The Precambrian basement rocks in the Bengbu and neighboring areas, located at the southeastern margin of the North China Craton, occur as granulite terrains and xenoliths in the Mesozoic dioritic porphyry.
This research investigates and reports on the petrology and geochemical characteristics of crystalline basement rocks in Ora-Ekiti,Southwestern Nigeria.Exhaustive geological investigation reveals migmatite,banded gnei...This research investigates and reports on the petrology and geochemical characteristics of crystalline basement rocks in Ora-Ekiti,Southwestern Nigeria.Exhaustive geological investigation reveals migmatite,banded gneiss,granite gneiss and biotite gneiss underlie the area.In reducing order of abundance,petrographic examination reveals that migmatite contains quartz,muscovite and opaque minerals.Banded geniuses contain quartz,biotite,plagioclase,and opaque minerals.Granite geniuses contain quartz,plagioclase,biotite,microcline and opaque;while biotite geniuses contain biotite,plagioclase,opaque minerals,and quartz.Silica contents in migmatite(69.50%-72.66%;ca.71.23%),banded gneiss(71.66%-77.1%;ca.75.23%),biotite gneiss(72.32%-76.18%;ca.73.83%)and granite gneiss(69.82%-73.15%;ca.71.95%)indicate the rocks are siliceous.High alumina contents in migmatite(12.18%),banded gneiss(10.28%),biotite gneiss(11.46%)and granite gneiss(9.97%)are comparable to similar rocks in the basement complex.All the rocks show Ba,Sr and Rb enrichment.Harker diagrams of Al_(2)O_(3)versus SiO_(2)and CaO versus SiO_(2)show negative trends while Na_(2)O versus SiO_(2),K_(2)O versus SiO_(2)and TiO_(2)versus SiO_(2)plots showed positive trends.This variation probably depicts extensive crystal fractionation in the magmatic systems that produced the rocks prior to metamorphism or partial melting of the precursor rock.SiO_(2)versus(Na_(2)O+K_(2)O)classifies the rocks as granite to granodiorite.The rocks are high K-calc-alkaline and calc-alkalic on SiO_(2)-K_(2)O plot.This shows the rocks are potassic meaning that they are formed from a potassium-rich source.The plot of Al_(2)O_(3)/(Na_(2)O+K_(2)O)versus Al_(2)O_(3)/(CaO+Na_(2)O+K_(2)O)reveals the crystalline rocks are orogenic and originated from granitoid with meta luminous affinity.The rocks consist of gneisses of no economic minerals,but the petrology reveals them as common rocks typical of metamorphic terrains and geochemical features of the rocks reveal they are felsic and of granitic composition.展开更多
The origin, age and evolution of the Precambrian metamorphic basement of southern China provide useful insights into early crustal development. Here, we present new laser ablation-inductively coupled plasma-mass spect...The origin, age and evolution of the Precambrian metamorphic basement of southern China provide useful insights into early crustal development. Here, we present new laser ablation-inductively coupled plasma-mass spectrometry （LA-ICP-MS） U-Pb age data for detrital zircons from five samples of the Precambrian metamorphic basement of the Xiangshan uranium orefield. Two of these samples, from the northern Xiangshan volcanic basin, yielded a total of 140 U-Pb ages that cluster within the Neoproterozoic （773-963 Ma; 79.3% of data points）, with the rest being scattered through the Paleoproterozoic and Mesoproterozoic, along with a single Archean age. These ages indicate that this basement material is associated with the Cathaysia Block. In comparison, the 172 concordant ages from the other three samples from the southern part of the Xiangshan volcanic basin cluster within the Neoproterozoic （767-944 Ma; 59.8%） as well as the Proterozoic （37.8%） and the Archean （2502-2712 Ma; 14.5%）. These samples are also free of zircons with Grenvillian ages, indicating that these units are associated with the southeastern Yangtze Block. Combining these data with the geochemistry of these units, which suggests that the metamorphosed sedimentary rocks within the northern and southern parts of the Xiangshan basin have a common component from a magmatic island arc that formed during the early Neoproterozoic, we infer that the basin was located along the boundary between the Cathaysian and Yangtze blocks. In addition, the zircons within the samples from the southern and northern parts of the Xiangshan basin show different pre-Neoproterozoic （963 Ma） age populations but similar post- Neoproterozoic zircon populations, indicating that the amalgamation of the Cathaysian and Yangtze blocks occurred after the Neoproterozoic （960 Ma）, with magmatism peaking at 830 Ma and rifting starting at -770 Ma, leading to the subsequent deposition （from bottom to top） of the Shenshan, Kuli, and Shangshi formations.展开更多
This study aims at identifying possible correlations between shapes, types of geophysical anomalies and borehole productivity according to geological and hydrogeotogical contexts. The methodology adopted was a two-pro...This study aims at identifying possible correlations between shapes, types of geophysical anomalies and borehole productivity according to geological and hydrogeotogical contexts. The methodology adopted was a two-pronged one--the first step sought to： （1） interpret the electrical resistivity values from horizontal profiling and vertical electrical sounding implemented in Seno province that preceded the drilling of 513 boreholes; （ii） interpret data from pumping tests carried out on boreholes having a discharge superior to 1 m3/h （＂positive borehole＂） by using Cooper-Jacob＇s method. In the second step, according to geology, authors tried to identify possible correlations between each of the qualitative geophysical parameters： ~shape of anomaly〉〉, tttype of anomaly〉〉 and ~〈type curve〉〉 on the one hand, and hydrogeological parameters such as discharge, alteration thickness, transmissivity and saturated level on the other. The results of this study have shown that the chances of having a positive borehole in Seno province are higher when the type of anomaly is TCC （80%）, shape of anomaly is ＂W＂ and when type curve is ＂H＂ （80%） for all geological formations. Granitic formations are those that record higher discharges while schists record high transmissivity values.展开更多
The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammitic schists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist...The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammitic schists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist and metabasitic rocks. The mineral assemblage of psammitic schist is muscovite + biotite + feldspar + quartz ± tourmaline ± titanite ± sillimanite and that of metabasitic rocks is amphibole + plagioclase + biotite ± apatite ± magnetite ± pyroxene ± garnet ± quartz. The migmatitic rock consists of leucosome and restite of various volume proportions; the former consists of muscovite + alkaline feldspar + quartz ± garnet ± plagioclase while the latter is either fragments of psammitic schist or those of metabasitic rock. The crystalline limestone consists of calcite that has been partly replaced by olivine. The olivine was subsequently altered to serpentine. Weak deformations as indicated by cleavages and fractures were imposed prominently on the psammitic schists, occasionally on metabasitic rocks, but not on migmatitic rocks. The basement experienced metamorphism up to temperature 606-778± and pressure 4.8-6.1 kbar (0.48-0.61 GPa), equivalent to amphibolite-granulite facies. The peak of the metamorphism is marked by a migmatization which occurred at several localities along the studied route 587-535 Ma ago. The basement also recorded a retrograde metamorphism of greenschist facies, during which biotite, garnet, amphibole, and pyroxene were partly altered to chlorite.展开更多
Based on analysis of core observation, thin sections, cathodoluminescence, scanning electron microscope(SEM), etc., and geochemical testing of stable carbon and oxygen isotopes composition, element content, fluid incl...Based on analysis of core observation, thin sections, cathodoluminescence, scanning electron microscope(SEM), etc., and geochemical testing of stable carbon and oxygen isotopes composition, element content, fluid inclusions, and formation water, the fluid interaction mechanism and diagenetic reformation of fracture-pore basement reservoirs of epimetamorphic pyroclastic rock in the Beier Sag, Hailar Basin were studied. The results show that:(1) Two suites of reservoirs were developed in the basement, the weathering section and interior section, the interior section has a good reservoir zone reaching the standard of type I reservoir.(2) The secondary pores are formed by dissolution of carbonate minerals, feldspar, and tuff etc.(3) The diagenetic fluids include atmospheric freshwater, deep magmatic hydrothermal fluid, organic acids and hydrocarbon-bearing fluids.(4) The reservoir diagenetic reformation can be divided into four stages: initial consolidation, early supergene weathering-leaching, middle structural fracture-cementation-dissolution, and late organic acid-magmatic hydrothermal superimposed dissolution. Among them, the second and fourth stages are the stages for the formation of weathering crust and interior dissolution pore-cave reservoirs, respectively.展开更多
基金financially supported by the Ph.D Foundation of the Ministry of Education of China(grant No.20133402130008)the National Basic Research Program of China(grant No.2015CB856104)the National Natural Science Foundation of China(grant No.41273036)
文摘The Precambrian basement rocks in the Bengbu and neighboring areas, located at the southeastern margin of the North China Craton, occur as granulite terrains and xenoliths in the Mesozoic dioritic porphyry.
文摘This research investigates and reports on the petrology and geochemical characteristics of crystalline basement rocks in Ora-Ekiti,Southwestern Nigeria.Exhaustive geological investigation reveals migmatite,banded gneiss,granite gneiss and biotite gneiss underlie the area.In reducing order of abundance,petrographic examination reveals that migmatite contains quartz,muscovite and opaque minerals.Banded geniuses contain quartz,biotite,plagioclase,and opaque minerals.Granite geniuses contain quartz,plagioclase,biotite,microcline and opaque;while biotite geniuses contain biotite,plagioclase,opaque minerals,and quartz.Silica contents in migmatite(69.50%-72.66%;ca.71.23%),banded gneiss(71.66%-77.1%;ca.75.23%),biotite gneiss(72.32%-76.18%;ca.73.83%)and granite gneiss(69.82%-73.15%;ca.71.95%)indicate the rocks are siliceous.High alumina contents in migmatite(12.18%),banded gneiss(10.28%),biotite gneiss(11.46%)and granite gneiss(9.97%)are comparable to similar rocks in the basement complex.All the rocks show Ba,Sr and Rb enrichment.Harker diagrams of Al_(2)O_(3)versus SiO_(2)and CaO versus SiO_(2)show negative trends while Na_(2)O versus SiO_(2),K_(2)O versus SiO_(2)and TiO_(2)versus SiO_(2)plots showed positive trends.This variation probably depicts extensive crystal fractionation in the magmatic systems that produced the rocks prior to metamorphism or partial melting of the precursor rock.SiO_(2)versus(Na_(2)O+K_(2)O)classifies the rocks as granite to granodiorite.The rocks are high K-calc-alkaline and calc-alkalic on SiO_(2)-K_(2)O plot.This shows the rocks are potassic meaning that they are formed from a potassium-rich source.The plot of Al_(2)O_(3)/(Na_(2)O+K_(2)O)versus Al_(2)O_(3)/(CaO+Na_(2)O+K_(2)O)reveals the crystalline rocks are orogenic and originated from granitoid with meta luminous affinity.The rocks consist of gneisses of no economic minerals,but the petrology reveals them as common rocks typical of metamorphic terrains and geochemical features of the rocks reveal they are felsic and of granitic composition.
基金financially supported by the National Natural Science Foundation of China(Grant No.41602069 and 41572185)the Fundamental Science on Radioactive Geology and Exploration Technology Laboratory(Grant No.RGET1402)+1 种基金the Natural Science Foundation of Jiangxi Province(Grant No.20171BAB213026)Science and technology research projectfrom the Education Department of Jiangxi Province(Grant No.GJJ150554)
文摘The origin, age and evolution of the Precambrian metamorphic basement of southern China provide useful insights into early crustal development. Here, we present new laser ablation-inductively coupled plasma-mass spectrometry （LA-ICP-MS） U-Pb age data for detrital zircons from five samples of the Precambrian metamorphic basement of the Xiangshan uranium orefield. Two of these samples, from the northern Xiangshan volcanic basin, yielded a total of 140 U-Pb ages that cluster within the Neoproterozoic （773-963 Ma; 79.3% of data points）, with the rest being scattered through the Paleoproterozoic and Mesoproterozoic, along with a single Archean age. These ages indicate that this basement material is associated with the Cathaysia Block. In comparison, the 172 concordant ages from the other three samples from the southern part of the Xiangshan volcanic basin cluster within the Neoproterozoic （767-944 Ma; 59.8%） as well as the Proterozoic （37.8%） and the Archean （2502-2712 Ma; 14.5%）. These samples are also free of zircons with Grenvillian ages, indicating that these units are associated with the southeastern Yangtze Block. Combining these data with the geochemistry of these units, which suggests that the metamorphosed sedimentary rocks within the northern and southern parts of the Xiangshan basin have a common component from a magmatic island arc that formed during the early Neoproterozoic, we infer that the basin was located along the boundary between the Cathaysian and Yangtze blocks. In addition, the zircons within the samples from the southern and northern parts of the Xiangshan basin show different pre-Neoproterozoic （963 Ma） age populations but similar post- Neoproterozoic zircon populations, indicating that the amalgamation of the Cathaysian and Yangtze blocks occurred after the Neoproterozoic （960 Ma）, with magmatism peaking at 830 Ma and rifting starting at -770 Ma, leading to the subsequent deposition （from bottom to top） of the Shenshan, Kuli, and Shangshi formations.
文摘This study aims at identifying possible correlations between shapes, types of geophysical anomalies and borehole productivity according to geological and hydrogeotogical contexts. The methodology adopted was a two-pronged one--the first step sought to： （1） interpret the electrical resistivity values from horizontal profiling and vertical electrical sounding implemented in Seno province that preceded the drilling of 513 boreholes; （ii） interpret data from pumping tests carried out on boreholes having a discharge superior to 1 m3/h （＂positive borehole＂） by using Cooper-Jacob＇s method. In the second step, according to geology, authors tried to identify possible correlations between each of the qualitative geophysical parameters： ~shape of anomaly〉〉, tttype of anomaly〉〉 and ~〈type curve〉〉 on the one hand, and hydrogeological parameters such as discharge, alteration thickness, transmissivity and saturated level on the other. The results of this study have shown that the chances of having a positive borehole in Seno province are higher when the type of anomaly is TCC （80%）, shape of anomaly is ＂W＂ and when type curve is ＂H＂ （80%） for all geological formations. Granitic formations are those that record higher discharges while schists record high transmissivity values.
文摘The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammitic schists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist and metabasitic rocks. The mineral assemblage of psammitic schist is muscovite + biotite + feldspar + quartz ± tourmaline ± titanite ± sillimanite and that of metabasitic rocks is amphibole + plagioclase + biotite ± apatite ± magnetite ± pyroxene ± garnet ± quartz. The migmatitic rock consists of leucosome and restite of various volume proportions; the former consists of muscovite + alkaline feldspar + quartz ± garnet ± plagioclase while the latter is either fragments of psammitic schist or those of metabasitic rock. The crystalline limestone consists of calcite that has been partly replaced by olivine. The olivine was subsequently altered to serpentine. Weak deformations as indicated by cleavages and fractures were imposed prominently on the psammitic schists, occasionally on metabasitic rocks, but not on migmatitic rocks. The basement experienced metamorphism up to temperature 606-778± and pressure 4.8-6.1 kbar (0.48-0.61 GPa), equivalent to amphibolite-granulite facies. The peak of the metamorphism is marked by a migmatization which occurred at several localities along the studied route 587-535 Ma ago. The basement also recorded a retrograde metamorphism of greenschist facies, during which biotite, garnet, amphibole, and pyroxene were partly altered to chlorite.
基金Supported by the PetroChina Science and Technology Project(2017-5307034-000002).
文摘Based on analysis of core observation, thin sections, cathodoluminescence, scanning electron microscope(SEM), etc., and geochemical testing of stable carbon and oxygen isotopes composition, element content, fluid inclusions, and formation water, the fluid interaction mechanism and diagenetic reformation of fracture-pore basement reservoirs of epimetamorphic pyroclastic rock in the Beier Sag, Hailar Basin were studied. The results show that:(1) Two suites of reservoirs were developed in the basement, the weathering section and interior section, the interior section has a good reservoir zone reaching the standard of type I reservoir.(2) The secondary pores are formed by dissolution of carbonate minerals, feldspar, and tuff etc.(3) The diagenetic fluids include atmospheric freshwater, deep magmatic hydrothermal fluid, organic acids and hydrocarbon-bearing fluids.(4) The reservoir diagenetic reformation can be divided into four stages: initial consolidation, early supergene weathering-leaching, middle structural fracture-cementation-dissolution, and late organic acid-magmatic hydrothermal superimposed dissolution. Among them, the second and fourth stages are the stages for the formation of weathering crust and interior dissolution pore-cave reservoirs, respectively.
