Age constraints on high-pressure/low-temperature metamorphism and sedimentation in the Luk Ulo Complex (Java, Indonesia)
Age constraints on high-pressure/low-temperature metamorphism and sedimentation in the Luk Ulo Complex (Java, Indonesia)
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Luk Ulo 杂岩体（印度尼西亚爪哇）高压/低温变质作用和沉积作用的年龄限制
DOI：
10.1016/j.lithos.2018.11.019
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发表时间：
2019
期刊：
影响因子：
3.5
通讯作者：
Baier H
中科院分区：
文献类型：
--
作者：
Hoffmann J;Bröcker M;Setiawan NI;Klemd R;Berndt J;Maulana A;Baier H
前新生代蓝片岩相和榴辉岩相岩石广泛分布于印度尼西亚中部地区，可能代表同一俯冲带的横向等价物。高压/低温（HP/LT）变质作用被认为发生在早白垩世，然而，这仅限于K-Ar年龄。这项研究是一个系统的重新调查的区域地质年代学记录的各种变质岩从这个带，并侧重于在中爪哇的卢克乌罗复杂。其中一个榴辉岩、两个绿帘蓝闪片岩和一个绿帘角闪岩的铷-锶多点等时线年龄为119-117 Ma（± 0.6-0.8 Ma）。这些年龄是类似于以前报道的K-Ar的结果，表明现有的数据并没有显着受到外来的Ar污染。相对较低的峰值变质温度（约。400 °C）的温度变化表明Rb-Sr同位素体系在冷却过程中没有受到扩散损失的显著影响。Rb-Sr年龄最有可能制约高压变质作用期间云母生长或重结晶的时间。高压和低压岩石的年龄匹配归因于遗传，但最初在俯冲复合体的不同深度同时形成的岩石的混合还不能完全排除。榴辉岩和蓝片岩相岩石的铷-锶白色云母年龄从中爪哇比西苏拉威西构造省（130-120马），揭示了一个以前未知的年龄差异，已被隐藏的精度较差的K-Ar数据集。在这一点上，目前还不清楚这种年龄差异是否与同一俯冲带或不同俯冲带内的作用有关。来自卢克乌罗杂岩的碎屑变质沉积岩的锆石人口主要是由一个突出的侏罗纪到石炭纪人口（约1000年）。320-180 Ma）与一个明显的二叠纪-三叠纪高峰（约。270-200 Ma）。另一个不太明显的古生代年龄信号出现在450-380 Ma。元古代和太古代的锆石颗粒非常罕见。至少有一些数据点在较低的年龄谱（约135 -117马）最有可能是有关的原地变质过程。最年轻的锆石颗粒明确的碎屑起源出现在约。160 Ma，为晚侏罗世最大沉积年龄。巴鲁杂岩（西苏拉威西）的其他碎屑锆石数据进一步证实了以前的研究结果，记录了中生代（三叠纪）、古生代（二叠纪、石炭纪、泥盆纪至奥陶纪）、中-古元古代亚群和罕见的太古代锆石的复杂年龄谱。最年轻的锆石表明最大沉积年龄约为2000年。255-250 Ma。新的和现有的U-Pb锆石数据表明，前变质盆地的历史记录在卢克Ulo和Barru复杂的连接到不同的源地形和沉积体系。
Pre-Cenozoic blueschist- and eclogite-facies rocks occur widely scattered in the central Indonesian region, possibly representing lateral equivalents of the same subduction zone. High-pressure/low-temperature (HP/LT) metamorphism is thought to have occurred during the Early Cretaceous, which however is only constrained by K–Ar ages. This study is part of a systematic re-investigation of the regional geochronological record of various metamorphic rocks from this belt and focuses on the Luk Ulo Complex in central Java. Rubidium–Sr multipoint isochrons of one eclogite, two epidote-glaucophane schists and one epidote amphibolite yielded Early Cretaceous (Aptian) ages of 119–117 Ma (± 0.6–0.8 Ma). These ages are similar to previously reported K–Ar results, indicating that the existing data had not significantly been compromised by extraneous Ar contamination. Relatively low peak metamorphic temperatures (ca. 400 °C) during the HP/LT stage suggest that the Rb–Sr isotopic system was not significantly affected by diffusive loss during cooling. The Rb–Sr ages most likely constrain the time of mica growth or recrystallization during high-pressure metamorphism. The matching ages of high-pressure and lower pressure rocks are attributed to inheritance, but mixing of rocks that originally had formed at the same time at different depths of the subduction complex cannot completely be ruled out yet. Rubidium–Sr white mica ages of eclogite- and blueschist-facies rocks from central Java are younger than those of similar rocks from the Western Sulawesi tectonic province (130–120 Ma), revealing a previously unknown age difference that had been hidden by the poorer precision of the K–Ar dataset. At this point, it remains unclear whether this age difference is related to processes operating within the same or in different subduction zones.The zircon populations of clastic metasedimentary rocks from the Luk Ulo Complex are dominated by a prominent Jurassic to Carboniferous population (ca. 320–180 Ma) with a distinct Permo-Triassic peak (ca. 270–200 Ma). Another less pronounced Paleozoic age signal shows up at 450–380 Ma. Proterozoic and Archean zircon grains are very rare. At least some data points at the lower end of the age spectrum (ca.135–117 Ma) most likely are related to in-situ metamorphic processes. The youngest zircon grains of unambiguous detrital origin show up at ca. 160 Ma, indicating a Late Jurassic maximum depositional age. Additional detrital zircon data for the Barru Complex (Western Sulawesi) further substantiate previous findings documenting a complex age spectrum with contributions of Mesozoic (Triassic), Paleozoic (Permian, Carboniferous, Devonian to Ordovician), Meso- to Paleoproterozoic subpopulations and rare Archean zircons. The youngest zircons indicate a maximum depositional age of ca. 255–250 Ma. New and existing U–Pb zircon data indicate that the pre-metamorphic basin histories recorded in the Luk Ulo and Barru complexes are linked to different source terrains and depositional systems.
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