Petrogenesis of the Triassic granitoids from the East Kunlun Orogenic Belt, NW China: Implications for continental crust growth from syn-collisional to post-collisional setting
Petrogenesis of the Triassic granitoids from the East Kunlun Orogenic Belt, NW China: Implications for continental crust growth from syn-collisional to post-collisional setting
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中国西北部东昆仑造山带三叠纪花岗岩的岩石成因：同碰撞到碰撞后大陆地壳生长的意义
DOI：
10.1016/j.lithos.2020.105513
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发表时间：
2020-07
期刊：
影响因子：
3.5
通讯作者：
Shao Fengli
中科院分区：
文献类型：
--
作者：
Kong Juanjuan;Niu Yaoling;Hu Yan;Zhang Yu;Shao Fengli
青藏高原北方东昆仑造山带东段广泛发育三叠纪花岗岩类。这些花岗岩类很好地记录了古特提斯洋（EKOB称之为阿尼玛卿洋）的演化。新的锆石U-Pb数据结合文献年龄表明，这些花岗岩代表了早三叠世（T1，~251-248 Ma）、中三叠世（T2，~247-238 Ma）至晚三叠世（T3，~234-214 Ma）的长期岩浆活动。三叠纪花岗岩类显示钙碱性I型花岗岩的亲和性和混合的幔-壳地球化学特征。T1花岗岩类具有安山质到长英质块状陆壳（BCC）的化学成分（例如，富含Rb、K和Pb，贫Nb、Ta、Sr、P和Ti），加上高ISr（0.7067-0.7148），负εNd（t）（−7.32至−1.66）和负至正εHf（t）（-5.11至3.59）以及（Dy/Yb）N= 1.1，表明T1花岗岩类是由俯冲的阿尼玛卿洋壳与陆源沉积物在斜长角闪岩相条件下熔融形成的。T2和T3花岗岩类可能起源于一个相对均一的源区，其ISr（0.7136 [T2]，0.7094 [T3]），εNd（t）（-5.83 [T2]，-5.97 [T3]）和εHf（t）（-3.52 [T2]，-3.58 [T3]）的平均值几乎一致。它们呈现埃达克质岩石的石榴石特征，可以用岩浆上升过程中年轻镁铁质下陆壳部分熔融并与上地壳成分混合来解释。这一过程与碰撞后软流圈上涌和地幔熔融引起的伸展作用有关，为镁铁质下地壳熔融提供了热量，形成了T2和T3花岗岩类。具有地幔特征（如εHf（t）> 0）和类BCC成分的T1花岗岩类代表了年轻闪长质向花岗岩类物质的净通量，支持沿着EKOB“大陆碰撞带是大陆地壳净生长的主要场所”的假说。T2和T3花岗岩类之间的成因联系意味着中三叠世（~247 Ma）以来EKOB已转变为后碰撞环境。这些假说对于理解从同碰撞到碰撞后的岩浆活动中新生地壳的起源和大陆地壳的生长具有重要的理论意义。
The Triassic granitoids are widespread in the eastern section of the East Kunlun Orogenic Belt (EKOB) on the northern Tibetan Plateau. These granitoids well record the evolution of the Paleo-Tethys oceans (named as A'nyemaqen Ocean in the EKOB). Our new zircon Usingle bondPb data together with ages in literature show that these granitoids represent long-lasting magmatism from the early (T1, ~251–248 Ma), middle (T2, ~247–238 Ma) to late (T3, ~234–214 Ma) Triassic. The Triassic granitoids display calc-alkaline I-type granite affinities and hybrid mantle-crust geochemical signatures. The T1granitoids possess andesitic to felsic bulk continental crust (BCC)-like chemical composition (e.g., enriched in Rb, K and Pb, depleted in Nb, Ta, Sr, P and Ti), coupled with high ISr(0.7067–0.7148), negative εNd(t)(−7.32 to −1.66) and negative to positive εHf(t)(−5.11 to 3.59) as well as (Dy/Yb)N= 1.1, suggesting that the T1granitoids were formed by melting of the subducted A'nyemaqen oceanic crust with terrigenous sediments under the amphibolite facies conditions in asyn-collisional setting. The T2and T3granitoids may be originated from a relatively homogeneous source with almost consistent mean values of ISr(0.7136 [T2], 0.7094 [T3]), εNd(t)(−5.83 [T2], −5.97 [T3]) and εHf(t)(−3.52 [T2], −3.58 [T3]). They present garnet signature of adakitic rocks and can be explained by partial melting of the juvenile mafic lower continental crust and mixing with upper crustal components during magma ascent. This process is considered to be associated with post-collisional extension which induced by asthenosphere upwelling and mantle melting, providing heat for mafic lower crust melting to form T2and T3granitoids. The T1granitoids with mantle signatures (e.g. εHf(t)> 0) as well as BCC-like compositions represent a net flux of juvenile dioritic to granitic materials adding to the continental crust, in support of the hypothesis of “continental collision zones are primary sites for net continental crust growth” along the EKOB. The genetic link between T2and T3granitoids means the EKOB had transformed to post-collisional setting since the middle Triassic (~247 Ma). All these hypotheses are conceptually important for understanding the origin of the juvenile crust and continental crustal growth through magmatism fromsyn-collisional to post-collisional settings.
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DOI：
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