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.

在了解北美的地质演化时，白垩纪中期（120 至 90 Ma，以下简称 mK）时期给我们带来了一个具有经济和构造意义的难题。加拿大的大部分石油和天然气储量都发生在这一时期。 mK 还见证了 BC 省和阿尔伯塔省大量含煤地层的开采和封存，并开发了巨大的金矿资源。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；位于育空地区和西北地区边界的巨大坎通 (Cantung) 和麦克通 (MacTung) 钨矿床；育空地区东部科迪勒拉山脉和不列颠哥伦比亚省北部可能存在宝石级祖母绿矿床；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的再利用，以及一系列含钻石金伯利岩管的喷发，这些矿管共同构成了4000 公里长、南北走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，但我们不知道是否有一个潜在的过程或构造环境可以解释这些资源的同时发育。金伯利岩走廊的发育表明该大陆的东西向延伸和岩石圈变薄与北大西洋的打开和分裂是一致的。然而，将 mK Bonanza 解释为大陆伸展的产物与大多数构造模型相悖，因为造山带的特征是 mK 褶皱带和塞尔文山脉。育空-不列颠哥伦比亚省的哥伦比亚河和美国连续的 mK 收缩被解释为北美和美洲之间相对收敛率增加的结果。推测 Panthalassan 海洋板片已俯冲到大陆西缘之下。 在该模型中，北美草原的 mK 地层被解释为响应大陆岩石圈压缩载荷而形成的前陆盆地。 mK 地层序列，用于测试由于科迪勒拉山脉下方大陆向西俯冲而导致的岩石圈减薄模型。在这种情况下，俯冲位于科迪勒拉山脉东侧下方。科迪勒拉山，不是西部；没有潘萨拉山俯冲带；科迪勒拉山及其冲断带占据了北美洲西倾俯冲带的上板块，形成了下板块，由于板块拉力而变薄。 ，以 mK 地层为重点的地球物理和地球动力学研究将测试大陆向西俯冲是否是一个可行的模型，可以协调科迪勒拉岩石圈同时期的缩短和增厚与岩石圈的减薄。北美克拉通，并解释了 mK 矿物和能源富矿。