TY - JOUR
T1 - Source and pressure effects in the genesis of the Late Triassic high Sr/Y granites from the Songpan-Ganzi Fold Belt, eastern Tibetan Plateau
AU - Zhan, Qiong Yao
AU - Zhu, Di Cheng
AU - Wang, Qing
AU - Weinberg, Roberto F.
AU - Xie, Jin Cheng
AU - Li, Shi Min
AU - Zhang, Liang Liang
AU - Zhao, Zhi Dan
PY - 2020/9
Y1 - 2020/9
N2 - The petrogenesis of granites with high Sr/Y signatures similar to adakitic rocks in continental settings is much debated. It is especially controversial whether these rocks are indicative of high-pressure magmatism (i.e., partial melting or crystallization fractionation) related to a thickened crust, or their high Sr/Y signatures are merely inherited from a high Sr/Y source. To address this, new chronological and geochemical data are presented for high Sr/Y granites from the Riluku batholith in eastern Tibetan Plateau. Zircon U-Pb dating and amphibole barometry suggest a final granite crystallization stage of ca. 207 Ma and an emplacement depth of ~14 km (~ 4 kbar), respectively. They are geochemically characterized by high Sr and low Y contents (481–1195 ppm and 6.62–20.6 ppm, respectively) with high Sr/Y and (La/Yb)N ratios (35–112 and 15–113, respectively). Enriched isotope character of the high Sr/Y granites, in combination with regional tectonics, indicates that these rocks are unlikely to be derived from partial melting of subducting oceanic crust. Low Cr (0.8–1.0 ppm), Ni (0.9–3.2 ppm), and Mg# (24–41) suggest that derivation from the partial melting of delaminated lower crust is also unlikely. Water-fluxed partial melting of crustal rocks at low pressure, which preferentially consumes plagioclase over micas, is inconsistent with the high contents of Rb (mostly >150 ppm) and low Sr/Rb ratios (mostly <5) of the samples. Reverse geochemical modeling, which simulated source composition under different pressures, indicates that evaluation of source compositions is critical to constrain the derivation pressure of the high Sr/Y granites. Our study emphasizes that high Sr/Y granites cannot be simply used to deduce a thickened crust at the time of magmatism without a priori knowledge of the nature of the source.
AB - The petrogenesis of granites with high Sr/Y signatures similar to adakitic rocks in continental settings is much debated. It is especially controversial whether these rocks are indicative of high-pressure magmatism (i.e., partial melting or crystallization fractionation) related to a thickened crust, or their high Sr/Y signatures are merely inherited from a high Sr/Y source. To address this, new chronological and geochemical data are presented for high Sr/Y granites from the Riluku batholith in eastern Tibetan Plateau. Zircon U-Pb dating and amphibole barometry suggest a final granite crystallization stage of ca. 207 Ma and an emplacement depth of ~14 km (~ 4 kbar), respectively. They are geochemically characterized by high Sr and low Y contents (481–1195 ppm and 6.62–20.6 ppm, respectively) with high Sr/Y and (La/Yb)N ratios (35–112 and 15–113, respectively). Enriched isotope character of the high Sr/Y granites, in combination with regional tectonics, indicates that these rocks are unlikely to be derived from partial melting of subducting oceanic crust. Low Cr (0.8–1.0 ppm), Ni (0.9–3.2 ppm), and Mg# (24–41) suggest that derivation from the partial melting of delaminated lower crust is also unlikely. Water-fluxed partial melting of crustal rocks at low pressure, which preferentially consumes plagioclase over micas, is inconsistent with the high contents of Rb (mostly >150 ppm) and low Sr/Rb ratios (mostly <5) of the samples. Reverse geochemical modeling, which simulated source composition under different pressures, indicates that evaluation of source compositions is critical to constrain the derivation pressure of the high Sr/Y granites. Our study emphasizes that high Sr/Y granites cannot be simply used to deduce a thickened crust at the time of magmatism without a priori knowledge of the nature of the source.
KW - Crustal thickness
KW - High Sr/Y granites
KW - Songpan-Ganzi Fold Belt
KW - Source compositions
UR - http://www.scopus.com/inward/record.url?scp=85085572266&partnerID=8YFLogxK
U2 - 10.1016/j.lithos.2020.105584
DO - 10.1016/j.lithos.2020.105584
M3 - Article
AN - SCOPUS:85085572266
VL - 368-369
JO - Lithos
JF - Lithos
SN - 0024-4937
M1 - 105584
ER -