C-type adakites have been commonly considered as a result of partial melting of the mafic lower continental crust (LCC) at high pressure, as supported by high P-T experiments on hydrous basalts. However, because the m...C-type adakites have been commonly considered as a result of partial melting of the mafic lower continental crust (LCC) at high pressure, as supported by high P-T experiments on hydrous basalts. However, because the mafic eclogitic LCC is generally dry, experiments on water-bearing materials cannot be used to constrain the melting processes of the dry mafic LCC. Due to the lack of systematic melting experimental studies on dry mafic rocks at crustal pressures, MELTs software was applied to simulating melting of the dry mafic LCC at 1–2 GPa. Comparison of model results with experimental data indicates that, when melting de-gree is greater than 20%, melts from the dry mafic LCC at 1–3 GPa cannot produce the C-type adakitic melt with high SiO2 con-tent (～70%). Although the limited experimental results about dry mafic rock melting at 1–2 GPa in the literature suggest that low degree melting (<10%) cannot produce silicic melt either, MELTs software simulation shows that, at pressure >1.8 GPa, low-degree melting can produce dacitic melt with high K2O/Na2O (～1) if SiO2 content of the melt is controlled by residual garnet. Furthermore, the simulation also suggests that, if pressure is <1.8 GPa, abundant plagioclase (plg) in the residual phase may de-crease SiO2 content in the melt to below 62%, much lower than that of the C-type adakites observed in eastern China. Given the high P-T conditions required to produce melts with high SiO2 and extremely low HREE contents, such melts could easily be con-taminated by other crustal-derived melts, implying that the C-type adakites from eclogite melting could be less commonly ob-served in the outcrops than previously believed. Besides the interpretation that garnet fractionates Sr, Y, and REE, high Sr/Y and La/Yb could be also produced by multiple ways such as inheriting the source features and fractional crystallizing clinopyroxene (cpx). Therefore, it may be problematic using high Sr/Y and La/Yb as criteria to identify adakites. Instead, REE patterns with strong depleti展开更多
The Lower Eocene Celtek Formation is located in the Sorgun district of thecity of Yozgat in Turkey.In the study area,Paleozoic,Campanian-Maastrichtian,Eocene,Miocene and Quaternary units are exposed.The Celtek Formati...The Lower Eocene Celtek Formation is located in the Sorgun district of thecity of Yozgat in Turkey.In the study area,Paleozoic,Campanian-Maastrichtian,Eocene,Miocene and Quaternary units are exposed.The Celtek Formation is noteworthy with its coal and oil shale deposits.Samples were collected from one exposure(YCOSK)and two boreholes(SJ and C boreholes)at the facility operated by the Yeni Celtek Coal Management.Concentrations of REE in oil shales from these localities were determined using the ICP-MS technique.REE and total organic carbon(TOC)values of a total of 32 samples were compared with normalized REE contents of various environments.TOC contents of the samples ranged from 1.37wt%to 11.8wt%(mean 4.96wt%).The averages of all samples for the all normalized values show similar patterns.Normalized REE patterns are represented by the enrichment in the order of LREE>MREE>HREE and display negative Ce and positive Eu anomalies.ΣREE vs.TOC were compared.ΣREE vs.TOC showed a weak positive correlation,whereasΣLREE vs.(M+HREE)andΣLREE vs.ΣREE were positively correlated.Regarding tectonic provenance characteristics,the Celtek Formation oil shales were formed in microenvironments with physicochemical conditions changing in character from oxic to euxinic,representing a transitional terrestrial–marine environment.展开更多
西格拉花岗岩体位于祁连东部的米屈花岗岩带上,空间上呈NW-NWW向展布,岩体由花岗闪长岩-花岗岩-正长岩组成,主要岩性为花岗闪长岩。LA-ICP-MS锆石U-Pb定年结果表明,西格拉花岗闪长岩存在两期岩浆作用,年龄分别为465.6±6.5Ma、443.2...西格拉花岗岩体位于祁连东部的米屈花岗岩带上,空间上呈NW-NWW向展布,岩体由花岗闪长岩-花岗岩-正长岩组成,主要岩性为花岗闪长岩。LA-ICP-MS锆石U-Pb定年结果表明,西格拉花岗闪长岩存在两期岩浆作用,年龄分别为465.6±6.5Ma、443.2±4.8Ma,其中,前者与祁连洋俯冲极性发生转变的时限（~463Ma）相近,而后者与祁连洋闭合的时间（~445Ma）相似。早期淡色花岗闪长岩具正铕异常（δEu=2.44）,晚期暗色花岗闪长岩则为弱负/正铕异常（δEu=0.94~1.32）,两者均显示出高Si、Al,富Na贫K,富集Ba、Sr、LREE,高Sr/Y值,低Y、HREE含量,亏损HFSE（Nb、Ta、Ti、P）的特征,与Martin et al.（2005）划分的高硅埃达克岩（HSA）相似。其源区可能均残留石榴子石、普通角闪石及少量金红石,而斜长石则大量参与部分熔融过程,推测早期花岗闪长岩的源区深度可能超过50km;整体上,由早期→晚期反映出加厚地壳减薄、地幔组分贡献增强的趋势;两者可能均为加厚下地壳物质部分熔融的产物。展开更多
基金supported by the National Natural Science Foundation of China (40773013)
文摘C-type adakites have been commonly considered as a result of partial melting of the mafic lower continental crust (LCC) at high pressure, as supported by high P-T experiments on hydrous basalts. However, because the mafic eclogitic LCC is generally dry, experiments on water-bearing materials cannot be used to constrain the melting processes of the dry mafic LCC. Due to the lack of systematic melting experimental studies on dry mafic rocks at crustal pressures, MELTs software was applied to simulating melting of the dry mafic LCC at 1–2 GPa. Comparison of model results with experimental data indicates that, when melting de-gree is greater than 20%, melts from the dry mafic LCC at 1–3 GPa cannot produce the C-type adakitic melt with high SiO2 con-tent (～70%). Although the limited experimental results about dry mafic rock melting at 1–2 GPa in the literature suggest that low degree melting (<10%) cannot produce silicic melt either, MELTs software simulation shows that, at pressure >1.8 GPa, low-degree melting can produce dacitic melt with high K2O/Na2O (～1) if SiO2 content of the melt is controlled by residual garnet. Furthermore, the simulation also suggests that, if pressure is <1.8 GPa, abundant plagioclase (plg) in the residual phase may de-crease SiO2 content in the melt to below 62%, much lower than that of the C-type adakites observed in eastern China. Given the high P-T conditions required to produce melts with high SiO2 and extremely low HREE contents, such melts could easily be con-taminated by other crustal-derived melts, implying that the C-type adakites from eclogite melting could be less commonly ob-served in the outcrops than previously believed. Besides the interpretation that garnet fractionates Sr, Y, and REE, high Sr/Y and La/Yb could be also produced by multiple ways such as inheriting the source features and fractional crystallizing clinopyroxene (cpx). Therefore, it may be problematic using high Sr/Y and La/Yb as criteria to identify adakites. Instead, REE patterns with strong depleti
基金financially supported by the Bozok University Project Coordination and Research Center (Scientific Research Projects Commission) (grant No. 2015 MMF/180)
文摘The Lower Eocene Celtek Formation is located in the Sorgun district of thecity of Yozgat in Turkey.In the study area,Paleozoic,Campanian-Maastrichtian,Eocene,Miocene and Quaternary units are exposed.The Celtek Formation is noteworthy with its coal and oil shale deposits.Samples were collected from one exposure(YCOSK)and two boreholes(SJ and C boreholes)at the facility operated by the Yeni Celtek Coal Management.Concentrations of REE in oil shales from these localities were determined using the ICP-MS technique.REE and total organic carbon(TOC)values of a total of 32 samples were compared with normalized REE contents of various environments.TOC contents of the samples ranged from 1.37wt%to 11.8wt%(mean 4.96wt%).The averages of all samples for the all normalized values show similar patterns.Normalized REE patterns are represented by the enrichment in the order of LREE>MREE>HREE and display negative Ce and positive Eu anomalies.ΣREE vs.TOC were compared.ΣREE vs.TOC showed a weak positive correlation,whereasΣLREE vs.(M+HREE)andΣLREE vs.ΣREE were positively correlated.Regarding tectonic provenance characteristics,the Celtek Formation oil shales were formed in microenvironments with physicochemical conditions changing in character from oxic to euxinic,representing a transitional terrestrial–marine environment.
文摘西格拉花岗岩体位于祁连东部的米屈花岗岩带上,空间上呈NW-NWW向展布,岩体由花岗闪长岩-花岗岩-正长岩组成,主要岩性为花岗闪长岩。LA-ICP-MS锆石U-Pb定年结果表明,西格拉花岗闪长岩存在两期岩浆作用,年龄分别为465.6±6.5Ma、443.2±4.8Ma,其中,前者与祁连洋俯冲极性发生转变的时限（~463Ma）相近,而后者与祁连洋闭合的时间（~445Ma）相似。早期淡色花岗闪长岩具正铕异常（δEu=2.44）,晚期暗色花岗闪长岩则为弱负/正铕异常（δEu=0.94~1.32）,两者均显示出高Si、Al,富Na贫K,富集Ba、Sr、LREE,高Sr/Y值,低Y、HREE含量,亏损HFSE（Nb、Ta、Ti、P）的特征,与Martin et al.（2005）划分的高硅埃达克岩（HSA）相似。其源区可能均残留石榴子石、普通角闪石及少量金红石,而斜长石则大量参与部分熔融过程,推测早期花岗闪长岩的源区深度可能超过50km;整体上,由早期→晚期反映出加厚地壳减薄、地幔组分贡献增强的趋势;两者可能均为加厚下地壳物质部分熔融的产物。
