Provenance, Age and Biomechanics of SuperContinental Weathering

超级大陆风化的起源、年龄和生物力学

• 批准号: 9018747
• 负责人: George Brimhall
• 金额: $ 19.55万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1991
• 资助国家: 美国
• 起止时间: 1991-02-01 至 1993-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9018747&HistoricalAwards=false
• 关键词: Provenance; Age; Biomechanics; SuperContinental; Weathering

There are a number of intrinsic properties of cratons unified in their pre-dispersal position in Gondwana. Exposure of deep crustal levels of this supercontinent is an essential precursor to continental weathering being vital to the on set and nature of the continental weathering process itself. These cratonal attributes include: the petrological and imeralogical character of the bedrock parent material, its unique thermal history, depletion in water and heat-producing elements, uplift, erosion and ultimate stability necessary for attainment of a state of tectonic quiescence when subjected to intense weathering. This transcontinental belt of deep continental crust exposed as graulite-charnockite-anorthosite bodies parallels the Gondwanide Orogen of Paleozoic and Early Mesozoic plate convergence affecting South America, Africa, India, Australia and Antarctica implicating Gondwana supercontinental scale weathering as the appropriate crustal unit of analysis rather than individual continental land masses. The necessity of viewing lateritic weathering on a supercontinental scale is further accentuated by the fact that the classical "residual" origin of lateritic bauxites is inconsistent with a recent discovery that wind-blown foreign dust consisting of gibbsite, hematite and goethite also bearing a component of resistant detrital minerals derived from basement rocks elsewhere (zircon, ilmenite, rutile and monazite) dominates near surface metal enrichment of bauxites and laterites. By considering the crustal processes preceding continental weathering as well as the surficial recycling and redistribution of chemically-resistant minerals accessed as a direct consequence of the petrology and mineralogy of the deep crust, we have formulated a testable model of deep crustal weathering systems. An integrated three-part project is planned addressing (1) the provenance of chemically-stable detrital minerals, especially zircon contaminating the upper portions of laterites, (2) age and duration of lateritic weathering in combination with correlations of paleo-weathering surfaces in Australia, West Africa and Brazil, and (3) mechanisms of subsurface transport and incorporation of detritus into the lateritic regolith during dilational biomechanical mixing of eolian dust by root growth cycles. Part I utilizes U-Pb ion microprobe dating of zircon using the SHRIMP to define the sources of mobile minerals and the depths of their translocation into laterite and bauxite weathering profiles. Part II involves 40Ar/39Ar laser dating of jarosite as well as manganese and iron oxides. Part III is laboratory experimentation using a soil mechanics cell capable of simulation root growth cycles. The proposed interdisciplinary research can contribute to further development of a much-needed long-term continental record of surficial environments to complement the marine stratigraphic record of global processes.

克拉通在冈瓦纳地区的分散前位置统一了许多内在性质。这个超大陆地壳深处的暴露是大陆风化的重要前兆，对大陆风化过程本身的背景和性质至关重要。这些克拉通属性包括：基岩母质的岩石学和岩石学特征，其独特的热历史，水和产热元素的枯竭，隆升，侵蚀和在剧烈风化作用下达到构造静止状态所必需的最终稳定性。这条由深陆壳组成的横贯大陆带暴露为花岗岩-绿绿岩-斜长岩体，与古生代冈瓦尼德造山带和早中生代板块辐合相平行，影响南美洲、非洲、印度、澳大利亚和南极洲暗示冈瓦纳超大陆尺度风化作为合适的地壳分析单位，而不是单个大陆地块。红土铝土矿的经典“残余”来源与最近的一项发现不一致，这一发现表明，风吹来的由三长石、赤铁矿和针铁矿组成的外来尘埃也含有来自其他地方基底岩石的抗碎屑矿物成分(锆石、钛铁矿、铝土矿和红土近地表金属富集以金红石和独居石为主。通过考虑大陆风化之前的地壳过程，以及作为深部地壳岩石学和矿物学直接结果而获得的抗化学物质的表面再循环和再分配，我们制定了深部地壳风化系统的可测试模型。计划进行一个综合的三部分项目，以解决(1)化学稳定的碎屑矿物的来源，特别是污染红土上部的锆石；(2)结合澳大利亚、西非和巴西的古风化面对比，红土风化的年龄和持续时间；(3)风沙在根系生长循环下的扩张生物力学混合过程中的地下运输和碎屑进入红土风化层的机制。第一部分利用SHRIMP法对锆石进行U-Pb离子微探针测年，确定了活动矿物的来源及其向红土和铝土矿风化剖面迁移的深度。第二部分涉及黄铁矾以及锰和铁氧化物的40Ar/39Ar激光测年。第三部分是实验室实验，使用能够模拟根系生长周期的土壤力学细胞。拟议的跨学科研究有助于进一步发展急需的陆地表面环境长期记录，以补充全球过程的海洋地层记录。