Important crustal growth in the Phanerozoic: Isotopic evidence of granitoids from east-central Asia
Important crustal growth in the Phanerozoic: Isotopic evidence of granitoids from east-central Asia
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DOI：
10.1007/bf02719146
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发表时间：
2000-03
影响因子：
1.9
通讯作者：
B. Jahn;Fu-Yuan Wu;D. Hong
中科院分区：
文献类型：
--
作者：
B. Jahn;Fu-Yuan Wu;D. Hong
一般认为，大陆地壳的生长在前寒武纪基本上已经完成，而新生代地壳的数量被认为微不足道。显生宙中生长可忽略不计的想法现在受到了挑战，因为在几个造山带中发现了500至100 Ma时期产生的大量幼年地壳。虽然在北美（加拿大科迪勒拉山脉，塞拉利昂内华达州和半岛山脉，阿巴拉契亚山脉）已记录基于Nd同位素数据的少年地壳的可观的量，新的地壳的质量形成在东中亚造山带（ECAOB），阿尔泰构造拼贴的东部，似乎是远远大于上述地壳的总和。新近发表的Nd-Sr同位素数据表明，ECAOB（新疆-蒙古西部-内蒙古-中国东北）南带以及蒙古和外贝加尔地区的中生代花岗岩类都是由亏损地幔成分为主的源区形成的。这些花岗岩类代表了新生代地壳的显著增长，虽然这条巨大的造山带中的大多数岩体属于钙碱性系列，但ECAOB也具有大量A型花岗岩侵位的特征。这些岩石的起源可能是多方面的，目前仍有广泛的争议。然而，ECAOB中A型花岗岩的Sr-Nd-O同位素数据和微量元素丰度模式清楚地表明它们的地幔起源，ECAOB和整个阿尔泰拼贴的演化很可能与弧杂岩的连续增生有关。然而，大量构造后A型花岗岩的侵位需要另一种机制--可能是通过一系列过程，包括块状玄武岩浆的底侵作用，基性岩的部分熔融产生花岗岩液体，随后是广泛的分离结晶。幼年地壳与再生地壳的比例，以及与弧有关的大陆地壳与地幔柱生成的大陆地壳的比例，仍有待于通过更系统的测年和同位素示踪研究加以评估。
The growth of the continental crust is generally believed to have been essentially completed in the Precambrian, and the amount of juvenile crust produced in the Phanerozoic is considered insignificant. Such idea of negligible growth in the Phanerozoic is now challenged by the revelation of very large volume of juvenile crust produced in the period of 500 to 100 Ma in several orogenic belts. While appreciable volumes of juvenile terranes in North America (Canadian Cordillera, Sierra Nevada and Peninsular Range, Appalachians) have been documented based on Nd isotopic data, the mass of new crust formed in the East-Central Asian Orogenic Belt (ECAOB), eastern part of the Altaid Tectonic Collage, appears to be much greater than the above terranes combined. New and published Nd-Sr isotope data indicate that the Phanerozoic granitoids from the southern belt of the ECAOB (Xinjiang-West Mongolia-Inner Mongolia-NE China) as well as from Mongolia and Transbaikalia were generated from sources dominated by a depleted mantle component. These granitoids represent a significant growth of juvenile crust in the Phanerozoic.Although most plutons in this huge orogenic belt belong to the calc-alkaline series, the ECAOB is also characterized by the emplacement of voluminous A-type granites. The origin of these rocks is probably multiple and is still widely debated. However, the isotopic data (Sr-Nd-O) and trace element abundance patterns of A-type granites from the ECAOB clearly indicate their mantle origin.The evolution of the ECAOB and the entire Altaid Collage is most likely related to successive accretion of arc complexes. However, the emplacement of a large volume of post-tectonic A-type granites requires another mechanism—probably through a series of processes including underplating of massive basaltic magma, partial melting of these basic rocks to produce granitic liquids, followed by extensive fractional crystallization. The proportion of juvenile to recycled, as well as that of arc-related to plume-generated, continental crust remains to be evaluated by more systematic dating and isotope tracer studies.