The mid-Cretaceous tectonic setting of North America: Reconciling Cordilleran compression with continental extension

北美白垩纪中期的构造环境：调和科迪勒拉挤压与大陆伸展

• 批准号: RGPIN-2019-04275
• 负责人: Johnston, Stephen
• 金额: $ 2.19万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=683671
• 关键词: mid; Cretaceous; tectonic; setting; North

The mid--Cretaceous (120 to 90 Ma, hereafter mK) period presents us with an economically and tectonically significant puzzle when it comes to understanding North America's geological evolution. It was during this time period that the bulk of Canada's oil and gas reserves were produced and sequestered, including the massive oil sand deposits of northern Alberta. The mK also saw the deposition of much of the coal--bearing strata of BC and Alberta; the development of an enormous gold endowment in BC, Yukon and Alaska, including the Tintina Gold Belt; formation of the massive Cantung and MacTung tungsten deposits that lie right on the Yukon-NWT border; emplacement of gem-quality emerald deposits in the eastern Cordillera of Yukon and northern BC; perhaps the development or at least the remobilization of Mississippi Valley Pb-Zn deposits including the Pine Point body; and the eruption of a series of diamondiferous kimberlite pipes that together define a 4000 km long, N--S striking kimberlite corridor that runs down the very centre of the continent. Despite the significance of this resource bonanza, we don't know whether there is an underlying process or tectonic setting that explains the coeval development of these disparate mineral and energy deposits. The development of the kimberlite corridor points to E-W extension and lithospheric thinning of the continent. Thinning of the continent is consistent with the mK opening of the N Atlantic and break-up of Pangea. However, explaining the mK Bonanza as a product of continental extension runs contrary to most tectonic models. Why? Because of the Cordilleran Orogen. The orogen is characterized by mK fold & thrust belts including the Brooks Range of Alaska; the Selwyn-Columbian of Yukon-BC; and the Sevier, of the conterminous US developed.  mK contraction is explained as a result of an increase in the relative rate of convergence between North America and the Panthalassan oceanic slabs inferred to have been subducting beneath the continent's west margin. In this model, mK strata of Prairie North America is interpreted as a foreland basin developed in response to compressive loading of the continental lithosphere. My proposal is to utilize the N American mK stratigraphic sequence to test a model of lithospheric thinning due to westward subduction of the continent beneath the Cordillera. In this scenario, subduction is beneath the east side of the Cordillera, not the west; there is no Panthalassan subduction zone; and the Cordillera and its thrust belts occupy the upper plate of west-dipping subduction zone.  Cratonic North America, forming the lower plate, thins due to slab pull. A suite of geological, geophysical and geodynamic studies focused on mK strata will test if westward subduction of the continent is a viable model that reconciles shortening and thickening of Cordilleran lithosphere coeval with thinning of cratonic N America, and explains the mK mineral and energy Bonanza.

白垩纪中期（120 ~ 90 Ma，以下简称mK）为我们理解北美的地质演化提供了一个具有经济和构造意义的难题。正是在这一时期，加拿大的大部分石油和天然气储备被生产和封存，包括北方阿尔伯塔的大量油砂矿床。在这一过程中，不列颠哥伦比亚省和阿尔伯塔省的大部分含煤地层都得到了沉积;不列颠哥伦比亚省、育空地区和阿拉斯加，包括廷蒂纳金矿带，都发现了大量的金矿;育空-西北地区边界上的Cantung和MacTung钨矿床大量形成;育空地区和不列颠哥伦比亚省北方的科迪勒拉山脉东部有宝石级的祖母绿矿床就位;也许是密西西比河谷铅锌矿床的开发或至少是重新活动，包括松角矿体;以及一系列含钻石的金伯利岩管的喷发，这些管道共同界定了一条4000公里长的南北走向的金伯利岩走廊，该走廊一直延伸到大陆的中心。尽管这一资源富矿的重要性，我们不知道是否有一个潜在的过程或构造环境，解释这些不同的矿物和能源矿床的同时代发展。金伯利岩走廊的发育表明大陆的东西向伸展和岩石圈减薄。大陆的变薄与北大西洋的mK打开和盘古大陆的分裂是一致的。然而，将mK富矿带解释为大陆伸展的产物与大多数构造模型相反。为什么？为什么？因为科迪勒拉山脉。造山带以mK褶皱和冲断带为特征，包括阿拉斯加的布鲁克斯山脉、育空-BC的塞尔温-哥伦比亚山脉和美国接壤的塞维尔山脉。 mK收缩的解释是由于北美和泛大洋板块之间的相对收敛率的增加，推断已俯冲到大陆的西缘之下。在这个模型中，北美草原区的mK地层被解释为一个前陆盆地的发展，在大陆岩石圈的压缩负荷。我的建议是利用北美mK地层序列来测试由于大陆向西俯冲到科迪勒拉之下而导致的岩石圈减薄模型。在这种情况下，俯冲作用发生在科迪勒拉山脉东侧下方，而不是西侧;没有泛海拉山俯冲带;科迪勒拉山脉及其冲断带占据了西倾俯冲带的上部板块。板块下部的板块是北美板块，由于板块拉力而变薄。一套地质，地球物理和地球动力学的研究集中在mK地层将测试如果向西俯冲的大陆是一个可行的模型，调和缩短和增厚的科迪勒拉岩石圈coeval与变薄的北美，并解释了mK矿物和能源富矿。