摘要
Dupal异常是一种广泛分布于南半球的大尺度地幔地球化学不均一现象,其成因机制和分布范围一直是地球科学研究的热点。由于Dupal异常概念提出时间较早,仅基于少量岩石样品,其概念存在模糊性和不确定性,目前仍缺乏统一的异常判别指标,影响了对异常分布范围和成因的认识,进而制约了对全球Dupal异常的进一步研究。本文选取印度洋洋底(包括洋中脊轴部和离轴区域)玄武岩的铅同位素数据,结合西南印度洋中脊和东南印度洋中脊的已知地球化学边界,采用K-means++聚类分析方法突出大尺度地球化学特征,初步遴选Δ7/4>2.5,Δ8/4>35作为Dupal异常的铅同位素判别标准。基于这一标准,识别出西北印度洋中脊欧文断裂带为Dupal异常边界,边界以南洋中脊区域显示较明显的异常。就其分布而言,整个印度洋洋中脊的Dupal异常分布于安德鲁-贝恩断裂带、澳大利亚-南极错乱带以及欧文断裂带所围限的区域;离轴区域的凯尔盖朗海底高原、Broken海脊、东经90度海岭、圣诞群岛、莫桑比克海底高原、厄加勒斯海底高原等也具有明显的Dupal异常;整体上印度洋Dupal异常呈现东西分带特征。基于印度洋洋底玄武岩数据识别的Dupal异常指标将为全球Dupal异常的研究提供参考。印度洋Dupal异常分布范围的厘定将为揭示其异常成因提供关键基础。
The Dupal anomaly is a large-scale mantle geochemical heterogeneity idly distributed in the southern hemisphere.Its distribution range and origin have always been the focus of geological research.As the first proposal of the Dupal anomaly was only based on very limited rock samples,its concept has long been ambiguous and uncertain.No unified discriminant index of anomaly has been reconciled,which affects the understanding of the anomaly distribution range and origin,and thus restricts the further study of the global Dupal anomaly.This paper assembled the lead isotopic data of basalts from the Indian Ocean(including the axis of mid-ocean ridges and off-axis regions),using the K-means++clustering analysis method to highlight large-scale geochemical characteristics.Combined with the well-known geochemical boundaries of the Southwest Indian Ridge and the Southeast Indian Ridge,the criteria for the Dupal anomaly could be defined asΔ7/4>2.5 andΔ8/4>35.Based on this criterion,the Owen fracture zone was recognized as the Dupal anomaly boundary for the Northwest Indian Ridge,with the south region of the boundary showing a more obvious Dupal anomaly.The Dupal anomaly region of the entire Indian Ocean mid-ocean ridges is located in the area bounded by the Andrew-Bain fracture zone,the Australia Antarctic Discordance and the Owen fracture zone.Off-axis regions,such as the Kerguelen Plateau,Broken Ridge,Ninetyeast Ridge,Christmas Islands,Mozambique Plateau,Agulhas Plateau,etc.,also exhibit strong Dupal anomalies.The Dupal anomaly distribution of the whole Indian Ocean shows linear gradient characteristics from west to east.The discrimination criteria of Dupal anomaly identified based on the Indian Ocean basalt will provide a reference for the global Dupal anomaly investigation.The delineation of the distribution range of the Indian Ocean Dupal anomaly will provide a key basis for revealing its origin.
作者
何虎
余星
胡航
许绪成
余娅娜
HE Hu;YU Xing;HU Hang;XU XuCheng;YU YaNa(Key Laboratory of Submarine Geosciences,Second Institute of Oceanography,Ministry of Natural Resources,Hangzhou 310012,China;Ocean College,Zhejiang University,Zhoushan 316021,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2024年第8期2601-2610,共10页
Acta Petrologica Sinica
基金
国家重点研发计划项目(2021YFF0501301)
国家自然科学基金项目(42172231)
自然资源部第二海洋研究所基本科研业务费专项(QNRC2202)联合资助。
