Timing of subduction and exhumation in a subduction channel: Evidence from slab melts from La Corea Mélange (eastern Cuba)
Timing of subduction and exhumation in a subduction channel: Evidence from slab melts from La Corea Mélange (eastern Cuba)
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DOI：
10.1016/j.lithos.2011.08.009
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发表时间：
2011-11
期刊：
影响因子：
3.5
通讯作者：
I. Blanco-Quintero;Y. Rojas‐Agramonte;A. Garcia‐Casco;A. Kröner;D. Mertz;C. Lázaro;J. Blanco-Moreno-J.-Blanco
中科院分区：
文献类型：
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作者：
I. Blanco-Quintero;Y. Rojas‐Agramonte;A. Garcia‐Casco;A. Kröner;D. Mertz;C. Lázaro;J. Blanco-Moreno-J.-Blanco
高压火成岩（英云闪长岩）是由增生到地幔楔上的俯冲玄武质岩石部分熔融而成，存在于La Corea蛇纹岩基质混杂岩（古巴东部）中，为厘米至米大小的块体，与高压母角闪岩块体内的横切脉一致。板状熔体具有埃达克质特征，与变基性岩部分熔融后形成的特征一致。温压计算表明英云闪长岩结晶时温度为620-680°C，压力为13- 15 kbar，退变质时温度降至250-300°C，压力为6 kbar，表明逆时针P-T路径（热俯冲-冷折返）。角闪岩在中等温度（700-750°C）和中等压力（13- 16千巴）下熔融所需的自由水被推断为在俯冲的原加勒比岩石圈的沉积物、蚀变玄武质地壳和蛇纹岩脱水后提供的。单颗粒锆石（SHRIMP）和多硅白云母40 Ar/39 Ar年龄数据表明该混杂岩的P-T-t演化为约110- 105 Ma的熔体结晶至约87- 84 Ma的冷却。约350°C。9千巴。这些数字与115 Ma前不久的斜脊俯冲相一致。此外，我们的数据表明非常缓慢的挖掘（约。1 mm/yr），直至70- 65 Ma区域弧-台碰撞事件中最后快速折返至地表。
High pressure igneous rocks (tonalites), generated by partial melting of subducted basaltic rocks accreted to the mantle wedge, are present in the La Corea serpentinite-matrix mélange (eastern Cuba) as centimeter- to meter-sized blocks and as concordant to crosscutting veins within high-pressure parent amphibolite blocks. The slab melts have adakitic signatures, in agreement with formation after partial melting of metabasite. Thermobarometric calculations indicate 620–680°C and 13–15kbar during crystallization of tonalites and down to 250–300°C, 6kbar during retrogression, indicating counter-clockwise P–T paths (hot subduction-cool exhumation). Free water required for melting of amphibolite at moderate temperature (700–750°C) and moderate pressure (13–16kbar) close to the wet basaltic solidus is inferred to have been provided after dehydration of sediments, altered basaltic crust and serpentinite of the subducting Proto-Caribbean lithosphere. Single zircon (SHRIMP) and phengite40Ar/39Ar age data constrain the P–T–t evolution of the mélange from the timing of crystallization of melts at ~110–105Ma to cooling at ~87–84Ma, ca. 350°C, ca. 9kbar. These figures are consistent with subduction of an oblique ridge, shortly before 115Ma. Furthermore, our data indicate very slow exhumation (ca. 1mm/yr) in the subduction channel during the oceanic convergence stage (120–70Ma) until final fast exhumation to the surface occurred at 70–65Ma during a regional arc-platform collision event.