Calibrating Orogenic Denudation using Detrital Mineral Geochronology

定义腹地变形和相关剥蚀的传统方法通常涉及基岩冷却历史和/或P-T-t路径的逐点校准。然后，为了推测更广泛的变形/剥蚀历史，有时会对几个地点的结果进行区域外推。对单个碎屑矿物定年的能力提供了一种校准变形和侵蚀的新技术，从而为从邻近山脉的盆地中已知年龄的地层中收集的碎屑矿物群体生成年龄。测量到的低于退火或闭合温度的冷却时间与沉积时间之间的时间差可以被解释为代表将矿物通过退火/闭合等温线抬升到侵蚀表面所需的时间，将其从整个流域的冷却和侵蚀历史中运输出来。最近的喜马拉雅研究表明，几乎每个样品中的一些颗粒都经历了非常迅速的冷却、侵蚀、运输和沉积（从冷却到沉积通常为1-2微米）。目前，碎屑矿物研究的解释受到许多不确定性的强烈限制。碎屑记录综合了各支流盆地的年龄信息。通常，过去对某一地点有贡献的排水集水区是未知的，随着时间的推移而变化，或者定义不清。汇水区内点源（可能是迅速隆起和剥落）的相对重要性尚不清楚。地形和气候变化对任何给定集水区总碎屑贡献的影响是未知的。由于这些不确定因素，只能用广义的、一般化的术语对碎屑年龄数据进行可靠的分析。如果知道空间贡献和下游混合之间的关系，就有可能从碎屑年龄种群中提取更多有用的信息。我们建议对碎屑矿物的年龄分布以及相关的地形、地貌和气候进行基线校准，以便了解控制今天可观察到的碎屑年龄种群的因素之间的相互作用。我们将研究从现代前陆延伸到西藏流域分水岭的喜马拉雅流域，包括气候和地形对比强烈的地区，推断或观察到基岩隆升速率显著差异的地区，以及基岩地质已知和确定年代的地区。该集水区主要由90米的数字高程数据集覆盖，该数据集为地形效应分析提供了基础。通过记录沿河道变化的碎屑年龄以及支流集水区的贡献，我们将评估碎屑信号对基岩年龄、推断或定义的基岩隆起或侵蚀速率、地形特征和气候影响的依赖。这种校准将使我们能够评估构造动态景观中这些相互作用因素所施加的关键控制，并将为后续碎屑矿物年龄研究的改进解释形成概念基础。此外，这种整合应该使我们能够评估利用碎屑矿物年龄来提取相对基岩侵蚀率的潜力：这是地貌研究中的一个关键问题。考虑到喜马拉雅和西藏隆升对全球气候的影响，以及喜马拉雅碰撞的构造意义，显然需要一个更坚实的基础来解释综合的隆升和侵蚀历史。

Burbank 9627865 Traditional methods of defining hinterland deformation and associated denudation typically have involved site-by-site calibration of bedrock cooling histories and/or P-T-t paths. Results from a few sites are then sometimes extrapolated regionally in order to speculate on broader deformational/denudational histories. The ability to date individual detrital minerals has provided a new technique to calibrate deformation and erosion, whereby ages are generated for populations of detrital minerals which were collected from strata of known age in a basin adjacent to a range. The measured temporal difference between the time of cooling below an annealing or closure temperature and the time of deposition can be interpreted as representing the time required to uplift a mineral through its annealing/closure isotherm to the erosional surface, transport it across the cooling and erosional history from an entire drainage basin. Recent Himalayan studies have shown that some grains in nearly every sample have experienced very rapid cooling, erosion, transport, and deposition (often 1-2 My from cooling to deposition). At present, the interpretation of detrital mineral studies is strongly limited by numerous uncertainties. The detrital record integrates age information from all tributary basins. Often the drainage catchment contributing to a given site in the past is unknown, changing through time, or poorly defined. The relative importance of point sources (perhaps rapidly uplifting and denuding) within a catchment is unknown. The impact of topographic and climatic variability on the total detrital contribution for any given catchment is unknown. These uncertainties permit detrital age data to be reliably analyzed only in broad, generalized terms. If the relationships among spatial contributions, and downstream mixing were known, much more useful information could potentially be extracted from detrital age populations. We propose a baseline calibration of age distributions of detrital minerals and related topography, geomorphology, and climate in order to understand the interactions among factors which control the detrital age populations as observable today. We will study a Himalayan drainage that extends from the modern foreland to the Tibetan drainage divide and that includes areas with strong climatic and topographic contrasts, areas for which marked differences in bedrock uplift rates have been inferred or observed, and areas in which the bedrock geology is quite well known and dated. The catchment is largely covered by a 90-m digital elevation data set that provides a basis for analysis of topographic effects. Through documentation of the changing detrital age population along the river course and the contributions from tributary catchments, we will assess the dependence of the detrital signal on bedrock ages, inferred or defined bedrock uplift or erosion rates, topographic characteristics, and climatic influences. This calibration will allow us to assess the key controls exerted by these interacting factors in a tectonically dynamic landscape and will form a conceptual basis for improved interpretation of subsequent detrital mineral age studies. Moreover, this integration should permit us to evaluate the potential for utilizing detrital mineral ages to extract relative bedrock erosion rates: a key problem in geomorphic studies. Given the global climatic effects attributed to Himalayan and Tibetan uplift, as well as tectonic significance of the Himalayan collision, a firmer basis for interpreting integrated uplift and erosion histories is clearly needed.