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Geological Study of Deccan Flood Basalts

德干溢流玄武岩地质研究

基本信息

批准号：
04041030
负责人：
FUJII Toshitsugu
金额：
$ 13.12万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-04041030/
关键词：
Flood Basalt Basalt Volcanism Primary Magma Deccan Plateau デカン玄武岩噴火機構岩脈

项目摘要

Field surveys at Deccan Plateau were carried out in three seasons ; January, 1993, October, 1993 and December, 1993 to January, 1994. During the first field season, east-west traverse of the region of Deccan flood basalt was carried out, and the basaltic agglutinates were recognized in the eastern portion of the plateau. This indicates that the eruption center of the flood basalt is not restricted at the western portion of the Deccan plateau. During the second field season, plateau basalt lava was found near Panna area, where no basaltic activity have not been described. This indicates that the distribution of the Deccan flood basalt should be revised to the further north and the erupted volume could be much larger than ever estimated.During the third field season, two different trends of dikes were recognized ; E-W and N-S. They sometimes cut each other, indicating the two different fissure systems were available during the Deccan plateau volcanism.More than 300 samples were analyzed with XRF. Most striking feature is that the magnesian basalt which contains more than 9wt % of MgO contains accumulated olivine phenocrysts and that the liquid composition should be less magnesian ; less than 7wt % of MgO. This indicates that the picrite primary magma cannot be the parental magma for the Deccan flood basalt. Also, the chemical trend within the Deccan flood basalt cannot be explained by simple fractional crystallization, but can be explained several different basaltic parental magmas with different alkali and titanium contents. Some of the primitive basaltic rocks were found to show chemical feature which resemble the partial melt of MORBs at high pressure. This may suggest that the source materials for the Deccan flood basalt may not be mantle peridotite, but MORBs which had subducted into the mantle in the much older time.

在德干高原的实地调查分三个季节进行：1993年1月、1993年10月和1993年12月至1994年1月。在第一个野外季节，对德干水淹玄武岩进行了东西走向的穿越，在高原东部识别出玄武岩胶结。这表明泛滥玄武岩的喷发中心并不局限于德干高原西部。在第二个野外季节，在盘纳地区附近发现了高原玄武岩熔岩，那里没有玄武岩活动的描述。这表明德干洪泛玄武岩的分布应该向更北的方向修正，喷发量可能比以往估计的要大得多。在第三个野外季节，发现了两种不同的岩脉走向：东西向和南北向。它们有时会相互切割，表明在德干高原火山爆发期间存在两种不同的裂隙系统。最显着的特征是镁玄武岩中含有积累的橄榄石斑晶，镁含量大于9wt%，液态成分应小于7wt%。这表明苦橄榄原生岩浆不可能是德干溢流玄武岩的母岩浆。此外，德干溢流玄武岩中的化学趋势不能用简单的分离结晶来解释，而是可以解释几种不同的玄武岩母岩浆，它们的碱和钛含量不同。发现一些原始玄武岩的化学特征类似于MORBs在高压下的部分熔融。这可能表明，德干洪泛玄武岩的物质来源可能不是地幔橄榄岩，而是更古老的俯冲到地幔中的MORBs。