The Guéra Massif, in South-Central Chad hosts granitic rocks that were emplaced during distinct intervals (595–590; ∼570; ∼560 Ma) of the Late Ediacaran Central African Orogenic Belt. To the northwest of the Guéra Massif, younger post-collisional granites (554–545 Ma) are found near Lake Fitri. The older (≥590 Ma) rocks have geochemical characteristics of collisional granites whereas the younger (≤570 Ma) rocks are similar to post-collisional granites. Biotite and amphibole were analyzed to constrain the magmatic conditions of the granites. The biotite from the collisional granites tends to have higher Al and Ti and lower Fe# (Fe#_average ≈ 0.67) than the post-collisional granites (Fe#_average ≈ 0.88). The average crystallization temperatures range from 696 ± 37 to 612 ± 8°C, with the average pressure of crystallization from 0.25 ± 0.09 to 0.13 ± 0.02 GPa, and redox conditions between the nickel-nickel oxide (NNO) and quartz-fayalite-magnetite (QFM) buffers. The biotite crystallization temperatures of the post-collisional rocks are generally lower than the collisional rocks (570 Ma = 630 ± 26 to 619 ± 30°C, 560 Ma = 626 ± 20 to 607 ± 4°C, 550 Ma = 639 ± 18 to 612 ± 13°C), but the crystallization pressures are similar (0.27 ± 0.05 to 0.14 ± 0.04 GPa). The redox conditions transition from the QFM buffer to the wüstite-magnetite (WM) buffer. In contrast, the biotite from the Lake Fitri post-collisional granites crystallized at higher pressure (0.39 ± 0.08 to 0.35 ± 0.03 GPa) but similar redox conditions. The amphiboles in the younger (∼590 Ma) collisional granites and the post-collisional granites yielded crystallization pressure estimates that are generally higher (∼0.6 to 0.1 GPa) than the biotite estimates but there is overlap. The difference in pressure may be due to the timing of crystallization and/or crystal redistribution. Overall, there appears to be a secular change from high to low temperature and pressure whereas the redox conditions appear to be spatially related. The biotite crystallization pressure of the Lake Fitri granites suggests they were likely emplaced into a different domain/terrane of the Saharan Metacraton than the Guéra Massif.

乍得中南部的瓜拉地块（GuéraMassif）拥有花岗岩岩石，这些岩石是在中埃迪卡拉南部中非造山带的不同间隔（595-590；〜570；〜560 Ma）内沉积的。在瓜拉地块的西北部，在菲特里湖附近发现了较年轻的碰撞后花岗岩（554–545 Ma）。年龄较大的岩石（≥590Ma）具有碰撞花岗岩的地球化学特征，而年龄较小的岩石（≤570Ma）与碰撞后花岗岩相似。对黑云母和闪石进行了分析，以约束花岗岩的岩浆条件。与碰撞后的花岗岩（_平均Fe＃）相比，碰撞花岗岩中的黑云母倾向于具有更高的Al和Ti和更低的Fe＃（_平均Fe＃≈0.67）。≈0.88）。平均结晶温度范围为696±37至612±8°C，平均结晶压力为0.25±0.09至0.13±0.02 GPa，镍-氧化镍（NNO）与石英-铁橄榄石-磁铁矿之间的氧化还原条件（QFM）缓冲区。碰撞后岩石的黑云母结晶温度通常低于碰撞岩石（570 Ma = 630±26至619±30°C，560 Ma = 626±20至607±4°C，550 Ma = 639±18至612±13°C），但结晶压力相似（0.27±0.05至0.14±0.04 GPa）。氧化还原条件从QFM缓冲区过渡到wustite-磁铁矿（WM）缓冲区。相反，来自菲特里湖碰撞后花岗岩的黑云母在较高压力（0.39±0.08至0.35±0.03 GPa）下结晶，但氧化还原条件相似。较年轻（约590 Ma）碰撞花岗岩和碰撞后花岗岩中的闪石产生的结晶压力估算值通常比黑云母估算值高（约0.6至0.1 GPa），但存在重叠。压力差可能是由于结晶的时间和/或晶体的重新分布。总体而言，从高温到低压，似乎出现了长期变化，而氧化还原条件似乎与空间相关。菲特里湖花岗岩的黑云母结晶压力表明，它们可能被放置在撒哈拉大克拉通的另一区域/地域中，而没有进入瓜拉断层块。压力差可能是由于结晶的时间和/或晶体的重新分布。总体而言，从高温到低压，似乎出现了长期变化，而氧化还原条件似乎与空间相关。菲特里湖花岗岩的黑云母结晶压力表明，它们可能被放置在撒哈拉大克拉通的另一区域/地域中，而没有进入瓜拉断层块。压力差可能是由于结晶的时间和/或晶体的重新分布。总体而言，从高温到低压，似乎出现了长期变化，而氧化还原条件似乎与空间相关。菲特里湖花岗岩的黑云母结晶压力表明，它们可能被放置在撒哈拉大克拉通的不同区域/地形中，而不是盖拉地块。