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Article

Zircon Systematics of the Shionomisaki Volcano–Plutonic Complex (Kii Peninsula, Japan): A Potential Tool for the Study of the Source Region of Silicic Magmas

by
Ulrich Knittel
1,*,
Monika Walia
2 and
Shigeyuki Suzuki
3
1
Research Unit Petrology and Fluid Processes, RWTH Aachen University, 52056 Aachen, Germany
2
Department of Geosciences, National Taiwan University, Taipei 106, Taiwan
3
Department of Earth Sciences, Okayama University, Okayama 700-8530, Japan
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(5), 537; https://doi.org/10.3390/min15050537
Submission received: 25 February 2025 / Revised: 22 April 2025 / Accepted: 7 May 2025 / Published: 18 May 2025
(This article belongs to the Special Issue Igneous Rocks as Archives of Earth's Geological History: Magma Processes and Continental Crust Evolution)
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Abstract

:
The Shionomisaki Igneous Complex is part of the Mid Miocene igneous province developed within the Shimanto Accretionary Complex in front of the volcanic front in SW Japan. The igneous rocks in this province mostly have silicic compositions. New U-Pb ages obtained for two samples from the Shionomisaki Complex at the southern tip of the Kii Peninsula (14.6 ± 0.4 Ma and 14.9 ± 0.4 Ma) fall into the range of previous age determinations (14.6 ± 0.2 to 15.4 ± 0.3 Ma). Hf isotopic compositions obtained for co-magmatic zircon (εHf(t) = −0.7 to +4.8) lie between typical values obtained for mantle-derived magmas and values obtained for old crustal rocks. They are thus consistent with previous interpretations that the magmas are mixtures of mantle and crustally derived magmas. In the modelling of the isotopic characteristics of the magmas, the sediments of the Shimanto belt are taken as the protolith of the silicic magmas. Xenocrystal zircon (i.e., zircon picked up during ascent and emplacement of the magma) found in the silicic igneous rocks exhibits a similar age pattern as detrital zircon of the Shimanto sediments. However, the age pattern obtained in this study for zircon cores, which are considered to be restitic zircon (i.e., zircon derived from the source of the anatectic melt), shows little semblance with the age pattern of Shimanto sediments. It is, therefore, tentatively suggested that the source area of the silicic magmas may not be identical with the sediments of the Shimanto Accretionary Complex.

1. Introduction

The subduction of oceanic crust usually leads to the generation of magmas that result in the formation of magmatic arcs. Commonly, the igneous centres closest to the trench form a well-defined volcanic front. Volcanism closer to the trench, i.e., in the forearc area, is rarely developed. One example is the intrusive/extrusive activity at about 15.5 to 13.5 Ma in the Cretaceous to Paleogene Shimanto Accretionary Complex (Figure 1) that extends along the Pacific Ocean side of south-western Japan (e.g., [1,2,3]). The tectonic setting of this magmatism, the processes leading to magma generation, and the sources of the magmas have been the topic of numerous studies (e.g., [3,4,5,6]); however, no consensus has been reached. Regarding the nature of the protolith of the anatectic, silicic magmas, there are two interpretations: one argues for continuous subduction, and as a consequence, the magmas should have been generated through the melting of the Shimanto sediments (e.g., [6]). The competing model calls for a collision event and suggests that underthrust “exotic” sialic crust is the source of the silicic magmas (e.g., [5,7]).
Zircon, one of the most commonly used minerals in geochronology, is able to survive crustal anatexis (e.g., [8]). Therefore, the study of zircon, inherited from the source of the magmas (commonly referred to as restitic zircon), may provide an indication of the nature of the protolith of silicic magmas (e.g., [9,10]).
This study deals with the Shionomisaki Igneous Complex, one of the Mid Miocene volcano–plutonic complexes that intrude in the Shimanto Accretionary Complex. This complex, located at the southern tip of the Kii Peninsula (Figure 2), presents the interesting case of being constituted of both silicic and mafic volcanics [4,11]. This led to the hypothesis that mafic magmas have intruded the lower crust, leading to its melting, and thus producing the siliceous melts (e.g., [4]).
The age of the igneous complex has been inferred to be 15–16 Ma, based on the radiolaria age of the Kumano group sediments, with the rhyolites interfingering [4,12,13]. Subsequently, Hoshi et al. [14] presented fission track ages ranging from 15.2 ± 0.3 to 13.1 ± 0.6 Ma for various petrologic units. Shinjoe et al. [15] presented U-Pb age data for zircons that essentially confirm previous age estimates. In a later publication [3], these authors report ages of 14.60 ± 0.22, 15.01 ± 0.19, and 15.38 ± 0.29 Ma for a dolerite, a rhyolite and a gabbro, respectively.
Here, additional U-Pb data and cathodoluminescence pictures for zircons are presented for a rhyolite and a granophyre. These data are then used to propose a way to investigate the source of these magmas. For the purpose of the present discussion, in this paper, we refer to zircon derived from the source of the magma as resititic zircon and to zircon derived from wall rocks as xenocrytic zircon (e.g., [9]). Restitic zircon that forms cores of the zircon grains may provide clues to the nature of the source rock of the acid melts.

2. Geological Setting and Samples

The Shimanto belt extends along the Pacific Ocean side of SW Japan (Figure 1). Its northern boundary is a regional, north-dipping thrust, the Butsuzo Tectonic Line (BTL). The belt is subdivided into a Cretaceous sub-belt and a Paleogene to Lower Miocene sub-belt by the Gobo–Totsugawa Tectonic Line. The Shimanto belt consists of thick marine clastic strata with minor oceanic crust-derived olistoliths (basaltic pillow lavas, hyaloclastites). The whole is severely deformed (e.g., [16]).
Within a short period, between 15.5 and 13.5 Ma, the Shimanto Accretionary Complex was the site of intrusive and extrusive igneous activity producing mainly silicic magmas. The Mid Miocene igneous complexes [3] exhibit a remarkable petrologic diversity (e.g., [5]). With respect to the Setouchi Volcanic Zone that developed slightly later and is considered to represent the volcanic front at 13 Ma (Tatsumi and Ishizaka, 1982 [17]), the Shimanto magmatic province is located in the forearc position.
Samples were collected from units previously not dated. Rhyolite sample J03-2 comes from a dike intruding the late Early to early Middle Miocene Kumano Formation [13]. These gently dipping shallow marine sediments (mainly sandstone and mudstone) overlay the deformed successions of the Shimanto Belt and are covered by Middle Miocene rhyolitic extrusive igneous rocks [18]. J03-2 contains phenocrysts of quartz with diameters of up to 2 mm, typical embayments, and reaction rims at the contact with the matrix. Other phenocrysts are sanidine and, less commonly, plagioclase that occasionally form glomerocrysts. The mafic mineral was probably biotite, which is largely altered to oxides and chlorite, possibly due to decreasing vapour pressure during ascent. The phenocrysts are set in a fine-grained, crystalline matrix.
Sample J03-3 is a granophyre with local graphic intergrowths of quartz and feldspar. Both K-feldspar and plagioclase are present; however, due to strong sericitisation, their relative volumes cannot be determined. Primary mafic minerals could not be observed, but secondary chlorite forms pseudomorphs after such minerals. The most common accessory mineral is sphene.

3. Analytical Procedures

The zircons were dated at the Department of Geosciences of the National Taiwan University using an Agilent 7500s quadrupole ICP-MS instrument (Argilent, Santa Clara, CA, USA) equipped with a Photon Machines 193 nm Analyte G2 excimer laser ablation system (Teledyne Photon Machines, Belgrade, MT, USA). The laser beam had a diameter of about 30 μm. The system was calibrated using the GJ-1 zircon standard [19], whereas the 91500 zircon and the Plešcovice zircon were used for data quality control. The 206Pb/238U ages obtained in the period of study were for 91500: 1062 ± 20 Ma (2σ) and for Plešcovice: 333.9 ± 6.8 Ma (2σ) compared to accepted values of 1062.4 ± 0.4 Ma and 337.1 ± 0.4 Ma, respectively [20,21]. All U-Th-Pb isotope ratios were calculated using the GLITTER 4.0 (GEMOC) software, and common lead was corrected using the common lead correction function proposed by Andersen [22]. The weighted mean U-Pb ages were calculated using Isoplot v. 3.0 [23]. Additional details of the analytical procedures are provided by Chiu et al. [24], Shao et al. [25], and Knittel et al. [26]. Cathodoluminescence (CL) images were obtained using a Quanta 200F (ELECMI, Zaragoza, Spain) scanning electron microscope equipped with a MiniCL in low vacuum mode in the Department of Geosciences at the National Taiwan University. For Phanerozoic zircons, we used 206Pb/238U ages in the plots and discussion, whereas for Precambrian grains, we use 207Pb/206Pb ages that are considered to be more reliable and have smaller errors. Discordance was calculated as disc = (1 − 206Pb/238Uage/207Pb/235Uage) × 100 for zircon younger than 1 Ga and as disc = (1 − 207Pb/206Pbage/206Pb/238Uage) × 100 for zircon older than 1 Ga.
Hf isotopic analysis of zircons was conducted using the Nu Plasma HR Multi-Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS) connected to a Photon Machines 193 nm Analyte G2 laser system at the Institute of Earth Sciences, Academia Sinica, Taipei. Lu-Hf isotopic analyses were carried out on zircon grains that were previously dated and, where possible, on the same spot with a beam diameter of ca. 50 μm. Some dated grains were too small for Hf isotope analysis. Mud Tank (MT) zircon standard was analysed in the beginning and at the end of each run, comprising 10 spot analyses to evaluate the accuracy of the data. The average 176Hf/177Hf ratio obtained during the analyses was 0.282501 ± 0.000028 (n = 17). This value is in good agreement with the average 176Hf/177Hf value reported in literature, which is 0.282504 ± 44 [27].
εHf(t) values were calculated with reference to the chondritic reservoir (CHUR) at the time of zircon crystallisation. The decay constant for 176Lu of 1.865 × 10−11 year−1 [28], the present-day chondritic ratios of 176Hf/177Hf and 176Lu/177Hf, respectively, of 0.282772 and 0.0332 [29] were adopted to calculate εHf(t) values.

4. Results

CL pictures of zircon from rhyolite sample J03-2 show that many grains contain cores with rounded or embayed shape, the boundaries cutting off earlier oscillatory zoning (e.g., J02-2-16 and -4; Figure 3). A few cores also show sector zoning or are uniform.
We determined the U-Pb age for 55 spots on 43 zircons (Supplementary Materials). For eleven grains, we analysed cores and rims separately. In one case, we analysed separately zones that are bright and dark in CL, respectively. Ages measured range from 13.5 ± 0.8 Ma to 2.69 ± 0.03 Ga (2σ errors). For rims, ages obtained range from 14.2 to 146 Ma. In a few cases, cores and rims have nearly identical ages (Figure 3, analyses J03-2-23 and -11); hence, the rims are not overgrowths on inherited or xenocrystic zircon but on earlier-formed crystals, or the core has been completely reset. The 14 youngest ages (11 grains) scatter in the range from 13.5 to 17.0 Ma (Figure 4). For the nine youngest analyses, an age of 14.41 ± 0.47 Ma [MSWD = 1.3] is obtained; excluding the youngest grain, an age of 14.62 ± 0.38 Ma [MSWD = 0.63] is calculated. Inherited zircons have ages ranging from 23 Ma to 2.69 Ga. Most grains older than 1 Ga are highly discordant. For a core–rim pair (grain 40) with 207Pb/206Pb ages of 2.54 and 2.69 Ga, a discordia with an upper intercept at 2.71 Ga can be calculated. Moreover, for the light–dark grain (grain 39, 207Pb/206Pb ages are 2.10 and 2.07 Ga) together with grain 31, a discordia with an upper intercept of 2.69 Ga is calculated. Hf isotopes range from εHf(t) = 0.8 to 2.8 for the grains with ages around 15 Ma. Older grains have εHf(t) values in the range from −6.3 to +2.9 (Supplementary Materials).
We carried out 33 analyses on zircons from the granophyre sample J03-3 (Supplementary Materials). These grains rarely have extensive rims (Figure 5). The thirteen youngest analyses scatter from 13 to 18 Ma (the 13.0 Ma analysis has a relatively large 2σ error of ±2.0 Ma). For the 11 youngest grains, an average age of 14.90 ± 0.36 Ma [MSWD = 0.92] is calculated. Thirteen grains have ages in the range from 17 to 262 Ma, and three grains in the range from 1.67 to 3.14 Ma. Five discordant grains form a discordica with an upper intercept at 1896 ± 21 Ma and a lower intercept at 24 ± 13 Ma [MSWD = 0.78], which corresponds to the age of the intrusion, considering the error. εHf(t) values of zircons dated at ca. 15 Ma are −0.7 to 10.3, whereas those of older grains younger than 300 Ma scatter in the range from −6.6 to +7.4. For the five Precambrian grains, εHf(t) values fall in the range from 2.0 to 27.8 (Supplementary Materials).

5. Discussion

For the rhyolite sample (J03-2), which comes from a dike north of the Shionomisaki Complex proper, we obtain ages from 13.5 to 17.0 Ma for grains that we interpret as juvenile zircons and for rims considered to have grown in the rhyolitic magma around cores of variable age. As stated above, average ages of 14.4 ± 0.5 Ma and 14.6 ± 0.4 Ma are obtained depending on whether the youngest grain is included or excluded from the calculation. These ages are slightly younger than the age of 15.01 ± 0.19 Ma reported by Shinjoe et al. [3] for rhyolite from the main Shionomisaki Complex.
For the granophyre (J03-2), we obtain an age of 14.9 ± 0.4 Ma on the basis of the 11 youngest zircons. Its age is thus indistinguishable from that of the rhyolite, considering the errors. It is also in the range of ages obtained by Shinjoe et al. [3] for mafic rocks of the complex of 14.6 ± 0.2 Ma and 15.4 ± 0.3 Ma.
The ages reported here (14.6–14.9 Ma) agree well with the age determined on the basis of biostratigraphy (15–16 Ma) and by fission track dating (14.5 ± 0.5 Ma; [14]). Hence, there is apparently no age gap between the U-Pb and the fission track age as observed by Orihashi et al. [30] in the Kumano igneous complex.
Regarding the origin of the silicic magmas, Terakado et al. [31] and Shinjoe [6], on the basis of Sr and Nd isotopic data, concluded that the magmas of the outer zone are mixtures between depleted, mantle-derived magmas and magmas derived from crustal components. These crustal components could be either old sialic crust or sedimentary rocks derived from old crustal rocks. Based on oxygen isotopic data, Ishihara and Matsuhisa reached the same conclusion [32]. The presence of components derived from old continental crust in the sources of Mesozoic granites in SW Japan was also advocated by Jahn [33].
The values of εHf(t) obtained in this study for co-magmatic zircon with one exception (+10.3) fall into the range from −0.7 to +4.8 (Figure 6), i.e., between typical mantle values (εHf(t) > 16) that were found, for example, for volcanics in the Coastal Range of Taiwan with εHf(t) values of up to +25 [34] and typical crustal values (εHf(t) < −5) as observed for Early Cretaceous detrital zircon from SE China that reflect the current crustal composition (εHf(t) −5 to −20, e.g., [35,36]. Therefore, the Hf isotopic data are consistent with the mixing models proposed [6,31,32].
It might be noteworthy that the Hf isotopic compositions obtained for the Shionomisaki Complex are very similar to those of the ca. 80 Ma Okayama Granite located north of eastern Shikoku [33,37] (Figure 1). It is one of the plutons for which Jahn [33] identified old crustal components. Sr isotopic studies [38,39] of this pluton also provided evidence for mixing between magmas with lower and higher Sr isotopic ratios, respectively. Furthermore, the initial Sr isotopic ratios (87Sr/86Sri = 0.7068–0.7074), similar to that of the Shionomisaki Complex (0.7081 [31]), lie between typical mantle values (87Sr/86Sr < 0.7045) and typical crustal values (87Sr/86Sri > 0.7090). It thus appears that similar processes operated in the genesis of silicic magmas emplaced in SW Japan since the Cretaceous period.
For the Mid Miocene igneous rocks, the depleted member could be represented by the basalts erupted in a few localities that have initial 87Sr/86Sr values of 0.70348–0.70362 and εNd(t) of 3.6–8.2 [6,31].
Regarding the silicic end-member, two possibilities have been discussed. Studies modelling the isotopic characteristics of the silicic magmas as mixtures of depleted and enriched components have used the isotopic characteristics of the Shimanto sediments as enriched end-member [6,31,32]. This is based on the observation that an accretionary complex is typically underlain by the subducting slab on the ocean-ward side and crustal rocks on the continent side, and the Mid-Miocene intrusions, in particular the Shionomisaki Complex, occur on the ocean-ward side. In contrast, Stein et al. [5] suggest that the silicic magmas originate in older crust that has been emplaced in the course of a collision of the SW Japanese margin with a continental fragment, as suggested on the basis of tectonic studies (i.e., [5,40]). They summarise preliminary data indicating pressures of up to 0.67–0.78 GPa for crustal xenoliths, well below the depth commonly expected for an accretionary complex [5]. Crustal profiles [41,42] show that the accretionary wedge corresponding to the Neogene Shimanto Accretionary Complex has a maximum thickness of 7 km. It is underlain by two blocks referred to as upper island arc crust and lower island arc crust, extending to depths of 20–30 km. The nature of these blocks is not known.
A distinction between these two possibilities on the basis of isotopic signatures may be impossible, as the sediments of the Shimanto Accretionary Complex are composed of old recycled crust from SE China, and a possible deep continental crust emplaced during a collision event may have similar isotopic characteristics [33].
A way to obtain more information on the sources of the magmas may lie in the study of inherited zircon contained in the magmatic rocks. Inherited zircons are crystals that did not crystallise from the host magma but were picked up either from the source rock that melted (restitic zircon) or from the wall rock of the intrusion (xenocrystic zircon) (e.g., [9]). Distinguishing restitic zircon from xenocrystic zircon is a complex problem. In the case of the present study, we assume that zircon cores overgrown by wide rims are probably restitic zircon (extended contact between melt and zircon), while inherited zircon with thin rims or no rims are xenocrystic zircon (short contact between melt and zircon). This assumption is supported by the data obtained by Shinjoe et al. [3], who aimed to analyse rim ages to date the magmatic event. These authors nevertheless found numerous zircons older than the magmatism. These grains are probably xenocrystic zircon, as they do not have young rims or only thin rims, possibly due to short contact with the magma. A comparison of the age spectra of the xenocrystic zircons of [3] with that of detrital zircon from the Shimanto Accretionary Complex shows a certain similarity, supporting the assumption that the zircons are derived from the host rocks of the intrusions (Figure 7). In particular, both patterns have significant peaks at 60–100 Ma and at 170–200 Ma. The Shimanto pattern also has a significant peak at 1.85–1.90 Ga that is not seen in the inherited zircons of the 14–15 Ma igneous rocks. However, after analysing the data for the discordant grains of [3], discordia with upper intercepts of 1837 ± 47 Ma and 1853 ± 68 Ma are found for the Kumano and Ohmine rocks, respectively (Figure 8). Lower intercept ages of 12 ± 10 Ma and 44 ± 10 Ma confirm that the lead loss occurred during the Mid-Miocene magmatic event. A second, poorly defined discordia with an upper intercept at 2060 ± 33 Ma and a lower intercept at 42 ± 19 Ma corresponds to a minor peak in the Shinamto pattern. In the granophyre sample, a discordia for discordant zircons with an upper intercept at 1896 ± 21 Ma is likewise found. The lack of inherited zircon of Precambrian age and the presence of zircon defining discordia with Precambrian upper intercepts may suggest that that the Precambrian zircons are damaged by radiation for a sufficiently long enough time that they experience significant lead loss during their extended period of contact with hot magma.
In contrast to the xenocrystic zircons [3], the 170–200 Ma peak is completely absent in the samples analysed in this study (Figure 7). This suggests that the resitic zircons possibly come from a source different from the Shimanto Accretionary Complex.

6. Conclusions

Two samples from the Shionomisaki Igneous Complex, which is part of the 14–15 Ma magmatic province in the fore-arc area of SW Japan, were investigated. U-Pb ages obtained for zircon are compatible with previously reported ages of the complex.
Hf isotopic compositions obtained for co-magmatic zircon are compatible with previous interpretations of Sr, Nd, and O isotopic systematics, which posit that the melts are mixtures of magmas derived from depleted mantle and magmas derived from old continental crust or sediments derived from old continental crust.
Inherited zircon contained in 14–15 Ma magmatic rocks from the Kii Peninsula has age patterns resembling the patterns of detrital zircon from the Shimanto Accretionary Complex. Since the patterns for the igneous rocks are based on rim analyses, they probably represent xenocrystic zircon, picked up from the host rocks of the igneous complexes. In contrast, the age patterns of the samples studied here include xenocrystic and restitic zircon, and their age pattern does not resemble that of detrital zircon from the Shimanto Accretionary Complex. Though much more data is required to substantiate this hypothesis, it is tentatively concluded that another old component contributes to the magmas of the Shionomisaki Complex.

7. Outlook

In the present contribution, a way to investigate the sources of Mid-Tertiary fore-arc magmas is suggested. It will be necessary to analyse a much larger number of zircon cores, in particular for grains with wide rims, to determine whether the preliminary observation stands the test based on a much larger database.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/min15050537/s1.

Author Contributions

Conceptualization, U.K. and S.S.; Investigation, M.W. and S.S.; Resources, S.S.; Writing—review & editing, U.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding author.

Acknowledgments

The authors wish to thank Hao-Yang Lee for help with the measurements of Hf isotope compositions and, in particular, Sun-Lin Chung for generous access to the lab facilities. Comments of three anonymous reviewers were helpful in shaping the final manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Tectonic setting of Japan (left) and simplified map of the central part of south-western Japan (right) showing the exposure of ca. 14–15 Ma igneous rocks (black dots [3]) and the outcrops of the Cretaceous (dark grey) and the Paleogene Shimanto Accretionary Complex (light grey). MTL = Median Tectonic Line separating Inner (north) and Outer (south) Zones of SW Japan, OB = Okayama Batholith.
Figure 1. Tectonic setting of Japan (left) and simplified map of the central part of south-western Japan (right) showing the exposure of ca. 14–15 Ma igneous rocks (black dots [3]) and the outcrops of the Cretaceous (dark grey) and the Paleogene Shimanto Accretionary Complex (light grey). MTL = Median Tectonic Line separating Inner (north) and Outer (south) Zones of SW Japan, OB = Okayama Batholith.
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Figure 2. Geological map of the Shionomisaki Complex based on Miyake [11]. Squares show sampling points of this study (with sample number and age) and Shinjoe et al. ([3], with age only). Note that the dyke from which J03-2 was taken is too small to be shown on the map.
Figure 2. Geological map of the Shionomisaki Complex based on Miyake [11]. Squares show sampling points of this study (with sample number and age) and Shinjoe et al. ([3], with age only). Note that the dyke from which J03-2 was taken is too small to be shown on the map.
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Figure 3. Cathodoluminescence pictures of zircon from sample J03-2 illustrate that cores may be as young as the rims but may also be much older. Older rim ages might be mixed ages. Circles show the analysis points, and they have a diameter of ca. 30 μm.
Figure 3. Cathodoluminescence pictures of zircon from sample J03-2 illustrate that cores may be as young as the rims but may also be much older. Older rim ages might be mixed ages. Circles show the analysis points, and they have a diameter of ca. 30 μm.
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Figure 4. Concordia diagrams for the studied samples; insets show the youngest zircons.
Figure 4. Concordia diagrams for the studied samples; insets show the youngest zircons.
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Figure 5. Cathodoluminescence pictures of zircon from sample J160403-3 illustrate that a few grains have younger rims that are usually too small to be analysed.
Figure 5. Cathodoluminescence pictures of zircon from sample J160403-3 illustrate that a few grains have younger rims that are usually too small to be analysed.
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Figure 6. εHf(t) vs. age diagram for zircons from the Shionomisaki Complex. Shown for comparison are the corresponding values for zircons from the Okajayama Batholith (field Ok, unpublished data of the author) and from the Shimanto belt (open circles, data from [26]).
Figure 6. εHf(t) vs. age diagram for zircons from the Shionomisaki Complex. Shown for comparison are the corresponding values for zircons from the Okajayama Batholith (field Ok, unpublished data of the author) and from the Shimanto belt (open circles, data from [26]).
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Figure 7. Histograms for U-Pb zircon ages for the two samples analysed in this study. Shown for comparison are data for inherited zircon from 14–15 Ma magmatic rocks from the Kii Peninsula [3] and detrital zircon from the Shimanto Accretionary Complex on the Kii Peninsula [43,44,45].
Figure 7. Histograms for U-Pb zircon ages for the two samples analysed in this study. Shown for comparison are data for inherited zircon from 14–15 Ma magmatic rocks from the Kii Peninsula [3] and detrital zircon from the Shimanto Accretionary Complex on the Kii Peninsula [43,44,45].
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Figure 8. Discordia for discordant zircons from the Kumano Volcanic Complex (left) and the Ohmine Dike (right); data from [3].
Figure 8. Discordia for discordant zircons from the Kumano Volcanic Complex (left) and the Ohmine Dike (right); data from [3].
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Knittel, U.; Walia, M.; Suzuki, S. Zircon Systematics of the Shionomisaki Volcano–Plutonic Complex (Kii Peninsula, Japan): A Potential Tool for the Study of the Source Region of Silicic Magmas. Minerals 2025, 15, 537. https://doi.org/10.3390/min15050537

AMA Style

Knittel U, Walia M, Suzuki S. Zircon Systematics of the Shionomisaki Volcano–Plutonic Complex (Kii Peninsula, Japan): A Potential Tool for the Study of the Source Region of Silicic Magmas. Minerals. 2025; 15(5):537. https://doi.org/10.3390/min15050537

Chicago/Turabian Style

Knittel, Ulrich, Monika Walia, and Shigeyuki Suzuki. 2025. "Zircon Systematics of the Shionomisaki Volcano–Plutonic Complex (Kii Peninsula, Japan): A Potential Tool for the Study of the Source Region of Silicic Magmas" Minerals 15, no. 5: 537. https://doi.org/10.3390/min15050537

APA Style

Knittel, U., Walia, M., & Suzuki, S. (2025). Zircon Systematics of the Shionomisaki Volcano–Plutonic Complex (Kii Peninsula, Japan): A Potential Tool for the Study of the Source Region of Silicic Magmas. Minerals, 15(5), 537. https://doi.org/10.3390/min15050537

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