Geochemical comparison of two suites of Cenozoic potassic volcanic rocks in western Yunnan reveals the existence of two mantle domains beneath this region, which corre- spond to their respective tectonic affinity. The...Geochemical comparison of two suites of Cenozoic potassic volcanic rocks in western Yunnan reveals the existence of two mantle domains beneath this region, which corre- spond to their respective tectonic affinity. The Erhai ultrapotassic rocks (42—24Ma) in western Yangtze Craton are characterized by LILE enrichment, HFSE depletion, low TiO2 content (<1%), high initial Sr/86Sr (0.7064—0.7094) and negative εNd (?3.84—?4.64). Geochemically similar to 87 K-rich volcanism in subduction setting, they were probably originated from a refractory spinel harzburgitic source metasomatized by subduction-related fluids. In contrast, the Maguan potas- sic magmas (<16Ma) in the South China Block show an OIB-type trace elemental signature, high TiO2 content (>2%), low initial 87 Sr/86Sr (0.7041—0.7060) and positive εNd (5.46—7.03). These features resemble the typical intraplate potassic rocks around the world. These rocks are thus interpreted as melting products of a fertile garnet lherzolitic source which has been infiltrated by small-volume, asthenosphere-derived silicate melts. The temporal and spatial distribution of these two types of K-rich rocks cannot be explained by any unified tectonic model. It is proposed that the Oligocene magmatism in the Erhai area may have resulted from convective thinning of the thickened lithosphere, whereas the post-Miocene volcanism in the Maguan area was related to the opening of South China Sea.展开更多
Recent seismic studies reveal a sharp velocity drop mostly at^70–100 km depth within the thick mantle keel beneath cratons, termed the mid-lithosphere discontinuity(MLD). The common presence of the MLD in cratonic re...Recent seismic studies reveal a sharp velocity drop mostly at^70–100 km depth within the thick mantle keel beneath cratons, termed the mid-lithosphere discontinuity(MLD). The common presence of the MLD in cratonic regions indicates structural and property layering of the subcontinental lithospheric mantle(SCLM). The nature and origin of the MLD, and many issues associated with the layering of the SCLM are essential to understand the formation and evolution of continents, and have become frontier subjects in the Earth sciences.展开更多
The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characteristics of the lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuo...The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characteristics of the lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuoba （汉诺坝）, located on the north edge of the intra-North China orogenic belt, are discussed based on the in-situ LAM-ICPMS detected trace element compositions of clinopyroxenes in the Hannuoba peridotitic xenoliths combined with detailed petrography and geochemistry studies. The Hannuoba lithospheric mantle was formed by different partial meltings of the primitive mantle. Most of the samples reflect the partial melting degree of lower than 5% with a few samples of 15%-20%. Major element compositions of the whole rocks and geochemical compositions of clinopyroxenes reveal the coexistence of both fertile and depleted mantle underneath the Hannuoba region during the Cenozoic. This was probably caused by the asthenospheric mantle replacing the aged craton mantle through erosion, intermingling and modification. Our conclusion is further supported by the existence of both carbonatitic magmatic material and silicate melt/ fluid metasomatism as magnified by the trace elements of the clinopyroxencs from the Hannuoba lithospherJc mantle.展开更多
依据236口井共2706组的静温数据以及25口井的系统测温数据，分析计算了渤海盆地地温梯度及大地热流；建立地壳分层结构模型，利用回剥法计算现今地幔热流、深部温度以及岩石圈厚度；在此基础上，利用地球动力学方法恢复本区热流演化史...依据236口井共2706组的静温数据以及25口井的系统测温数据，分析计算了渤海盆地地温梯度及大地热流；建立地壳分层结构模型，利用回剥法计算现今地幔热流、深部温度以及岩石圈厚度；在此基础上，利用地球动力学方法恢复本区热流演化史。结果表明：渤海盆地背景地温梯度为32.2℃/km，热流值为64.8 mW/m2；盆地现今热岩石圈厚度在61～69 km 之间，地幔热流占地表热流的比例在60％左右，属于“热幔冷壳”型岩石圈热结构，盆地地壳底部或莫霍面温度变动在548～749℃之间；热流演化的特征与盆地的构造演化背景吻合，新生代以来盆地经历了3期岩石圈减薄并加热的过程，在东营组沉积末期热流达到最高（70～83 mW/m2），这期间盆地内产出多期碱性玄武岩，表明盆地经历了波及地幔的裂谷过程，随后进入热沉降期，热流逐渐降低，盆地向坳陷型转变。展开更多
基金supported by the National Natural Science Foundation of China(Grant No.49925308)the Chinese Academy of Sciences(Gramt Nos.KZCX2-SW-117,KZCX2-101 and KZCX2-209).
文摘Geochemical comparison of two suites of Cenozoic potassic volcanic rocks in western Yunnan reveals the existence of two mantle domains beneath this region, which corre- spond to their respective tectonic affinity. The Erhai ultrapotassic rocks (42—24Ma) in western Yangtze Craton are characterized by LILE enrichment, HFSE depletion, low TiO2 content (<1%), high initial Sr/86Sr (0.7064—0.7094) and negative εNd (?3.84—?4.64). Geochemically similar to 87 K-rich volcanism in subduction setting, they were probably originated from a refractory spinel harzburgitic source metasomatized by subduction-related fluids. In contrast, the Maguan potas- sic magmas (<16Ma) in the South China Block show an OIB-type trace elemental signature, high TiO2 content (>2%), low initial 87 Sr/86Sr (0.7041—0.7060) and positive εNd (5.46—7.03). These features resemble the typical intraplate potassic rocks around the world. These rocks are thus interpreted as melting products of a fertile garnet lherzolitic source which has been infiltrated by small-volume, asthenosphere-derived silicate melts. The temporal and spatial distribution of these two types of K-rich rocks cannot be explained by any unified tectonic model. It is proposed that the Oligocene magmatism in the Erhai area may have resulted from convective thinning of the thickened lithosphere, whereas the post-Miocene volcanism in the Maguan area was related to the opening of South China Sea.
基金supported by the National Natural Science Foundation of China (41225016, 41688103, 91414301)Chinese Academy of Sciences
文摘Recent seismic studies reveal a sharp velocity drop mostly at^70–100 km depth within the thick mantle keel beneath cratons, termed the mid-lithosphere discontinuity(MLD). The common presence of the MLD in cratonic regions indicates structural and property layering of the subcontinental lithospheric mantle(SCLM). The nature and origin of the MLD, and many issues associated with the layering of the SCLM are essential to understand the formation and evolution of continents, and have become frontier subjects in the Earth sciences.
基金This paper is supported by the Research Foundation for OutstandingYoung Teachers , China University of Geosciences ( Wuhan )(CUGQNL0510)the National Natural Science Foundation of China(No .40425002) .
文摘The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characteristics of the lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuoba （汉诺坝）, located on the north edge of the intra-North China orogenic belt, are discussed based on the in-situ LAM-ICPMS detected trace element compositions of clinopyroxenes in the Hannuoba peridotitic xenoliths combined with detailed petrography and geochemistry studies. The Hannuoba lithospheric mantle was formed by different partial meltings of the primitive mantle. Most of the samples reflect the partial melting degree of lower than 5% with a few samples of 15%-20%. Major element compositions of the whole rocks and geochemical compositions of clinopyroxenes reveal the coexistence of both fertile and depleted mantle underneath the Hannuoba region during the Cenozoic. This was probably caused by the asthenospheric mantle replacing the aged craton mantle through erosion, intermingling and modification. Our conclusion is further supported by the existence of both carbonatitic magmatic material and silicate melt/ fluid metasomatism as magnified by the trace elements of the clinopyroxencs from the Hannuoba lithospherJc mantle.
文摘依据236口井共2706组的静温数据以及25口井的系统测温数据，分析计算了渤海盆地地温梯度及大地热流；建立地壳分层结构模型，利用回剥法计算现今地幔热流、深部温度以及岩石圈厚度；在此基础上，利用地球动力学方法恢复本区热流演化史。结果表明：渤海盆地背景地温梯度为32.2℃/km，热流值为64.8 mW/m2；盆地现今热岩石圈厚度在61～69 km 之间，地幔热流占地表热流的比例在60％左右，属于“热幔冷壳”型岩石圈热结构，盆地地壳底部或莫霍面温度变动在548～749℃之间；热流演化的特征与盆地的构造演化背景吻合，新生代以来盆地经历了3期岩石圈减薄并加热的过程，在东营组沉积末期热流达到最高（70～83 mW/m2），这期间盆地内产出多期碱性玄武岩，表明盆地经历了波及地幔的裂谷过程，随后进入热沉降期，热流逐渐降低，盆地向坳陷型转变。
