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Article

Petrogenesis and Tectonic Implications of the Oligocene Dalongtan Shoshonitic Syenite Porphyry in Central Yunnan, Southeastern Tibetan Plateau: Constraints from Geochronology, Geochemistry and Sr-Nd-Hf Isotopes

by
Hang Yang
1,
Anlin Liu
1,*,
Peng Wu
1,* and
Feng Wang
1,2
1
Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China
2
Yunnan Metallurgy Resources Exploration Co., Ltd., Kunming 651100, China
*
Authors to whom correspondence should be addressed.
Minerals 2024, 14(3), 282; https://doi.org/10.3390/min14030282
Submission received: 31 January 2024 / Revised: 25 February 2024 / Accepted: 4 March 2024 / Published: 8 March 2024
(This article belongs to the Special Issue Petrogenesis, Magmatism and Geodynamics of Orogenic Belts)
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Abstract

:
Shoshonitic rocks are widely distributed in post-collisional settings and provide key information on deep geodynamic mechanisms and magmatic evolution. In this paper, we present petrographic, zircon U-Pb age-related, trace elemental, Hf isotopic, bulk-rock elemental, and Sr-Nd isotopic data of the Dalongtan shoshonitic syenite porphyries (DSSPs) in central Yunnan, southeastern Tibet. The DSSPs formed at 33.2 ± 0.3 Ma in a post-collisional setting. They define linear trends on Harker diagrams, and they display similar trace element patterns and enriched bulk-rock Sr-Nd isotopes [(87Sr/86Sr)i = 0.70964–0.70968, εNd(t) = −12.9 to −12.7] and zircon Hf isotopes (εHf(t) = −15.7 to −13.1) to the coeval mantle-derived potassic mafic rocks. This suggests that the DSSPs were fractionated from the lithospheric mantle-derived mafic magmas. The DSSPs, along with the coeval felsic and mafic magmatic rocks (37.2–32.3 Ma), exhibit a planar distribution on the SE Tibet and predate the left-lateral shearing of the Ailaoshan–Red River shear zone (ARSZ) (32–22 Ma), suggesting that there are no genetic relationships between them. The DSSPs have geochemical characteristics similar to those of A-type granites, with high total alkalinity (10.39–11.17 wt.%), HFSE concentrations (Zr + Nb + Ce + Y = 890.2–1054.3 ppm), Ga/Al ratios (10,000 × Ga/Al = 2.95–3.46), whole-rock zircon saturation temperatures (906–947 °C), and oxygen fugacity (ΔFMQ = +3.30–+4.65), indicating that they are products of the high-temperature melting of the lithosphere as a result of asthenosphere upwelling in extensional settings. Based on our data and regional observations, it is proposed that the generation of the DSSPs may be linked to the convective thinning of the thickened lithospheric mantle following the India–Asia collision.

1. Introduction

Shoshonitic rocks are a type of alkaline and high-potassium magmatic rock characterized by high alkalinity (K2O + Na2O > 5 wt.%), high K2O/Na2O ratios (>0.5), low TiO2 (<1.3 wt.%), high and variable Al2O3 (9–20 wt.%) contents, and enrichment in large-ion lithophile elements (LILEs) and light rare-earth elements (LREEs) [1]. These rocks can be classified into mafic and felsic types and occur in a variety of tectonic settings, including magmatic arcs [2] and post-collisional settings [3,4]. They are commonly triggered by distinct mantle processes involving slab breakoff [5] or lithospheric removal [6] under a thick lithosphere and thus provide an opportunity to understand deep geodynamic mechanisms and magmatic evolution [7,8]. It is widely accepted that the origin of mafic shoshonitic magma can be attributed to the partial melting of the subcontinental lithospheric mantle (SCLM) at depths of 50–150 km [9,10]. In contrast, the origin of felsic shoshonitic rocks is considerably more complex and controversial, involving mixing between enriched-mantle-derived melt and felsic crustal magma [11], the partial melting of the potassium-rich lower crust [12,13], the partial melting of the metasomatically enriched mantle associated with subduction [14], or the differentiation of mantle-derived mafic potassium-rich magmas [15,16]. These controversies mean that the petrogenesis and tectonic mechanisms of these rocks need to be further revealed.
In southeastern Tibet, Eocene–Oligocene potassic magmatic suites (including felsic shoshonitic rocks) commonly occur in the Ailaoshan–Red River shear zone (ARSZ), documenting the post-collisional processes of the India–Asia collision and providing significant magmatic evidence of crustal and mantle evolution [17,18]. Although numerous studies have been carried out on these felsic shoshonitic rocks [7,15,19,20,21,22,23], their petrogenesis and tectonic mechanisms remain controversial. The continued debate primarily revolves around two key aspects: (1) Which component, the thickened mafic lower crust or the lithospheric mantle, is responsible for the source region? (2) Is the emplacement of these potassic suites genetically linked to the left-lateral shearing of the ARSZ? In contrast to other felsic shoshonitic intrusions composed of orthoclase, amphibole, and biotite on the SE Tibetan Plateau [15,20,21], the Oligocene DSSPs are characterized by widespread sanidine phenocrysts and are spatially distant from the ARSZ and positioned closer to the interior of the Yangtze Craton. These samples are unique and provide an opportunity to reveal the petrogenesis and tectonic mechanisms of felsic shoshonitic rocks.
In this paper, we present zircon U-Pb ages, trace elemental and Hf isotopic data, and bulk-rock elemental and Sr-Nd isotopic data for the DSSPs in central Yunnan, southeastern Tibet. Our new data, together with data from adjacent regions in the literature [16,20,21,24,25], allow us to decipher the origin of felsic shoshonitic rocks and clarify their genetic relations to the ARSZ. Thus, this paper provides not only important insights into the genesis of felsic shoshonitic rocks on the SE Tibetan Plateau but also a good example of constrained tectonic mechanisms for the emplacement of potassic magmas in post-collisional settings.

2. Geological Setting and Petrography

The Himalayan–Tibetan Plateau formed via the India–Eurasia collision, which has been ongoing since the Cenozoic era, making it a prime example of a continent–continent collision orogenic belt on Earth [26,27,28,29,30]. Tectonically, the southeastern part of the Tibetan Plateau primarily comprises the Songpan–Garzê, Qiangtang (Simao Block in western Yunnan), and Lhasa terranes, as well as the Yangtze Craton, which are separated by the Jinsha and Bangong–Nujiang sutures (Figure 1a) [29,30]. The India–Asia collision resulted in remarkable potassic magmatism on the Tibetan Plateau and its southeastern margin, leading to the formation of the Eocene–Oligocene potassic magmatic suite, known as the Ailaoshan–Jinshajiang potassic igneous belt [8,29]. This magmatic suite is found not only in the vicinity but also distal to the Jinsha suture and the ARSZ, spanning over a distance of 2000 km across the Qiangtang terrane and western Yangtze Craton (WYC) (Figure 1a,b) [18,29]. It encompasses a wide range of lithologies, including both mafic and felsic compositions (Figure 1b).
The NW–SE-trending ARSZ is a major strike-slip shear zone in southwest China (Figure 1b), which extends for >1000 km from the Eastern Himalayan Syntaxis to the South China Sea [31] and consists of sets of metamorphic complexes in western Yunnan and north Vietnam [32]. It represents a significant outcome of Cenozoic intracontinental deformation, where localized transtensional or extensional movements potentially superimposed upon the early trans-lithospheric Jinsha suture, thereby shaping its geological characteristics [17,33]. Cenozoic potassic magmatic suites associated with the India–Asia collision are widespread in the general vicinity of the ARSZ (Figure 1b) [17,18]. The resultant potassic magmatic rocks exhibit a range of compositions, spanning from mafic to felsic. Mafic rocks (36.6–33.7 Ma) are dominated by lamprophyre dykes [4,17,34] with a few potassic lavas [4], whereas the felsic rocks form small-volume intrusions [8,24] comprising adakite-like granite, adakite-like or shoshonitic quartz monzonite, and shoshonitic syenite in lithology, some of which host porphyry-type mineralization [30,35,36]. The shoshonitic syenite porphyries are widely distributed in the Jianchuan, Liuhe, Yao’an, and Dalongtan areas of the southeastern Tibetan Plateau (Figure 1b).
Minerals 14 00282 g001
Figure 1. (a) Simplified tectonic map of SE Tibet (modified after [30]); (b) simplified geological map showing the distribution and age of Cenozoic potassic magmatic rocks in western Yunnan (modified after [18]); (c) geological sketch map of the Dalongtan syenite porphyry, showing the locations of the studied samples. Literature data are from [22,37,38,39,40,41] and references therein and are given in Supplementary Table S1.
Figure 1. (a) Simplified tectonic map of SE Tibet (modified after [30]); (b) simplified geological map showing the distribution and age of Cenozoic potassic magmatic rocks in western Yunnan (modified after [18]); (c) geological sketch map of the Dalongtan syenite porphyry, showing the locations of the studied samples. Literature data are from [22,37,38,39,40,41] and references therein and are given in Supplementary Table S1.
Minerals 14 00282 g001
This study focuses on DSSPs in the western margin of the Yangtze Craton but ~50 km east of the ARSZ (Figure 1b). The studied syenite porphyries form small-volume intrusions that occurred within Jurassic mudstones (Figure 1c and Figure 2a). The greyish-white syenite porphyry is characterized by a porphyritic texture and a massive structure (Figure 2). The phenocrysts are mainly composed of sanidine (~85%) and a minor amount of biotite (~15%), which make up about 40% of the whole rock (Figure 2). The groundmass is dominated by fine-grained alkaline feldspar (mainly sanidine and orthoclase) (25–30%), with smaller concentrations of plagioclase (10%), interstitial biotite (10%), and minor quartz (~5%) (Figure 2). The accessory minerals comprise zircon, titanite, monazite, allanite, and apatite.

3. Analytical Methods

Zircon in situ U-Pb dating, Lu-Hf isotopes, and bulk-rock Sr-Nd isotopes were determined at the Wuhan SampleSolution Analytical Technology Co., Ltd., Wuhan, China. Bulk-rock major and trace elements were measured at the Northwest Geological Testing Center, a laboratory of the China Nonferrous Metal Mining Group Co., Ltd., Xi’an, China.

3.1. Zircon Trace Elemental Analyses, U-Pb Dating, and Hf Isotopic Analyses

The processing of samples for zircon separation included crushing, initial heavy liquid separation, and subsequent magnetic separation. Hand-selected representative zircon grains were then mounted in epoxy resin, polished to approximately half of their thickness, and photographed under both reflected and transmitted light conditions. Cathodoluminescence (CL) imaging was employed to investigate the structures of zircon grains and analyze selected regions of interest.
Zircon U-Pb ages and trace elements for DLT-1 were measured using an Agilent 7900 ICP-MS instrument that was furnished with a 193 nm laser. The spot size and frequency of the laser were set to 32 µm and 5 Hz, respectively. Zircon Tanz and glass NIST610 were used as external standards for U-Pb dating and trace element calibration, respectively. The specific operating conditions for the laser ablation system, the ICP-MS instrument, and data reduction were implemented in accordance with the methodology outlined in [42]. ICPMSDataCal(ver 9.0) [43] was used for data reduction, and ISOPLOT (ver 3.0) [44] was used for age calculation and concordia diagrams.
Zircon in situ Hf isotope analysis was conducted using a Neptune Plus MC-ICP-MS equipped with a 193 nm Geolas HD excimer ArF laser ablation system. Lu-Hf isotopic data were acquired with a spot size of 44 μm. To ensure the reliability of the analysis data, three international zircon standards of Plešovice, 91,500, and GJ-1 were analyzed at the same time as the actual samples. Plešovice was used for external standard calibration to further optimize the analysis and test results. 91,500, and GJ-1 were used as the second standard to monitor the quality of data correction. The average 176Hf/177Hf ratios for Plešovice, 91,500, and GJ-1 were 0.2824780 ± 0.0000044 (2SD, n = 28), 0.282289 ± 0.000010 (2SD, n = 8), and 0.2819989 ± 0.0000091 (2SD, n = 8), respectively. These values are in close agreement with the recommended values [45].

3.2. Bulk-Rock Major and Trace Elemental Analyses

Fresh samples were selected and ground in an agate mortar to a grain size of <200 mesh. The bulk-rock major elements were analyzed using X-ray fluorescence (XRF) with a ZSX Primus II spectrometer. This showed that the duplicate and rock standard analyses of the samples exhibited relative standard deviations below 1%. Bulk-rock trace element concentrations were determined using X-7 ICP-MS with an analytical precision of ≥10%. Detailed operating conditions of the ICP-MS instrument and data reduction have been described by [46].

3.3. Bulk-Rock Sr-Nd Isotopic Analyses

The Sr and Nd elements were separated following the ion exchange column procedures, and their isotope ratios were measured using a Thermo-Finnigan Neptune MC-ICP-MS. For mass discrimination correction through internal normalization, a portion of the international standard solution with a concentration of 200 μg/L was utilized, leading to 88Sr/86Sr and 146Nd/144Nd ratios of 8.375209 and 0.7219 [47], respectively. During the testing process, the international NIST 987 standard and the GSB 04-3258-2015 standard were measured for every eight unknown samples analyzed. The analysis of the 87Sr/86Sr and 43Nd/144Nd ratios in the NIST 987 and GSB 04-3258-2015 standard solution resulted in measurements of 0.710244 ± 8 (2SD, n = 5) and 0.512440 ± 6 (2SD, n = 9), respectively, which are consistent with published (0.710248 ± 12; 0.512438 ± 6, respectively) values within the range of experimental error [48,49].

4. Results

4.1. Zircon Trace Elemental and U-Pb Results

The U-Pb dating and trace element analysis results are provided in Table 1 and Table 2, respectively, and illustrated through cathodoluminescence (CL) images and concordia diagrams, as well as normalized rare-earth element (REE) patterns (Figure 3). The zircon grains from the DSSPs are elongate, euhedral grains with a length of 80–200 µm (Figure 3a). They are usually transparent, with clearly oscillatory zoning, without inherited cores under CL images (Figure 3a). They have 1.2–8.1 ppm of Pb, 206–1863 ppm of Th, and 147–934 ppm of U, with Th/U = 1.3–2.0 (Table 1), and exhibit REE patterns characteristic of typical magmatic zircons [50]. The aforementioned features collectively indicate that the zircons have a typical magmatic origin [51]. The 206Pb/238U ages of 21 zircon grains from sample DLT-1 are 32.2–35.6 Ma, with a weighted average of 33.2 ± 0.3 Ma (MSWD = 1.5) (Figure 3b).
Table 1. LA-ICP-MS U-Pb data for zircon from the DSSP (DLT-1) in central Yunnan.
Table 1. LA-ICP-MS U-Pb data for zircon from the DSSP (DLT-1) in central Yunnan.
SpotPbThUCommon PbTh/U207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb207Pb/235U206Pb/238UConcordance
ppmppmppmppmRatio1σRatio1σRatio1σAge1σAge1σAge1σ
DLT-1-011.83378.13239.630.001.60.046710.005630.030540.003010.005120.0001335.3266.630.63.032.90.992%
DLT-1-022.30511.77283.440.041.80.047400.004820.032050.002580.005080.0001177.9216.632.02.532.70.798%
DLT-1-032.51517.11307.390.281.70.052260.004790.036510.002750.005320.00011298.2211.136.42.734.20.793%
DLT-1-043.23583.36440.630.161.30.048060.003400.033500.002200.005100.00009101.9159.233.52.232.80.697%
DLT-1-052.15443.20269.020.001.60.046370.004750.032720.002760.005260.0001116.8238.932.72.733.80.796%
DLT-1-065.001119.07602.310.001.90.047320.003200.033130.002010.005170.0000864.9155.533.12.033.20.599%
DLT-1-071.33251.01167.790.001.50.053740.007370.036260.004160.005270.00014361.2312.936.24.133.90.993%
DLT-1-086.071282.36739.770.001.70.048560.002910.034340.001830.005200.00007127.9133.334.31.833.40.597%
DLT-1-091.53276.03208.060.001.30.054430.006640.035600.003250.005260.00014387.1277.735.53.233.80.995%
DLT-1-101.62324.37202.070.001.60.059060.007920.037610.003710.005300.00017568.6291.637.53.634.11.190%
DLT-1-116.921516.30833.370.031.80.049970.003220.033940.001870.005060.00007194.5154.633.91.832.50.595%
DLT-1-121.59303.59206.710.001.50.046820.004990.032800.003370.005170.0001239.0237.032.83.333.20.798%
DLT-1-138.081862.66934.020.022.00.046850.002150.033590.001570.005220.0000642.7103.733.51.533.60.499%
DLT-1-141.17206.09146.560.361.40.050590.006970.035730.003910.005540.00016220.4301.835.63.835.61.199%
DLT-1-156.641413.88850.060.461.70.051880.003100.035410.001970.005000.00006279.7106.535.31.932.20.490%
DLT-1-162.53454.44343.950.091.30.047390.004570.032800.002850.005100.0000977.9205.532.82.832.80.699%
DLT-1-171.90358.39237.780.001.50.048250.005320.033330.002470.005470.00030122.3231.533.32.435.21.994%
DLT-1-186.671371.96818.030.001.70.047210.002800.033840.002060.005190.0000761.2133.333.82.033.40.498%
DLT-1-191.40272.84181.020.041.50.054060.006850.035080.003790.005050.00011372.3287.035.03.732.50.792%
DLT-1-213.43715.40405.040.001.80.050020.004210.036030.002470.005440.00011194.5194.435.92.435.00.797%
DLT-1-223.23747.15393.340.001.90.046990.004260.031570.002480.005150.0000955.7198.131.62.433.10.695%
Table 2. LA-ICP-MS trace elemental (ppm) data for zircon from the DSSP (DLT-1) in central Yunnan.
Table 2. LA-ICP-MS trace elemental (ppm) data for zircon from the DSSP (DLT-1) in central Yunnan.
SpotAge (Ma)TiYNbLaCePrNdSmEuGdTbDyHoErTmYbLuHfTaUEu/Eu*Ce/Ce*ΔFMQ
0132.98.875741.880.0288.40.213.224.162.6220.15.3953.318.473.914.913326.274090.592400.721263.41
0232.79.266712.450.061080.364.016.143.0023.86.3164.821.187.017.315129.673550.652830.66883.57
0334.28.946572.340.021070.284.045.382.9922.86.1262.720.085.016.615129.576170.683070.711153.51
0432.87.6314266.650.061550.365.017.263.9831.19.7211241.519039.736572.977010.894410.691253.99
0533.89.766552.520.031050.264.325.072.9323.26.1062.320.182.916.815229.978470.582690.691213.52
0633.27.8111615.420.031910.396.108.694.5234.99.9710134.614930.227653.977371.106020.691484.06
0733.910.35351.540.0375.00.262.954.792.5718.15.2851.917.270.713.912223.972660.501680.74863.30
0833.44.6810525.280.041790.313.956.573.5228.98.4388.031.113627.425550.083031.007400.661724.21
0933.87.386102.270.0288.10.213.554.362.4219.75.3754.318.880.016.114629.377590.622080.671223.68
1034.19.106251.960.0388.30.233.855.342.7619.85.7857.619.481.315.814128.369650.492020.721123.53
1132.56.8912597.200.052170.385.558.534.3634.69.9410436.415832.930059.682661.338330.671694.11
1233.28.716052.100.0388.70.263.594.732.5019.95.6256.618.779.115.613828.576540.632070.671023.56
1333.65.6413718.140.062500.385.879.244.8438.511.011439.617234.831460.881761.349340.671954.43
1435.67.025721.800.0378.80.263.784.362.5020.15.4654.117.875.014.712926.072330.521470.68903.84
1532.24.3518338.390.062390.547.7911.95.9550.414.115054.023548.544587.582371.408500.631324.65
1735.26.165862.160.0189.40.293.434.422.3419.65.2553.417.875.815.213327.077970.602380.65953.75
1833.44.6810785.740.011800.314.045.633.3628.18.0885.630.113429.025950.984321.208180.671774.14
1932.58.815361.640.0376.90.283.224.362.4318.74.8949.316.768.013.611923.872170.531810.70833.42
2135.08.178183.790.041400.374.846.463.6729.07.8176.725.010320.318336.078571.004050.691143.83
2233.110.28603.950.061530.425.287.523.9431.88.1882.326.710921.518636.677430.943930.671073.81
Notes: the calculation method for zircon oxybarometer (ΔFMQ) refers to [52].
Minerals 14 00282 g003
Figure 3. (a) Zircon U-Pb concordia diagrams and CL images for representative zircons from the DSSPs (DLT-1); (b) chondrite-normalized REE patterns of zircons from the DSSPs (DLT-1). The locations of U-Pb and Hf-isotope analyses are indicated by red and yellow circles, respectively. Magmatic, hydrothermal zircons, and chondrite data are from [50] and [53], respectively.
Figure 3. (a) Zircon U-Pb concordia diagrams and CL images for representative zircons from the DSSPs (DLT-1); (b) chondrite-normalized REE patterns of zircons from the DSSPs (DLT-1). The locations of U-Pb and Hf-isotope analyses are indicated by red and yellow circles, respectively. Magmatic, hydrothermal zircons, and chondrite data are from [50] and [53], respectively.
Minerals 14 00282 g003

4.2. Geochemical and Isotopic Results

4.2.1. Major and Trace Elements

The bulk-rock elemental compositions for the DSSPs are provided in Table 3. The syenite porphyry samples in this study exhibit similar geochemical characteristics to other syenite porphyries in the region (Figure 4), characterized by their alkali-rich nature and elevated K2O contents. All the Dalongtan samples fall within the alkaline quartz monzonite field in the TAS diagram (Figure 4a), with high total-alkali (Na2O + K2O = 10.39–11.17 wt.%) contents and felsic signatures (SiO2 = 67.55–68.66 wt.%). They are characterized by high K2O (5.47–5.74 wt.%) contents and K2O/Na2O ratios of 1.0 to 1.2, belonging to the shoshonitic magmatic series (Figure 4b,c). Different from other intrusions, the DSSPs are peraluminous (Figure 4d), with A/CNK [molar Al2O3/(CaO + Na2O + K2O)] = 1.04–1.19 (Table 3). In the Harker diagrams, all the syenite porphyry samples, including DSSPs, define linear trends with coeval potassic mafic rocks in the WYC (Figure 5a–g), suggesting that these mafic and felsic counterparts should be genetically connected, perhaps by fractional crystallization.
Table 3. Bulk-rock major (wt.%), trace element (ppm), and Sr-Nd isotopic data for the DSSP in central Yunnan.
Table 3. Bulk-rock major (wt.%), trace element (ppm), and Sr-Nd isotopic data for the DSSP in central Yunnan.
SampleDLT-1DLT-2DLT-3DLT-4DLT-5DLT-6DLT-7
SiO268.3468.6267.5568.6368.6268.6668.50
TiO20.360.330.460.330.360.330.35
Al2O316.9516.5917.3716.6516.8416.8216.98
Fe2O3T2.662.603.462.662.772.692.66
MnO0.060.070.070.070.080.060.05
MgO0.140.150.250.150.150.160.14
CaO0.410.440.400.490.360.360.32
Na2O5.425.494.645.435.325.265.32
K2O5.615.685.745.545.475.635.64
P2O50.040.050.050.040.040.040.03
LOI0.500.451.220.410.650.620.73
Total99.7499.6799.6499.7299.7099.6099.46
K2O/Na2O1.031.031.241.021.031.071.06
K2O + Na2O11.0311.1710.3910.9710.7910.8910.96
A/NK1.131.091.251.121.151.141.14
A/CNK1.081.041.191.051.101.091.10
Mg#9.2810.1312.3610.059.7010.379.64
Li9.6110.2024.1010.6114.488.5813.97
Be12.6612.219.3312.4414.2611.7912.51
Sc1.962.032.311.601.611.621.89
V22.1422.5728.7022.4120.8623.8722.11
Cr12.544.083.544.114.084.514.57
Co21.826.724.014.9414.0717.2718.56
Ni1.491.461.532.191.291.341.31
Cu11.746.168.718.107.999.685.64
Zn60.0457.4488.6861.4859.4653.7361.81
Ga29.6628.5030.6527.4926.3330.8028.72
Rb265.29267.58265.08245.79251.66259.77275.24
Sr820.55793.51894.77810.75750.33784.67772.60
Y31.8232.8730.1528.8346.8827.0434.54
Zr618.70643.57759.67603.64603.46574.22579.69
Nb53.1954.9655.2352.9652.1251.4650.69
Mo0.510.333.770.550.730.640.96
Sn3.753.715.804.944.384.373.87
Cs2.372.515.852.722.753.422.91
Ba565.38500.68717.40544.53472.10781.06499.41
La227.81233.10200.56213.40334.93171.96262.69
Ce323.06322.93187.05336.97302.42237.44229.24
Pr34.6634.8833.9831.8853.6124.6640.49
Nd99.68100.1899.4194.16161.6173.72116.01
Sm12.5212.1912.4311.6120.289.4014.39
Eu2.762.872.902.644.142.413.18
Gd11.5711.5910.3010.8816.408.6312.21
Tb1.401.391.261.252.101.071.53
Dy6.036.075.585.529.314.936.59
Ho1.011.020.940.931.480.851.09
Er3.143.112.892.924.462.603.25
Tm0.480.460.440.430.620.400.49
Yb2.922.912.702.523.552.352.92
Lu0.430.440.410.400.520.370.42
Hf18.3519.2324.1120.6318.3717.4017.09
Ta2.392.412.522.342.472.442.39
Tl1.141.211.901.271.231.451.14
Pb79.97107.40113.94102.45122.2037.8567.38
Th70.1671.0864.4773.3675.4975.2372.60
U11.0410.1212.7011.239.599.899.28
ƩHREE26.9826.9924.5224.8638.4321.2028.49
ƩLREE700.48706.14536.32690.65876.98519.59665.99
ƩREE727.46733.13560.85715.51915.42540.79694.48
Eu/Eu*0.690.730.760.710.670.800.71
Ce/Ce*0.800.780.510.890.500.790.49
Sr/Y25.7924.1429.6728.1216.0129.0222.37
(La/Yb)N55.9057.4753.2160.8467.7052.4464.54
TZr (°C)911911947906912906907
87Rb/86Sr0.9362--0.8779-0.9586-
87Sr/86Sr0.710078--0.710085-0.710132-
(87Sr/86Sr)i0.70964--0.70967-0.70968-
147Sm/144Nd0.0759--0.0745-0.0771-
143Nd/144Nd0.511949--0.511955-0.511964-
(143Nd/144Nd)i0.511933--0.511939-0.511947-
εNd(t)–12.9--–12.8-–12.7-
TDM2 (Ma)1900--1889-1876-
Notes: Eu/Eu* = 2 × EuN/(SmN + GdN); the calculation method for the zircon saturation temperature (°C) refers to [54]. All initial isotopic ratios are corrected to t = 33.2 Ma.
Similar to the coeval syenite porphyries in the WYC, the DSSPs are enriched in incompatible elements such as the LREEs and LILEs (e.g., Rb, Th, and K) but are depleted in HFSEs (e.g., Nb, Ta, P, and Ti) (Figure 6). In addition, the DSSPs show pronounced negative Ba and P anomalies (Figure 6b). They also exhibit high LREE/HREE ratios [(La/Yb)N = 52.4–67.7, average 58.9], negative Eu anomalies (Eu/Eu* = 0.67–0.80, average 0.72), and variable Ce anomalies (Ce/Ce* = 0.49–0.89, average 0.72) (Figure 6a). It should be noted that the DSSPs do not exhibit adakite-like affinities, with low Sr/Y ratios (16.0–29.7) and high Y (27.0–46.9 ppm) and Yb (2.35–3.55 ppm) contents (Table 3).

4.2.2. Sr-Nd Isotopes

The bulk-rock Sr-Nd isotopic data for the DSSPs are listed in Table 3 and plotted in Figure 7. The DSSPs investigated here exhibit relatively uniform Sr-Nd isotopic compositions (Figure 7), with high (87Sr/86Sr)i ratios (0.70964–0.70968) and strongly negative εNd(t) values (−12.9 to −12.7) (Figure 7a). Their two-stage Nd isotope-depleted mantle model ages (TDM2) are concentrated at 1.9 Ga (Table 3). Moreover, these intrusions have relatively higher (87Sr/86Sr)i ratios but lower εNd(t) values compared to those of the amphibolite xenoliths, and they fall within the compositional range of the potassic mafic rocks in the WYC (Figure 7a).

4.2.3. Zircon Lu-Hf Isotopes

An in situ zircon Hf isotopic analysis was performed on twelve zircon grains (Table 4). Zircon spot analyses from the DSSPs (DLT-1) show 176Hf/177Hf ratios ranging from 0.282308 to 0.282380, with concentrated and negative εHf(t) values ranging from −15.7 to −13.1. The two-stage Hf mantle model ages (TDM2) range from 1.9 to 2.1 Ga. Compared with zircons from the coeval syenite porphyries in the WYC, the zircon grains from the DSSPs (DLT-1) have the most negative εHf(t) values (Figure 8).

5. Discussion

5.1. Spatiotemporal Distribution of Cenozoic Potassic Magmas in SE Tibet and Their Link to Left-Lateral Shearing of the ARSZ

In the southeastern Tibetan Plateau, Eocene–Oligocene potassic igneous rocks, including felsic shoshonitic rocks, are spatially distributed along the NW–SE-trending ARSZ (Figure 1) [18,29]. Due to their similar spatial distribution relationships, this potassic magmatic belt along the ARSZ has long been considered to be caused by left-lateral shearing [31,37]. Nevertheless, recent geological observations and geochronology show that numerous coeval potassic rocks exhibit planar emplacement, and they extend up to ~160–270 km to the east within the Yangtze Craton and westward into the Simao Block up to ~70 km [17], rather than exhibiting a linear distribution along the ARSZ (Figure 1a,b).
Numerous thermochronological data indicate that the left-lateral shearing along the ARSZ lasted until ca. 21.7 Ma (the late crosscutting leucocratic dikes) [32,62,63]. However, the exact timing of its initiation is still up for debate. The onset of the left-lateral shearing was argued to be (1) earlier than 36 Ma [37] or 35 Ma [64] or (2) at ca. 34 Ma [62], 31 Ma [65], or 29.9–22.6 Ma [63] based on the ages of a series of intrusions and metamorphic complexes within or outside the ARSZ, respectively. Recently, the onset of the left-lateral shearing was restricted to ca. 32 Ma between the latest pre-kinematic alkaline granites and the early folded leucogranites within the ARSZ [18,32,65]. This initial age is also supported by the predated (>32 Ma) clockwise P-T-t paths of regional metamorphic complexes [66]. Therefore, the left-lateral shearing along the ARSZ was predominant between 32 Ma and 22 Ma.
Our new U-Pb zircon date in Dalongtan (~50 km to the east of the ARSZ), combined with previously obtained high-precision dates of potassic rocks within and outside the ARSZ, further narrows down the time span of concentrated felsic magmatism to a duration ranging from 37.2 to 32.3 Ma (Figure 9; Supplementary Table S1), which coincided with mafic magmatism (36.6–33.7 Ma). Therefore, the Eocene–Oligocene potassic magmatism in the SE Tibet predates the initiation of the ARSZ (32–22 Ma) (Figure 9). In conclusion, there is no temporal or spatial correlation between the occurrence of shearing movement and the accompanying potassic magmatism, thus indicating a lack of genetic association between the two phenomena.

5.2. Petrogenesis of the DSSPs

The syenite porphyries in this study are shoshonitic, with high K2O (5.47–5.74 wt.%) contents and K2O/Na2O ratios (1.0–1.2), which are compatible with those of previously described syenite porphyries in the general vicinity of the ARSZ (Figure 4 and Figure 5).
These syenitic samples have different trace element patterns and Sr-Nd isotopic compositions than the asthenosphere-derived MORB [67,68,69] and Cenozoic Maguan OIB [70] (Figure 6 and Figure 7), indicating that the shoshonitic rocks are unlikely to be derived from the typical depleted asthenosphere. No inherited zircons and enclaves were observed within the DSSPs (Figure 3), together with the relatively uniform zircon Hf isotopes (Figure 8), indicating a lack of magma mixing in the DSSPs. The K-rich lower crust, through partially melting, may be a replaceable source for the shoshonitic felsic intrusions [13]. However, the juvenile and ancient Yangtze lower crusts represented by the Liuhe garnet–amphibolite xenoliths [36] and the Kongling amphibolites [71], respectively, have low K2O (average K2O < 1.75 wt.%) contents. Therefore, their melting could only produce magmas with low K2O/Na2O ratios and not K2O-enriched melts like the DSSPs. Furthermore, the partial melting of the thickened mafic lower crust in the WYC usually forms adakite-like granites or quartz monzonites with high Sr/Y ratios [15,24], which differ significantly from the non-adakitic DSSPs. The DSSPs also show different Sr-Nd isotopic compositions from lower-middle crustal amphibolite xenoliths hosted by the Eocene–Oligocene potassic felsic intrusions in the WYC (Figure 7a), indicating that these intrusions were probably not derived from mafic crustal sources. The different trace element patterns between the DSSPs and the thickened lower crust in the WYC (Figure 6) further indicate that they are not genetically related.
Alternatively, the DSSPs could be genetically related to the coeval potassic mafic rocks in the WYC. The following evidence indicates that these shoshonitic felsic intrusions evolved from potassic mafic melts derived from the metasomatized lithospheric mantle (e.g., [17,34]): (1) they are contemporaneous and spatially closely related (Figure 1 and Figure 9); (2) they are characterized by linear trends in most major element vs. SiO2 diagrams (Figure 4 and Figure 5); (3) they exhibit similar REE and multielement normalized patterns (Figure 6); (4) they have similar Sr-Nd isotopic compositions (Figure 7), in particular, the DSSPs have Sr-Nd-Hf isotopic compositions that are consistent with the range of the adjacent potassic mafic rocks in the Yao’an (Figure 7 and Figure 8); and (5) the DSSPs show high whole-rock zircon saturation temperatures (906–947 °C) (Table 3).
The SiO2 contents (67.55–68.66 wt.%) of the DSSPs exceed the range that can be directly attributed to melting of the mantle, as the lithospheric mantle cannot generate melts with SiO2 concentrations higher than those of dacite (SiO2 < 55 wt.%; [72]). Nevertheless, despite the increase in SiO2 content, the εNd(t) values and (87Sr/86Sr)i ratios of the DSSPs consistently remain constant, suggesting that the process of fractional crystallization is dominant and ruling out the possibility of crustal contamination or assimilation (Figure 7b–d) [73]. Considering the geochemical similarities between the studied syenite porphyries and the contemporaneous potassic mafic suites in the WYC (Figure 4, Figure 5, Figure 6 and Figure 7), it is likely that the formation of the former was a result of the fractional crystallization of the latter. The dominant crystallizing phases are probably olivine, clinopyroxene, apatite, and plagioclase, as evidenced by the negative correlation between TiO2, Fe2O3T, MgO, CaO, P2O5, Cr, and Ni with SiO2; the positive correlation between Al2O3, K2O, and Na2O with SiO2; and the negative Eu anomalies (Figure 4 and Figure 5). The depletion of Ba may be associated with the fractional crystallization of plagioclase (Figure 6b). The negative Ce anomalies indicate that the DSSPs originated from a relatively oxidized environment, which is consistent with the high oxygen fugacity (ΔFMQ = +3.30–+4.65) (Table 2). Furthermore, the DSSPs have high whole-rock zircon saturation temperatures, indicating their formation in high-temperature environments, which is supported by the widespread sanidine phenocrysts.
The DSSPs have Nd model ages of ca. 1.9 Ga and depleted Hf mantle model ages of 1.9 to 2.1 Ga (Table 3 and Table 4). A metasomatized lithospheric mantle of ancient origin is expected to exhibit enduringly low Lu/Hf ratios as a result of selective metasomatic Hf enrichment, leading to the generation of melts with markedly negative εHf(t) signatures [74]. The negative εHf(t) values of the DSSPs (–15.7–−13.1; Table 4; Figure 8) are consistent with the derivation from a metasomatized lithospheric mantle. The presence of old Hf and Nd model ages ranging from 1.9 to 2.1 Ga in the DSSPs indicates that the metasomatism of the lithospheric mantle may have occurred during the Paleoproterozoic Era.
In conclusion, the DSSPs are inferred to originate from the fractional crystallization of potassic mafic magmas derived from the ancient metasomatized lithospheric mantle. This is similar to the post-collisional shoshonitic magmatism observed in the Yao’an region [7,21,22].

5.3. Geodynamic and Tectonic Implications

The DSSPs were emplaced at 33.2 ± 0.3 Ma, coinciding with the ages of the potassic mafic rocks (36.6–33.7 Ma) and potassic felsic magmatic suites (37.2–32.3 Ma) within and outside the ARSZ (Figure 9). These post-collisional Cenozoic magmatic suites exhibit synchronicity and a close spatial association (Figure 1b), indicating their control by identical geodynamic processes.
The Eocene–Oligocene potassic mafic magmas in the WYC are generally thought to be derived from the partial melting of the metasomatized SCLM [17,34], which might have been triggered by the left-lateral shearing of the ARSZ [31,37], eastward continental subduction along strike-slip faults in SE Tibet [75], or lithospheric thinning by convective removal [30,59] or delamination [34,76] of the thickened SCLM.
As discussed above (Section 5.1), there are no temporal, spatial, or genetic relationships between the potassic magmatism and the ARSZ activity. Additionally, given that the genesis of the potassic mafic rocks in the WYC is closely linked to dynamic SCLM processes [29], a functional relationship between potassic magmas and continental subduction can also be ruled out.
It is known that the lithospheric mantle and crust in the WYC experienced progressive thickening as a result of the India–Asia collision during the Cenozoic Era [29]. The melting of the thickened source region mentioned above usually requires the introduction of additional heat, as neither normal geothermal gradients nor radiogenic heating are sufficient to cause partial melting [77,78]. In this scenario, asthenosphere upwelling following the removal of the lithospheric mantle represents a credible mechanism for initiating partial melting in the thickened mafic lower crust and SCLM [79,80]. Nevertheless, the lack of contemporaneous and directly sourced mafic rocks from the asthenosphere along the Ailaoshan–Jinshajiang belt implies that the complete removal of the lithospheric mantle may not have necessarily taken place in the WYC [4]. Therefore, it is more plausible that convective thinning, rather than delamination, was responsible for the removal of the lithospheric mantle. This hypothesis is corroborated by the seismic tomography described by Lei et al. [81] and Hu et al. [82]; that is, there is a ~300 km-wide mantle diapir derived from a depth of ~450 km beneath the WYC.
It is noteworthy that the DSSPs have geochemical characteristics similar to those of A-type granites, with high total alkalinity (10.39–11.17 wt.%), HFSE concentrations (Zr + Nb + Ce + Y = 890.2–1054.3 ppm) (Figure 10a), Ga/Al ratios (10,000 × Ga/Al = 2.95–3.46) (Figure 10b), whole-rock zircon saturation temperatures (906–947 °C), and oxygen fugacity (ΔFMQ = +3.30–+4.65) (Table 2 and Table 3). A-type granites form through the crystallization of magmas at relatively high temperatures and are commonly associated with extensional tectonic (e.g., post-collisional) settings [83]. Their origin is closely linked to the emplacement of mantle-derived magma or the upwelling of the asthenosphere [84], with the trigger mechanism for high-temperature melting being the convective removal of the lower lithospheric mantle in post-collisional settings [85]. Hence, the presence of Dalongtan A-type granites presents new evidence that supports the hypothesis of lithospheric mantle melting caused by asthenosphere upwelling, which is triggered by the convective removal of the lithospheric mantle beneath the WYC.
Based on the analyses provided in this paper, together with previous studies (e.g., [24,36,59]), we propose that the upwelling of the hot asthenosphere following the convective thinning of the thickened lower SCLM may cause a thermal anomaly, resulting in the generation of potassic mafic melts through the partial melting of the metasomatized lithospheric mantle [17,34]. Consequently, the fractionation of potassic mafic magmas led to the formation of shoshonitic felsic intrusions (e.g., DSSPs), while the injection of potassic mafic magmas into a previously thickened lower crust resulted in the partial melting and formation of potassic adakite-like rocks (such as the Beiya and Machangqing adakite-like porphyries; [24,59]) (Figure 11).

6. Conclusions

  • The DSSPs were emplaced at 33.2 ± 0.3 Ma and are coeval with those of the Eocene–Oligocene potassic mafic and felsic rocks that are widespread on the SE Tibetan Plateau. This potassic magmatism exhibits no temporal, spatial, or genetic relationships with the ARSZ activity.
  • The DSSPs were formed through the fractionation of potassic mafic magmas that originated from the ancient metasomatized lithospheric mantle.
  • The DSSPs have geochemical features similar to those of A-type granites. The convective thinning of the thickened lower SCLM can induce an upwelling of the asthenosphere, which serves as a triggering mechanism for the generation of Dalongtan A-type granites by facilitating the required high-melting temperature.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/min14030282/s1: Table S1: Compilation of ages for the Cenozoic potassic rocks within and outside the ARSZ in western Yunnan. References [87,88,89,90,91,92,93,94,95,96,97,98,99,100] are cited in the Supplementary Materials.

Author Contributions

Conceptualization, H.Y. and A.L.; methodology, H.Y. and P.W.; software, H.Y.; validation, H.Y. and A.L.; formal analysis, H.Y. and A.L.; investigation, H.Y., P.W., A.L. and F.W.; resources, P.W. and A.L.; data curation, H.Y. and F.W.; writing—original draft preparation, H.Y.; writing—review and editing, A.L. and P.W.; visualization, H.Y.; supervision, F.W.; project administration, A.L. and P.W.; funding acquisition, A.L. and P.W. All authors have read and agreed to the published version of the manuscript.

Funding

This study was jointly supported by the National Natural Science Foundation of China (42102047, 41102049), the Applied Basic Research Projects of Yunnan Province (202401CF070095), the Yunnan Ten Thousand Talents Plan Young & Elite Talents Project (YNWR-QNBJ-2018-272), the YM Lab Project (2011), and the Innovation Team of Yunnan Province (2012).

Data Availability Statement

All data are contained within the article.

Acknowledgments

We thank the anonymous reviewers for their constructive comments and suggestions.

Conflicts of Interest

Feng Wang is employees of Yunnan Metallurgy Resources Exploration Co., Ltd. The paper reflects the views of the scientists and not the company.

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Figure 2. (a–d) Representative field images and photomicrographs of the DSSPs. Abbreviations: Bt = biotite, Or = orthoclase, and San = sanidine.
Figure 2. (a–d) Representative field images and photomicrographs of the DSSPs. Abbreviations: Bt = biotite, Or = orthoclase, and San = sanidine.
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Figure 4. Major element geochemical plots for the DSSPs. (a) TAS diagram [55,56]. (b) K2O vs. SiO2 diagram [57]. (c) K2O vs. Na2O diagram. (d) A/CNK vs. SiO2 diagram [58]. Data sources: coeval potassic mafic rocks in the WYC from [24,25] and references therein; the coeval syenite porphyries in the WYC from [16,20,21].
Figure 4. Major element geochemical plots for the DSSPs. (a) TAS diagram [55,56]. (b) K2O vs. SiO2 diagram [57]. (c) K2O vs. Na2O diagram. (d) A/CNK vs. SiO2 diagram [58]. Data sources: coeval potassic mafic rocks in the WYC from [24,25] and references therein; the coeval syenite porphyries in the WYC from [16,20,21].
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Figure 5. (a–i) SiO2 vs. major and trace element diagrams for the DSSPs. Grey fields indicate experimental melt compositions derived from shoshonitic amphibolites [15].
Figure 5. (a–i) SiO2 vs. major and trace element diagrams for the DSSPs. Grey fields indicate experimental melt compositions derived from shoshonitic amphibolites [15].
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Figure 6. (a) Chondrite-normalized REE and (b) primitive-mantle-normalized trace element patterns for the DSSPs. Data for normalization and the OIB, N-, and E-MORB values are from [53]. Orange fields are for potassic mafic rocks in the WYC [4]; shaded fields are Neoproterozoic juvenile thickened lower crust, which is revised after crustal amphibolite xenoliths [36]; and black fields with dashed outline are for adakite-like rocks in the WYC [24,59].
Figure 6. (a) Chondrite-normalized REE and (b) primitive-mantle-normalized trace element patterns for the DSSPs. Data for normalization and the OIB, N-, and E-MORB values are from [53]. Orange fields are for potassic mafic rocks in the WYC [4]; shaded fields are Neoproterozoic juvenile thickened lower crust, which is revised after crustal amphibolite xenoliths [36]; and black fields with dashed outline are for adakite-like rocks in the WYC [24,59].
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Figure 7. Plots of (a) (87Sr/86Sr)i vs. εNd(t), (b) SiO2 vs. εNd(t), (c) SiO2 vs. (87Sr/86Sr)i, and (d) 1000/Sr vs. (87Sr/86Sr)i for the DSSPs. Estimated endmembers and fields of the Cenozoic Maguan OIB, MORB, EMI, EMⅡ, amphibolite xenoliths (lower-middle continental crust of Yangtze Craton), and potassic mafic rocks are from [7,24,59] and references therein. The Yao’an potassic mafic rocks are from [7,17].
Figure 7. Plots of (a) (87Sr/86Sr)i vs. εNd(t), (b) SiO2 vs. εNd(t), (c) SiO2 vs. (87Sr/86Sr)i, and (d) 1000/Sr vs. (87Sr/86Sr)i for the DSSPs. Estimated endmembers and fields of the Cenozoic Maguan OIB, MORB, EMI, EMⅡ, amphibolite xenoliths (lower-middle continental crust of Yangtze Craton), and potassic mafic rocks are from [7,24,59] and references therein. The Yao’an potassic mafic rocks are from [7,17].
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Figure 8. Plots of zircon U-Pb ages vs. εHf(t) values for the DSSPs. The orange and gray fields represent episodes of major juvenile crustal growth of the WYC in the Neoproterozoic and late Permian, respectively [60]. Data sources: coeval potassic mafic rocks in the WYC from [24,61] and references therein.
Figure 8. Plots of zircon U-Pb ages vs. εHf(t) values for the DSSPs. The orange and gray fields represent episodes of major juvenile crustal growth of the WYC in the Neoproterozoic and late Permian, respectively [60]. Data sources: coeval potassic mafic rocks in the WYC from [24,61] and references therein.
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Figure 9. Compilation of Ar-Ar and U-Pb ages for potassic felsic and mafic rocks on SE Tibetan Plateau. Fields for left-lateral shearing along the ARSZ are from [32]; those for potassic felsic and mafic rocks are from [22,37,38,39,40] and references therein and are given in Supplementary Table S1.
Figure 9. Compilation of Ar-Ar and U-Pb ages for potassic felsic and mafic rocks on SE Tibetan Plateau. Fields for left-lateral shearing along the ARSZ are from [32]; those for potassic felsic and mafic rocks are from [22,37,38,39,40] and references therein and are given in Supplementary Table S1.
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Figure 10. Genetic-type diagrams for granitic rocks. (a) (Na2O + K2O)/CaO vs. Zr + Nb + Ce + Y plots [85]. (b) Zr vs. 10,000 × Ga/Al plots [86].
Figure 10. Genetic-type diagrams for granitic rocks. (a) (Na2O + K2O)/CaO vs. Zr + Nb + Ce + Y plots [85]. (b) Zr vs. 10,000 × Ga/Al plots [86].
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Figure 11. Petrogenetic model for the generation of the post-collisional potassic mafic and felsic rocks in the WYC (modified from [16,24,36,78]). (a) In the Eocene (37–32Ma), the lower part of the overthickened lithospheric mantle adjacent to the Jinsha suture was convectively removed, which led to upwelling of asthenosphere, partial melting of lower crust and the metasomatic domains within residual SCLM; (b) partial melting of residual SCLM produced potassic mafic magmas. Some potassic mafic magmas form shoshonitic felsic intrusions through differentiation.
Figure 11. Petrogenetic model for the generation of the post-collisional potassic mafic and felsic rocks in the WYC (modified from [16,24,36,78]). (a) In the Eocene (37–32Ma), the lower part of the overthickened lithospheric mantle adjacent to the Jinsha suture was convectively removed, which led to upwelling of asthenosphere, partial melting of lower crust and the metasomatic domains within residual SCLM; (b) partial melting of residual SCLM produced potassic mafic magmas. Some potassic mafic magmas form shoshonitic felsic intrusions through differentiation.
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Table 4. Zircon Hf isotopic data for the DSSP in central Yunnan.
Table 4. Zircon Hf isotopic data for the DSSP in central Yunnan.
Spot176Yb/177Hf176Lu/177Hf176Hf/177Hf1σ176Hf/177HfiεHf(0)εHf(t)TDM1 (Ma)TDM2 (Ma)fLu/Hf
DLT-1-020.0237020.0007310.2823720.0000140.282371−14.2−13.512331965−0.98
DLT-1-040.0446460.0013410.2823800.0000140.282380−13.9−13.112411946−0.96
DLT-1-050.0207030.0006050.2823600.0000160.282360−14.6−13.812451990−0.98
DLT-1-060.0475780.0014050.2823670.0000140.282366−14.3−13.612621976−0.96
DLT-1-080.0532780.0016080.2823450.0000130.282344−15.1−14.413002025−0.95
DLT-1-090.0192410.0005810.2823650.0000130.282365−14.4−13.712371979−0.98
DLT-1-120.0216640.0006530.2823470.0000130.282347−15.0−14.312652020−0.98
DLT-1-130.0431840.0012140.2823080.0000190.282307−16.4−15.713392108−0.96
DLT-1-140.0341210.0010280.2823550.0000130.282354−14.8−14.112662002−0.97
DLT-1-180.0353770.0010570.2823460.0000130.282345−15.1−14.412802023−0.97
DLT-1-210.0256930.0007910.2823280.0000150.282328−15.7−15.012962063−0.98
DLT-1-220.0385500.0011740.2823500.0000140.282349−14.9−14.212782013−0.96
Notes: constants used in calculation: (176Lu/177Hf)CHUR = 0.0332; (176Hf/177Hf)CHUR,0 = 0.282772; (176Lu/177Hf)DM = 0.0384; (176Hf/177Hf)DM = 0.28325; λ = 1.867 × 10−11 a−1; and t = 33.2 Ma.
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Yang, H.; Liu, A.; Wu, P.; Wang, F. Petrogenesis and Tectonic Implications of the Oligocene Dalongtan Shoshonitic Syenite Porphyry in Central Yunnan, Southeastern Tibetan Plateau: Constraints from Geochronology, Geochemistry and Sr-Nd-Hf Isotopes. Minerals 2024, 14, 282. https://doi.org/10.3390/min14030282

AMA Style

Yang H, Liu A, Wu P, Wang F. Petrogenesis and Tectonic Implications of the Oligocene Dalongtan Shoshonitic Syenite Porphyry in Central Yunnan, Southeastern Tibetan Plateau: Constraints from Geochronology, Geochemistry and Sr-Nd-Hf Isotopes. Minerals. 2024; 14(3):282. https://doi.org/10.3390/min14030282

Chicago/Turabian Style

Yang, Hang, Anlin Liu, Peng Wu, and Feng Wang. 2024. "Petrogenesis and Tectonic Implications of the Oligocene Dalongtan Shoshonitic Syenite Porphyry in Central Yunnan, Southeastern Tibetan Plateau: Constraints from Geochronology, Geochemistry and Sr-Nd-Hf Isotopes" Minerals 14, no. 3: 282. https://doi.org/10.3390/min14030282

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