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991.
JIAN PING WU RONG SHENG ZENG YUE HONG MING Institute of Geophysics China Seismological Bureau Beijing China 《地震学报(英文版)》1998,11(6):677-686
ntroductionThedeterminationoffineradialvelocitystructureofuppermantleplaysanimportantroleininvestigationofmantlecompositiona... 相似文献
992.
《International Geology Review》2012,54(8):920-939
Mesozoic mafic dikes in the Gan-Hang tectonic belt (GHTB) provide an opportunity to explore both the nature of their mantle source(s) and the secular evolution of the underlying Mesozoic lithospheric mantle in the region. The geochronology and primary geochemical and Sr–Nd–Pb isotopic compositions of Group 1 (middle section of GHTB) and Group 2 (the rest of the section) dolerite dikes spanning the GHTB were investigated. K–Ar ages indicate that dikes of both groups were emplaced during the Cretaceous (131–69 Ma). The dikes are doleritic in composition and are enriched in both large ion lithophile elements (LILEs; e.g. Rb, Ba, and Pb) and light rare earth elements (LREEs), with a wide range of Eu anomalies, but are depleted in high field strength elements (HFSEs; e.g. Nb, Ta, and Ti) and heavy rare earth elements (HREEs). Dikes sampled in the middle section of the GHTB (Group 1) show more pronounced REE differentiation and a greater contribution from crustal material than those from the east and west sections (Group 2) and are similar to GHTB volcanic rocks in exhibiting a slight enrichment in LREEs. The dolerites are further characterized by a wide range in 87Sr/86Sr i ?=?0.7041–0.7110, 143Nd/144Nd i ?=?0.511951–0.512758, ?Nd t ?=?–10.4 to?+5.6, and Pb isotopic ratios (206Pb/204Pb i ?=?18.1–18.3, 207Pb/204Pb i ≈ 15.6, and 208Pb/204Pb i ?=?38.2–38.7). The dikes have undergone fractional crystallization of olivine, clinopyroxene, plagioclase, and Ti-bearing phases, except for dikes from the Anding area, which possibly experienced fractionation of plagioclase. Geochemically, all the dike samples originated from mantle sources ranging in composition from depleted to enriched that contained a component of foundered lower crust; crustal contamination during the ascent of these magmas was negligible. In the context of the late Mesozoic lithospheric extension across South China, mafic dike magmatism was likely triggered by the reactivation of deep faults, which promoted foundering of the lower crust and subsequent mantle upwelling in the GHTB. 相似文献
993.
断裂及岩浆活动对幔源CO2气成藏的作用--以济阳坳陷为例 总被引:3,自引:0,他引:3
尽管CO2气在地壳浅层运聚成藏与常规的烃气相似,都要求有丰富的源、储层、圈闭、输导系统和盖层,但在成因或来源上与烃气有天壤之别.通过对与CO2气田(藏)有关的深大断裂、火成岩进行综合研究认为,岩浆是CO2运移的载体,火成岩的发育则是断裂时空同步活动的重要标志,幔源CO2气的成藏要素最为重要的是“运”,即要有直接或间接与地幔相连的深大断裂,而且,作为一条断裂通道的活动要时空同步.故而CO2气田(藏)的形成,同断裂活动和岩浆活动有着密切的关系.断裂对CO2气田(藏)形成的控制作用表现为:(1)深大断裂控制CO2成藏带;(2)边界断裂及其派生的不同方向、不同级别的断裂控制了盆地内CO2气田(藏)的形成与分布. 相似文献
994.
Temporal Evolution of Magmatism in the Northern Volcanic Zone of the Andes: The Geology and Petrology of Cayambe Volcanic Complex (Ecuador) 总被引:3,自引:1,他引:3
SAMANIEGO PABLO; MARTIN HERVE; MONZIER MICHEL; ROBIN CLAUDE; FORNARI MICHEL; EISSEN JEAN-PHILIPPE; COTTEN JOSEPH 《Journal of Petrology》2005,46(11):2225-2252
In the Northern Volcanic Zone of the Andes, the Cayambe VolcanicComplex consists of: (1) a basal, mostly effusive volcano, theViejo Cayambe, whose lavas (andesites and subordinate dacitesand rhyolites) are typically calc-alkaline; and (2) a younger,essentially dacitic, composite edifice, the Nevado Cayambe,characterized by lavas with adakitic signatures and explosiveeruptive styles. The construction of Viejo Cayambe began >1·1Myr ago and ended at 1·0 Ma. The young and still activeNevado Cayambe grew after a period of quiescence of about 0·6Myr, from 0·4 Ma to Holocene. Its complex history isdivided into at least three large construction phases (Angurealcone, Main Summit cone and Secondary Summit cone) and compriseslarge pyroclastic events, debris avalanches, as well as periodsof dome activity. Geochemical data indicate that fractionalcrystallization and crustal assimilation processes have a limitedrole in the genesis of each suite. On the contrary, field observations,and mineralogical and geochemical data show the increasing importanceof magma mixing during the evolution of the volcanic complex.The adakitic signature of Nevado Cayambe magmas is related topartial melting of a basaltic source, which could be the lowercrust or the subducted slab. However, reliable geophysical andgeochemical evidence indicates that the source of adakitic componentis the subducted slab. Thus, the Viejo Cayambe magmas are inferredto come from a mantle wedge source metasomatized by slab-derivedmelts (adakites), whereas the Nevado Cayambe magmas indicatea greater involvement of adakitic melts in their petrogenesis.This temporal evolution can be related to the presence of thesubducted Carnegie Ridge, modifying the geothermal gradientalong the WadatiBenioff zone and favouring slab partialmelting. KEY WORDS: adakites; 40Ar/39Ar dating; Cayambe volcano; Ecuador; mantle metasomatism; Andes 相似文献
995.
Sounding of electrical structure of the crust and upper mantle along the eastern border of Qinghai-Tibet Plateau and its tectonic significance 总被引:2,自引:0,他引:2
Sounding and study on electrical structure of the crust and upper mantle within the eastern border region of Qinghai-Tibet Plateau by using the magnetotelluric sounding (simply MT) method permitted us to understand the characteristics of specific electrical structure in the region. The sounding result clearly revealed that: (1) The Xianshuihe fault zone represents a large-scale lithospheric fault and is an important boundary fault of the rhombic Sichuan-Yunnan block. (2) The sounded region is a strong earthquake-prone zone. The different crustal media of blocks on both sides of the fault became an important deep background for the strong seismo-active zone. (3) A large-scale low-resistivity layer is found to exist at a depth more than ten kilometers beneath the northern part of the rhombic Sichuan-Yunnan block. Its electrical resistivity is only several to tens Ω?m. The layer northeastward extends down at an angle of 45°. It is related to an obstacle to the lateral squeeze of Qinghai-Tibet Plateau and eastward flow of mass by the rigid block. It is inferred from the characteristics of electrical property of deep media that the northern part of the recent rhombic Sichuan-Yunnan block is in a thermal state and is one of the recently fairly active blocks. (4) The lithosphere in the sounded region is gradually thickened from the western segment (northern Sichuan-Yunnan block) to east (Yangtze block). 相似文献
996.
997.
998.
N. R. Karmalkar R. A. Duraiswami N. V. Chalapathi Rao D. K. Paul 《Journal of the Geological Society of India》2009,73(5):657-679
Mantle derived xenoliths in India are known to occur in the Proterozoic ultrapotassic rocks like kimberlites from Dharwar
and Bastar craton and Mesozoic alkali igneous rocks like lamrophyres, nephelinites and basanites. The xenoliths in kimberlites
are represented by garnet harzburgites, lherzolites, wehrlite, olivine clinopyroxenites and kyaniteeclogite varieties. The
PT conditions estimated for xenoliths from the Dharwar craton suggest that the lithosphere was at least 185 km thick during
the Mid-Proterozoic period. The ultrabasic and eclogite xenoliths have been derived from depths of 100–180 km and 75–150 km
respectively. The Kalyandurg and Brahmanpalle clusters have sampled the typical Archaean subcontinental lithospheric mantle
(SCLM) with a low geotherm (35 mW/m2) and harzburgitic to lherzolitic rocks with median Xmg
olivine > 0.93. The base of the depleted lithosphere at 185–195 km depth is marked by a 10–15 km layer of strongly metasomatised
peridotites (Xmg
olivine > ∼0.88). The Anampalle and Wajrakarur clusters 60 km to the NW show a distinctly different SCLM; it has a higher geotherm
(37.5 to 40 mW/m2) and contains few subcalcic harzburgites, and has a median Xmg
olivine = 0.925. In contrast, the kimberlites of the Uravakonda and WK-7 clusters sampled quite fertile (median Xmg
olivine ∼0.915) SCLM with an elevated geotherm (> 40 mW/m2).
The lamrophyres, basanites and melanephelinites associated with the Deccan Volcanic Province entrain both ultramafic and mafic
xenoliths. The ultramafic group is represented by (i) spinel lherzolites, harzburgites, and (ii) pyroxenites. Single pyroxene
granulite and two pyroxene granulites constitutes the mafic group. Temperature estimates for the West Coast xenoliths indicate
equilibration temperatures of 500–900°C while the pressure estimates vary between 6–11 kbar corresponding to depths of 20–35
km. This elevated geotherm implies that the region is characterized by abnormally high heat flow, which is also supported
by the presence of linear array of hot springs along the West Coast. Spinel peridotite xenoliths entrained in the basanites
and melanephelinites from the Kutch show low equilibrium temperatures (884–972°C). The estimated pressures obtained on the
basis of the absence of both plagioclase and garnet in the xenoliths and by referring the temperatures to the West Coast geotherm
is ∼ 15 kbar (40–45 km depth). The minimum heat flow of 60 to 70 mW/m2 has been computed for the Kutch xenolith (Bhujia hill), which is closely comparable to the oceanic geotherm. Xenolith studies
from the West Coast and Kutch indicate that the SCLM beneath is strongly metasomatised although the style of metasomatism
is different from that below the Dharwar Craton. 相似文献
999.
共和盆地地热能分布特征与聚集机制分析 总被引:4,自引:0,他引:4
位处青藏高原北部的青海省共和盆地,是一个自中生代以来形成的断陷盆地,周界由深大活动断裂控制,其内堆积有大厚度的第四纪和新近纪地层,揭露厚度达900~1440m,基底由印支期花岗岩组成,调(勘)查资料显示,盆地内具有热流值较高的特征,基底花岗岩地热梯度大于5℃,热异常明显。青藏高原宽频地震探测资料显示,共和盆地所在的东昆仑地块上地幔存在着一条宽达150km的低速带,其与巴颜喀拉地块深地幔中以大型低速异常体为特征的地幔热柱相关联,该低速带延伸到地壳,在共和盆地及其周边一带地表以下1~40km的不同部位形成热流异常区,导致在盆地浅部形成丰富的以干热岩、地下热水为主的地下热能资源,其不仅在城镇供暖方面具有现实推广意义,而且在发电等能源利用中潜力巨大。 相似文献
1000.