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

白垩纪中期(120-90 Ma，以下简称MK)是理解北美地质演化的一个具有重大经济意义和构造意义的难题。正是在这一时期，加拿大的大部分石油和天然气储量被生产和封存，包括阿尔伯塔省北部的大量油砂矿藏。MK地区还经历了卑诗省和艾伯塔省大部分含煤地层的沉积；在公元前、育空和阿拉斯加开发了巨大的金矿资源，包括廷蒂纳金矿带；形成了位于育空-西北部边界的大型广东钨矿床和麦克洞钨矿床；在育空地区东部的科迪勒拉和公元前北部侵位了宝石级翡翠矿床；可能是密西西比河谷铅锌矿床的发展，至少是重新抬升了包括松点体在内的铅锌矿床；以及一系列含钻石的金伯利岩管的喷发，这些金伯利岩管道共同定义了一条长4000公里的北S走向的金伯利岩走廊。尽管这种资源丰富意义重大，但我们不知道是否有潜在的过程或构造背景来解释这些不同矿藏和能源矿藏的同时代发展。金伯利岩走廊的发育指向大陆的东西向伸展和岩石圈减薄。大陆的减薄与北大西洋的MK开张和盘古大陆的解体相一致。然而，将MK Bonanza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？因为科迪勒山造山带。造山带的特征是MK褶皱冲断带，包括阿拉斯加的布鲁克斯山脉、育空-公元前的塞尔文-哥伦布山脉和毗邻的美国发达的塞维尔。MK收缩被解释为北美和潘特拉桑洋板块之间的相对会聚速度增加的结果，推测它们是俯冲到大陆西缘之下的。在该模型中，北美草原MK地层被解释为响应大陆岩石圈挤压载荷而发育的前陆盆地。我的建议是利用北美MK地层序列来测试岩石圈变薄的模型，这是由于科迪勒拉之下的大陆向西俯冲造成的。在这种情况下，俯冲位于科迪勒拉的东侧之下，而不是西侧；没有潘特拉山俯冲带；科迪勒拉及其逆冲带占据了西倾俯冲带的上板块。形成下板块的克拉通北美由于板片拉动而变薄。一系列以MK地层为重点的地质、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，可以协调科迪勒岩石圈的缩短和增厚与北美克拉通的减薄，并解释MK矿物和能源的富矿。

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.