Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary
Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary
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阿拉斯加山脉缝合带内的白垩纪至中新世岩浆作用、沉积和折返：多相重新激活的地体边界
DOI：
10.1130/ges02014.1
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发表时间：
2019
期刊：
影响因子：
2.5
通讯作者：
Benowitz, J.
中科院分区：
文献类型：
--
作者：
Trop, J.;Benowitz, J.
阿拉斯加山脉缝合带暴露出白垩纪至第四纪海相和非海相的沉积岩和火山岩，夹在南部增生的弗兰格里亚复合地体的海相岩石和北部较古老的大陆地体之间。新的U-Pb锆石年龄、40 Ar/39 Ar、喆和AFT冷却年龄、地球化学成分和地质现场观测结果，为碰撞缝合带内白垩纪至中新世岩浆活动、沉积和变形的时间提供了更好的约束。我们的研究结果与地震活跃的迪纳里断层的不明确位移史有关，该断层将缝合带一分为二。在坎特维尔组沉积地层中，新发现的迪纳里断裂带北部凝灰岩的U-Pb锆石年龄约为72 ~ 68 Ma。迪纳里断裂带以南的熔岩样品产生了约69 Ma 40 Ar/39 Ar年龄和典型弧组合的地球化学组成，包括玄武岩-安山岩-粗面岩，相对高的k，以及由板块贡献的高浓度不相容元素（例如，高Cs， Ba和Th）。晚白垩世的熔岩和膨润土，连同区域广泛的同生钙碱性岩体，记录了缝合带内收缩变形和变质作用的弧岩浆作用。晚白垩世火山和沉积地层局部覆有始新世Teklanika组火山岩，其地球化学成分介于弧形和板内亲和之间。现代Teklanika河碎屑锆石资料表明，Teklanika火山活动的高峰出现在约57 Ma，这也反映在Cantwell组膨润土的锆石Pb损失上。Teklanika组火山活动可能反映了假设的板块断裂和古新世-始新世的转换边缘构造。根据新的40 Ar/39 Ar年龄，基性脉群在约38 ~ 25 Ma沿迪纳里断裂带侵位。沿迪纳里断裂带的岩脉可能是在大约46-40 Ma期间，由于阿拉斯加南部俯冲洋板块从北北向北西方向改变，导致走滑伸展而局部化的。Diking代表了阿拉斯加山脉中部和东部最后一次有记录的重要岩浆活动，包括沿德纳里断层。两种构造模式可以解释更原始的始新世-渐新世岩浆侵位：晚白垩世-古新世弧根和/或增厚的缝合带岩石圈的剥离，或可能在古新世板块断裂期间形成的板块窗口。阿拉斯加山脉中部迪纳里断裂带南侧暴露的河流地层记录了同生沉积与岩脉作用和推断的走滑位移同时发生。根据岩石形态和最年轻的碎屑锆石，沉积发生在约29 Ma。U-Pb碎屑锆石年代学和碎屑成分数据表明，河流地层来自于阿拉斯加山脉内目前暴露的沉积和火成岩基岩，包括目前暴露在断层对面（北）侧的白垩纪地层。物源数据可能表明约29 Ma地层与推断的沉积物源有大约150公里或更多的右偏移，但可能存在不同程度的滑动。
The Alaska Range suture zone exposes Cretaceous to Quaternary marine and nonmarine sedimentary and volcanic rocks sandwiched between oceanic rocks of the accreted Wrangellia composite terrane to the south and older continental terranes to the north. New U-Pb zircon ages, 40 Ar/39 Ar, ZHe, and AFT cooling ages, geochemical compositions, and geological field observations from these rocks provide improved constraints on the timing of Cretaceous to Miocene magmatism, sedimentation, and deformation within the collisional suture zone. Our results bear on the unclear displacement history of the seismically active Denali fault, which bisects the suture zone. Newly identified tuffs north of the Denali fault in sedimentary strata of the Cantwell Formation yield ca. 72 to ca. 68 Ma U-Pb zircon ages. Lavas sampled south of the Denali fault yield ca. 69 Ma 40 Ar/39 Ar ages and geochemical compositions typical of arc assemblages, ranging from basalt-andesite-trachyte, relatively high-K, and high concentrations of incompatible elements attributed to slab contribution (eg, high Cs, Ba, and Th). The Late Cretaceous lavas and bentonites, together with regionally extensive coeval calc-alkaline plutons, record arc magmatism during contractional deformation and metamorphism within the suture zone. Latest Cretaceous volcanic and sedimentary strata are locally overlain by Eocene Teklanika Formation volcanic rocks with geochemical compositions transitional between arc and intraplate affinity. New detrital-zircon data from the modern Teklanika River indicate peak Teklanika volcanism at ca. 57 Ma, which is also reflected in zircon Pb loss in Cantwell Formation bentonites. Teklanika Formation volcanism may reflect hypothesized slab break-off and a Paleocene–Eocene period of a transform margin configuration. Mafic dike swarms were emplaced along the Denali fault from ca. 38 to ca. 25 Ma based on new 40 Ar/39 Ar ages. Diking along the Denali fault may have been localized by strike-slip extension following a change in direction of the subducting oceanic plate beneath southern Alaska from N-NE to NW at ca. 46–40 Ma. Diking represents the last recorded episode of significant magmatism in the central and eastern Alaska Range, including along the Denali fault. Two tectonic models may explain emplacement of more primitive and less extensive Eocene–Oligocene magmas: delamination of the Late Cretaceous–Paleocene arc root and/or thickened suture zone lithosphere, or a slab window created during possible Paleocene slab break-off. Fluvial strata exposed just south of the Denali fault in the central Alaska Range record synorogenic sedimentation coeval with diking and inferred strike-slip displacement. Deposition occurred ca. 29 Ma based on palynomorphs and the youngest detrital zircons. U-Pb detrital-zircon geochronology and clast compositional data indicate the fluvial strata were derived from sedimentary and igneous bedrock presently exposed within the Alaska Range, including Cretaceous sources presently exposed on the opposite (north) side of the fault. The provenance data may indicate∼ 150 km or more of dextral offset of the ca. 29 Ma strata from inferred sediment sources, but different amounts of slip are feasible.
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