TY - JOUR
T1 - Decoding the onset of ca. 3.8 Ga continental nuclei in Anshan, North China
T2 - A review integrated with 1:10,000 geological mapping, zircon U–Pb dating, and Si–O–Nd–Hf–W isotopes
AU - Lei, Kai
AU - Wang, Ya Fei
AU - Zhang, Qing
AU - Zhang, Jia Hui
AU - Jin, Wei
AU - Zheng, Pei Xi
AU - Li, Xian Hua
N1 - Publisher Copyright:
© 2023
PY - 2023/12
Y1 - 2023/12
N2 - The Archean Anshan Complex (AAC) in northeastern China is one of the best-preserved ca. 3.8 Ga outcrops worldwide, which are key to understanding the evolution of the early Earth. In this study, we carried out 1:10,000 geological mapping and integrated this with published whole-rock geochemical, zircon U–Pb age, and O–Nd–Hf–W isotopic data, along with new zircon U–Pb and Si–O isotopic data. We used these data to establish a geochronological framework for the AAC and investigate its origins and tectonic setting, and differentiation of the early Earth. Our new mapping shows that the AAC can be divided into several rock associations based on the zircon U–Pb ages and lithologies: (1) Eoarchean (ca. 3.8 Ga) trondhjemitic gneiss and meta-quartz diorite; (2) Paleoarchean (ca. 3.3 Ga) gneiss and migmatite; (3) Mesoarchean (ca. 3.1 Ga) granitic gneiss; (4) Mesoarchean (ca. 3.0 Ga) monzogranite; (5) Neoarchean (ca. 2.5 Ga) K-rich granite; and (6) Archean supracrustal rock. The ca. 3.8 Ga rocks are exclusively exposed as enclaves within the ca. 3.3 Ga gneiss and migmatite unit at Dongshan, Guodishan, Shengousi, and Hujiamiao. Some ca. 3.8 Ga components at Baijiafen and Dongshan cannot be visually identified due to strong deformation and migmatization. The ca. 3.8 Ga Anshan trondhjemitic gneiss and meta-quartz diorite have coupled heavy Si–O isotopic compositions, indicative of the involvement of supracrustal silicified materials in their sources. (La/Yb)N ratios vary widely in the different ca. 3.8 Ga rock types (i.e., 9–53 for the trondhjemitic gneisses and 3–8 for the meta-quartz diorites), indicating they formed at different pressures. We suggest the ca. 3.8 Ga trondhjemitic gneisses were derived by partial melting of a subducted slab, and the 3.8 Ga meta-quartz diorites might have been derived by partial melting of a mantle wedge that had been metasomatized by fluids released from the subducted slab. Highly variable εNd(t) (−4.5 to +10.1) and εHf(t) (−3.8 to +6.1) values of the ca. 3.8 Ga rocks indicate that their protoliths involved at least two end-member components that were derived from enriched and ultra-depleted mantle reservoirs. Finally, the 182W excess (μ182W = +8.3 to +12.9) of the ca. 3.8 Ga rocks might be due to either early mantle differentiation or a lack of late accreted materials. However, 142Nd isotopes (μ142Nd = +1.8 to +9.2) of these ca. 3.8 Ga rocks do reveal a differentiation event in the early Earth that produced two end-member reservoirs with positive and negative μ142Nd anomalies. We conclude that plate tectonics likely had an important role in the onset of continental nuclei in North China at ca. 3.8 Ga, and the precursors of these oldest rocks can be used to decipher multiple mantle–crust differentiation events during 4.5–3.8 Ga.
AB - The Archean Anshan Complex (AAC) in northeastern China is one of the best-preserved ca. 3.8 Ga outcrops worldwide, which are key to understanding the evolution of the early Earth. In this study, we carried out 1:10,000 geological mapping and integrated this with published whole-rock geochemical, zircon U–Pb age, and O–Nd–Hf–W isotopic data, along with new zircon U–Pb and Si–O isotopic data. We used these data to establish a geochronological framework for the AAC and investigate its origins and tectonic setting, and differentiation of the early Earth. Our new mapping shows that the AAC can be divided into several rock associations based on the zircon U–Pb ages and lithologies: (1) Eoarchean (ca. 3.8 Ga) trondhjemitic gneiss and meta-quartz diorite; (2) Paleoarchean (ca. 3.3 Ga) gneiss and migmatite; (3) Mesoarchean (ca. 3.1 Ga) granitic gneiss; (4) Mesoarchean (ca. 3.0 Ga) monzogranite; (5) Neoarchean (ca. 2.5 Ga) K-rich granite; and (6) Archean supracrustal rock. The ca. 3.8 Ga rocks are exclusively exposed as enclaves within the ca. 3.3 Ga gneiss and migmatite unit at Dongshan, Guodishan, Shengousi, and Hujiamiao. Some ca. 3.8 Ga components at Baijiafen and Dongshan cannot be visually identified due to strong deformation and migmatization. The ca. 3.8 Ga Anshan trondhjemitic gneiss and meta-quartz diorite have coupled heavy Si–O isotopic compositions, indicative of the involvement of supracrustal silicified materials in their sources. (La/Yb)N ratios vary widely in the different ca. 3.8 Ga rock types (i.e., 9–53 for the trondhjemitic gneisses and 3–8 for the meta-quartz diorites), indicating they formed at different pressures. We suggest the ca. 3.8 Ga trondhjemitic gneisses were derived by partial melting of a subducted slab, and the 3.8 Ga meta-quartz diorites might have been derived by partial melting of a mantle wedge that had been metasomatized by fluids released from the subducted slab. Highly variable εNd(t) (−4.5 to +10.1) and εHf(t) (−3.8 to +6.1) values of the ca. 3.8 Ga rocks indicate that their protoliths involved at least two end-member components that were derived from enriched and ultra-depleted mantle reservoirs. Finally, the 182W excess (μ182W = +8.3 to +12.9) of the ca. 3.8 Ga rocks might be due to either early mantle differentiation or a lack of late accreted materials. However, 142Nd isotopes (μ142Nd = +1.8 to +9.2) of these ca. 3.8 Ga rocks do reveal a differentiation event in the early Earth that produced two end-member reservoirs with positive and negative μ142Nd anomalies. We conclude that plate tectonics likely had an important role in the onset of continental nuclei in North China at ca. 3.8 Ga, and the precursors of these oldest rocks can be used to decipher multiple mantle–crust differentiation events during 4.5–3.8 Ga.
KW - Anshan Complex
KW - Eoarchean
KW - Geological mapping
KW - North China Craton
KW - Si–O–Nd–Hf–W isotopes
KW - Zircon U–Pb age
UR - http://www.scopus.com/inward/record.url?scp=85175242752&partnerID=8YFLogxK
U2 - 10.1016/j.earscirev.2023.104606
DO - 10.1016/j.earscirev.2023.104606
M3 - Review article
AN - SCOPUS:85175242752
SN - 0012-8252
VL - 247
JO - Earth-Science Reviews
JF - Earth-Science Reviews
M1 - 104606
ER -