The lack of a comprehensive whole-rock geochemical and mineralogical dataset for the Archean granitoids of the Aravalli-Banded Gneissic Complex(BGC),northwest India,results in significant challenges for their correct ...The lack of a comprehensive whole-rock geochemical and mineralogical dataset for the Archean granitoids of the Aravalli-Banded Gneissic Complex(BGC),northwest India,results in significant challenges for their correct characterization and assessment of their antiquity.The new field,mineralogical and geochemical data classify the Jaisamand granitoids into sanukitoids,TTGs,and transitional TTGs,which are most likely coeval in nature.The obtained results,in conjuncture with the previously published geochemical and geochronological results of the Aravalli-BGC granitoids,unveil the Neoarchean affinity of the Jaisamand pluton.The TTGs were generated by the melting of a subducting slab(metabasite)at shallow(high-HREE-Y TTGs)to moderate depths(medium-HREE-Y TTGs)above the garnet-in line but still within the plagioclase stability field,with garnet-poor residue.The ascending TTG melts were transformed into sanukitoids through differential interaction with the overlying mantle wedge peridotite.The TTG melts,generated at different pressures,interacted with older TTGs at lower and middle crustal levels to form the transitional TTGs.The coexistence of high-HREE-Y and medium-HREE-Y TTGs and sanukitoids suggests a subduction-related setting for the Jaisamand granitoids.The heat required for simultaneous melting at shallow and deeper depths during the Neoarchean was provided by the upwelling asthenosphere due to slab break-off.The study also revealed the occurrence of altered granitoids in the Jaisamand pluton,showing evidence of albitization and silicification.These rocks do not represent the pristine mineralogy and should be carefully examined to avoid misleading interpretations,particularly for the Archean granitoids.展开更多
华北克拉通具有3.8Ga以上的演化历史,TTG是其地质记录的最重要载体。华北克拉通太古宙(特别是中太古代以前)地质演化在很大程度上与TTG岩石密切相关。在华北克拉通,始太古代(3.6~4.0Ga)TTG岩石仅在鞍本地区被发现,但冀东地区已在多种变...华北克拉通具有3.8Ga以上的演化历史,TTG是其地质记录的最重要载体。华北克拉通太古宙(特别是中太古代以前)地质演化在很大程度上与TTG岩石密切相关。在华北克拉通,始太古代(3.6~4.0Ga)TTG岩石仅在鞍本地区被发现,但冀东地区已在多种变质碎屑沉积岩中发现大量3.6~3.88Ga碎屑锆石;古太古代(3.2~3.6Ga)TTG岩石在鞍本、冀东、信阳地区被识别出来;中太古代(2.8~3.2Ga)TTG岩石在鞍本、冀东、胶东、鲁山等地存在;可把新太古代(2.5~2.8Ga)进一步划分为早期和晚期两个阶段:新太古代早期(2.6~2.8Ga)TTG岩石已在10余个地区被发现,新太古代晚期(2.5~2.6Ga)TTG岩石几乎在每一个太古宙基底岩石出露区都存在。野外地质、锆石定年、元素地球化学和Nd-Hf同位素组成研究表明,中太古代以前TTG岩石局部存在,主要分布于Wan et al.(2015)所划分的三个古陆块中;新太古代TTG岩石广泛分布,是陆壳增生最重要时期岩浆作用的产物。TTG岩石类型随时代变化,3.1~3.8Ga和2.7~2.9Ga TTG岩石分别主要为奥长花岗岩和英云闪长岩;2.5~2.6Ga期间花岗闪长岩大规模出现,并有壳源花岗岩广泛分布,表明这时陆壳已有相当的成熟度。奥长花岗岩轻重稀土分异程度从弱到强的时间出现在~3.3Ga;2.5~3.3Ga的TTG岩石轻重稀土分异程度变化很大,表明其形成条件存在很大差异。TTG岩石主要为新生地壳,但也有相当部分为壳内再循环产物或形成过程中受到陆壳物质影响。华北克拉通中太古代以前的主要构造机制是板底垫托或地幔翻转作用,新太古代晚期板块构造体制可能已起作用。展开更多
基金the Ministry of Earth Sciences,New Delhi(MoES/P.O/(Geo)/100(2)/2017).
文摘The lack of a comprehensive whole-rock geochemical and mineralogical dataset for the Archean granitoids of the Aravalli-Banded Gneissic Complex(BGC),northwest India,results in significant challenges for their correct characterization and assessment of their antiquity.The new field,mineralogical and geochemical data classify the Jaisamand granitoids into sanukitoids,TTGs,and transitional TTGs,which are most likely coeval in nature.The obtained results,in conjuncture with the previously published geochemical and geochronological results of the Aravalli-BGC granitoids,unveil the Neoarchean affinity of the Jaisamand pluton.The TTGs were generated by the melting of a subducting slab(metabasite)at shallow(high-HREE-Y TTGs)to moderate depths(medium-HREE-Y TTGs)above the garnet-in line but still within the plagioclase stability field,with garnet-poor residue.The ascending TTG melts were transformed into sanukitoids through differential interaction with the overlying mantle wedge peridotite.The TTG melts,generated at different pressures,interacted with older TTGs at lower and middle crustal levels to form the transitional TTGs.The coexistence of high-HREE-Y and medium-HREE-Y TTGs and sanukitoids suggests a subduction-related setting for the Jaisamand granitoids.The heat required for simultaneous melting at shallow and deeper depths during the Neoarchean was provided by the upwelling asthenosphere due to slab break-off.The study also revealed the occurrence of altered granitoids in the Jaisamand pluton,showing evidence of albitization and silicification.These rocks do not represent the pristine mineralogy and should be carefully examined to avoid misleading interpretations,particularly for the Archean granitoids.
文摘华北克拉通具有3.8Ga以上的演化历史,TTG是其地质记录的最重要载体。华北克拉通太古宙(特别是中太古代以前)地质演化在很大程度上与TTG岩石密切相关。在华北克拉通,始太古代(3.6~4.0Ga)TTG岩石仅在鞍本地区被发现,但冀东地区已在多种变质碎屑沉积岩中发现大量3.6~3.88Ga碎屑锆石;古太古代(3.2~3.6Ga)TTG岩石在鞍本、冀东、信阳地区被识别出来;中太古代(2.8~3.2Ga)TTG岩石在鞍本、冀东、胶东、鲁山等地存在;可把新太古代(2.5~2.8Ga)进一步划分为早期和晚期两个阶段:新太古代早期(2.6~2.8Ga)TTG岩石已在10余个地区被发现,新太古代晚期(2.5~2.6Ga)TTG岩石几乎在每一个太古宙基底岩石出露区都存在。野外地质、锆石定年、元素地球化学和Nd-Hf同位素组成研究表明,中太古代以前TTG岩石局部存在,主要分布于Wan et al.(2015)所划分的三个古陆块中;新太古代TTG岩石广泛分布,是陆壳增生最重要时期岩浆作用的产物。TTG岩石类型随时代变化,3.1~3.8Ga和2.7~2.9Ga TTG岩石分别主要为奥长花岗岩和英云闪长岩;2.5~2.6Ga期间花岗闪长岩大规模出现,并有壳源花岗岩广泛分布,表明这时陆壳已有相当的成熟度。奥长花岗岩轻重稀土分异程度从弱到强的时间出现在~3.3Ga;2.5~3.3Ga的TTG岩石轻重稀土分异程度变化很大,表明其形成条件存在很大差异。TTG岩石主要为新生地壳,但也有相当部分为壳内再循环产物或形成过程中受到陆壳物质影响。华北克拉通中太古代以前的主要构造机制是板底垫托或地幔翻转作用,新太古代晚期板块构造体制可能已起作用。
