Geochemical constraints on the multistage evolution of the Yilashan ophiolite, central Tibet

Xiang zhen Xu; Fahui Xiong; Basem Zoheir; Jinyu Yan; Boyang Zhang; Ran Zhang; Jingsui Yang

doi:10.1016/j.oregeorev.2022.105283

Geochemical constraints on the multistage evolution of the Yilashan ophiolite, central Tibet

Xiang zhen Xu
, Fahui Xiong^*
, Basem Zoheir
, Jinyu Yan
, Boyang Zhang
, Ran Zhang
, Jingsui Yang

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

3 Scopus citations

Abstract

The Yilashan ophiolite in the southern part of the central Bangong-Nujiang suture zone comprises variably deformed harzburgite, dunite, and less abundant gabbro and pyroxenite pods and crosscutting veins. Cr-spinels in podiform chromitite bodies are characterized by high Cr# (64.3–74.3), high Mg# (58.2–67.5), and consistently low contents of TiO₂ (≤0.12 wt%). Primary melt calculations designate parental boninitic magmas with Al₂O_3(liquid) contents of 11.67–13.49 wt%, and (FeO/MgO)_liquid values of 0.92–1.12. Whole-rock geochemical data of fresh pyroxenite samples are characterized by negative K, Ta, Nb and Zr anomalies, no Eu anomaly, and chondrite-normalized REE patterns comparable to the N-MORB melts. The gabbro samples, in contrast, are high-K calc-alkaline, with elevated contents of LILE (Rb, K, Th) and depleted HFSE (i.e., Nb, Ta, P, Ti), consistent with subduction-related magmas. The fractionated chondrite-normalized REE patterns, high LREE/HREE values, and negative Eu anomalies of these gabbroic rocks are similar to the island arc basalts. Pyroxenite shows high PPGE/IPGE values, variable Pd/Ir (55.7–316.7), and left-leaning primitive mantle-normalized PGE pattern, whereas massive chromitite is enriched in IPGE relative to PPGE. The PGE patterns of pyroxenite and chromitite, though distinct, depict significant fractionation and partial melting in their formation. The elevated contents of PPGEs in pyroxenite suggest derivation from sulfur-saturated magmas as chromitite crystallization scavenged the compatible IPGEs from the parental melt. This assumption is supported by clinopyroxene in pyroxenite with variable Al₂O₃ contents and variable Cr₂O₃ contents (0.32 to 0.73 wt%). For the fractionated gabbro unit, zircons yielding a concordia U-Pb age of 162.8 ± 3.0 Ma and widely variable ε_Hf(t) values (−9.2 to +12.0) suggest formation from heterogenous or reworked source materials during a Middle Jurassic subduction increment in the Neo-Tethyan Ocean.

Original language	English
Article number	105283
Journal	Ore Geology Reviews
Volume	153
DOIs	https://doi.org/10.1016/j.oregeorev.2022.105283
State	Published - Feb 2023
Externally published	Yes

Bibliographical note

Publisher Copyright:
© 2023 The Authors

Keywords

High-Cr chromitites
MORB and boninitic magmas
Mantle partial melting
Reworking and subduction zone processes
Yilashan ophiolite

ASJC Scopus subject areas

Geology
Geochemistry and Petrology
Economic Geology

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10.1016/j.oregeorev.2022.105283

Cite this

@article{250b55d55e8e44efa7162081e86de7b7,

title = "Geochemical constraints on the multistage evolution of the Yilashan ophiolite, central Tibet",

abstract = "The Yilashan ophiolite in the southern part of the central Bangong-Nujiang suture zone comprises variably deformed harzburgite, dunite, and less abundant gabbro and pyroxenite pods and crosscutting veins. Cr-spinels in podiform chromitite bodies are characterized by high Cr\# (64.3–74.3), high Mg\# (58.2–67.5), and consistently low contents of TiO2 (≤0.12 wt\%). Primary melt calculations designate parental boninitic magmas with Al2O3(liquid) contents of 11.67–13.49 wt\%, and (FeO/MgO)liquid values of 0.92–1.12. Whole-rock geochemical data of fresh pyroxenite samples are characterized by negative K, Ta, Nb and Zr anomalies, no Eu anomaly, and chondrite-normalized REE patterns comparable to the N-MORB melts. The gabbro samples, in contrast, are high-K calc-alkaline, with elevated contents of LILE (Rb, K, Th) and depleted HFSE (i.e., Nb, Ta, P, Ti), consistent with subduction-related magmas. The fractionated chondrite-normalized REE patterns, high LREE/HREE values, and negative Eu anomalies of these gabbroic rocks are similar to the island arc basalts. Pyroxenite shows high PPGE/IPGE values, variable Pd/Ir (55.7–316.7), and left-leaning primitive mantle-normalized PGE pattern, whereas massive chromitite is enriched in IPGE relative to PPGE. The PGE patterns of pyroxenite and chromitite, though distinct, depict significant fractionation and partial melting in their formation. The elevated contents of PPGEs in pyroxenite suggest derivation from sulfur-saturated magmas as chromitite crystallization scavenged the compatible IPGEs from the parental melt. This assumption is supported by clinopyroxene in pyroxenite with variable Al2O3 contents and variable Cr2O3 contents (0.32 to 0.73 wt\%). For the fractionated gabbro unit, zircons yielding a concordia U-Pb age of 162.8 ± 3.0 Ma and widely variable εHf(t) values (−9.2 to +12.0) suggest formation from heterogenous or reworked source materials during a Middle Jurassic subduction increment in the Neo-Tethyan Ocean.",

keywords = "High-Cr chromitites, MORB and boninitic magmas, Mantle partial melting, Reworking and subduction zone processes, Yilashan ophiolite",

author = "Xu, \{Xiang zhen\} and Fahui Xiong and Basem Zoheir and Jinyu Yan and Boyang Zhang and Ran Zhang and Jingsui Yang",

note = "Publisher Copyright: {\textcopyright} 2023 The Authors",

year = "2023",

month = feb,

doi = "10.1016/j.oregeorev.2022.105283",

language = "English",

volume = "153",

journal = "Ore Geology Reviews",

issn = "0169-1368",

publisher = "Elsevier B.V.",

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TY - JOUR

T1 - Geochemical constraints on the multistage evolution of the Yilashan ophiolite, central Tibet

AU - Xu, Xiang zhen

AU - Xiong, Fahui

AU - Zoheir, Basem

AU - Yan, Jinyu

AU - Zhang, Boyang

AU - Zhang, Ran

AU - Yang, Jingsui

PY - 2023/2

Y1 - 2023/2

N2 - The Yilashan ophiolite in the southern part of the central Bangong-Nujiang suture zone comprises variably deformed harzburgite, dunite, and less abundant gabbro and pyroxenite pods and crosscutting veins. Cr-spinels in podiform chromitite bodies are characterized by high Cr# (64.3–74.3), high Mg# (58.2–67.5), and consistently low contents of TiO2 (≤0.12 wt%). Primary melt calculations designate parental boninitic magmas with Al2O3(liquid) contents of 11.67–13.49 wt%, and (FeO/MgO)liquid values of 0.92–1.12. Whole-rock geochemical data of fresh pyroxenite samples are characterized by negative K, Ta, Nb and Zr anomalies, no Eu anomaly, and chondrite-normalized REE patterns comparable to the N-MORB melts. The gabbro samples, in contrast, are high-K calc-alkaline, with elevated contents of LILE (Rb, K, Th) and depleted HFSE (i.e., Nb, Ta, P, Ti), consistent with subduction-related magmas. The fractionated chondrite-normalized REE patterns, high LREE/HREE values, and negative Eu anomalies of these gabbroic rocks are similar to the island arc basalts. Pyroxenite shows high PPGE/IPGE values, variable Pd/Ir (55.7–316.7), and left-leaning primitive mantle-normalized PGE pattern, whereas massive chromitite is enriched in IPGE relative to PPGE. The PGE patterns of pyroxenite and chromitite, though distinct, depict significant fractionation and partial melting in their formation. The elevated contents of PPGEs in pyroxenite suggest derivation from sulfur-saturated magmas as chromitite crystallization scavenged the compatible IPGEs from the parental melt. This assumption is supported by clinopyroxene in pyroxenite with variable Al2O3 contents and variable Cr2O3 contents (0.32 to 0.73 wt%). For the fractionated gabbro unit, zircons yielding a concordia U-Pb age of 162.8 ± 3.0 Ma and widely variable εHf(t) values (−9.2 to +12.0) suggest formation from heterogenous or reworked source materials during a Middle Jurassic subduction increment in the Neo-Tethyan Ocean.

AB - The Yilashan ophiolite in the southern part of the central Bangong-Nujiang suture zone comprises variably deformed harzburgite, dunite, and less abundant gabbro and pyroxenite pods and crosscutting veins. Cr-spinels in podiform chromitite bodies are characterized by high Cr# (64.3–74.3), high Mg# (58.2–67.5), and consistently low contents of TiO2 (≤0.12 wt%). Primary melt calculations designate parental boninitic magmas with Al2O3(liquid) contents of 11.67–13.49 wt%, and (FeO/MgO)liquid values of 0.92–1.12. Whole-rock geochemical data of fresh pyroxenite samples are characterized by negative K, Ta, Nb and Zr anomalies, no Eu anomaly, and chondrite-normalized REE patterns comparable to the N-MORB melts. The gabbro samples, in contrast, are high-K calc-alkaline, with elevated contents of LILE (Rb, K, Th) and depleted HFSE (i.e., Nb, Ta, P, Ti), consistent with subduction-related magmas. The fractionated chondrite-normalized REE patterns, high LREE/HREE values, and negative Eu anomalies of these gabbroic rocks are similar to the island arc basalts. Pyroxenite shows high PPGE/IPGE values, variable Pd/Ir (55.7–316.7), and left-leaning primitive mantle-normalized PGE pattern, whereas massive chromitite is enriched in IPGE relative to PPGE. The PGE patterns of pyroxenite and chromitite, though distinct, depict significant fractionation and partial melting in their formation. The elevated contents of PPGEs in pyroxenite suggest derivation from sulfur-saturated magmas as chromitite crystallization scavenged the compatible IPGEs from the parental melt. This assumption is supported by clinopyroxene in pyroxenite with variable Al2O3 contents and variable Cr2O3 contents (0.32 to 0.73 wt%). For the fractionated gabbro unit, zircons yielding a concordia U-Pb age of 162.8 ± 3.0 Ma and widely variable εHf(t) values (−9.2 to +12.0) suggest formation from heterogenous or reworked source materials during a Middle Jurassic subduction increment in the Neo-Tethyan Ocean.

KW - High-Cr chromitites

KW - MORB and boninitic magmas

KW - Mantle partial melting

KW - Reworking and subduction zone processes

KW - Yilashan ophiolite

UR - https://www.scopus.com/pages/publications/85146051790

U2 - 10.1016/j.oregeorev.2022.105283

DO - 10.1016/j.oregeorev.2022.105283

M3 - Article

AN - SCOPUS:85146051790

SN - 0169-1368

VL - 153

JO - Ore Geology Reviews

JF - Ore Geology Reviews

M1 - 105283

ER -

Geochemical constraints on the multistage evolution of the Yilashan ophiolite, central Tibet

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

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