A mixed source for the Late Triassic Garzê-Daocheng granitic belt and its implications for the tectonic evolution of the Yidun arc belt, eastern Tibetan Plateau
A mixed source for the Late Triassic Garzê-Daocheng granitic belt and its implications for the tectonic evolution of the Yidun arc belt, eastern Tibetan Plateau
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DOI：
10.1016/j.lithos.2017.07.002
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发表时间：
2017-09
期刊：
影响因子：
3.5
通讯作者：
Tao Wu;Long Xiao;S. Wilde;Changqian Ma;Jia-Xi Zhou
中科院分区：
文献类型：
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作者：
Tao Wu;Long Xiao;S. Wilde;Changqian Ma;Jia-Xi Zhou
义敦弧带东部晚三叠世存在多个花岗质岩体，本文对其中七个岩体进行了研究。自西向东依次为苏错玛（235 ± 2 Ma）、阿吉森多（224 ± 2 Ma）、加多错（218 ± 1 Ma）、错角玛（219 ± 1 Ma）、马雄沟（225 ± 2 Ma）、东错（222 ± 3 Ma）和稻城（220 ± 2 Ma）岩体。多数岩体具有花岗岩成分，富含SiO2、Al 2 O3和K2 O + Na 2 O，而MgO、FeO* 和CaO含量较低。它们具有相似的微量元素模式，高场强元素（HFSE，例如，Nb和Ta）和富集大离子亲石元素（LILE，例如，Rb、Th和U）。苏措玛、加多措和东措岩体中的样品具有相似的锆石Hf同位素组成（εHf（t）分别为− 1.8 ~ − 0.3、− 3.1 ~ 0.4和− 4.6 ~ − 1.4），而阿吉森多岩体中的样品显示出更多的非放射成因Hf（εHf（t）= − 11.9 ~ − 4.8）。苏错玛岩体的87 Sr/86 Sr初始值最低（0.7060-0.7090），εNd（t）负值最小（-4.9 ~-3.3）;阿吉森多岩体的87 Sr/86 Sr初始值最高（0.7111-0.7160），εNd（t）负值最大（-7.9和-11.3）。所有样品具有相似的高放射成因Pb同位素组成（206 Pb/204 Pb = 18.6-19.4; 207 Pb/204 Pb = 15.7-15.8; 208 Pb/204 Pb = 39.1-40.4）。根据新的地球化学资料，确定了本区花岗岩类多为I型花岗岩，岩浆源区为变质的康定杂岩（被认为是扬子板块西部的基底）和基底的变质沉积物的混合物。而阿吉森多岩体中的花岗岩为S型花岗岩，是基底变质沉积物部分熔融的产物，只有少数组分来自康定杂岩。结合对先前发表的研究结果的评估，这些新的数据表明，在约1000年左右有一个主要的岩浆高峰。216 Ma，晚三叠世岩浆活动向甘孜-理塘缝合带东方向逐渐年轻。我们认为，板片回滚，随后板片断裂，最好地解释了这些花岗岩体的起源。
Many Late Triassic granitic plutons are present in the eastern Yidun arc belt (EYAB), and seven have been investigated in this study. From west to east, they are: the Sucuoma (235 ± 2 Ma), Ajisenduo (224 ± 2 Ma), Jiaduocuo (218 ± 1 Ma), Cuojiaoma (219 ± 1 Ma), Maxionggou (225 ± 2 Ma), Dongcuo (222 ± 3 Ma) and Daocheng (220 ± 2 Ma) plutons. Most of the plutons have granitic compositions and contain high SiO2, Al2O3and K2O + Na2O, but low MgO, FeO* and CaO contents. They have similar trace element patterns, with depletion in high field strength elements (HFSE, e.g., Nb and Ta) and enrichment in large-ion lithophile elements (LILE, e.g., Rb, Th and U). Samples from the Sucuoma, Jiaduocuo and Dongcuo plutons have similar zircon Hf isotopic compositions (εHf(t) = − 1.8 to − 0.3, − 3.1 to 0.4 and − 4.6 to − 1.4, respectively), whereas those from the Ajisenduo pluton exhibit more unradiogenic Hf (εHf(t) = − 11.9 to − 4.8). Additionally, the Sucuoma pluton has the lowest initial87Sr/86Sr values (0.7060–0.7090) but the least negative εNd(t) (− 4.9 to − 3.3) values, whereas samples from the Ajisenduo pluton have the highest initial87Sr/86Sr values (0.7111–0.7160), but the most negative εNd(t) values (− 7.9 and − 11.3). All the samples have similar high radiogenic Pb isotopic compositions (206Pb/204Pb = 18.6–19.4;207Pb/204Pb = 15.7–15.8;208Pb/204Pb = 39.1–40.4). Based on the new geochemical data, it is determined that most of the granitoids are I-type granites and the magma source was a mixture of the metamorphic Kangding Complex, which is considered to be the basement of the western Yangtze Craton, and metasediments from the basement. However, the samples from the Ajisenduo pluton are S-type granites that were derived from partial melting of basement metasediments with only limited components from the Kangding Complex. Together with an evaluation of previously-published work, these new data indicate a dominant magmatic peak at ca. 216 Ma for the Late Triassic granitoids of the YAB and that the ages of Late Triassic magmatism become younger eastward towards the Garzê-Litang suture zone. We consider that slab roll-back, with subsequent slab break-off, best explains the origin of these granitic plutons.