Solidification pressures and ages recorded in mafic microgranular enclaves and their host granite: An example of the world's youngest Kurobegawa granite

IF 1 4区 地球科学 Q4 GEOSCIENCES, MULTIDISCIPLINARY
Island Arc Pub Date : 2022-09-12 DOI:10.1111/iar.12462
Kota Suzuki, Tetsuo Kawakami, Shigeru Sueoka, Ayu Yamazaki, Saya Kagami, Tatsunori Yokoyama, Takahiro Tagami
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Abstract

Solidification pressures and ages of mafic microgranular enclaves (MMEs) and their host granite were determined and compared based on Al-in-hornblende geobarometry and U–Pb zircon dating in two sample localities in the Kurobegawa Granite. In sample KRG19-A03 from the middle unit of the pluton, the MME and the host granite yielded 0.18 ± 0.03 to 0.24 ± 0.04 GPa and 0.16 ± 0.03 to 0.23 ± 0.04 GPa, respectively. The MME and the host granite of sample KRG19-B08b from the lower unit, respectively, yielded 0.12 ± 0.02 to 0.21 ± 0.03 GPa and 0.13 ± 0.02 to 0.18 ± 0.03 GPa. In each sample locality, the estimated solidification pressures of the MME and its host granite overlap. The weighted mean ages were calculated as 0.775 ± 0.045 Ma and 0.831 ± 0.055 Ma for the MME and the host granite of KRG19-A03, respectively. The MME and the host granite of KRG19-B08b, respectively, yielded 0.672 ± 0.033 Ma and 0.735 ± 0.042 Ma. The ages for MMEs tend to be younger than the host granites, although they overlap within uncertainty. Zircon commonly occurs as the matrix minerals in both lithologies, meanwhile, zircon also occurs as early phases in plagioclase cores only in the host granites. Such differences in mode of occurrence of zircon suggest that the age variation reflects the differences in timing of zircon crystallization between the lithologies. Therefore, the MMEs record the same solidification pressures as the host granites and better represent the final solidification timing of the pluton. From these data of the MMEs, an average exhumation rate of each sample locality was estimated as 7.1–14.5 mm/year (KRG19-A03) and 5.5–14.4 mm/year (KRG19-B08b). These exhumation rates are much larger than that of the ca. 5.6–5.2 Ma Shiaidani Granodiorite (0.93–2.5 mm/year), implying that drastic change of the exhumation rate took place between ca. 5.2 Ma and ca. 0.83 Ma.

在基性微颗粒包裹体及其宿主花岗岩中记录的凝固压力和年龄:世界上最年轻的黑北川花岗岩的一个例子
利用al -角闪石地球气压测定法和U-Pb锆石定年法测定了黑北川花岗岩中基性微颗粒包体(MMEs)及其寄主花岗岩的凝固压力和凝固年龄。在岩体中单元的KRG19-A03样品中,MME和寄主花岗岩分别产生0.18±0.03 ~ 0.24±0.04 GPa和0.16±0.03 ~ 0.23±0.04 GPa。下单元KRG19-B08b样品的MME和寄主花岗岩分别产生0.12±0.02 ~ 0.21±0.03 GPa和0.13±0.02 ~ 0.18±0.03 GPa。在每个样品位置,MME及其宿主花岗岩的估计凝固压力重叠。KRG19-A03岩浆岩和寄主花岗岩的加权平均年龄分别为0.775±0.045 Ma和0.831±0.055 Ma。KRG19-B08b的MME和寄主花岗岩分别产生0.672±0.033 Ma和0.735±0.042 Ma。MMEs的年龄往往比寄主花岗岩年轻,尽管它们在不确定范围内重叠。锆石通常作为基质矿物存在于两种岩性中,同时,锆石也仅在寄主花岗岩中以早期阶段出现在斜长石岩芯中。锆石赋存方式的差异表明,年龄的变化反映了不同岩性锆石结晶时间的差异。因此,MMEs记录了与寄主花岗岩相同的凝固压力,较好地反映了岩体的最终凝固时间。各样地的平均掘出率分别为7.1 ~ 14.5 mm/年(KRG19-A03)和5.5 ~ 14.4 mm/年(KRG19-B08b)。其掘出速率远高于约5.6 ~ 5.2 Ma石岱尼花岗闪长岩(0.93 ~ 2.5 mm/年),表明在约5.2 ~ 0.83 Ma之间发生了剧烈的掘出速率变化。
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来源期刊
Island Arc
Island Arc 地学-地球科学综合
CiteScore
2.90
自引率
26.70%
发文量
32
审稿时长
>12 weeks
期刊介绍: Island Arc is the official journal of the Geological Society of Japan. This journal focuses on the structure, dynamics and evolution of convergent plate boundaries, including trenches, volcanic arcs, subducting plates, and both accretionary and collisional orogens in modern and ancient settings. The Journal also opens to other key geological processes and features of broad interest such as oceanic basins, mid-ocean ridges, hot spots, continental cratons, and their surfaces and roots. Papers that discuss the interaction between solid earth, atmosphere, and bodies of water are also welcome. Articles of immediate importance to other researchers, either by virtue of their new data, results or ideas are given priority publication. Island Arc publishes peer-reviewed articles and reviews. Original scientific articles, of a maximum length of 15 printed pages, are published promptly with a standard publication time from submission of 3 months. All articles are peer reviewed by at least two research experts in the field of the submitted paper.
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