Microdiamond in a low-grade metapelite from a Cretaceous subduction complex, western Kyushu, Japan
Microdiamond in a low-grade metapelite from a Cretaceous subduction complex, western Kyushu, Japan
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DOI：
10.1038/s41598-020-68599-7
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发表时间：
2020-07
影响因子：
4.6
通讯作者：
T. Nishiyama;H. Ohfuji;Kousuke Fukuba;M. Terauchi;Ukyo Nishi;Kazuki Harada;Kouhei Unoki;Yousuke Mo
中科院分区：
文献类型：
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作者：
T. Nishiyama;H. Ohfuji;Kousuke Fukuba;M. Terauchi;Ukyo Nishi;Kazuki Harada;Kouhei Unoki;Yousuke Mo
变质岩中的微金刚石是超高压（UHP）变质作用的标志，主要发生在大陆碰撞带。除柯石英和微金刚石外，大多数超高压矿物在折返过程中已部分或全部退变质，因此，柯石英和微金刚石的发现对识别超高压变质作用和了解变质岩的构造历史至关重要。微金刚石通常作为矿物如石榴石中的内含物出现。本文报道了在日本九州西部长崎变质杂岩的西曾野组中发现的一种变质岩基质中的微金刚石集合体。Nishisonogi单元代表白垩纪俯冲杂岩，被认为是绿帘石-蓝片岩亚相变质单元，变岩是Nishisonogi单元中蛇纹岩混杂岩的成员。根据石墨的拉曼显微光谱，Nishisonogi装置的温度条件为450 °C。显微金刚石和镁碳酸盐的共存表明，在高于2.8GPa的压力下，显微金刚石从C-O-H流体中沉淀出来。这是日本首次报道的变质微金刚石，揭示了西曾木单元隐藏的超高压历史。日本列岛九州的构造演化应根据这一发现重新考虑。
Microdiamonds in metamorphic rocks are a signature of ultrahigh-pressure (UHP) metamorphism that occurs mostly at continental collision zones. Most UHP minerals, except coesite and microdiamond, have been partially or completely retrogressed during exhumation; therefore, the discovery of coesite and microdiamond is crucial to identify UHP metamorphism and to understand the tectonic history of metamorphic rocks. Microdiamonds typically occur as inclusions in minerals such as garnet. Here we report the discovery of microdiamond aggregates in the matrix of a metapelite from the Nishisonogi unit, Nagasaki Metamorphic Complex, western Kyushu, Japan. The Nishisonogi unit represents a Cretaceous subduction complex which has been considered as an epidote–blueschist subfacies metamorphic unit, and the metapelite is a member of a serpentinite mélange in the Nishisonogi unit. The temperature condition for the Nishisonogi unit is 450 °C, based on the Raman micro-spectroscopy of graphite. The coexistence of microdiamond and Mg-carbonates suggests the precipitation of microdiamond from C–O–H fluid under pressures higher than 2.8 GPa. This is the first report of metamorphic microdiamond from Japan, which reveals the hidden UHP history of the Nishisonogi unit. The tectonic evolution of Kyushu in the Japanese Archipelago should be reconsidered based on this finding.