Precambrian Research ( IF 3.8 ) Pub Date : 2021-03-04 , DOI: 10.1016/j.precamres.2021.106123 Hao Liu , Xu-Ping Li , Fan-Mei Kong , Hans-Peter Schertl , Shao-Ting Ma , Xiao-Man Wang
Following the first petrological studies on UHT metamorphic pelitic granulite of the Tuguiwula area, Jining complex, North China Craton, considerable work has been done in the past decades that revealed an anti-clockwise P-T path, reaching a maximum pressure range at ca.10 kbar. In this study, we re-investigated pelitic granulite from this locality and determined four distinct metamorphic stages, Pmax (M2), Tmax (M3), cooling (M4), and decompression (M5), which document a clockwise P-T trajectory, providing evidence for an early high-pressure metamorphic scenario at pressures >11.8 kbar. The Pmax (M2) conditions were calculated using garnet domains with highest XCa (grt) isopleths, which contain inclusions of kyanite. The entire mineral assemblage in equilibrium is Grt + Ky + Qz + Rt + Kfs + liq ± Ilm, suggesting minimum pressures of 11.8 kbar. The Tmax metamorphism (M3) is characterized by the assemblage Grt + Qz + Pl + Ilm + Kfs + Sil + liq. Geothermobarometrical studies which include two-feldspar geothermometry and Zr-in-rutile thermometry yields a P-T range of 990 °C−995 °C and 9–10 kbar, indicating an ultra-high temperature (UHT) metamorphic overprint. The subsequent retrograde metamorphic stages M4 and M5 are characterized by the formation of Bt + Sil + Qz + symplectites and cordierite replacing garnet rims, suggesting P-T conditions of 840 °C−960 °C/8.5–9.5 kbar and 800 °C−850 °C/5.5–6.8 kbar, respectively. SHRIMP U-Pb age dating provided a weighted mean 207Pb/206Pb age of 1911.6 ± 4.5 Ma that represents the timing of the UHT metamorphic stage. The current study on pelitic granulite documents two novel results which have a significant impact on the geotectonic evolution: (1) a clockwise P-T path instead of an anticlockwise one was derived, and (2) P-T estimates are much higher than those reported from previous studies of both, pressure and temperature. The available P-T data of the pre-HP metamorphic stage together with the clockwise P-T trajectory, UHT-, cooling- and decompression-stages of the current study reflect a possible collision or subduction origin.
中文翻译:
早期的高压历史是在华北克拉通的昆多岩带的Tuguiwula地区形成了胶粒状的超高温花岗石。
在对华北克拉通济宁地区图吉乌拉地区的超高温变质珍珠岩粒岩进行了首次岩石学研究之后,在过去的几十年中已经进行了大量工作,揭示了逆时针PT路径,最大压力范围约为10 kbar 。在这项研究中,我们从该位置重新调查了黄铁质花岗岩,并确定了四个不同的变质阶段:P max(M2),T max(M3),冷却(M4)和减压(M5),它们记录了顺时针PT轨迹,为压力> 11.8 kbar的早期高压变质情况提供了证据。使用具有最高X Ca的石榴石域来计算P max(M2)条件(grt)等值线,其中包含蓝晶石的内含物。处于平衡状态的整个矿物组合为Grt + Ky + Qz + Rt + Kfs + liq±Ilm,表明最小压力为11.8 kbar。T max变质(M3)的特征是组合Grt + Qz + Pl + Ilm + Kfs + Sil + liq。地热大气法研究包括两长石地热法和Zr-金红石温度计,产生的PT范围为990°C-995°C和9-10 kbar,表明超高温(UHT)变质叠印。随后的逆行变质阶段M4和M5的特征是形成Bt + Sil + Qz +代晶石和堇青石代替石榴石边缘,表明PT温度分别为840°C-960°C / 8.5-9.5 kbar和800°C-850°C / 5.5-6.8 kbar。SHRIMP U-Pb年龄测年提供了1911.6±4.5 Ma的加权平均207 Pb / 206 Pb年龄,它代表了UHT变质阶段的时间。当前关于胶质花岗岩的研究记录了两个新的结果,这些结果对大地构造演化有重大影响:(1)顺时针PT路径而不是逆时针路径;(2)PT估算值远高于先前研究报告的估算值压力和温度的关系。HP前变质阶段的可用PT数据以及顺时针PT 当前研究的轨迹,UHT,冷却和减压阶段反映了可能的碰撞或俯冲起源。