Collaborative Research: Timing and Geodynamic Significance of Mesozoic Basement Tectonism and Basin Evolution in the Southwestern North American Cordillera

合作研究：北美科迪勒拉山脉西南部中生代基底构造和盆地演化的时代和地球动力学意义

• 批准号: 0408730
• 负责人: Andrew Barth
• 金额: $ 12.22万
• 依托单位: Indiana University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-07-01 至 2007-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0408730&HistoricalAwards=false
• 关键词: Collaborative; Research; Timing; Geodynamic; Significance

Retroarc foreland basins record the timing and magnitude of uplift and erosion within the interiors of mountain belts, and the nature of the sediments filling such basins can be used to investigate the nature of deformation at continental margins. This project is evaluating the timing of foreland deformation and deposition in retroarc foreland basins in the southwestern North American Cordillera to constrain the timing of magmatism in the continental margin magmatic arc and shortening in the foreland. High precision dates from plutons in the Cordilleran arc suggest high volume batholith emplacement was a relatively short-lived phenomenon superimposed on a much less voluminous background magmatic flux. Precise geochronologic control on evolution of the foreland fold and thrust belt is necessary to better establish the nature of orogen-wide stress field over long time scales, and thus clarify whether foreland shortening is a cause or consequence of arc magmatism.In this study, of the McCoy basin of southeastern California/southwestern Arizona and in equivalent basins in Sonora Mexico are being studied. The age and source area of these sediments is being determined by dating detrital zircons using a combination of ion microprobe and inductively coupled plasma-mass spectrometer techniques. Previous application of ion microprobe dating to the lowermost and uppermost parts of the McCoy Mountains Formation has demonstrated that most of the formation is Cretaceous in age, in contrast to previous studies, which have suggested that much or most of the unit was deposited during the Jurassic. Furthermore, dating of granitic rocks that intrude the McCoy Mountains Formation in southeastern California has shown that the most of the formation is older than about 75 million years. However, studies in southwestern Arizona by previous workers have implied that a significant fraction of the unit must be younger than 78 million years. Unless rates of sedimentation in Arizona were anomalously high, this requires either that the age estimates in Arizona are incorrect or that the McCoy Mountains formation must young significantly to the east, which would also imply that deformation migrated eastward with time. These two alternatives are being discriminated using the zircon dating techniques used in this study.Deposition of the McCoy Mountains Formation is believed to be largely the result of deformation in the Maria fold and thrust belt. Thus, brackets on the timing of the Maria deformation will be provided by the dating of McCoy sediments. In addition, various isotopic techniques are being utilized to directly date structures within the Maria belt. These include potassium-argon dating of minerals that grew in the McCoy Mountains formation during metamorphism of the Maria belt and uranium-lead determination of the igneous age of granitic rocks that intruded synchronously with deformation.Preliminary data from this study suggest that lag time for foreland basin detrital zircon deposition is very short; thus this retroarc foreland basin sequence can yield a record of whether lithospheric thickening by foreland shortening may have contributed to high volume batholith magmatism, or whether shortening served as a space-making mechanism or gravitational response to batholith emplacement and lithospheric thickening in the arc.

弧后前陆盆地记录了山脉内部隆起和侵蚀的时间和幅度，填充这些盆地的沉积物的性质可用于研究大陆边缘变形的性质。该项目正在评估北美科迪勒拉西南部弧后前陆盆地中前陆变形和沉积的时间，以限制大陆边缘岩浆弧中岩浆活动和前陆缩短的时间。高精度的日期从科迪勒拉弧的岩体表明，高容量的岩基侵位是一个相对短暂的现象叠加在一个体积小得多的背景岩浆流量。精确的地质年代学控制前陆褶皱和冲断带的演化是必要的，以更好地建立在长时间尺度上的造山带应力场的性质，从而澄清前陆缩短是弧magmaticity.In这项研究的原因或后果，麦考伊盆地东南部加州/西南亚利桑那州和同等盆地在索诺拉墨西哥正在研究。这些沉积物的年龄和来源地区正在确定年龄的碎屑锆石使用离子微探针和电感耦合等离子体质谱仪技术相结合。之前应用离子探针测年技术对麦考伊山脉组的最低和最高部分进行了测年，结果表明，该地层的大部分年龄为白垩纪，而之前的研究表明，该地层的大部分或大部分沉积于侏罗纪。此外，对侵入加州东南部麦考伊山脉地层的花岗岩的测年表明，该地层的大部分年龄超过7500万年。然而，之前的工作人员在亚利桑那州西南部的研究表明，该单位的很大一部分必须小于7800万年。除非亚利桑那州的沉积速率非常高，否则要么亚利桑那州的年龄估计是不正确的，要么麦考伊山脉的形成必须向东明显年轻，这也意味着变形随时间向东迁移。这两种可能性正在使用本研究中使用的锆石测年技术进行区分。麦考伊山组的沉积被认为主要是玛丽亚褶皱和冲断带变形的结果。因此，玛丽亚变形时间的括号将由麦考伊沉积物的年代测定提供。此外，各种同位素技术正在被用来直接确定玛丽亚带内结构的年代。其中包括对玛丽亚带变质作用期间生长在麦考伊山组中的矿物进行的钾氩定年和对与变形同步侵入的花岗质岩石进行的火成岩年龄的铀铅测定。因此，这个弧后前陆盆地序列可以提供一个记录，即岩石圈增厚是否是由前陆缩短造成的，或缩短是否作为一个空间制造机制或重力反应的岩基侵位和岩石圈增厚的弧。