A wealth of geological and geochemical evidence indicates that plate tectonics was initiated in the Archean,though its style differing from that in the Phanerozoic,largely due to higher temperatures of convective mant...A wealth of geological and geochemical evidence indicates that plate tectonics was initiated in the Archean,though its style differing from that in the Phanerozoic,largely due to higher temperatures of convective mantle.Understanding the specific characteristics for the operation of ancient plate tectonics is critical for deciphering the formation and evolution of continental crust on early Earth,as well as the progressive development of Earth’s habitability.Through an in-depth analysis of geology and geochemistry for two events of late Archean crustal growth in the North China Craton,this study suggests that Archean plate tectonics would likely undergo the gradual evolution from immature to mature phases.The North China Craton experienced two major episodes of crustal growth at~2.9-2.7 and~2.6-2.5 Ga,respectively,represented by peaks in isotopic model ages of Archean felsic gneisses and widespread mafic rocks in greenstone belts.Although the preserved mafic rocks in greenstone belts generally exhibit arc-like trace element signatures,the early mafic crust formed at~2.9-2.7 Ga is limited in volume,with most of it having been reworked within several hundred million years.Tonalite-trondhjemite-granodiorite(TTG),produced by partial melting of such mafic crust,show zircon Hf-O isotope compositions indicative of sources consisting of seawater-hydrothermally altered oceanic crustal rocks with varying ages,suggesting that the early mafic crust was likely dominated by oceanic basalts.The medium-to low-pressure signatures of TTG rocks further imply that the oceanic crust was not subducted deeply to mantle depths,but instead was accreted to the margin of proto-continental nuclei due to aborted subduction.In contrast,the~2.6-2.5 Ga crustal growth event preserved a greater volume of mafic rocks.For these mafic rocks,the enrichment of incompatible elements correlates with water contents estimated from whole-rock major elements,indicating that their arc-like trace element features were associated with fluid metasomatism of the source region.Integrated with regional geological evidence from~2.5 Ga,such as ophiolites containing ultrahigh-pressure mineral inclusions and eclogite-facies remnants of oceanic crust,these observations suggest that modern-style plate subduction was likely in operation by the end of the Late Archean.Therefore,the modern plate tectonics regime did not emerge abruptly,but underwent a gradual evolution controlled by the thermal state of plate margins.It is this evolving tectonic regime that drove the significant crustal growth during the Archean.The two distinct episodes of crustal growth ultimately led to the formation of the North China Craton.展开更多
松嫩地块位于兴蒙造山带东部,其内及周边地区早前寒武纪的岩石记录报道极少。笔者对黑龙江省龙江县大泉子屯碎裂岩化花岗岩进行年代学和地球化学研究表明,该岩石的锆石LA ICP MS U-Pb年龄为(2 579±15)Ma(n=20,MSWD=0.49),代表了花...松嫩地块位于兴蒙造山带东部,其内及周边地区早前寒武纪的岩石记录报道极少。笔者对黑龙江省龙江县大泉子屯碎裂岩化花岗岩进行年代学和地球化学研究表明,该岩石的锆石LA ICP MS U-Pb年龄为(2 579±15)Ma(n=20,MSWD=0.49),代表了花岗岩的结晶年龄,为新太古代晚期,地球化学特征显示该花岗岩为富钠花岗岩,具TTG中奥长花岗岩特征。本套新太古代花岗岩为松嫩地块及其周边地区的首次报道,证实了龙江地区存在早前寒武纪地质记录,为本区新太古代TTG岩石组合的寻找提供依据,也说明松嫩地块及其周边地区不仅存在古元古代岩浆活动记录、也存在新太古代岩浆活动记录,同时为松嫩地块及其周边大量的新太古代岩浆成因碎屑锆石的来源研究提供依据,为兴蒙造山带中残留的早期地质记录研究及兴蒙造山带的构造格局划分提供新材料。展开更多
基金supported by the National Natural Science Foundation of China(Grant No.42472258)the Shandong Provincial Natural Science Foundation for Excellent Young Scholars(Grant No.ZR2023YQ036).
文摘A wealth of geological and geochemical evidence indicates that plate tectonics was initiated in the Archean,though its style differing from that in the Phanerozoic,largely due to higher temperatures of convective mantle.Understanding the specific characteristics for the operation of ancient plate tectonics is critical for deciphering the formation and evolution of continental crust on early Earth,as well as the progressive development of Earth’s habitability.Through an in-depth analysis of geology and geochemistry for two events of late Archean crustal growth in the North China Craton,this study suggests that Archean plate tectonics would likely undergo the gradual evolution from immature to mature phases.The North China Craton experienced two major episodes of crustal growth at~2.9-2.7 and~2.6-2.5 Ga,respectively,represented by peaks in isotopic model ages of Archean felsic gneisses and widespread mafic rocks in greenstone belts.Although the preserved mafic rocks in greenstone belts generally exhibit arc-like trace element signatures,the early mafic crust formed at~2.9-2.7 Ga is limited in volume,with most of it having been reworked within several hundred million years.Tonalite-trondhjemite-granodiorite(TTG),produced by partial melting of such mafic crust,show zircon Hf-O isotope compositions indicative of sources consisting of seawater-hydrothermally altered oceanic crustal rocks with varying ages,suggesting that the early mafic crust was likely dominated by oceanic basalts.The medium-to low-pressure signatures of TTG rocks further imply that the oceanic crust was not subducted deeply to mantle depths,but instead was accreted to the margin of proto-continental nuclei due to aborted subduction.In contrast,the~2.6-2.5 Ga crustal growth event preserved a greater volume of mafic rocks.For these mafic rocks,the enrichment of incompatible elements correlates with water contents estimated from whole-rock major elements,indicating that their arc-like trace element features were associated with fluid metasomatism of the source region.Integrated with regional geological evidence from~2.5 Ga,such as ophiolites containing ultrahigh-pressure mineral inclusions and eclogite-facies remnants of oceanic crust,these observations suggest that modern-style plate subduction was likely in operation by the end of the Late Archean.Therefore,the modern plate tectonics regime did not emerge abruptly,but underwent a gradual evolution controlled by the thermal state of plate margins.It is this evolving tectonic regime that drove the significant crustal growth during the Archean.The two distinct episodes of crustal growth ultimately led to the formation of the North China Craton.
文摘松嫩地块位于兴蒙造山带东部,其内及周边地区早前寒武纪的岩石记录报道极少。笔者对黑龙江省龙江县大泉子屯碎裂岩化花岗岩进行年代学和地球化学研究表明,该岩石的锆石LA ICP MS U-Pb年龄为(2 579±15)Ma(n=20,MSWD=0.49),代表了花岗岩的结晶年龄,为新太古代晚期,地球化学特征显示该花岗岩为富钠花岗岩,具TTG中奥长花岗岩特征。本套新太古代花岗岩为松嫩地块及其周边地区的首次报道,证实了龙江地区存在早前寒武纪地质记录,为本区新太古代TTG岩石组合的寻找提供依据,也说明松嫩地块及其周边地区不仅存在古元古代岩浆活动记录、也存在新太古代岩浆活动记录,同时为松嫩地块及其周边大量的新太古代岩浆成因碎屑锆石的来源研究提供依据,为兴蒙造山带中残留的早期地质记录研究及兴蒙造山带的构造格局划分提供新材料。
