important to detect Escherichia coli (E. coli). Our research regarding all these chemical compositions shows that all the values are low and under the environmental limit according to the Georgian standards. We measured chemical parameters of all these samples by Atomic Absorption Spectroscopy (AAS) in the chemical laboratory of Ivane Javakhishvili Tbilisi State University, country of Georgia.

Petrology and Geochemistry of Basement Complex Rocks in Okom-Ita Area, Oban Massif, Southeastern Nigeria

The determination of the mineralogical composition of rocks that underlie Okom-Ita area, in Oban Massif became necessary for the interpretation of the petrogenesis and protoliths of rocks in the area. Twelve representative rock samples were selected for thin section petrography and bulk rock geochemical analysis. The results reveal that the dominant intrusive rocks in Okom-Ita area are pegmatites, quartz veins and dolerites emplaced within gneisses, schists and phyllites host rocks. The quartz veins and pegmatites are leucocratic consisting predominantly of quartz, plagioclase and subordinate amount of Muscovites. The dolerite is dark grey, fine to medium grained and texturally ophitic and consists dominantly of pyroxenes, olivine and opaques. Three varieties of gneisses were recognized: feldspathic, banded and biotite gneisses. The gneisses, schists, and phyllites are dominated by SiO2 in the range of (60% - 75%). The rocks exhibit higher molecular concentration {Al2O3 > (CaO + Na2O + K2O)}, high alkali concentration with Na2O > K2O, high Al2O3 to alkali ratios and low TiO2, CaO and MgO concentrations. These distribution trends suggest a compensation for the high silica and alumina concentrations and support a granitic protolith for the pegmatites and their host gneisses and schists. The dolerites and amphibolites are impoverished in SiO2, but relatively enriched in lime and alkali oxides. Plots in the AFM, TiO2-K2O-P2O5 and Na2O/Al2O3-K2O/Al2O3 diagrams show that the pegmatite was derived from calc-alkaline magmatic source, while the dolerite was derived from tholeiitic basalt magma.

Geochemistry of Sedimentary Rocks and Its Relation to Crustal Evolution and Mineralization in Southwest Yangtze Massif,China

Through a systematic study on trace elements and REE geochemistry of mudstonedeposited in the basin and lower slope environments during Upper Proterozoic to Triassic in theSouthwest Yangtze Massif, three gaxhemical abnormal horizons of which the gerehemicalcharacteristics are quite different from those of other horizons have been established for the firsttime. They are the Lower Cambrian, the Upper Devonian and the Upper Permian. As compared with the crustal evolution in this area, these three geochemical abnormal horizons are correspoding to the pullingapart perieds of gcotectonic cycles, which illustrates that the uncommon depositional sources Pouring into the basin from the earth’s interior may be one of themost important causes to originate the geochemical anomalies in these horizons. Thus it can berealized that the gaxhemistry of opst-Archean sedimentary rocks has a great deal to do with thecrustal evolution and it can be used as a tracer to analyze the crustal evolution. The elements inthis area are mainly concentrated in these geochemical abnormal horizons, and the degree of enrichment and deficiency of trace elements in other horizons is very limited. A series of researchon mineralization indicates that the main strata-bound ore deposits discovered in the SouthwestYangtze Massif occur in the Cambrian, Devonian and Permian-Triassic strata. The results ofisotope tracer research have also proved that most of the metallogenic elements in these ore dePosits came from the host strata, which illustrates that the geochemical abnormal horizons mayhave made great contributions to these ore-forming processes. Thus it can be concluded that itis only the particular horizons corresponding to the particular periods of earth’s evolution thatcan they be the significant source beds because only in these uncommon horizons there can behighly enriched metallogenic elements, which may be one of the most important reasons for explaining the time-bound nature of mineralization.