Extensional basin evolution in the Cordillera Blanca, Peru: Stratigraphic and isotopic records of detachment faulting and orogenic collapse in the Andean hinterland
Extensional basin evolution in the Cordillera Blanca, Peru: Stratigraphic and isotopic records of detachment faulting and orogenic collapse in the Andean hinterland
复制标题
秘鲁布兰卡山脉的伸展盆地演化：安第斯腹地滑脱断层和造山塌陷的地层和同位素记录
DOI：
10.1029/2010tc002666
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发表时间：
2010
期刊：
影响因子：
4.2
通讯作者：
M. Grove
中科院分区：
文献类型：
--
作者：
M. Giovanni;B. Horton;C. Garzione;B. McNulty;M. Grove
沉积学、物源、氧同位素和40 Ar/39 Ar结果提供了秘鲁安第斯山脉伸展腹地盆地晚新生代演化的见解。5-6.5公里长的布兰卡山脉构成了安第斯褶皱冲断带中平行于活动收缩构造的低角度正断层的冰川下盘。长约200 km、WSW倾斜（19°-36°）的Cordillera Blanca拆离断层容纳了>12-15 km的倾滑位移，导致上盘上拆离盆地的沉降，该盆地由上中新世-上新世Lloclla组的约1300 m砾岩、砂岩、粉砂岩和有限的碳酸盐填充。岩相组合归因于湖泊扇三角洲至近端河流为主的冲积扇沉积。物源数据记录了沉积物在西北方向轴向扩散期间侏罗纪至中新世火山岩和沉积岩的下盘去顶。物源数据记录了来自中新世上部Cordillera Blanca岩基的下盘衍生花岗岩碎屑的外观以及横向WSW定向运输的变化。盆地填充物的特征和保存的变化表明断层随时间沿沿着走向传播。Lloclla组底部凝灰岩的40 Ar/39 Ar黑云母年龄为5.4 ± 0.1 Ma，将初始伸展和沉降限制在中新世晚期。对古湖水成分的估计显示，δ 18 O（VSMOW）值非常负（−13.6‰至−18.2‰），表明在最早的正断层和盆地演化期间，布兰卡山脉已经达到了与现代相当的高海拔。这些结果支持的模型表明，大幅缩短，地壳增厚，和表面隆起的必要的前兆条件下产生的科迪勒拉布兰卡拆离断层。
Sedimentologic, provenance, oxygen isotope, and 40Ar/39Ar results provide insights into late Cenozoic evolution of an extensional hinterland basin in the Peruvian Andes. The 5–6.5 km Cordillera Blanca composes the glaciated footwall of a low‐angle normal fault parallel to active contractional structures in the Andean fold‐thrust belt. The ∼200 km long, WSW dipping (19°–36°) Cordillera Blanca detachment fault accommodated >12–15 km of dip‐slip displacement, inducing subsidence of the hanging‐wall supradetachment basin, which is filled by ∼1300 m of conglomerate, sandstone, siltstone, and limited carbonate of the upper Miocene‐Pliocene Lloclla Formation. Lithofacies associations are attributed to lacustrine fan‐delta to proximal, stream‐dominated alluvial fan sedimentation. Provenance data record footwall unroofing of Jurassic through Miocene volcanic and sedimentary rocks during NW directed, axial dispersal of sediment. Provenance data record the appearance of footwall‐derived granite clasts from the upper Miocene Cordillera Blanca batholith and a change to transverse, WSW directed transport. Variations in the character and preservation of basin fill suggest along‐strike propagation of the fault through time. Initial extension and subsidence is constrained to the latest Miocene by an 40Ar/39Ar biotite age of 5.4 ± 0.1 Ma for a basal tuff in the Lloclla Formation. Estimation of paleolake water composition shows very negative δ18O(VSMOW) values (−13.6‰ to−18.2‰), indicating that high elevations comparable to modern were already attained in the Cordillera Blanca during earliest normal faulting and basin evolution. These results lend support to models suggesting that substantial shortening, crustal thickening, and surface uplift were necessary precursor conditions for the generation of the Cordillera Blanca detachment fault.