| 长江中下游庐枞火山岩盆地南侧钾质侵入岩带的成因 |
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| 引用本文： | 薛怀民,马芳,曹光跃,王一鹏,郭秀艳.长江中下游庐枞火山岩盆地南侧钾质侵入岩带的成因[J].地质学报,2016,90(9):2233-2257. |
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| 作者姓名： | 薛怀民 马芳 曹光跃 王一鹏 郭秀艳 |
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| 作者单位： | 中国地质科学院地质研究所，北京，100037,北京大学地球与空间科学学院，北京，100871,中国地质科学院地质研究所，北京，100037,内蒙古自治区克什克腾旗国土资源局, 内蒙古克什克腾， 025350,内蒙古自治区克什克腾旗国土资源局, 内蒙古克什克腾， 025350 |
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| 摘 要： | 庐枞火山岩盆地南侧的钾质侵入岩带由正长岩-石英正长岩-正长花岗岩组成,以石英正长岩为主。它们的形成时间介于123"130 Ma之间,峰值约为126 Ma,其中正长岩和石英正长岩的形成时间稍早,而正长花岗岩的形成时间略晚。整个钾质侵入岩带的侵位时间晚于庐枞盆地内的橄榄玄粗质火山作用约4"7 Ma,也是长江中下游地区除最东段的宁镇地区外中生代最晚的岩浆活动产物之一。地球化学上,该钾质侵入岩带以高钾、富碱、富集Rb、Th、U、K等强不相容元素和轻稀土元素、亏损高场强元素Nb、Ta和Ti为特征。它们的母岩浆主要是由富集型上地幔部分熔融形成的,从正长岩经石英正长岩到正长花岗岩的演化主要受矿物的分离结晶作用控制,地壳物质同化所起的影响不大。但与同样来自富集型上地幔部分熔融的庐枞盆地内火山杂岩的母岩浆相比,前者的母岩浆来源深度可能更大些或其中包含了更多来自软流圈地幔的组分。两者的演化路径也完全不同,钾质侵入岩带的母岩浆除经历过高压下的分离结晶作用外,晚期在低压下还经历过长石为主,可能还有黑云母的分离结晶,甚至上地壳物质一定程度的混染作用;而盆地内火山杂岩的母岩浆低压下矿物的分离结晶作用及上地壳物质的混染都不明显。庐枞盆地南缘的富钾侵入岩与盆地内的火山杂岩一样,地球化学上都具有明显的大陆弧的特征,暗示它们的岩浆源区可能形成于俯冲带环境,意味着扬子地块北缘先前(推测为古元古代晚期)曾发生过俯冲作用,上地幔的交代富集可能就与这次的俯冲作用有关。
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| 关 键 词： | 钾质侵入岩 富集地幔 庐枞盆地 古俯冲环境 大陆弧 长江中下游 |
| 收稿时间： | 2016/3/11 0:00:00 |
| 修稿时间： | 5/8/2016 12:00:00 AM |
Petrogenesis of Potassic Intrusive Rocks along the Southern Margin of the Luzong Volcanic Basin, Middle and Lower Yangtze River Reaches, China |
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| XUE Huaimin,MA Fang,CAO Guangyue,WANG Yipeng and GUO Xiuyan.Petrogenesis of Potassic Intrusive Rocks along the Southern Margin of the Luzong Volcanic Basin, Middle and Lower Yangtze River Reaches, China[J].Acta Geologica Sinica,2016,90(9):2233-2257. |
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| Authors: | XUE Huaimin MA Fang CAO Guangyue WANG Yipeng and GUO Xiuyan |
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| Institution: | Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037,School of Earth and Space Sciences, Peking University, Beijing, 100871,Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037,Hexigten Banner Bureau of Land and Resources, Department of Land and Resources of Inner Mongolian, Hexigten 025350, Inner Monglia and Hexigten Banner Bureau of Land and Resources, Department of Land and Resources of Inner Mongolian, Hexigten 025350, Inner Monglia |
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| Abstract: | The potassic intrusive belt, distributing along the southern margin of the Luzong volcanic basin, comprises syenite, quartz syenite, and syenogranite, and quartz syenite constitutes the greatest part of the belt. They formed from about 123 to 130 Ma, with a peak about 126 Ma, the emplacement of the syenite and quartz syenite were a litter earlier than the syenogranite. The emplacement of the potassic intrusive belt were later than the volcanism in the Luzong basin by about 4~7 Ma as a whole, and it was also one of latest products of the Mesozoic magmatism in the Middle and Lower Yangtze River reaches except the easternmost part (Ningzhen district). This potassic intrusive rocks are characterized by high K and alkali, indicateing enrichment in strong incompatible elements (LILE) such as Rb, Th, U and K as well as light rare earth elements (LREE), depletion in high field strong elements (HFSE) such as Nb, Ta and Ti in geochemistry. Their parental magma mainly came from partial melting of the enriched subcontinental lithospheric mantle, and evolution from syenite to quartz syenite to syenogranite was mainly controlled by fractional crystallization, but the assimilation of crustal material only played a minor role even if existing. Compared with the volcanic complex developed in the Luzong basin, their parental magma also came from partial melting of the enriched mantle, the parental magma of
the potassic intrusive belt may come from deeper or containing more material from asthenospheric mantle. The evolutional processes between the parental magma of the potassic intrusive belt and the volcanic complex in the Luzong basin are of great difference, the former not only had undergone high pressure fractional crystallization, but also had undergone low pressure fractional crystallization, dominant feldspar, possible biotite, as well as minor contamination of upper crust. But low pressure fractional crystallization and upper crustal contamination process are unconspicuous for the latter. Geochemical features of the potassic intrusive belt and the volcanic complex in the Luzong basin all indicate continental arc setting, implying that subduction had happened previously (infer it happened in the late stang of Paleoproterozoic) along the northern margin of the Yangtze Craton. The metasomatism of upper mantle may be related with the subduction. |
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| Keywords: | potassic intrusive enriched mantle Luzong basin Paleo subduction setting continental arc middle and lower Yangtze River reaches |
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