Abstract Recent research has identified abundant Early Permian to Late Triassic ultramafic-mafic rocks along the west Jinsha to Garze-Litang suture, central NE Tibetan Plateau. However, the petrogenesis and tectonic setting of these rocks are hotly debated. This paper presents a combination of zircon U Pb ages, major and trace element concentrations, and Sr Nd isotopic data for mafic rocks from the Zhiduo Complex in the west Jinsha suture. Three geochemical subgroups are recognized among these rocks; metagabbros showing arc-type affinity (Group 1; 286–268 Ma); isotropic gabbros with an oceanic-island basalt-like signature (Group 2; 252 ± 2 Ma); and pillow/massive basalts (Group 3; ca. 235 Ma) having back-arc basin basalt affinity. Group 1 rocks exhibit moderate-high MgO (5.98–8.07 wt%) and Al2O3 (13.75–17.40 wt%) contents and are characterized by subduction-type trace element patterns and high initial 87Sr/86Sr ratios (0.71155–0.71261) and low eNd(t) values (−7.0 to −6.0), indicating that they originated from a spinel lithospheric mantle metasomatized by slab-derived fluids. Group 2 rocks have high contents of TiO2 (2.28–4.96 wt%), total Fe2O3 (11.67–14.80 wt%), Nb (18.3–22.8 ppm), and Ta (1.52–1.81 ppm) and more radiogenic Nd isotopes [eNd(t) = +0.3 to +0.9]. These data show that they were derived from a spinel + garnet mantle source enriched by plume-type components. Group 3 rocks possess high MgO (7.29–9.29 wt%), Cr (427–488 ppm), and Ni (215–238 ppm) contents but low Nb (5.00–5.60 ppm) and Ta (0.36–0.84 ppm), coupled with low Sr (initial 87Sr/86Sr = 0.70523–0.70567) and high Nd isotopes [eNd(t) = +3.1 to +3.5]. These values suggest that they were sourced from a garnet + spinel mantle affected by slight plume contamination. Combined with previous structural and geochemical studies, the ultramafic-mafic rocks of the Zhiduo Complex and arc magmatic rocks from nearby regions indicate an integrated Early Permian to Late Triassic oceanic basin–arc–back-arc system developed in the central NE Tibetan Plateau. Thus, the west Jinsha to Garze-Litang represents a mature Paleo-Tethys Ocean rather than small back-arc basins. Southward subduction and associated back-arc spreading led to the genesis of widespread late Paleozoic to early Mesozoic magmatic rocks in the hinterland and along the northern margin of the North Qiangtang Block.

中文翻译：

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青藏高原中部晚古生代至早中生代古特提斯构造演化: 知多基性-超镁铁质杂岩的洞察

摘要 最近的研究已经在青藏高原中部的金沙西至甘孜-理塘缝合带发现了丰富的早二叠世至晚三叠世超基性-基性岩。然而，这些岩石的成因和构造环境引起了激烈的争论。本文结合了西金沙缝合带直多杂岩体的锆石 U Pb 年龄、主要和微量元素浓度以及 Sr Nd 同位素数据。在这些岩石中识别出三个地球化学亚群；显示弧型亲和性的metagabbros（第1组；286-268 Ma）；具有大洋岛玄武岩特征的各向同性辉长岩（第 2 组；252 ± 2 Ma）；和具有弧后盆地玄武岩亲合力的枕状/大块玄武岩（第 3 组；约 235 Ma）。第 1 组岩石表现出中高 MgO (5.98–8.07 wt%) 和 Al2O3 (13.75–17. 40 wt%) 含量，并以俯冲型微量元素模式和高初始 87Sr/86Sr 比 (0.71155–0.71261) 和低 eNd(t) 值（-7.0 至 -6.0）为特征，表明它们起源于尖晶石岩石圈地幔被板块衍生流体交代。第 2 组岩石的 TiO2 (2.28–4.96 wt%)、总 Fe2O3 (11.67–14.80 wt%)、Nb (18.3–22.8 ppm) 和 Ta (1.52–1.81 ppm) 和更多放射性 Nd 同位素 [eNd( t) = +0.3 到 +0.9]。这些数据表明它们来源于富含羽状成分的尖晶石+石榴石地幔源。第 3 组岩石具有高 MgO (7.29–9.29 wt%)、Cr (427–488 ppm) 和 Ni (215–238 ppm) 含量但低 Nb (5.00–5.60 ppm) 和 Ta (0.36–0.84 ppm)，耦合具有低 Sr（初始 87Sr/86Sr = 0.70523–0.70567）和高 Nd 同位素 [eNd(t) = +3.1 至 +3.5]。这些值表明它们来自受到轻微羽状污染影响的石榴石 + 尖晶石地幔。结合先前的构造和地球化学研究，智多杂岩的超基性-基性岩和附近地区的弧形岩浆岩表明青藏高原中部发育早二叠世至晚三叠世大洋盆地-弧-弧后系统。因此，西金沙至甘孜—理塘代表的是成熟的古特提斯洋，而非弧后小盆地。南下俯冲和相关的弧后扩张导致了北羌塘地块腹地和北缘广泛分布的晚古生代至早中生代岩浆岩的成因。结合先前的构造和地球化学研究，智多杂岩的超基性-基性岩和附近地区的弧形岩浆岩表明青藏高原东北部中部发育早二叠世至晚三叠世大洋盆地-弧-弧后系统。因此，西金沙至甘孜—理塘代表的是成熟的古特提斯洋，而非弧后小盆地。南下俯冲和相关的弧后扩张导致了北羌塘地块腹地和北缘广泛分布的晚古生代至早中生代岩浆岩的成因。结合先前的构造和地球化学研究，智多杂岩的超基性-基性岩和附近地区的弧形岩浆岩表明青藏高原东北部中部发育早二叠世至晚三叠世大洋盆地-弧-弧后系统。因此，西金沙至甘孜—理塘代表的是成熟的古特提斯洋，而非弧后小盆地。南下俯冲和相关的弧后扩张导致了北羌塘地块腹地和北缘广泛分布的晚古生代至早中生代岩浆岩的成因。西金沙至甘孜理塘代表成熟的古特提斯洋，而非弧后盆地。南下俯冲和相关的弧后扩张导致了北羌塘地块腹地和北缘广泛分布的晚古生代至早中生代岩浆岩的成因。西金沙至甘孜理塘代表成熟的古特提斯洋，而非弧后盆地。南下俯冲和相关的弧后扩张导致了北羌塘地块腹地和北缘广泛分布的晚古生代至早中生代岩浆岩的成因。