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Late miocene to recent arc-forearc response to plate tectonics surrounding the Panama triple junction, southern Central America.

机译：晚中新世至最近弧前臂对中美洲南部巴拿马三重交界处板块构造的响应。

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摘要

This dissertation explores how the changing plate tectonics surrounding the Panama (CO-NZ-CA) Triple Junction along the southern Central American Convergent Margin has affected the evolution of the upper plate of this system since the Middle Miocene, with a focus on study areas in the arc, inner forearc and outer forearc regions inboard of the triple junction. New structural and geomorphic analyses on the Burica peninsula, an outer forearc peninsula located only ∼100 km inboard the Panama Triple Junction, reveal that the peninsula is dominated primarily by contractional deformation along three listric thrust faults that root in the underlying plate boundary. The geometry and spatial distribution of these thrusts indicate that this deformation occurs primarily in response to the change in crustal thickness occurring as a result of eastern migration of the flank of the Cocos Ridge coeval with migration of the Panama Triple Junction at a rate of ∼55 mm/yr to the southeast. Mapping and detailed elevation surveys reveal eight marine terraces on the peninsula with a distribution of inner edge elevations indicating that uplift is spatially uniform from north to south along-strike in this area. Age control provided by 14C, OSL and soil chronosequences indicate that the terraces within the easternmost portion of the peninsula range in age from Marine Isotope Stage (MIS)-3 to Holocene, a result that indicates that this portion of the peninsula is younger than ∼60 ka. Time-averaged uplift rates calculated from marine terraces and other Quaternary marine deposits yield consistent uplift rates that range between 2.1 +/- 0.1 to 7.7 +/- 0.5 mm/yr for samples older than 1 ka and between 6.9 +/- 1.0 to 19.3 +/- 8.0 mm/yr for samples younger than 1 ka. We interpret this temporal distribution in uplift rates to suggest that the 8 terraces preserved on the peninsula are produced co-seismically wherein the anomalously high uplift rates calculated from the youngest samples ( 1 ka) are not yet averaged over a complete seismic cycle. These observations, combined with (1) shortening estimates from balanced cross-sections indicating that minimum shortening decreases from northwest to southeast as well as (2) the observation of growth strata within the youngest marine units, are consistent with a space-for-time model for triple junction migration.;New geomorphic and longitudinal profile analyses combined with revised plate reconstruction models provide a new perspective with which to view the evolution of the Central American volcanic arc. We identify a low-relief surface in the northeastern flanks of the Cordillera de Talamanca, the late Miocene volcanic arc of southern Costa Rica, which, combined with longitudinal profile analyses, suggests the existence of a transient landscape within this region. Rock uplift calculations based on channel reconstruction by extrapolation of the current low-relief surface estimate that the rock uplift associated with this transient is on the order of ∼2 km since the inception of the transient. Our results from a synthesis of radiometric ages combined with newly revised plate reconstruction models suggest that arc cessation between both the Cordillera de Talamanca and the Cordillera Central of western Panama occurred coeval with the initiation of oblique subduction of the Nazca plate during the late Miocene. This revision to previous plate reconstruction models, which relies on revised magnetic plate anomalies associated with the extinction of the Sandra Rift in the east Panama basin, suggests the existence of a North Nazca microplate prior to ∼8-9 Ma, as well as a 2-fold decrease in convergence rate at this time. These results suggest that initiation of shallow subduction of the Cocos Ridge at the Middle American Trench, which has long been associated with the volcanic extinction of the Cordillera de Talamanca, occurred at ∼ 1.5-2 Ma: more than ∼7 million years after the extinction of the Central American volcanic arc.;We also use new geologic, stratigraphic and geomorphic data along with age constraints to characterize the Late Pleistocene to Holocene sequence of deposits associated with edifice failure and sector collapse of the active Volcan Baru (alt. 3374 m) in westernmost Panama. This new stratigraphic control provides new constraints on the timing of thrusting associated with termination of the Fila Costena inner forearc thrust belt, which is migrating to the southeast coeval with the Panama Triple Junction. Radiocarbon dating of organic material, together with 40Ar/39Ar ages from clasts within the deposits, identify at least three debris avalanche events (DA1, DA2 and DA3). Preliminary volume estimates for the youngest deposit (DA3) range from a minimum of ∼30 km3 to a maximum of ∼60 km3. Radiocarbon analysis of wood and other organic material extracted from this debris avalanche (n=3) yield ages that range between 8, 625 +/- 75 YBP and 12, 845 +/- 55 YBP. The oldest deposit contains a soil profile that appears significantly more developed than younger deposits and yields ages > 44,000 YBP. 40Ar/39Ar dating of plagioclase feldspar crystals extracted from clasts within the DA1 deposit, however, yield dates as young as 231 +/- 32 ka, constraining the lower age boundary. We map and distinguish three lithofacies for the debris avalanche, which we establish on the basis of surface morphology, abundance of clasts, and matrix composition. Finally, we also present new results regarding the kinematics, timing and evolution of the Fila Costena Thrust Belt for many of the thrusts that intersect the volcanic units characterized here. These results include new shortening amounts based on balanced cross-sections within thrusts that cut surficial lahar units, as well as the recognition of new thrust structures that place constraints on thrust timing within this region.
机译：本文探讨了自中新世中期以来，沿中美洲南部会聚缘南部的巴拿马（CO-NZ-CA）三重交界处变化的板块构造如何影响了该系统的上板块的演化。三重结内侧的弧，前内侧内侧和外侧外侧区域。对位于巴拿马三结交界以内仅约100 km的外前臂半岛Burica半岛的新结构和地貌分析表明，该半岛主要由沿变形的塑性变形控制，该变形沿根植于下伏板块边界的三个倾斜冲断层。这些推力的几何形状和空间分布表明，这种变形主要是由于地壳厚度的变化而发生的，该变化是由于科科斯山脊侧面的东部迁移和巴拿马三结的迁移以〜55的速率而发生的。东南毫米/年。测绘和详细的海拔调查显示，半岛上有8个海洋阶地，其内边缘海拔高度分布表明，该区域的隆升在北走向南沿走向是空间均匀的。 14C，OSL和土壤时间序列提供的年龄控制表明，该半岛最东端的阶地的年龄范围从海洋同位素阶段（MIS）-3到全新世，结果表明该半岛的这一部分比〜年轻。 60 ka。根据海洋阶地和其他第四纪海相沉积物计算的时间平均上升速率产生的持续上升速率在1 KA以上的样本中介于2.1 +/- 0.1至7.7 +/- 0.5 mm / yr之间，在6.9 +/- 1.0至19.3之间对于小于1 ka的样品，+ /-8.0毫米/年。我们解释了隆升速率的这种时间分布，以表明在半岛上保留的8个阶地是同震产生的，其中从最年轻的样本（<1 ka）计算出的异常高的隆升速率尚未在整个地震周期中平均。这些观察结果与（1）从平衡截面得出的缩短量估计值相结合，表明从西北到东南最小的缩短量减少，以及（2）在最年轻的海洋单元中观察到的生长层，与时空一致。新的地貌和纵向剖面分析与修订的板块重建模型相结合提供了一个新的视角，可以用来观察中美洲火山弧的演化。我们在哥斯达黎加南部的中新世晚期火山弧Cadillera de Talamanca的东北侧确定了一个低浮雕表面，结合纵向剖面分析表明该区域内存在短暂景观。基于通过对当前低浮雕表面进行外推的渠道重建进行的岩石隆起计算估计，与该瞬变有关的岩石隆起自瞬态发生以来约为2 km。我们的辐射年龄综合结果与新修订的板块重建模型相结合，表明中新世晚期纳斯卡板块俯冲俯冲开始时，塔拉曼卡山脉和巴拿马西部科迪勒拉中心之间的灭弧同时发生。对先前板块重建模型的修订依赖于修订后的磁性板块异常，该异常与巴拿马东部盆地桑德拉裂谷的灭绝有关，这表明在〜8-9 Ma之前存在北纳斯卡微板块，还有一个2此时的收敛速度降低了两倍。这些结果表明，中美洲海沟中的科科斯山脊浅层俯冲的起始时间与1.52 Ma：距灭绝后约700万年有关，长期以来一直与塔拉曼卡山脉的火山灭绝有关。我们还使用新的地质，地层和地貌数据以及年龄限制来表征与活动火山巴鲁（海拔3374 m）的建筑物破坏和扇形塌陷有关的晚更新世至全新世沉积物序列在最西部的巴拿马。这种新的地层控制对与Fila Costena内前臂逆冲带终止相关的逆冲时机提供了新的约束，该区域正与巴拿马三重交界处向东南部过渡。有机物的放射性碳测年以及沉积物中碎屑的40Ar / 39Ar年龄，至少可以识别出三个碎片雪崩事件（DA1，DA2和DA3）。最小储量（DA3）的初步数量估算范围从最小约30 km3到最大约60 km3。从碎片雪崩中提取的木材和其他有机材料的放射性碳分析（n = 3），其产生年龄介于8、625 +/- 75 YBP和12之间，845 +/- 55 YBP。最老的矿床的土壤剖面看来比年轻的矿床发育得多，且年龄> 44,000 YBP。从DA1矿床中的碎屑中提取的斜长石长石晶体的40Ar / 39Ar年代，但是，其生成年代早于231 +/- 32 ka，限制了年龄的下限。我们绘制并区分了碎屑雪崩的三个岩相，这是我们根据表面形态，岩屑丰度和基质组成建立的。最后，我们还提供了有关Fila Costena推力带的运动学，时间和演化的新结果，这些推力与这里表征的火山单元相交的许多推力。这些结果包括基于推力内横截面平衡的新缩短量，这些推力可削减表层拉哈单元，以及对新推力结构的认识，这些新推力结构对该区域内的推力时机施加了限制。

著录项

  • 作者

    Morell, Kristin D.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Geology.;Geomorphology.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 189 p.
  • 总页数 189
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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