内蒙古早二叠世板块窗上岩浆活动:对古亚洲洋俯冲过程和地壳增生的启示

IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Solid Earth Sciences Pub Date : 2022-06-15 DOI:10.1016/j.sesci.2022.02.001
Jialiang Li , Jingao Liu , James M. Scott , Chen Wu , Di-Cheng Zhu , Liangliang Zhang
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引用次数: 2

摘要

确定俯冲带的岩浆岩组合对于理解相关的地球动力学演化具有重要意义。古亚洲洋的最终闭合时间和确切的俯冲过程一直存在争议,阻碍了我们对中亚造山带构造演化的认识。本文对内蒙古北部西乌金琴地区早二叠世辉长花岗闪长岩进行了研究。辉长岩的轻稀土元素[(La/Yb)N = 0.8]和重稀土元素(HREE) [(Gd/Yb)N = 1.1]的含量与N- morb相当。全岩εNd(t)值为+7.7 ~ +8.7,锆石εHf(t)值为+8.7 ~ +10.6。这些基性岩石被解释为被板块衍生流体交代的衰竭地幔部分熔融的产物,随后发生了部分结晶和轻微的地壳污染。这些花岗闪长岩的化学性质与典型的埃达克岩相似,具有类似morb的全岩SrNd同位素组成(87Sr/86Sri = 0.7028-0.7029;εNd(t) = +8.2 ~ +8.5),正锆石εHf(t) = +13.4 ~ +15.9,表明它们起源于俯冲的板块熔体,与地幔楔橄榄岩发生反应。UPb锆石定年显示,n - morb型辉长岩和阿达基花岗闪长岩分别在~ 297 Ma和~ 290 Ma侵位。我们的新数据表明,存在同时期的板块衍生埃达奇岩和板块流体交代软流层衍生的n - morb型岩石,表明俯冲作用至少持续到早二叠世。这种联系与蒙古北部的伸展性岩浆作用共同记录了晚石炭世-早二叠世古亚洲洋脊向北俯冲的过程。该模型与该区岩浆活动的空间分布和年龄一致,εNd(t) -εHf (t)为正。洋脊俯冲和诱发的板块窗可能在古生代CAOB的地壳生长中发挥了关键作用,并由此推断在整个地球历史上的其他增生造山带中也发挥了关键作用。
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Early Permian magmatism above a slab window in Inner Mongolia, North China: Implications for the Paleo-Asian Ocean subduction processes and accretionary crustal growth

Identifying magmatic rock associations in a subduction zone is substantial for understanding the related geodynamic evolution. The final closure time of the Paleo-Asian Ocean and the exact subduction processes have continuously been controversial, hindering our recognition of the tectonic evolution of the Central Asian Orogenic Belt (CAOB). Here we investigated the Early Permian gabbros-granodiorites from Xi Ujimqin in the northern Inner Mongolian region. The gabbros have slightly depleted light rare-earth elements [(La/Yb)N = 0.8] and flat heavy rare earth elements (HREE) [(Gd/Yb)N = 1.1] that are comparable to those of N-MORB. They show depletion in Nb and Ta, positive whole-rock εNd(t) values of +7.7 to +8.7 and zircon εHf(t) values of +8.7 to +10.6. These mafic rocks are interpreted to be products of partial melting of depleted mantle that had been metasomatized by slab-derived fluids, with subsequent fractional crystallization and minor crustal contamination. These granodiorites chemically resemble typical adakites and have MORB-like whole-rock SrNd isotopic compositions (87Sr/86Sri = 0.7028–0.7029; εNd(t) = +8.2–+8.5) and positive zircon εHf(t) (+13.4–+15.9) values, suggesting that they originated from the subducted slab-melts and reacted with mantle wedge peridotite. UPb zircon dating shows emplacement of N-MORB-type gabbros and adakitic granodiorites at ∼297 Ma and ∼290 Ma, respectively. Our new data indicate the presence coeval slab-derived adakites and slab fluid-metasomatized asthenosphere-derived N-MORB-type rocks, indicating that subduction lasted until at least the Early Permian. Such an association along with the extension-related magmatism in northern Mongolia recorded the northward ridge subduction of the Paleo-Asian Ocean during the Late Carboniferous–Early Permian. This model is consistent with the spatial distribution and the ages of magmatic activity with positive εNd(t)–εHf(t) values from this region. Ridge subduction and induced slab windows probably played a key role in Paleozoic crustal growth of CAOB, and by inference in the other accretionary orogens throughout Earth history.

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来源期刊
Solid Earth Sciences
Solid Earth Sciences GEOSCIENCES, MULTIDISCIPLINARY-
CiteScore
3.60
自引率
5.00%
发文量
20
审稿时长
103 days
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