Zircon U-Pb and geochemical signatures in high-pressure, low-temperature metamorphic rocks as recorders of subduction zone processes, Sikinos and Ios islands, Greece
Zircon U-Pb and geochemical signatures in high-pressure, low-temperature metamorphic rocks as recorders of subduction zone processes, Sikinos and Ios islands, Greece
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DOI：
10.1016/j.chemgeo.2021.120447
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发表时间：
2021-11
期刊：
影响因子：
3.9
通讯作者：
Eirini M. Poulaki;D. Stockli;Megan E. Flansburg;M. Gevedon;L. Stockli;J. Barnes;K. Soukis;K. Kitajima;J. Valley
中科院分区：
文献类型：
--
作者：
Eirini M. Poulaki;D. Stockli;Megan E. Flansburg;M. Gevedon;L. Stockli;J. Barnes;K. Soukis;K. Kitajima;J. Valley
锆石U-Pb定年是一种强有力的、广泛使用的地质年代学技术，用于确定岩浆、高级和低级变质作用的时间和速率，以及沉积物的物源。锆石的微量元素（TE）组成也记录了锆石生长过程中的岩浆和变质过程。在这项研究中，锆石激光烧蚀分流（LA-SS）-ICP-MS U-Pb和TE深度剖面和新的二维锆石填图技术与氧同位素分析相结合（二次离子质谱，西姆斯）重建的时间和变质条件记录的重结晶和生长的锆石轮辋，这为研究俯冲带高压/低温（HP/LT）变质岩的岩石构造演化提供了有价值的信息。这些技术被应用到锆石颗粒从HP/LT变质岩的基克拉迪蓝片岩单元（CBU）和基克拉迪基底（CB）的Sikinos和Ios岛，希腊，经历了变质和变形与俯冲和随后的弧后折返。锆石记录了~50 Ma和~ 26 Ma的多期非岩浆锆石边生长。始新世变质边缘与HP/LT变质作用有关，并在两个单位中观察到，这表明可能并置之前或期间俯冲和相关的HP变质作用。始新世边缘及其相应的核的TE浓度和δ 18 O值之间的相似性是重结晶和沉淀作为锆石生长机制的指示。与此相反，渐新世锆石边缘似乎仅限于沿CB-CBU接触沿着的< 0.5 km厚的区域，其特征为石榴石分解，并显示出重稀土元素富集和较高的δ 18 O值相比，在边缘的核心，与一个模型，建议交代渗透的流体来自脱水的沉积岩在渐进俯冲和底侵弧后延伸之前。这种变质作用似乎是静态的性质，并不支持主要的晚新生代复活的接触作为一个伸展剪切带在弧后伸展。
Zircon U-Pb dating is a powerful and widely used geochronologic technique to constrain the timing and rates of magmatic and high and lower-grade metamorphic processes, as well as sediment provenance. Zircon trace element (TE) compositions also record magmatic and metamorphic processes during zircon growth. In this study, zircon laser ablation split-stream (LA-SS)-ICP-MS U-Pb and TE depth-profiling and novel two-dimensional zircon mapping techniques are used in combination with oxygen isotope analyses (secondary ion mass spectrometry, SIMS) to reconstruct the timing and metamorphic conditions recorded by recrystallization and growth of zircon rims, which provide valuable insight into the petro-tectonic evolution of high-pressure/low-temperature (HP/LT) metamorphic rocks formed in subduction zones. These techniques are applied to zircon grains from HP/LT metamorphic rocks of the Cycladic Blueschist Unit (CBU) and Cycladic Basement (CB) on Sikinos and Ios islands, Greece, which experienced metamorphism and deformation associated with subduction and subsequent back-arc exhumation. Zircon records multiple episodes of non-magmatic zircon rim growth at ~50 Ma and ~ 26 Ma. Eocene metamorphic rims are associated with HP/LT metamorphism and are observed in both units, suggesting likely juxtaposition prior to or during subduction and associated HP metamorphism. The similarity between TE concentrations and δ18O values of the Eocene rims and their corresponding cores is an indicator for re-crystallization and precipitation as a mechanism of zircon growth. In contrast, Oligocene zircon rims appear to be restricted to a < 0.5 km thick zone along the CB-CBU contact, characterized by garnet break-down, and show HREE enrichment and higher ẟ18O values in the rims compared to the cores, consistent with a model suggesting metasomatic infiltration of fluids derived from dehydrating sedimentary rocks during progressive subduction and underplating prior to back-arc extension. This metamorphism appears to be static in nature and does not support major late Cenozoic reactivation of the contact as an extensional shear zone during back-arc extension.