Partial Melting and Counterclockwise P–T Path of Subducted Oceanic Crust (Sierra del Convento Mélange, Cuba)
Partial Melting and Counterclockwise P–T Path of Subducted Oceanic Crust (Sierra del Convento Mélange, Cuba)
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DOI：
10.1093/petrology/egm074
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发表时间：
2007-11
影响因子：
3.9
通讯作者：
A. Garcia‐Casco;C. Lázaro;Y. Rojas‐Agramonte;A. Kröner;R. Torres-Roldán;Kenya Núñez;F. Neubauer;G. Millán;I. Blanco-Quintero
中科院分区：
文献类型：
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作者：
A. Garcia‐Casco;C. Lázaro;Y. Rojas‐Agramonte;A. Kröner;R. Torres-Roldán;Kenya Núñez;F. Neubauer;G. Millán;I. Blanco-Quintero
在 Sierra del Convento me¤ lange（古巴）发现了俯冲洋壳的部分熔融。这种蛇纹岩基质 me¤ lange 包含大洋中脊玄武岩 (MORB) 衍生的缺乏斜长石的绿帘石 (cid:1) 石榴石角闪岩，与过铝质长角闪岩密切相关。场关系、主要元素块体岩石成分、矿物组合、峰值变质条件（约750 8 C，14^16 kbar）、实验证据和理论相关系支持俯冲角闪岩湿熔融形成长角闪岩^英闪岩。相关系和质量平衡计算表明共晶和包晶熔融反应的特征是反应物斜长石的化学计量系数大，并表明该相在熔融时完全消耗。长石^英长岩熔体的岩浆组合，由斜长石、石英、绿帘石、(cid:1) 钠长石、(cid:1) 斜长石和 (cid:1) 蓝晶石组成，在深度 (14^15 kbar) 结晶。熔体的过铝成分与实验证据一致，解释了岩浆钠长石和（残余）的存在蓝晶石，并对板岩岩浆岩的解释产生了重要的限制。计算的 P^T 条件表明折返期间逆时针 P^T 路径，此时逆行蓝片岩相叠印由绿辉石、蓝闪石、阳起石、透闪石、钠长石、硬钠长石、钠长石、（斜）黝帘石、绿泥石、泵贝利石和白云母组成，在角闪岩和长辉石中形成。古巴东部俯冲洋壳的部分熔融在加勒比地区是独一无二的，对该地区的板块构造解释具有重要影响，因为它支持了白垩纪早期（约120 Ma）年轻海洋岩石圈开始俯冲的情景。逆时针 P^T 路径是由持续俯冲过程中随后的折返引起的。岩石圈。
Partial melting of subducted oceanic crust has been identified in the Sierra del Convento me ¤ lange (Cuba). This serpentinite-matrix me ¤ lange contains blocksof mid-ocean ridgebasalt (MORB)-derived plagioclase-lacking epidote (cid:1) garnet amphibolite intimately associated with peraluminous trondhjemitic^tonalitic rocks. Field relations, major element bulk-rock compositions, mineral assemblages, peak metamorphic conditions ( c. 750 8 C, 14^16 kbar), experimental evidence, and theoretical phase relations support formation of the trondhjemitic^tonalitic rocks by wet melting of subducted amphibolites. Phase relations and mass-balance calculations indicate eutectic- and peritectic-like melting reactions characterized by large stoichiometric coefficients of reactant plagioclase and suggest that this phase was completely consumed upon melting. The magmatic assemblages of the trondhjemitic^tonalitic melts, consisting of plagioclase, quartz, epidote, (cid:1) paragonite, (cid:1) pargasite, and (cid:1) kyanite, crystallized at depth (14^15 kbar).The peraluminous composition of the melts is consistent with experimental evidence, explains the presence of magmatic paragonite and (relict) kyanite, and places important constraints on the interpretation of slab-derived magmatic rocks. Calculated P^T conditions indicate counterclockwise P^T paths during exhumation, when retrograde blueschist-facies overprints, composed of combinations of omphacite, glaucophane, actinolite, tremolite, paragonite, lawsonite, albite, (clino)zoisite, chlorite, pumpellyiteandphengite, wereformedintheamphibolitesandtrondh-jemites. Partial melting of subducted oceanic crust in eastern Cuba is unique in the Caribbean realm and has important consequencesfor the plate-tectonic interpretation of the region, as it supports a scenario of onset of subduction of a young oceanic lithosphere during the early Cretaceous ( c. 120 Ma). The counterclockwise P^T paths were caused by ensuing exhumation during continued subduction. lithosphere.