Where did the Arizona‐Plano Go? Protracted Thinning Via Upper‐ to Lower‐Crustal Processes
Where did the Arizona‐Plano Go? Protracted Thinning Via Upper‐ to Lower‐Crustal Processes
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DOI：
10.1029/2021jb023850
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发表时间：
2022-03
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通讯作者：
G. Jepson;B. Carrapa;S. George;L. Reeher;P. Kapp;G. Davis;S. Thomson;C. Amadori;C. Clinkscales;Sean Jones;A. Gleadow;B. Kohn
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作者：
G. Jepson;B. Carrapa;S. George;L. Reeher;P. Kapp;G. Davis;S. Thomson;C. Amadori;C. Clinkscales;Sean Jones;A. Gleadow;B. Kohn
中-新生代法拉隆板块俯冲到北美之下，在白垩纪晚期在美国西南部形成了一个区域性的广泛造山高原，类似于现代的安第斯高原中部。在内华达州和亚利桑那州南部，全岩地球化学的估计表明，晚白垩世地壳厚度达到了60 - 55公里。现代地壳厚度为128公里，需要显着的新生代地壳减薄。在这里，我们比较了详细的低温热年代学从卡塔利纳变质核杂岩（MCC）整个亚利桑那州南部的岩石Sr/Y地壳厚度估计。我们确定了三个冷却期。一个小的冷却阶段发生在2.40 Ma之前，有限的证据剥蚀和2.10 km的地壳减薄。26-19Ma主要冷却发生在拆离断层作用和MCC形成期间，相当于剥蚀量为0.8km，地壳减薄量为0.8km。最后，我们记录了17 - 11 Ma与盆地和山脉延伸相关的冷却阶段，对应于0.55 km的剥蚀和0.99 km的地壳减薄。在MCC和盆岭伸展事件期间，低温热年代学记录的剥蚀量可以用地壳厚度的相应减少来解释。然而，相对有限的折返之前，拆离断层在20.26 Ma记录的热年代学是不足以解释地壳减薄的幅度（20.10 km），在整个岩石地壳厚度记录。因此，我们认为亚利桑那平原的地壳减薄是通过韧性中地壳到下地壳的流动促进的，并且在拆离断层和盆地和山脉延伸之前的50 - 30 Ma限制了上地壳的延伸。
Mesozoic‐Cenozoic subduction of the Farallon slab beneath North America generated a regionally extensive orogenic plateau in the southwestern US during the latest Cretaceous, similar to the modern Central Andean Plateau. In Nevada and southern Arizona, estimates from whole‐rock geochemistry suggest crustal thicknesses reached ∼60–55 km by the Late Cretaceous. Modern crustal thicknesses are ∼28 km, requiring significant Cenozoic crustal thinning. Here, we compare detailed low‐temperature thermochronology from the Catalina metamorphic core complex (MCC) to whole rock Sr/Y crustal thickness estimates across southern Arizona. We identify three periods of cooling. A minor cooling phase occurred prior to ∼40 Ma with limited evidence of denudation and ∼10 km of crustal thinning. Major cooling occurred during detachment faulting and MCC formation at 26–19 Ma, corresponding to ∼8 km of denudation and ∼8 km of crustal thinning. Finally, we document a cooling phase at 17–11 Ma related to Basin and Range extension that corresponds with ∼5 km of denudation and ∼9 km of crustal thinning. During the MCC and Basin and Range extension events, the amount of denudation recorded by low‐temperature thermochronology can be explained by corresponding decreases in the crustal thickness. However, the relatively limited exhumation prior to detachment faulting at ∼26 Ma recorded by thermochronology is insufficient to explain the magnitude of crustal thinning (∼10 km) observed in the whole rock crustal thickness record. Therefore, we suggest that crustal thinning of the Arizona‐plano was facilitated via ductile mid‐ to lower‐crustal flow, and limited upper‐crustal extension at 50–30 Ma prior to detachment faulting and Basin and Range extension.