Rheology of some continental lower crustal rocks
Rheology of some continental lower crustal rocks
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DOI：
10.1016/0040-1951(90)90342-6
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发表时间：
1990-10
期刊：
影响因子：
2.9
通讯作者：
K. Wilks;N. Carter
中科院分区：
文献类型：
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作者：
K. Wilks;N. Carter
为了深入了解大陆下地壳（CLC）中所选含辉长岩岩石的流变学，对下地壳出露地体中的三个麻粒岩和一个微辉长岩进行了变形，使其变形到约100 °。在0.8-1.0 GPa的围压、600-900°C的温度和10−4−10−7s−1的恒定应变率下，约10%的应变。最广泛的工作是在基性Pikwitonei和长英质阿迪朗达克麻粒岩。Pikwitonei（Mg-角闪石-plag（An 70 −2 px））只有有限的T，ε范围的表观稳态行为，在T ε 800°Catε= 10−5−10− 6 s −1时应变软化，显然与发展中的剪切带有关。这种应变软化在Pc = 0.8-1.0 GPa at T = 850°C，ε= 10−6s− 1时对压力不敏感，尽管主要的应变调节机制随着压力的增加从半脆性/碎裂转变为晶体塑性（包括动态再结晶）。斜长石似乎承担更多的蠕变应变比角闪石在大多数实验条件下，除了在那些运行斜长石和角闪石重结晶发生。Kapuskasing（plag-cpx-gt）麻粒岩在800°C和850°C下变形10−6s− 1，在应力水平仅略大于Pikwitonei的稳定状态下变形。静水微辉长岩和阿迪朗达克麻粒岩明显较弱，后者表现出均匀的半脆性稳态行为在整个范围内的条件下进行调查。对于阿迪朗达克（2 felds-2 px-gt-qtz）麻粒岩，石英（21%）似乎在这些低应变下控制蠕变速率，稳态力学数据很好地拟合蠕变幂律，其中A = 8 × 10− 3 MPa −ns−1，Qc= 243 kJ/mol，n = 3.1。Pikwitonei和微辉长岩的这种流动定律和初步的幂律蠕变关系外推到一系列的物理条件，假设包括那些在大陆莫霍面支持地质和地球物理推断，机械不连续性发生在这个过渡区，下地壳一般是较弱的材料。此外，染色软化所表现出的Pikwitonei可能直接承担在中低地壳深度的拆离带的发展过程中的变质作用。
To gain insight into the rheology of selected feldspar-bearing rocks from the continental lower crust (CLC), three granulites from exposed lower crustal terrains and a microgabbro have been deformed to ca. ~10% strain at confining pressures of 0.8–1.0 GPa, temperatures of 600–900°C, and constant strain-rates of 10−4−10−7s−1. The most extensive work was done on the mafic Pikwitonei and felsic Adirondack granulites. The Pikwitonei (Mg-hornblende-plag (An70−2 px) has only a limitedT,ϵ range of apparent steady-state behavior, and strain-softens atT⩾ 800°Catϵ= 10−5−10−6s−1, apparently associated with developing shear zones. This strain-softening is pressure-insensitive fromPc= 0.8–1.0 GPa atT= 850°C,ϵ= 10−6s−1even though the dominant strain accommodation mechanisms change from semibrittle/cataclastic to crystal plastic (including dynamic recrystallization) with increasing pressure. Plagioclase appears to bear more of the creep strain than amphibole at most experimental conditions except in those runs where both plagioclase and amphibole recrystallization occurs. Kapuskasing (plag-cpx-gt) granulite, deformed at 800°C and at 850°C, 10−6s−1has deformed in the steady-state at stress levels only slightly greater than the Pikwitonei. The Stillwater microgabbro and Adirondack granulite are appreciably weaker and the latter exhibits homogeneous semibrittle steady-state behavior over the entire range of conditions investigated. For the Adirondack (2 felds-2 px-gt-qtz) granulite, quartz (21%) appears to control the creep rate at these low strains, and steady-state mechanical data fit well a creep power law withA= 8 × 10−3MPa−ns−1,Qc= 243 kJ/mol andn= 3.1. Extrapolation of this flow law and of preliminary power law creep relations for the Pikwitonei and microgabbro to a range of physical conditions assumed to encompass those at the continental Moho supports geological and geophysical inferences that a mechanical discontinuity occurs at this transition zone, with the lower crust generally being the weaker material. In addition, the stain-softening exhibited by the Pikwitonei may bear directly on the development of detachment zones at mid- to lower-crustal depths during prograde metamorphism.