High-resolution garnet chronometry and the rates of metamorphic processes
High-resolution garnet chronometry and the rates of metamorphic processes
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DOI：
10.1016/0012-821x(91)90109-u
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发表时间：
1991-12
影响因子：
5.3
通讯作者：
K. Burton;R. O’nions
中科院分区：
文献类型：
--
作者：
K. Burton;R. O’nions
挪威北部Sulitjelma角闪岩相变质沉积物中石榴石的Sm单键Nd、U单键Pb和Rb单键Sr年龄与矿物生长的压力（P）和温度（T）条件直接相关。该样品中石墨层和非石墨层之间的矿物反应差异记录了Barrovian区域变质作用期间经历的P-T和时间（t）历史。石墨层中的石榴石是在462 ± 16°C、5.2 ± 0.5kbar、低H2O条件下的变质作用中生长的，获得了可靠的147 Sm单键143 Nd和238 U单键206 Pb年龄，分别为434.1 ± 1.2Ma和433.9 ± 1.0Ma。相反，在达到540 ± 18°C和8.0 ± 1.0kbar的P-T条件之前，在相邻的无石墨层中不会发生石榴石生长，并且响应于544 ± 16°C和7.0 ± 1.0kbar的最后基质平衡的轻微加热和减压而继续生长。该组合中无包裹体的石榴石边缘记录了147 Sm单键143 Nd和238 U单键206 Pb年龄，分别为424.6 ± 1.2Ma和423.4 ± 1.7Ma。这些结果提供了精确估计的平均加热速率和埋藏速率在俯冲变质作用期间分别为8.6 - 4.4+7.5°C Ma-1和0.8 - 0.5+0.9km Ma-1。无石墨组合中共存的硅酸盐之间的Rb和Sr交换在变质作用的“高峰”之后持续了约37 Ma，并且在隆升期间需要约4.0°C Ma− 1的平均冷却速率。这些结果说明了一个明确的反应历史和矿物生长的时间之间的关系，并提供了明确的限制伴随区域变质作用的热和构造过程的速度。
Garnets in an amphibolite-facies metasediment from Sulitjelma, North Norway yield precise and concordant Smsingle bondNd, Usingle bondPb and Rbsingle bondSr ages that relate directly to the pressure (P) and temperature (T) conditions of mineral growth. Differential mineral reaction between graphitic and non-graphitic layers within this sample preserves a record of theP-Tand time (t) history experienced during Barrovian regional metamorphism. Garnets in graphitic layers grew during prograde metamorphism at462 ± 16°C and5.2 ± 0.5kbar under conditions of lowaH2O, and yield indistinguishable147Smsingle bond143Nd and238Usingle bond206Pb ages of434.1 ± 1.2Ma and433.9 ± 1.0Ma, respectively. In contrast, garnet growth in adjacent graphite-free layers did not occur untilP-Tconditions of540 ± 18°C and8.0 ± 1.0kbar were attained, with continued growth in response to minor heating and decompression with final matrix equilibration at544 ± 16°C and7.0 ± 1.0kbar. The inclusion-free garnet rims in this assemblage record indistinguishable147Smsingle bond143Nd and238Usingle bond206Pb ages of424.6 ± 1.2Ma and423.4± 1.7Ma, respectively. These results provide precise estimates for average heating and burial rates during prograde metamorphism of 8.6−4.4+7.5°C Ma−1and 0.8−0.5+0.9km Ma−1, respectively. Rb and Sr exchange between coexisting silicates in the graphite-free assemblage continued for some 37 Ma after the “peak” of metamorphism, and require an average cooling rate of about 4.0°C Ma−1during uplift. These results illustrate a clear relationship between reaction history and the timing of mineral growth and provide definitive constraints on the rates of thermal and tectonic processes accompanying regional metamorphism.