Deformation correlations,stress field switches and evolution of an orogenic intersection:The Pan-Afr

来源 :Geoscience Frontiers | 被引量 : 0次 | 上传用户:bolen9999
下载到本地 , 更方便阅读
声明 : 本文档内容版权归属内容提供方 , 如果您对本文有版权争议 , 可与客服联系进行内容授权或下架
论文部分内容阅读
Age calibrated deformation histories established by detailed mapping and dating of key magmatic time markers are correlated across all tectono-metamorphic provinces in the Damara Orogenic System.Correlations across structural belts result in an internally consistent deformation framework with evidence of stress field rotations with similar timing,and switches between different deformation events.Horizontal principle compressive stress rotated clockwise ~180°in total during Kaoko Belt evolution,and~135° during Damara Belt evolution.At most stages,stress field variation is progressive and can be attributed to events within the Damara Orogenic System,caused by changes in relative trajectories of the interacting Rio De La Plata,Congo,and Kalahari Cratons.Kaokoan orogenesis occurred earliest and evolved from collision and obduction at ~590 Ma,involving E-W directed shortening,progressing through different transpressional states with ~45° rotation of the stress field to strike-slip shear under NW-SE shortening at ~550-530 Ma.Damaran orogenesis evolved from collision at ~555-550 Ma with NW-SE directed shortening in common with the Kaoko Belt,and subsequently evolved through ~90°rotation of the stress field to NE-SW shortening at ~512-508 Ma.Both Kaoko and Damara orogenic fronts were operating at the same time,with all three cratons being coaxially convergent during the 550-530 Ma period;Rio De La Plata directed SE against the Congo Craton margin,and both together over-riding the Kalahari Craton margin also towards the SE.Progressive stress field rotation was punctuated by rapid and significant switches at ~530-525 Ma,~508 Ma and ~505 Ma.These three events included:(1)Culmination of main phase orogenesis in the Damara Belt,coinciding with maximum burial and peak metamorphism at 530-525 Ma.This occurred at the same time as termination of transpression and initiation of transtensional reactivation of shear zones in the Kaoko Belt.Principle compressive stress switched from NW-SE to NNW-SSE shortening in both Kaoko and Damara Belts at this time.This marks the start of Congo-Kalahari stress field overwhelming the waning Rio De La Plata-Congo stress field,and from this time forward contraction across the Damara Belt generated the stress field governing subsequent low-strain events in the Kaoko Belt.(2)A sudden switch to E-W directed shortening at ~508 Ma is interpreted as a far-field effect imposed on the Damara Orogenic System,most plausibly from arc obduction along the orogenic margin of Gondwana(Ross-Delamerian Orogen).(3)This imposed stress field established a N-S extension direction exploited by decompression melts,switch to vertical shortening,and triggered gravitational collapse and extension of the thermally weakened hot orogen core at ~505 Ma,producing an extensional metamorphic core complex across the Central Zone. Age calibrated deformation histories established by detailed mapping and dating of key magmatic time markers are correlated across all tectono-metamorphic provinces in the Damara Orogenic System. Correlations across structural belts result in an internally consistent deformation framework with evidence of stress field rotations with similar timing, and switches between different deformation events. Horizontally principle compressive stress rotated clockwise ~ 180 ° in total during Kaoko Belt evolution, and ~ 135 ° during Damara Belt evolution. At stress stages variation is at progressive and can be attributed to events within the Damara Orogenic System, caused by changes in relative trajectories of the interacting Rio De La Plata, Congo, and Kalahari Cratons. Kaokoan orogenesis occurred from early and evolved from collision and obduction at ~ 590 Ma, involving EW directed shortening, progressing through different transpressional states with ~ 45 ° rotation of the stress field to strike-slip shear under NW-SE shortening at ~ 550-530 Ma. Damaran orogenesis evolved from collision at ~ 555-550 Ma with NW-SE directed shortening in common with the Kaoko Belt, and subsequently evolved through ~ 90 ° rotation of the stress field to NE -SW shortening at ~ 512-508 Ma.Both Kaoko and Damara orogenic fronts were operating at the same time, with all three cratons being coaxially convergent during the 550-530 Ma period; Rio De La Plata directed SE against the Congo Craton margin, and both together over-riding the Kalahari Craton margin also towards the SE. Progressive stress field rotation was punctuated by rapid and significant switches at ~ 530-525 Ma, ~ 508 Ma and ~ 505 Ma. These three events included: (1) Culmination of main phase orogenesis in the Damara Belt, coinciding with maximum burial and peak metamorphism at 530-525 Ma. Hissis at the same time as termination of transpression and initiation of transtensional reactivation of shear zones in the Kaoko Belt. Principle of compressive stress switched from NW-SE to NNW-SSE shortening in both Kaoko and Damara Belts at this time. This marks the start of Congo-Kalahari stress field overwhelming the waning Rio De La Plata-Congo stress field, and from this time forward contraction across the Damara Belt generated the stress field governing subsequent low-strain events in the Kaoko Belt. (2) A sudden switch to EW directed shortening at ~ 508 Ma is interpreted as a far-field effect imposed on the Damara Orogenic System, most plausibly from arc obduction along the orogenic margin of Gondwana (Ross-Delamerian Orogen). (3) This imposed stress field established a NS extension direction exploited by decompression melts, switch to vertical shortening, and triggered gravitational collapse and extension of the thermally weakened hot orogen core at ~ 505 Ma, producing an extensional metamorphic core complex across the Central Zone.
其他文献
向德龙的印纽作品题材众多,精巧耐看,他使一块块僵硬的石头呈现出富于灵动的艺术活力。其刻刀下的篆刻印章作品,无论是白文和朱文,运用多种篆刻技法,或以刀戳石,粗细不一,或
期刊
目前,不论国内的还是国外的企业绩效评价体系,许多企业集团在使用了这些评价方法后发现很难达到理想的效果。这是因为:1、现行的绩效评价方法大多是通过多家、甚至上万家企业总
学位
期刊
本文通过对荣华二采区10
期刊
基层党建是推动企业长远发展的重要力量,随着国家重视度的提升,越来越多的企业开始加大力度对基层党建工作进行建设.分析企业基层党建工作的开展意义,从组织机制、工作形式、
尊敬的老师、亲爱的同学们:rn大家好!能站在庄严的国旗下演讲,我倍感荣幸.今天,我要演讲的题目是《我们的使命》.rn当看到探险家在风雪飘摇的绝境中忍受着各种难以想象的困难
期刊
随着科学技术的发展和市场全球化竞争程度的加剧,越来越多的企业在异地设立分公司或被委托加工企业,以此来扩大自身的市场份额,提高产品的市场占有率。为了保证顾客对品牌的忠诚