Two orogenic cycles recorded by eclogites in the Yuka–Luofengpo terrane: implications for the Mesoproterozoic to early Paleozoic tectonic evolution of the North Qaidam orogenic belt, China.
Two orogenic cycles recorded by eclogites in the Yuka–Luofengpo terrane: implications for the Mesoproterozoic to early Paleozoic tectonic evolution of the North Qaidam orogenic belt, China.
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尤卡·落风坡地体榴辉岩记录的两次造山旋回:对柴达木北造山带中元古代至早古生代构造演化的启示.
DOI：
10.1016/j.precamres.2019.105449
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发表时间：
2019
影响因子：
3.8
通讯作者：
Luo F H
中科院分区：
文献类型：
--
作者：
Ren Y F;Chen D L;Zhu X H;Ren Z L;Gong X K;Luo F H
记录两个造山旋回的榴辉岩不仅包含有关最近造山旋回期间俯冲和折返机制的基本信息，而且还可以提供对较早造山旋回的洞察。这类岩石是破译具有多造山史的造山带构造演化的理想工具。以中国西北部的柴达木北造山带为例，我们首次发现了保存两个造山旋回记录的榴辉岩。第一次造山事件发生在约929-916 Ma，第二次造山事件发生在约439-430 Ma。两个事件的变质温度条件分别为5.0~7.0kbar/6 16~6 6 9 °C和2 9.0~32.5kbar/6 2 0~6 70 °C。锆石U-Pb测年得出这些榴辉岩的原岩年龄为1280~1070 Ma，比北青藏高原其他榴辉岩的原岩年龄要早得多。榴辉岩具有球粒陨石标准化的稀土元素配分模式，呈扁平或亏损轻稀土元素，类似于今天的N-MORB和E-MORB。榴辉岩中的岩浆锆石核具有较高的εHf(T)值，在8.4 ± 4.0~18.1 ± 1.1之间，与亏损地幔在不确定度范围内相当，表明其来自年轻的地壳起源。我们的资料表明，榴辉岩原岩可能是在大洋俯冲过程中侵位在活动大陆边缘的前Rodinia中元古代洋壳，并经历了与Rodinia和早古生代大陆深俯冲融合有关的新元古代变质作用。利用已发表的榴辉岩及其寄主片麻岩资料，我们重建了NQOB中元古代至早古生代的构造演化。考虑到NQOB与邻近塔里木地块中-新元古代演化的相似性，我们认为柴达木地块是新元古代塔里木地块向东的延伸。
Eclogites documenting two orogenic cycles not only contain essential information on subduction and exhumation mechanisms during the most recent orogenic cycle, but can also provide insights into the earlier cycle. Such rocks are ideal for deciphering the tectonic evolution of orogenic belts with a multi-orogenic history. This is the case for the North Qaidam orogenic belt (NQOB) in northwest China where, for the first time, we have discovered eclogites that preserve a record of two orogenic cycles. The first orogenic event occurred at ca. 929–916 Ma and the second at ca. 439–430 Ma. The metamorphicP–Tconditions of these two events were 5.0–7.0 kbar/616–669 °C and 29.0–32.5 kbar/620–670 °C, respectively. Zircon U–Pb dating yielded protolith ages of 1280–1070 Ma for these eclogites, which are much older than the protolith ages for other eclogites in the NQOB. The eclogites exhibit chondrite-normalized rare earth element patterns that are flat or depleted in light rare earth elements, similar to present-day N- and E-MORB. Magmatic zircon cores from the eclogites have highεHf(t) values of 8.4 ± 4.0 to 18.1 ± 1.1, comparable to depleted mantle within uncertainty, and indicating a juvenile crustal origin. Our data show that the eclogite protoliths were probably pre-Rodinia Mesoproterozoic oceanic crust that was emplaced in an active continental margin during oceanic subduction, and experienced Neoproterozoic metamorphism related to the amalgamation of Rodinia and early Paleozoic continental deep subduction. Using published data for all eclogites and their host gneisses, we reconstructed the Mesoproterozoic to early Paleozoic tectonic evolution of the NQOB. Given the similar Meso–Neoproterozoic evolution of the NQOB and adjacent Tarim Block, we suggest that the Qaidam Block was the eastward extension of the Tarim Block during the Neoproterozoic.