多金属结壳生长间断期与磷酸盐化事件的关系

王洋; 方念乔

doi:10.12284/hyxb2021017

多金属结壳生长间断期与磷酸盐化事件的关系

doi: 10.12284/hyxb2021017

王洋^1,,
方念乔^1, ,

中国地质大学海洋学院，北京 100083

基金项目: 中国大洋矿产资源研究开发协会“十三五”资源环境项目（DY135-C1-1-06）

详细信息

作者简介:
王洋（1991-），男，北京市人，博士研究生，主要从事多金属结壳与古海洋学研究。E-mail：dreamcontrue@sina.com

通讯作者:
方念乔（1949-），男，教授，博士生导师，主要从事大地构造与古海洋学研究。E-mail：Fangnq@cugb.edu.cn

中图分类号: P736.3
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出版历程
- 收稿日期: 2019-11-01
- 修回日期: 2020-08-26
- 网络出版日期: 2021-01-20
- 刊出日期: 2021-01-25

The relationship between the growth discontinuity of polymetallic crusts and phosphatization events

Wang Yang^1
,,
Fang Nianqiao^{1
, ,}

School of Ocean Sciences, China University of Geosciences, Beijing 100083, China

摘要

摘要: 磷酸盐化的发生会造成多金属结壳主要成矿元素的贫化，总体上抑制结壳的生长。磷酸盐化作用呈幕式在太平洋内发生，已有研究将其发生期次与多金属结壳中的磷酸盐化层位及其P、Ca等元素地球化学特征对应，为结壳的年代厘定提供证据。然而，由于磷酸盐化多次发生且在结壳多个层位中显现，首先需要厘定出较为可靠的多金属结壳年代框架，才能与磷酸盐化事件相互佐证。本研究通过定年范围较大，同时可以识别结壳中存在的生长间断的Co-Os法定年体系，为中、西太平洋6块多金属结壳定年，并参考肉眼识别的磷酸盐化矿化特征和地球化学特征佐证年代框架，同时分析磷酸盐化作用对结壳成矿的影响。39～34 Ma和27～21 Ma的两次大规模磷酸盐化期次全部对应多金属结壳的大规模间断期，而71 Ma、55 Ma和31 Ma等小规模磷酸盐化事件多数可在多金属结壳的层位和地球化学特征中识别，对应P和Ca百分含量的飙升和峰值特征。这一方面证实了磷酸盐化的发生整体抑制了结壳的生长，且具有广泛的影响范围和明确的时代区间，另一方面则佐证了多金属结壳年代框架的准确性。
- 磷酸盐化 /
- 多金属结壳 /
- 古海洋事件 /
- 辅助定年 /
- 生长间断
Abstract: The occurrence of phosphatization will lead to the dilution of major ore-forming elements in polymetallic crusts and thus inhibit the growth of crusts in general. Phosphatization occurred in the Pacific Ocean in an episodic manner, and the occurrence periods correspond to the phosphatization layers in crusts and the geochemical characteristics of P, Ca and other elements, providing evidence for the dating of crusts. However, due to the frequent occurrence of phosphatization in multiple layers of crusts, a more reliable age frame needs to be determined before it can be mutually corroborated with phosphatization events. In this study, the Co-Os dating system with large dating range and the ability to determine hiatus was applicated in dating for the crust samples from central Pacific and western Pacific. With the naked eye identification of phosphatization mineralization features and geochemical profile characteristics, the age frames were proved and the effect of phosphatization on crust mineralization were discussed. The two large-scale phosphatization phases of 39–34 Ma and 27–21 Ma all correspond to the large-scale discontinuous phases of the crusts, while most small-scale phosphatization events in 71 Ma, 55 Ma and 31 Ma can be identified in the layers and geochemical profiles, corresponding to the rising and peak characteristics of P and Ca content. On the one hand, it is confirmed that the occurrence of phosphatization inhibits the growth of crusts, and has a wide range of influence area and a clear time interval in Pacific. On the other hand, it proves the accuracy of the chronological framework of polymetallic crusts.
- phosphatization /
- polymetallic crusts /
- paleoceanographyic events /
- age frame proving /
- growing hiatus

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图 1 多金属结壳及其结构构造分层示意图

I：下部致密层；II：中部疏松层；III：上部较致密层

Fig. 1 The layered structure of polymetallic crusts

I: Lower dense layer; II: middle loose layer; III: upper sub-dence layer

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图 2 多金属结壳年代框架

年代框架由Co经验公式法结合Os同位素标准曲线法获得。灰色框体为标准曲线（据文献[19]），实心圆为结壳Os同位素组成测定值，横坐标上的黑色线段为生长期，*样品MP3D10的Os同位素数据见文献[4]，样品CLD34-2和CLD50的数据见文献[20]

Fig. 2 Age frame of polymetallic crusts

The age frame is obtained by cobalt experiential formula and osmium isotope standard curve method. Gray background is standard curve (from the reference [19]); solid circles are measured Os isotopic composition; black segments are the growing periods; *the Os isotopic data of sample MP3D10 are shown in reference [4], and the data of samples CLD34-2 and CLD50 are shown in reference [20]

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图 3 中、西太平洋多金属结壳磷酸盐化指示元素P、Ca质量百分含量年代剖面

实心菱形是P质量百分比含量，空心圆形是Ca质量百分比含量；点线框体和虚线分别是两次大规模和3次小规模磷酸盐化事件对应年代；*样品MP3D10的P、Ca数据见文献[4]，样品CLD34-2和CLD50的数据见文献[20]

Fig. 3 Weight percentage contents of phosphatization indicator elements P and Ca in age profile of polymetallic crusts from the central Pacific and western Pacific

P weight percentage contents for solid diamonds, Ca weight percentage contents for hollow circles; corresponding age of two large-scale and three small-scale phosphatization events for point line frames and dotted lines respectively; *the P, Ca data of sample MP3D10 are shown in reference [4], and the data of samples CLD34-2 and CLD50 are shown in reference [20]

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图 4 中、西太平洋多金属结壳Co、Mg、Ni、P、Ca元素的百分含量年代剖面

*样品MP3D10的元素百分含量数据见文献[4]，样品CLD34-2和CLD50的数据见文献[20]

Fig. 4 Weight percentage contents of Co, Mg, Ni, P and Ca in age profile of polymetallic crusts from the central Pacific and western Pacific

*The element content data of sample MP3D10 are shown in reference [4], and the data of samples CLD34-2 and CLD50 are shown in reference [20]

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表 1 多金属结壳分层结构构造与磷酸盐化痕迹描述

Tab. 1 The description of layered structure and phosphatization characteristics in crusts

样品名称	层位	磷酸盐化程度	宏观描述	磷酸盐化痕迹
MS1	III	弱	结核状结壳，环绕核心生长	无
	I	弱	整体致密，按生长纹理大致可分为5层，无明显疏松层	无
MHD79	III	强	亮黑色−黑褐色，致密块状，组成纯净，横纵节理发育，贝壳状断口	无
	II	强	黄白色−黄褐色，质地疏松，杂质较多	夹有较多灰白−黄白色团块和细脉
	I	强	亮黑色−黑褐色，致密块状，片理发育	夹有黄褐色薄膜状薄层
CLD34−2	III	弱	黑褐色，致密块状，组成纯净，具柱状构造	夹有不规则黄褐色细脉
CLD50	III	强	黑褐色，同心圆构造，具柱状构造	无
	II	强	黑褐色，多孔，充填大量碎屑，构造杂乱	充填黄褐色细脉
	I	强	亮黑色，组成纯净，具平行纹层构造，具生物痕迹	充填黄绿色岩屑
MP3D10	III	强	黑褐色，致密块状	无
	II	强	黑褐色−黄褐色，裂隙和孔洞多，含大量杂质	含土黄色、灰白色斑点或斑块状沉积物杂质
	I	强	亮黑色−黄白色，致密块状，节理裂隙发育	具树枝状疑似碳氟磷灰石矿物
MP3D22	III	弱	褐黑色，呈层状，金属光泽	夹有灰白色条带
	II	弱	灰黑−黄褐色，裂隙和孔洞多	具灰白色填充物
	I	弱	亮黑色，致密块状，组成纯净	不规则磷酸盐细脉和颗粒

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参考文献(20)

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