Basalt and basaltic andesite metamorphosed at greenschist facies occurs with conglomerate layers at the bottom of the Paleoproterozoic Hutuo Group in the Wutai Mountains area, North China Craton. Detailed geological s...Basalt and basaltic andesite metamorphosed at greenschist facies occurs with conglomerate layers at the bottom of the Paleoproterozoic Hutuo Group in the Wutai Mountains area, North China Craton. Detailed geological surveying confirms that these volcanic rocks are conformable within the neighboring sedimentary rocks. The SHRIMP results on basaltic andesite are divided into two groups. In one group the 207Pb/206Pb ages are from 2433 to 2558 Ma, which is consistent with the basement crustal age in Fuping and Wutai areas. In the other group, 13 grains yielded a weighted mean 207Pb/206Pb age of 2140±14 Ma. The latter is interpreted as the eruption age of the basaltic andesite, and gives the age of the base of the Hutuo Group. This result further suggests that the Hutuo Group formed in the middle Paleoproterozoic, not the early Palaeoproterozoic or late Archaean, as thought before, and is related to a 2.2-2.1 Ga rifting event in the Central North China Craton.展开更多
The Noorabad-Harsin ophiolite is a part of the eastern Mediterranean-Zagros-Oman Tethyan ophiolites. This area is located in the south-southwest of the main Zagros thrust zone. This ophiolite consists of peridotites, ...The Noorabad-Harsin ophiolite is a part of the eastern Mediterranean-Zagros-Oman Tethyan ophiolites. This area is located in the south-southwest of the main Zagros thrust zone. This ophiolite consists of peridotites, serpentinites and pegmatite gabbros as mantle sequence whereas crustal sequence is composed of locally layered gabbros, isotropic gabbros, sheeted dike complex, basaltic to andesitic lavas and sedimentary rocks （radiolarites and Late Cretaceous pelagic limes- tones）. The diabase dikes are enriched in LREE relative to HREE （La（n）/Yb（n）=1.7-3.3）. Also, the andesites are enriched in LREE relative to HREE （La（n）/Yb（n）=3.1-5.37） and the pillow lavas are enriched in LILE （Th（n）/La（n）=2.1） while show a depletion in HFSE （Nb（n）/La（n）=0.07-0.2）. The basaltic-andesitic lavas exhibiting mainly calc-alkaline, with minor island-arc tholeiitic affinities, are characterized by enrichment in LILE and LREE and depletion in HFSE. These geochemical characteristics compared with other Tethyan ophiolites along the Bitlis-Zagros suture zone reveal a supra- subduction zone environment for the genesis of the Noorabad-Harsin ophiolites.展开更多
在阿吾拉勒东段玉希莫勒盖达坂地区大哈拉军山组主要是一套以安山质(粗安质)-英安质(粗面质-粗面英安质)火山熔岩和火山碎屑岩为主的火山岩建造。根据岩石地球化学特征,本文在大哈拉军山组火山岩的上部厘定出了钙碱性玄武安山岩—高钾...在阿吾拉勒东段玉希莫勒盖达坂地区大哈拉军山组主要是一套以安山质(粗安质)-英安质(粗面质-粗面英安质)火山熔岩和火山碎屑岩为主的火山岩建造。根据岩石地球化学特征,本文在大哈拉军山组火山岩的上部厘定出了钙碱性玄武安山岩—高钾钙碱性玄武安山岩—粗安岩(橄榄安粗岩系)组合。微量元素地球化学特征显示,三类岩石形成于岛弧环境,钙碱性玄武安山岩的形成与板片俯冲作用有关,而高钾钙碱性玄武安山岩和粗安岩的形成则与俯冲板片断裂诱发的软流圈上涌作用有关。钙碱性玄武安山岩—高钾钙碱性玄武安山岩—粗安岩组合的存在说明阿吾拉勒东段在晚石炭世由于俯冲板片的断裂,构造体制由挤压转变为伸展。玉希莫勒盖达坂大哈拉军山组上部的火山岩组合与世界许多著名铜-金矿集区(如Papua New Guinea)的火山岩组合相似,显示该地区晚石炭世具有良好的铜、金成矿条件。展开更多
基金supported by the Basic Foundation of Scientific Research Work from Ministry of Science and Technology of China (J0721 and J0907)National Commission on Stratigraphy of China (1212010511702-01)China Geological Survey (1212010611801)
文摘Basalt and basaltic andesite metamorphosed at greenschist facies occurs with conglomerate layers at the bottom of the Paleoproterozoic Hutuo Group in the Wutai Mountains area, North China Craton. Detailed geological surveying confirms that these volcanic rocks are conformable within the neighboring sedimentary rocks. The SHRIMP results on basaltic andesite are divided into two groups. In one group the 207Pb/206Pb ages are from 2433 to 2558 Ma, which is consistent with the basement crustal age in Fuping and Wutai areas. In the other group, 13 grains yielded a weighted mean 207Pb/206Pb age of 2140±14 Ma. The latter is interpreted as the eruption age of the basaltic andesite, and gives the age of the base of the Hutuo Group. This result further suggests that the Hutuo Group formed in the middle Paleoproterozoic, not the early Palaeoproterozoic or late Archaean, as thought before, and is related to a 2.2-2.1 Ga rifting event in the Central North China Craton.
文摘The Noorabad-Harsin ophiolite is a part of the eastern Mediterranean-Zagros-Oman Tethyan ophiolites. This area is located in the south-southwest of the main Zagros thrust zone. This ophiolite consists of peridotites, serpentinites and pegmatite gabbros as mantle sequence whereas crustal sequence is composed of locally layered gabbros, isotropic gabbros, sheeted dike complex, basaltic to andesitic lavas and sedimentary rocks （radiolarites and Late Cretaceous pelagic limes- tones）. The diabase dikes are enriched in LREE relative to HREE （La（n）/Yb（n）=1.7-3.3）. Also, the andesites are enriched in LREE relative to HREE （La（n）/Yb（n）=3.1-5.37） and the pillow lavas are enriched in LILE （Th（n）/La（n）=2.1） while show a depletion in HFSE （Nb（n）/La（n）=0.07-0.2）. The basaltic-andesitic lavas exhibiting mainly calc-alkaline, with minor island-arc tholeiitic affinities, are characterized by enrichment in LILE and LREE and depletion in HFSE. These geochemical characteristics compared with other Tethyan ophiolites along the Bitlis-Zagros suture zone reveal a supra- subduction zone environment for the genesis of the Noorabad-Harsin ophiolites.
文摘黑山头组玄武岩-玄武安山岩组合是西准噶尔早石炭世海相火山-沉积建造的重要组成部分,其与高Mg安山岩及O型adakite共生。此次分析的所有样品均为玄武质岩石,Si O2含量为49.62%~55.68%,平均为52.70%;明显高Ti O2（1.16%~1.99%）,平均为1.56%;显著富Na2O而贫K2O,Na2O为3.17%~6.35%,平均为4.90%,Na2O/K2O为1.19~26.08,绝大多数样品该比值〉4（平均8.93）。样品明显富集Nb、Sr、Zr等,Nb含量均〉7×10-6（7.29×10-6~12.32×10-6,平均为9.48×10-6）;全部样品Sr均〉400×10-6（618×10-6~1107×10-6,平均为825×10-6）;Zr〉158×10-6（159×10-6~217×10-6,平均为182.6×10-6）;Zr/Y比值〉4（6.63~11.09,平均为8.62）。显著高于一般岛弧玄武质岩类。轻稀土明显富集而重稀土亏损显著,且有基本一致的弱正Eu异常。（La/Nb）PM比值〉0.7（1.23~2.26,平均1.94）,（87Sr/86Sr）i=0.7035~0.7039;143Nd/144Nd=0.5128~0.5129;εNd（t）=5.49~7.13。这些地球化学特征与Sajona et al.（1993,1994,1996）确立的富Nb岛弧玄武岩基本一致,而与一般岛弧玄武岩有显著区别。这一发现,为确认西准噶尔早石炭世存在富Nb岛弧玄武岩提供了地球化学佐证,丰富了新疆乃至我国富Nb岛弧玄武岩的产地与层位,也为确认本区早石炭世岛弧构造环境提供了重要依据。
文摘在阿吾拉勒东段玉希莫勒盖达坂地区大哈拉军山组主要是一套以安山质(粗安质)-英安质(粗面质-粗面英安质)火山熔岩和火山碎屑岩为主的火山岩建造。根据岩石地球化学特征,本文在大哈拉军山组火山岩的上部厘定出了钙碱性玄武安山岩—高钾钙碱性玄武安山岩—粗安岩(橄榄安粗岩系)组合。微量元素地球化学特征显示,三类岩石形成于岛弧环境,钙碱性玄武安山岩的形成与板片俯冲作用有关,而高钾钙碱性玄武安山岩和粗安岩的形成则与俯冲板片断裂诱发的软流圈上涌作用有关。钙碱性玄武安山岩—高钾钙碱性玄武安山岩—粗安岩组合的存在说明阿吾拉勒东段在晚石炭世由于俯冲板片的断裂,构造体制由挤压转变为伸展。玉希莫勒盖达坂大哈拉军山组上部的火山岩组合与世界许多著名铜-金矿集区(如Papua New Guinea)的火山岩组合相似,显示该地区晚石炭世具有良好的铜、金成矿条件。
