Ultrahigh temperature metamorphism recorded in the Lüliang Complex, Trans-North China Orogen: P–T–t evolution and heating mechanism
Ultrahigh temperature metamorphism recorded in the Lüliang Complex, Trans-North China Orogen: P–T–t evolution and heating mechanism
复制标题
DOI：
10.1016/j.precamres.2022.106900
复制
发表时间：
2022-12
影响因子：
3.8
通讯作者：
Cheng Lu;J. Qian;C. Yin;Peng Gao;Minjie Guo;Wanfeng Zhang
中科院分区：
文献类型：
--
作者：
Cheng Lu;J. Qian;C. Yin;Peng Gao;Minjie Guo;Wanfeng Zhang
识别来自热造山带的超高温（UHT）变质作用并建立其压力-温度-时间（P-T-t）路径将为构造演化和造成极端条件的热源（地幔/基性岩浆vs地壳放射性元素）提供重要见解。本文对具有代表性的古元古代热碰撞造山带——跨华北造山带l<s:1>梁杂岩的基性麻粒岩、泥质麻粒岩进行了岩石学、矿物化学、相平衡模拟、地温气压计计算、年代学和热源研究。岩石记录顺时针的p -p路径，包括麻粒岩相峰期和峰后逆行期。基性麻粒岩中的石榴石+辉石+高钛角闪石组合和泥质麻粒岩中的石榴石+长石+硅线石组合约束了8.2 ~ 10 kbar和880 ~ 959℃的热峰，表明UHT条件。锆石和独居石U-Pb测年、角闪石40ar /39Ar测年和锆石ti -in-锆石温度计算表明，岩石可能经历了1.92 ~ 1.80 Ga的缓慢逆行变质作用，冷却速率为2.0 ~ 2.5℃/Ma。新发现的UHT变质作用，结合以往的地质资料，证实了TNCO在1.97 - 1.80 Ga之间的长期构造-热演化。经计算，增厚地壳中放射性元素衰变产生的热流为37 ~ 77 mW/m2（平均为56 mW/m2），足以达到UHT条件。因此，我们认为放射性加热可能是长寿命热造山带如TNCO中UHT变质的重要加热机制。
Identifying ultrahigh temperature (UHT) metamorphism from hot orogens and establishing its pressure–temperature–time (P–T–t) path will provide notable insights into tectonic evolution and heat source (mantle/mafic magma vs crustal radioactive elements) responsible for the extreme conditions. We report here a combined investigation of petrography, mineral chemistry, phase equilibria modelling, geothermobarometer calculation, geochronology and heat source for mafic and pelitic granulites from the Lüliang Complex, Trans-North China Orogen (TNCO), a representative Paleoproterozoic hot collisional orogen. The rocks record clockwiseP–Tpaths, including granulite-facies peak and post-peak retrograde stages. Garnet + pyroxene + high-Ti hornblende-bearing assemblage in the mafic granulite and garnet + feldspar + sillimanite-bearing assemblage in the pelitic granulite constrain the thermal peaks at 8.2–10 kbar and 880–959 °C, suggesting UHT conditions. Zircon and monazite U–Pb dating, hornblende40Ar/39Ar dating and Ti-in-zircon thermometer calculation indicate that the rocks may have experienced sluggish retrograde metamorphism from 1.92 to 1.80 Ga, with a cooling rate of 2.0–2.5 °C/Ma. The newly discovered UHT metamorphism, combined with previous geological data, validates a long-lived tectono-thermal evolution from 1.97 to 1.80 Ga in the TNCO. The calculated heat flow produced by the decay of radioactive elements in the thickened crust is 37–77 mW/m2(with an average of 56 mW/m2), which is high enough to achieve UHT conditions. Therefore, we suggest that radioactive heating can be an important heating mechanism for UHT metamorphism in a long-lived hot orogen like the TNCO.