Geochronology and Zr-in-rutile thermometry of high-pressure/low temperature metamorphic rocks from the Bantimala complex, SW Sulawesi, Indonesia
Geochronology and Zr-in-rutile thermometry of high-pressure/low temperature metamorphic rocks from the Bantimala complex, SW Sulawesi, Indonesia
复制标题
DOI：
10.1016/j.lithos.2018.11.020
复制
发表时间：
2019
期刊：
影响因子：
3.5
通讯作者：
Mischa Böhnke;M. Bröcker;A. Maulana;R. Klemd;J. Berndt;H. Baier
中科院分区：
文献类型：
--
作者：
Mischa Böhnke;M. Bröcker;A. Maulana;R. Klemd;J. Berndt;H. Baier
印度尼西亚中部地区榴辉岩相和蓝片岩相变质作用的时间框架尚不明确。相对于其地理范围，同位素年龄数据的区域覆盖范围不足以明确解释印度尼西亚中部增生碰撞杂岩的地质演化。这项研究报告了苏拉威西西南部班蒂马拉杂岩的高压/低温（HP/LT）岩石的新地质年代学限制，进一步证实了白垩纪 HP/LT 变质作用对更大区域的重要性。榴辉岩和富含蓝闪石岩石的多点 Rb-Sr 矿物等时线显示了狭窄范围的白云母年龄 (130-120Ma)，解释为后期峰值 HP 条件，比之前发布的 K-Ar 年龄谱 (137-113Ma) 更小、更精确。与 K-Ar 年龄的密切相似性表明，这些分析仅受到外来 Ar 成分的轻微污染（如果有的话），这并没有显着损害现有数据集的地质相关性。这项研究的一个重要结果是苏拉威西岛西南部（130-120Ma）和爪哇（约118Ma）高压/低温岩石之间区域年龄差异的新证据。不能排除不同俯冲带的存在，但这些地点之间的 P-T 和年龄差异可以与表明同一俯冲复合体中形成的模型相一致。锆石在所研究的 HP/LT 岩石组中非常罕见，但两块富含蓝绿石的岩石适合进行 U-Pb 锆石测年，并表明晚三叠世 - 早侏罗世原岩年龄（约 205-185Ma）。退行榴辉岩的锆石群记录了更复杂的历史，包括火成岩结晶、变质重结晶或生长、继承和不同程度的铅损失的证据。变质锆石边缘产生的 U-Pb 年龄大多在 135-110Ma 范围内，大致证实了由 K-Ar 和 Rb-Sr 白云母地质年代学确定的变质年龄。比原岩年龄显着老的锆石（2.55-1.4Ga 和 400-260Ma）被解释为代表来自俯冲沉积物的碎屑颗粒，这些碎屑颗粒已融入直接源自受污染地幔源的镁铁质熔体中。对于任何玄武质或辉长岩来源的榴辉岩和/或蓝片岩相岩石，尚未描述可能在地幔熔体形成过程中包含的大陆衍生碎屑锆石的存在。
The timeframe of eclogite- and blueschist-facies metamophism in the central Indonesian region is poorly defined. Relative to its geographic extent, the regional coverage of isotopic age data is insufficient for an unambiguous interpretation of the geologic evolution of the Central Indonesian Accretionary Collision Complex. This study reports new geochronological constraints for high-pressure/low-temperature (HP/LT) rocks from the Bantimala Complex, SW Sulawesi, which further substantiate the importance of Cretaceous HP/LT metamorphism for the larger region. Multipoint Rb–Sr mineral isochrons of eclogites and glaucophane-rich rocks display a narrow range of white mica ages (130–120 Ma), interpreted to postdate peak-HP conditions, which is considerably smaller and more precise than the previously published K–Ar age spectrum (137–113 Ma). The close similarity with K–Ar ages suggests that these analyses were only slightly contaminated, if at all, with an extraneous Ar component, which did not significantly compromise the geological relevance of the existing dataset. An important result of this study is the emerging evidence for regional age differences between HP/LT rocks from SW Sulawesi (130–120 Ma) and Java (ca. 118 Ma). The existence of different subduction zones cannot be excluded butP–Tand age differences between these occurrences can be reconciled with a model suggesting formation in the same subduction complex. Zircon is very rare in the studied HP/LT rock suite, but two glaucophane-rich rocks were suitable for U–Pb zircon dating and indicate Late Triassic–Early Jurassic protolith ages (ca. 205–185 Ma). The zircon population of a retrogressed eclogite records a more complex history including evidence for igneous crystallization, metamorphic recrystallization or growth, inheritance and variable degrees of Pb-loss. Metamorphic zircon rims mostly yielded U–Pb ages in the 135–110 Ma range that broadly confirm metamorphic ages determined by K–Ar and Rb–Sr white mica geochronology. Zircons that are significantly older (2.55–1.4 Ga and 400–260 Ma) than the protolith age are interpreted to represent detrital grains from subducted sediments that had been incorporated in mafic melts directly derived from a contaminated mantle source. The presence of continentally-derived detrital zircons that have presumably been included during melt formation in the mantle have not yet been described for any eclogite- and/or blueschist-facies rock of basaltic or gabbroic parentage.