西昆仑西北缘柯牙吾齐超镁铁岩的发现及成因

The discovery of ultramafic rocks in the northwestern margin of west Kunlun is of great significance for discussing the tectonic evolution and related mineral resources potential in the western section of west Kunlun. This work conducted microscopic identification, and major and trace element tests on seven ultramafic rock samples. Results show that the ultramafic rocks occur as intermittent veins, and are dominated by serpentinized pyroxene perido-tite. The ultramafic rocks are characterized by relatively low SiO₂ (42.14% ~ 47.43%), low Ti O₂(0.03%-0.24%), high Mg^# (24.69% ~ 31.22%), high FeO^T(7.05% ~ 11.65%)and low alkali(K₂O + Na₂O = 0.55%-0.88%). Mg^# values range from 79. 98 to 86. 70. The m/f ratio of the samples lies in a range of 3. 96 ~ 7. 82. The total amount of REE (£ REE) in the samples is not high (11.41 x 10 6-17. 84 x 10 6), and the LREE/HREE ratio is 2. 81-5. 69. <5Eu shows weakly positive Eu anomaly. The content of compatible elements(Ni, Cr and Co)is high. In the primitive mantle-normalized spider diagram of trace elements, they are enriched in LILE(Rb, Ba, U, Sr and Pb), and relatively depleted in HFSE(Nb, P, Zr, Hf, Ti, etc.), indicating the enrichment of light rare earth elements. Combined with regional tectonic setting, it is suggested that the closure of the Paleotethys ocean resulted in the extension after collision in the Late Triassic, and the magma from the loss mantle was transformed by subduction fluid or melt in the early stage, and intruded along deep fault, which experienced certain crust mixing in the process to finally form the Keyawuqi ultramafic rocks. © 2022 Editorial Board of Geology and Exploration. All rights reserved.

Discovery and genesis of the Keyawuqi ultramafic rocks in the northwestern margin of West Kunlun