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: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=737527
• 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.

中白垩纪（120 ~ 90 Ma，以下简称mK）时期为我们理解北美的地质演化提供了一个经济上和构造上的重大难题。正是在这一时期，加拿大的大部分石油和天然气储备被开采和封存，包括阿尔伯塔省北部的大量油砂矿床。mK也看到了BC省和阿尔伯塔省大部分含煤地层的沉积；在不列颠哥伦比亚省、育空地区和阿拉斯加开发了大量的黄金资源，包括Tintina黄金带；位于育空-西北交界的块状粤东和粤东钨矿床的形成；育空地区东部科迪勒拉和不列颠哥伦比亚省北部宝石级祖母绿矿床的定位包括Pine Point矿体在内的密西西比河谷铅锌矿床的开发或至少是重新开采；以及一系列钻石金伯利岩管道的喷发，这些管道共同形成了一条4000公里长、南北向的金伯利岩走廊，一直延伸到大陆的正中心。尽管这一资源富矿具有重要意义，但我们不知道是否存在一个潜在的过程或构造环境来解释这些不同的矿物和能源矿床的同期发展。金伯利岩走廊的发育表明大陆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背道而驰。为什么?因为科迪勒拉造山带。造山带的特征是mK褶皱和冲断带，包括阿拉斯加的布鲁克斯山脉；育空- bc的塞尔温-哥伦比亚人；以及毗邻美国的塞维尔河。mK收缩被解释为北美和Panthalassan海洋板块之间相对收敛速度增加的结果，据推测，这些板块已经俯冲到大陆西缘之下。在该模型中，北美大草原mK地层被解释为响应大陆岩石圈压缩负荷而发育的前陆盆地。我的建议是利用北美mK地层层序来测试一个岩石圈变薄的模型，这个模型是由于科迪勒拉山脉下大陆向西俯冲造成的。在这种情况下，俯冲发生在科迪勒拉山脉的东侧，而不是西侧；无泛海带俯冲带；科迪勒拉及其冲断带占据西倾俯冲带的上板块。形成下板块的北美克拉通板块由于板块拉力而变薄。以mK地层为中心的一系列地质、地球物理和地球动力学研究将检验大陆向西俯冲是否是一种可行的模式，这种模式可以调和科迪勒拉岩石圈同期的缩短和增厚与北美克拉通的变薄，并解释mK矿物和能源的丰富。