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首页> 外文期刊>International Geology Review >Temporal Changes in Deformation Mode: From Failure to Flow in the Colorado River Extensional Corridor
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Temporal Changes in Deformation Mode: From Failure to Flow in the Colorado River Extensional Corridor

机译：变形模式的时间变化：从破坏到科罗拉多河伸展走廊的水流

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The Colorado River Extensional Corridor (CREC) of southeastern California, southern Nevada, and western Arizona experienced up to 100 percent extension between approx 23 and 12 Ma. Extension was accommodated by low-angle normal faulting in the upper and middle crust, subvertical brittle failure of the lower crust, emplacement of mantle-derived magma in a crustal-scale fracture, and, later, crustal flow. Evidence for brittle, whole-crustal failure includes geophysical observations, structural analysis, geochronology, thermochronology, geobarometry, and paleomagnetic studies of surface exposures of syntectonic, mantle-derived mafic plutonic sheets emplaced as subvertical, crustal-scale intrusions tracking the zone of maximum extension. Their subsurface extent and geometry are interpreted from the shape and magnitude of the Colorado River gravity high, a 10-20 mGal positive gravity anomaly that follows the belt of core complexes west of the Colorado River for approx 150 km along strike. In the southern Sacramento Mountains (latitude 34 deg 40 min N), mid-crustal rocks exposed in the footwall of the extensional fault system comprise brittle-deformed, syntectonic intrusive rocks emplaced into variably mylonitized gneiss and granite as three intrusive pulses between 19.1 and approx 6 Ma. Mingled, mantle-derived diorite and granite accommodated 5-18 km magmatic extension (10-20 percent total extension) in the CREC at this latitude. Analogous regions interpreted to be undergoing brittle failure of the lower crust include the East African, Baikal, and Rio Grande rifts. Each exhibit lower-crustal seismicity on normal faults with dips >= 70 deg. Miocene conditions in the CREC are interpreted to include high strain rates (10~(16)s~(-1) to 10~(14)s~(-1)) and moderate heat flow, both conditions considered necessary for brittle lower-crustal failure in the East African Rift. Lower-crustal flow was initiated after magmatism, buoying mid-crustal rocks to shallow structural levels, as low-angle normal faulting in the upper and middle crust accommodated extension. Ductile flow of the lower crust allowed the maintenance of nearly constant crustal thickness and created domed core complexes in areas of extreme extension. In the Colorado River extensional corridor, the lower and middle crust behaved ductilely only in late stages of extension, after brittle failure of the lower crust. This change from brittle failure to ductile flow indicates a change in style of deformation from narrow rift-zone to core-complex mode.
机译：加利福尼亚东南部，内华达州南部和亚利桑那州西部的科罗拉多河延伸走廊（CREC）在大约23至12 Ma之间经历了高达100％的延伸。上地壳和中地壳的低角度正断层，下地壳的亚垂直脆性破坏，地幔尺度裂缝中来自地幔的岩浆位置，以及后来的地壳流动来适应伸展作用。脆性，全壳破坏的证据包括地球物理观测，结构分析，地质年代学，热年代学，地质气压学以及对构造，地幔源性铁镁质岩体的表面暴露进行古地磁研究，这些沉积物被构造成垂直下，地壳尺度的侵入体，追踪最大延伸区域。它们的地下范围和几何形状是根据科罗拉多河重力高的形状和大小来解释的，这是一个10-20 mGal的正重力异常，沿着罢工沿科罗拉多河以西的岩心复合带延伸约150 km。在萨克拉曼多南部山区（北纬34度40分钟），伸展断层系统下盘中露出的中地壳岩石包括脆性变形的同构造侵入岩，在19.1到大约1之间的大约3个侵入脉冲中，它们分别被变成具糊状的片麻岩和花岗岩。 6麻在这个纬度上，混杂的，来自地幔的闪长岩和花岗岩在CREC中容纳了5-18 km的岩浆扩展（占总扩展的10-20％）。被解释为下地壳脆性破裂的类似地区包括东非，贝加尔湖和里奥格兰德裂谷。在倾斜度大于等于70度的正常断层上，每个地震都表现出较低的地壳地震活动性。 CREC中的中新世条件被解释为包括高应变率（10〜（16）s〜（-1）到10〜（14）s〜（-1））和适度的热流，这两个条件都被认为是较低脆性的必要条件。东非大裂谷地壳破裂。岩浆作用后开始下地壳流动，使中地壳岩石浮起至浅层构造水平，因为上地壳和中地壳的低角度正断层适应了延伸。下地壳的延性流动使地壳厚度几乎保持恒定，并在极度延伸的区域形成了穹顶形的岩心复合体。在科罗拉多河伸展走廊中，下地壳脆性破坏后，下地壳和中地壳仅在伸展的后期才具有延性。从脆性破坏到延性流动的这种变化表明，变形形式从狭窄的裂谷带转变为岩心复杂模式。

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