Metamorphic and deformational processes in the Franciscan Complex, California: Some insights from the Catalina Schist terrane
Metamorphic and deformational processes in the Franciscan Complex, California: Some insights from the Catalina Schist terrane
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加利福尼亚州方济会综合体的变质和变形过程：卡塔利娜片岩地体的一些见解
DOI：
10.1130/0016-7606(1975)86
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发表时间：
1975
影响因子：
4.9
通讯作者：
J. Platt
中科院分区：
文献类型：
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作者：
J. Platt
在圣卡塔利娜岛上，蓝片岩在结构上被蓝闪绿片岩覆盖，绿片岩又被角闪岩和超镁质岩单元覆盖。这三个单元沿亚水平变质后逆冲构造并置；角闪岩构造块体沿绿片岩和蓝片岩之间的逆冲方向分布。估计蓝片岩变质的物理条件约为300℃、9 kb，绿片岩约为450℃、8 kb，角闪岩约为600℃、10 kb。我认为变质作用发生在一个新开始的俯冲带，在热上挂壁橄榄岩下方发育了一个反向的热梯度。变质后沿不同倾角面向东逆冲可以解释目前的构造关系。方济各杂岩中其他地方的蓝帘-绿帘岩片岩、角闪岩和榴辉岩的构造块可能是类似变质带的残余物。逆热梯度只存在于俯冲的早期阶段，这就解释了为什么这些块体是方济各杂岩中最古老的岩石。向西跨越方济各的年龄和变质等级的总体下降是由于连续的逆冲和逐渐年轻的超地壳物质片的增生，同时伴随着隆起和侵蚀。各东倾构造片的压力-温度（P-T）变质条件下倾增加。在任何给定的时间，更古老的、更偏东的岩片将进一步隆起，因此暴露边缘的变质等级将向东和构造向上增加。如果侵蚀在一段时间内比吸积快，较年轻的岩片将在较低的压力下比较老的较高的压力下变质。简单的逆断层作用可以产生观测到的不同变质等级岩石的交错。
On Santa Catalina Island, blueschist is structurally overlain by glaucophanic greenschist, which is overlain in turn by a unit of amphibolite and ultramafic rock. These three units are juxtaposed along sub-horizontal postmetamorphic thrusts; tectonic blocks of amphibolite are distributed along the thrust between the greenschist and the blueschist. Physical conditions of metamorphism are estimated to be approximately 300°C and 9 kb for blueschist, 450°C and 8 kb for greenschist, and 600°C and 10 kb for amphibolite. I suggest that metamorphism occurred in a newly started subduction zone, where an inverted thermal gradient developed below the hot hanging-wall peridotite. Postmetamorphic eastward underthrusting along surfaces of varying dip can explain the present structural relationships. Tectonic blocks of glaucophane-epidote schist, amphibolite, and eclogite elsewhere in the Franciscan Complex may be disrupted remnants of similar metamorphic zones. The inverted thermal gradient will only exist in the early stages of subduction, which explains why the blocks are the oldest rocks in the Franciscan Complex. The gross decrease in age and metamorphic grade westward across the Franciscan results from successive underthrusting and accretion of progressively younger slices of supercrustal material, concurrent with uplift and erosion. Pressure-temperature (P-T) conditions of metamorphism in each east-dipping tectonic slice will increase down-dip. At any given time, older, more easterly slices will have been uplifted further, hence metamorphic grade in the exposed edges will increase eastward and structurally upward. If erosion is faster than accretion for a time, younger slices will be metamorphosed at lower pressures than were the older higher ones. Simple reverse faulting can then produce the observed interleaving of rocks of different metamorphic grade.