Petrogenesis of Late Devonian I- and A-type granitoids, and associated mafic microgranular enclaves in the northwestern North Qaidam Orogenic Belt, China: Implications for continental crust growth during the post-collisional stage
Petrogenesis of Late Devonian I- and A-type granitoids, and associated mafic microgranular enclaves in the northwestern North Qaidam Orogenic Belt, China: Implications for continental crust growth during the post-collisional stage
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中国柴达木造山带西北部晚泥盆世 I 型和 A 型花岗岩及相关镁铁质微粒包体的岩石成因：对碰撞后阶段大陆地壳生长的影响
DOI：
10.1016/j.lithos.2022.106857
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发表时间：
2022
期刊：
影响因子：
3.5
通讯作者：
Moritz Robert
中科院分区：
文献类型：
--
作者：
Yan Maoqiang;Wei Junhao;Zhang Daohan;Zhao Zhixin;Turlin François;Li Huan;Li Guomeng;Xu Chongwen;Zhang Xinming;Moritz Robert
碰撞后岩浆侵入体及其镁铁质微粒包体（MMEs）是研究花岗岩成因、壳幔相互作用和陆壳改造与生长的重要资料。对柴北缘牛鼻子梁岩体中的MMEs及其寄主岩体牛鼻子梁I型长英质复式岩体（花岗岩和花岗闪长岩）和大铜沟A2型铝质黑云母花岗岩进行了岩石学和地球化学综合研究。通过对全岩主量元素、微量元素、Sr单键Nd同位素组成、斜长石、角闪石和黑云母的电子探针显微分析、锆石U单键Pb定年和Hf同位素测定，表明研究岩石形成于晚泥盆世（约1000年）。382 Ma）。牛鼻子梁复式长英质岩体为偏铝质钙碱性-高钾钙碱性I型花岗岩。牛鼻子梁复式长英质岩体中的MMEs具有低SiO2（52- 64wt%）和高MgO（2.8- 4.9wt%）的特征。MMEs和寄主花岗岩都富集轻稀土元素（LREEs）和大离子亲石元素（LILEs），而贫P和高场强元素（HFSEs）。牛鼻子梁的MMEs和寄主花岗岩类样品的Sr-Nd-Hf同位素组成基本一致，其初始Sr同位素比值分别为0.70545-0.70633（MMEs），0.70555-0.70742（MMEs全岩εNd（382 Ma）值分别为−2.95 ~+1.6、−0.25 ~+3.5，锆石εHf（382 Ma）值分别为+2.2 ~+10.2、+1.3 ~+10.4。牛鼻子梁复式长英质岩体是由新生壳源熔体和亏损幔源熔体按40：60比例混合而成。大同沟黑云母花岗岩具有较高的TFe_2 O_3/（TFe_2 O_3 + MgO）、TiO_2/MgO、Ga/Al和Y/Nb比值，较高的锆石饱和温度（802-846 °C），较高的高场强元素（如Fe_2 O_3、Mg_2 O_3、Fe_2 O_3、Mg_2 O、Fe_2 O_3、Fe_2 O_2、Fe_2 O_3、Fe_2 Zr、Nb和Y）、中等（Na 2 O + K2 O）浓度以及低Eu和Sr浓度。间隙黑云母具有高的Fe 2 O3，但低的MgO浓度，类似于铝A型花岗岩。上述特征表明大同沟黑云母花岗岩为铝质A2型花岗岩。考虑到黑云母花岗岩具有较高的初始Sr同位素组成（0.72218-0.72652）、较低的εNd（382 Ma）（−6.73 ~ −6.31）和较老的两期Nd模式年龄（1640-1674 Ma），我们认为黑云母花岗岩是由奥陶-志留纪英云闪长岩组成的花岗岩类在HT-LP条件下部分熔融形成的。本区同时代I型和铝质A2型花岗岩类的形成可能与岩石圈地幔拆沉作用和软流圈上涌有关。390 Ma.牛鼻子梁地区的I型花岗岩类和MMEs代表了年轻地幔向地壳的净增加，鉴于同期I型花岗岩类的广泛分布，碰撞后岩浆活动对NQOB的陆壳生长有重要贡献。
Post-collisional magmatic intrusions and their mafic microgranular enclaves (MMEs) can provide significant insights into granite petrogenesis, crust-mantle interaction, and the reworking and growth of the continental crust. A combined petrological and geochemical study was carried out on MMEs and their host Niubiziliang I-type felsic composite pluton (granite and granodiorite) and aluminous A2-type Datonggou biotite granite from the Niubiziliang batholith in the northwestern segment of the North Qaidam Orogenic Belt (NQOB), China. This study presents whole-rock major- and trace elements and Srsingle bondNd isotopic compositions, electron probe microanalyses of plagioclase, hornblende, and biotite, and zircon Usingle bondPb dating and Hf isotopes.Zircon Usingle bondPb dating demonstrates that the studied rocks formed during the Late Devonian (ca. 382 Ma). The Niubiziliang composite felsic pluton samples yield a metaluminous calc-alkaline to high-K calc-alkaline I-type granitic composition. The MMEs from Niubiziliang composite felsic pluton have low SiO2(52–64 wt%) and high MgO (2.8–4.9 wt%) concentrations. Both MMEs and host granites are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and are depleted in P and high field strength elements (HFSEs). All MMEs and host granitoids samples from Niubiziliang have indistinguishable Sr-Nd-Hf isotopic compositions characterized by initial Sr isotope ratios of 0.70545–0.70633 (MMEs), 0.70555–0.70742 (host rock), whole-rock εNd (382 Ma)values of −2.95 to +1.6, −0.25 to +3.5, and zircon εHf(382Ma)values of +2.2 to +10.2, +1.3 to +10.4, respectively. The Niubiziliang composite felsic pluton is a product of mixing juvenile crust-derived and depleted mantle-derived melts in a 40:60 proportion. MMEs crystallized from the same source as the host granite, and they were formed by self-mixing with the earlier crystallized cumulates when they were affected by the emplacement of subsequent hot magmas.The Datonggou biotite granite has high TFe2O3/(TFe2O3+ MgO), TiO2/MgO, Ga/Al, and Y/Nb ratios, high zircon saturation temperatures (802–846 °C), high HFSE concentrations (e.g., Zr, Nb, and Y), moderate (Na2O + K2O) concentrations, and low Eu and Sr concentrations. Interstitial biotite has high Fe2O3but low MgO concentrations, similar to those of aluminous A-type granite. The above-mentioned characteristics imply that the Datonggou biotite granite is an aluminous A2-type granite. Considering their high initial Sr isotopic composition (0.72218–0.72652), low εNd (382 Ma)(−6.73 to −6.31), and comparatively old two-stage Nd model ages (1640–1674 Ma), we suggest the biotite granite was generated by partial melting of Ordovician-Silurian granitoids with tonalitic compositions at HT-LPconditions. The formation of coeval I- and aluminous A2-type granitoids in this region was probably related to the lithospheric mantle delamination and associated asthenospheric upwelling at ca. 390 Ma. The I-type granitoids and MMEs from the Niubiziliang area represent a net addition of juvenile mantle to the crust and, given the wide distribution of contemporaneous I-type granitoids, the post-collisional magmatism has significantly contributed to the growth of the continental crust in the NQOB.