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Article

Tectonic Setting of the Neoproterozoic Gabbroic Intrusions in the Luanchuan Area, Southern Margin of the North China Craton: Constraints from Ilmenite and Biotite Mineralogy

by
Jianhan Huang
1,
Zhenzhen Huang
2,
Danli Chen
3,
Kekun Li
4,
Xiaoxiao Huang
1,
Minghao Ren
1,* and
Yazhou Fan
1,*
1
College of Geosciences and Engineering, North China University of Water Resources and Electric Power, Zhengzhou 450046, China
2
Zhejiang Academy of Surveying and Mapping, Hangzhou 311100, China
3
Henan Third Geological Exploration Institute Co., Ltd., Zhengzhou 450014, China
4
Henan Geological Bureau, China Chemical Geology and Mine Bureau, Zhengzhou 450011, China
*
Authors to whom correspondence should be addressed.
Minerals 2025, 15(6), 602; https://doi.org/10.3390/min15060602
Submission received: 15 April 2025 / Revised: 27 May 2025 / Accepted: 1 June 2025 / Published: 3 June 2025
(This article belongs to the Section Mineral Deposits)
Browse Figures
Versions Notes

Abstract

:
The Luanchuan Neoproterozoic gabbroic intrusions are located at the southern margin of the North China Craton (NCC), intruding into the marble and schist from the Nannihu and Meiyaogou Formations of the Neoproterozoic Luanchuan Group. The gabbroic rocks consist of plagioclase (30%–50%) and amphibole (40%–60%), with minor ilmenite (2%–5%), biotite (1%–3%), and titanite (~1%). Based on the occurrence and mineral chemistry, two types of biotites were identified. The first type of biotite (Bt I) is brown, with a fine- to micro-grained anhedral texture, occurring around the magmatic ilmenite and coexisting with titanite. Bt I is characterized by high TiO2 and FeO contents, with TiO2 > 2 wt% (2.03 wt%–3.15 wt%) and FeO ranging from 19.94 wt% to 22.08 wt%. The other type of biotite (Bt II) is light grayish-brown to dark reddish-brown, with a medium- to coarse-grained euhedral texture, coexisting with grayish-green amphibole. Bt II exhibits lower TiO2 (1.40 wt%–1.90 wt%) and FeO contents (18.03 wt%–21.42 wt%). The K2O (7.56 wt%–9.32 wt%) and SiO2 (34.49 wt%–37.04 wt%) contents of Bt I are slightly lower than those of Bt II (8.28 wt%–9.73 wt% and 35.18 wt%–37.52 wt%, respectively). Despite the low Ti content in biotites, the mineral occurrence indicates that both types of biotite yield a magmatic origin, resulting from the reactions between early crystallized minerals and residual magma. Bt I originated from the reaction between ilmenite and residual magma, while Bt II resulted from the production of the reaction between clinopyroxne and residual magma. Ilmenite exhibits low MgO and Fe2O3 contents but high FeO and MnO contents, suggesting genetic similarities to the Skaergaard and Panzhihua intrusions. Both types of biotites record consistent temperatures (T = 766 to 818 °C), pressures (P = 5.30–8.80 kbar), and oxygen fugacities (log fO2 = −12.35 to −14.06), aligning with those of the Fanshan complex and the Falcon Island intrusion. The mineralogy of ilmenite and biotite indicates that the Luanchuan gabbroic intrusions formed in a continental rift setting, which is considered to be associated with the breakup of the Rodinia supercontinent.

1. Introduction

The North China Craton (NCC), one of the world’s oldest continents, experienced the Paleoproterozoic amalgamation of the Columbia supercontinent and a final collision at ~1.8 Ga, followed by extensive extension [1,2,3,4,5,6,7,8]. Since the late Paleoproterozoic, the southern margin of the NCC has been separated from the Columbia supercontinent (Xiong’er rift) and remained a passive continental margin until the late Neoproterozoic. During the middle to late Neoproterozoic, intense magmatism occurred owing to the breakup of Rodinia [9], forming an approximately 1500 km long, E–W-trending alkaline magmatic belt (Figure 1a) [9,10,11,12,13,14,15]. This belt is dominated by syenite (trachyte) and mafic intrusions that are interpreted to have formed in a continental rift environment, possibly related to a mantle plume [16,17] or to extensional tectonics following the collision of the North Qinling terrane [13,14,18,19]. The Luanchuan gabbroic intrusions, which have the potential to form magmatic Ti-Fe deposits [20], are representative intrusions within this Neoproterozoic alkaline magmatic belt [11]. Previous studies have focused on the geochronology and geochemistry of the Luanchuan gabbroic intrusions [19,21,22]. These results indicate that the Luanchuan gabbroic intrusions were formed during the Neoproterozoic (830–870 Ma; [19,21,22]), characterized by high potassium contents. These gabbroic intrusions have SiO2 contents ranging from 44.8 to 50.1 wt%, and plot in the alkali-basalt field on the Zr/TiO2–Nb/Y diagram [19]. They belong to silica-undersaturated alkaline mafic intrusions, exhibiting geochemical characteristics of Ocean Island Basalt (OIB)-type mafic cumulates [19,22], indicating that the southern margin of the NCC has experienced multiple extensional tectonic cycles [9,12,23]. However, mineralogical studies of the Luanchuan gabbroic intrusions are limited, and the physicochemical conditions during its formation remain unclear. Recently, distinct reaction textures were discovered in the Luanchuan gabbro, where magmatic ilmenite was replaced by biotite and titanite during the late-stage processes of magma crystallization. These late-stage magmatic reactions provide critical information on system compositions and physicochemical conditions, shedding light on the tectonic setting for the intrusions [24,25,26,27,28,29,30,31,32,33,34,35]. Therefore, this study conducts detailed mineralogical investigations on ilmenite and biotite in the Luanchuan gabbroic intrusions. Compositions of ilmenite and biotite were determined with electron probe microanalysis (EPMA), and the temperature (T), pressure (P), and oxygen fugacity (fO2) during its evolution were calculated. Combined with regional geology and physicochemical conditions, this work provides new constraints on the tectonic evolution of the southern margin of the NCC.
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Figure 1. Simplified tectonic map of the southern margin of the NCC and the Qinling orogenic belt (a), modified from [18]). The geological sketch of the Luanchuan gabbroic intrusions (b), modified from [23]).
Figure 1. Simplified tectonic map of the southern margin of the NCC and the Qinling orogenic belt (a), modified from [18]). The geological sketch of the Luanchuan gabbroic intrusions (b), modified from [23]).
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2. Geological Background

The Luanchuan district is situated at the southern margin of the NCC (Figure 1a). The study area comprises the Archean Taihua Group, Paleoproterozoic Xiong’er Group, Guandaokou Group, Neoproterozoic Luanchuan Group, Paleozoic Taowan Group, and Kuanping Group from north to south (Figure 1b; [10,11,23]). The Neoproterozoic Luanchuan Group extends as a narrow NW–SE-trending belt along the Luonan–Luanchuan fault (LLF, Figure 1b), forming a composite syncline. It is internally segmented by complex thrust systems and several nearby NNW-trending ductile shear zones, exhibiting a kinematic characteristic of oblique subduction with left lateral displacement [36]. The Luanchuan Group is further divided into the Sanchuan, Nannihu, Meiyaogou, and Dahongkou Formations [11,19,37], primarily composed of sandstone, marble, schist, phyllite, and alkaline volcanic rocks [11].
The Luanchuan Neoproterozoic gabbroic intrusions cover an area of approximately 25 km2, occurring as dikes and veins, intruding into the marble and schist of the Nannihu and Meiyaogou Formations. In the Meiyaogou area (northern Luanchuan), it intrudes conformably, with well-exposed dikes extending over 5 km in length and 400 to 500 m in width [11]. Due to the intense folding of the Luanchuan Group, these gabbroic intrusions have undergone metamorphism and deformation. Calc-silicate hornfel zones with widths ranging from several meters to tens of meters often develop at the contact zones, and localized jade mineralization has been identified, such as Yiyuan nephrite [21], Shuangshan nephrite [38], and Laozhuang nephrite [39]. The alkaline volcanic rocks of the Dahongkou Formation are dominated by trachyte, with subordinate trachytic agglomerate, breccia, dolerite, and mafic tuff, accompanied by abundant syenite porphyry [11] and yield ages of 860–840 Ma [12,23,40]. These rocks have generally undergone varying degrees of regional, dynamic, and hydrothermal metamorphism, with mineral assemblages indicative of greenschist-facies conditions [11,16,41,42].

3. Petrography and Analytical Methods

3.1. Petrography

The weathered surface of the Luanchuan gabbro exhibits a grayish-brown to gray color, whereas the fresh surface is dark gray to grayish-black, featuring medium- to coarse-grained gabbroic textures and a massive structure (Figure 2a,b), with occasional weak cumulate banding. The gabbro mainly consists of plagioclase (30%–50%) and amphibole (40%–60%), with minor ilmenite (2%–5%), biotite (1%–3%), and titanite (~1%) (Figure 2b–d). Ilmenite occurs as medium- to fine-grained subhedral-anhedral interstitial grains, ranging from 0.5 mm to 1 mm in size and commonly displaying corona textures with titanite and biotite. Some ilmenite grains are entirely replaced by biotite and titanite (Figure 2c,e,f). Based on their occurrence and mineral chemistry, two types of biotite are identified, resulting from reactions between early crystallized minerals and residual magma. The first type (Bt I) is dark brown, forming anhedral fine flaky aggregates and coexisting with titanite around ilmenite (Figure 2c,e,f). The second type (Bt II) is light gray to grayish brown, forming subhedral–anhedral flaky aggregates, and is associated with amphibole and plagioclase (Figure 2d). Amphibole is grayish-green to light brown, shows distinct pleochroism, and occurs as coarse aggregates or irregular fine prismatic clusters with grain sizes up to 5 mm (Figure 2c,d). Plagioclase is grayish-white, euhedral-subhedral, with grain sizes of 3 mm–5 mm, and is mostly altered to saussurite, featuring distinct polysynthetic twinning (Figure 2b–d).

3.2. Sampling and Analytical Methods

Samples of the Luanchuan gabbroic intrusions were collected from outcrops (Figure 1b). Fresh specimens were prepared as thin sections for in situ major elements analysis. After careful petrographic examination under transmitted and reflected light microscopy, representative biotite and ilmenite grains were selected for electron microprobe analysis (EMPA). The analysis was performed on polished thin sections at Guangzhou Tuoyan Testing Technology Co., Ltd. (Guangzhou, China), using a JEOL JXA-iSP100 electron microprobe (JEOL Ltd., Tokio, Japan) equipped with wavelength-dispersive spectrometers. Instrument parameters included an acceleration voltage of 15 kV, a beam current of 20 nA, and a focused beam diameter of 5 µm. The background measurement time was set to half of the peak measurement time and remained constant throughout the analysis. The standard materials (corresponding element) used for calibration were diopside (Si and Ca), spodumene (Al), NiO (Ni), MnO2 (Mn), orthoclase (K), albite (Na), olivine (Mg), magnetite (Fe), Cr2O3 (Cr), and rutile (Ti). All data were corrected using the ZAF (atomic number, absorption, and fluorescence) method, and the analytical precision for oxide concentrations was better than 2%.

4. Results

4.1. Ilmenite

The compositions of ilmenite and the calculated results are listed in Table 1. Ilmenite shows limited compositional variation, with TiO2 contents ranging from 49.92 wt% to 53.75 wt%, FeOcalc from 43.50 wt% to 45.73 wt%, and Fe2O3calc showing a broader range from below detection limit (b.d.l) to 5.52 wt%. MnO ranges from 1.12 wt% to 1.85 wt%, while MgO, Cr2O3, and V2O3 contents remain low (MgO ≤ 0.41 wt%, Cr2O3 ≤ 0.08 wt%, and V2O3 ≤ 0.21 wt%). In the TiO2-MgO-FeOT diagram, data points are plotted within the ilmenite solid-solution field (Figure 3a); in the TiO2-FeOcalc-Fe2O3calc diagram, the points lie above the line connecting ilmenite (FeTiO3) and hematite (Fe2O3) (Figure 3b). Additional ilmenite compositional diagrams are provided in Figure S1.
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Figure 3. Classification of ilmenite from Luanchuan gabbroic intrusions. (a) the TiO2-MgO-FeOT diagram after [43]; (b) the TiO2-FeOcalc-Fe2O3calc diagram after [44]. Abbreviations: Spl—spinel; MW—magnesiowüstite, Ilm—ilmenite, Arm—armalcolite.
Figure 3. Classification of ilmenite from Luanchuan gabbroic intrusions. (a) the TiO2-MgO-FeOT diagram after [43]; (b) the TiO2-FeOcalc-Fe2O3calc diagram after [44]. Abbreviations: Spl—spinel; MW—magnesiowüstite, Ilm—ilmenite, Arm—armalcolite.
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4.2. Biotite

The composition of biotites and the corresponding calculated results are listed in Table 2. Biotite (Bt I), which coexists with titanite around ilmenite, is characterized by elevated Ti and Fe contents (Figure 4a), with TiO2 ranging from 2.03 wt% to 3.15 wt% and FeOT from 19.94 wt% to 22.08 wt%. SiO2 ranges from 34.49 wt% to 37.04 wt%, Al2O3 from 14.20 wt% to 16.79 wt%, MgO from 9.80 wt% to 11.87 wt%, and K2O from 7.56 wt% to 9.32 wt%. Biotite (Bt II), which coexists with plagioclase and amphibole, contains TiO2 (from 1.40 wt% to 1.90 wt%) and FeOT (from 18.03 wt% to 21.42 wt%). SiO2 ranges from 35.18 wt% to 37.52 wt%, Al2O3 from 14.69 wt% to 16.89 wt%, MgO from 10.37 wt% to 12.57 wt%, and K2O from 8.28 wt% to 9.73 wt%. H2O content ranges from 2.95 wt% to 3.35 wt% in Bt I, and from 3.38 wt% to 3.48 wt% in Bt II. The compositional correlation diagrams of biotite are presented in Figure S2.
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Figure 4. The different types of biotites from the Luanchuan gabbroic intrusions on (a) the FeOT vs. TiO2 diagrams, (b) the Mg-(Fe2++Mn)-(AlVI+Fe3++Ti) classification diagram of [45], (c) the feal vs. mgli diagram from [46], fields of biotites from different rocks after [34], 1—mafic igneous rocks, 2—alkaline igneous rocks, 3—high-grade metamorphic rocks, 4—low-grade metamorphic rocks, data from the global GEOROC database (http://georoc.mpch-mainz.gwdg.de/georoc, accessed on 1 March 2025). (d) The Fe/(Mg + Fe) vs. AlTotal diagram is from [47], and the biotite data of Kings River, Falcon Island, and Fanshan are from [29,30,47], respectively.
Figure 4. The different types of biotites from the Luanchuan gabbroic intrusions on (a) the FeOT vs. TiO2 diagrams, (b) the Mg-(Fe2++Mn)-(AlVI+Fe3++Ti) classification diagram of [45], (c) the feal vs. mgli diagram from [46], fields of biotites from different rocks after [34], 1—mafic igneous rocks, 2—alkaline igneous rocks, 3—high-grade metamorphic rocks, 4—low-grade metamorphic rocks, data from the global GEOROC database (http://georoc.mpch-mainz.gwdg.de/georoc, accessed on 1 March 2025). (d) The Fe/(Mg + Fe) vs. AlTotal diagram is from [47], and the biotite data of Kings River, Falcon Island, and Fanshan are from [29,30,47], respectively.
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Table 2. The compositions of biotite in the Luanchuan gabbroic intrusions.
Table 2. The compositions of biotite in the Luanchuan gabbroic intrusions.
No.49 50 53 84 85 86 92 93 71 79 80 101 114 117 119 120 123 124 128 130 131
SampleSBG22-4-1MYG22-3-5SHC22-3-8
LocationShibaogou (111°34′54″, 33°50′01″)Meiyaogou (111°38′18″, 33°47′54″)Shuanghecun (111°24′02″, 33°53′51″)
Rockcoarse-grained gabbroilmenite-bearing medium-grained gabbroilmenite-bearing fine-grained gabbro
TypeBiotite I (TiO2 > 2.00 wt%)Biotite II (TiO2 < 2.00 wt%)
SiO234.49 34.63 35.73 35.63 37.04 35.33 35.81 36.15 35.18 36.57 35.61 36.42 37.52 37.20 37.01 37.44 37.18 37.15 37.15 36.83 37.16
TiO23.15 3.14 2.66 2.55 2.99 3.12 2.25 2.03 1.88 1.72 1.90 1.51 1.50 1.40 1.41 1.66 1.71 1.58 1.59 1.52 1.50
Al2O316.45 16.79 15.83 15.79 14.20 14.98 14.80 15.12 15.84 14.69 14.85 16.89 16.53 16.73 16.39 16.54 16.49 16.47 16.46 16.48 16.27
Cr2O30.02 0.04 0.03 0.09 0.04 0.06 0.04 0.02 0.04 0.01 0.03 0.09 b.d.l0.02 0.19 0.06 0.05 0.02 b.d.l0.02 b.d.l
FeOT22.08 20.93 20.80 20.65 19.94 20.73 21.65 21.74 20.64 20.88 21.42 18.03 19.26 19.22 19.49 19.57 19.79 19.73 19.46 19.64 20.03
Fe2O3calc5.16 5.50 10.60 11.48 9.10 11.02 9.45 6.22 9.55 9.16 8.89 7.26 4.29 3.62 5.85 3.93 3.82 3.63 3.46 6.43 4.82
FeOcalc17.44 15.98 11.26 10.32 11.75 10.82 13.15 16.14 12.05 12.64 13.41 11.49 15.40 15.96 14.23 16.04 16.35 16.47 16.35 13.85 15.69
MnO0.13 0.11 0.09 0.07 0.09 0.10 0.13 0.14 0.12 0.12 0.12 0.08 0.12 0.15 0.16 0.18 0.17 0.21 0.18 0.17 0.17
MgO9.80 9.94 9.99 11.55 11.87 11.11 11.08 10.85 11.71 12.00 11.62 12.57 10.87 10.67 10.90 10.37 10.45 10.50 10.60 10.59 10.61
NiOb.d.lb.d.l0.02 0.01 0.03 0.02 0.04 0.02 0.04 b.d.lb.d.l0.05 0.02 0.02 0.01 0.04 0.02 0.03 0.03 b.d.lb.d.l
CaO0.06 0.01 1.85 0.49 0.40 0.57 0.13 0.09 0.13 0.14 0.10 0.25 0.01 0.04 0.11 0.01 0.01 0.01 b.d.l0.25 0.06
Na2O0.17 0.16 0.37 0.08 0.11 0.12 0.06 0.08 0.05 0.04 0.03 0.22 0.12 0.06 0.12 0.05 0.05 0.04 b.d.l0.09 0.10
K2O9.23 8.97 7.61 7.56 8.39 7.74 8.41 9.32 8.28 8.60 8.69 8.61 9.41 9.62 9.05 9.50 9.58 9.67 9.73 8.85 9.37
H2Ocalc3.12 3.09 2.95 3.23 3.08 3.02 3.26 3.35 3.39 3.42 3.38 3.42 3.44 3.48 3.42 3.42 3.43 3.46 3.48 3.40 3.43
Total99.21 98.36 99.00 98.84 99.09 98.01 98.60 99.53 98.25 99.11 98.64 98.86 99.25 98.97 98.85 99.23 99.29 99.23 99.04 98.48 99.19
Site assignment of biotite (A1M3T4O10W2)
T.Si2.682.682.742.682.802.702.742.772.682.762.722.732.832.822.802.832.822.822.822.792.82
T.Al1.211.221.061.100.971.071.021.031.120.991.041.141.031.051.031.021.041.041.041.041.02
T.Fe3+0.110.100.200.220.240.230.240.200.210.250.240.130.140.130.160.140.140.140.140.170.16
sum. T4.004.004.004.004.004.004.004.004.004.004.004.004.004.004.004.004.004.004.004.004.00
M.Al0.290.320.370.300.300.280.310.330.300.320.300.360.440.450.430.450.430.440.440.430.43
M.Mg1.141.151.141.281.331.271.261.231.321.341.321.391.201.191.221.151.171.171.191.191.18
M.Fe2+1.131.030.720.650.740.690.841.030.770.800.860.720.971.010.901.011.041.051.040.880.99
M.Fe3+0.190.220.410.430.280.410.300.160.340.270.280.280.100.070.170.080.080.070.060.200.11
M.Ti0.190.190.160.150.180.190.130.120.110.100.110.090.090.080.090.100.100.090.090.090.09
M.Cr0.000.000.000.010.000.000.000.000.000.000.000.010.000.000.010.000.000.000.000.000.00
M.Mn0.010.010.010.000.010.010.010.010.010.010.010.000.010.010.010.010.010.010.010.010.01
Sum. M2.952.922.812.822.832.842.862.892.862.842.872.842.812.822.822.812.832.832.832.802.82
Vacancy. M0.050.080.190.180.170.160.140.110.140.160.130.160.190.180.180.190.170.170.170.200.18
A.K0.910.890.750.730.810.760.830.910.810.830.850.830.910.930.880.920.930.940.940.860.91
A.Na0.030.020.060.010.020.020.010.010.010.010.010.030.020.010.020.010.010.010.000.010.01
A.Ca0.010.000.150.040.030.050.010.010.010.010.010.020.000.000.010.000.000.000.000.020.00
Sum. A0.940.910.950.780.860.830.850.930.830.850.870.880.930.940.900.930.940.940.940.890.93
Vacancy. A0.060.090.050.220.140.170.150.070.170.150.130.120.070.060.100.070.060.060.060.110.07
W.OH1.611.601.511.621.551.541.661.711.721.721.721.711.731.761.731.731.741.751.761.721.74
W.O2−0.390.400.490.380.450.460.340.290.280.280.280.290.270.240.270.270.260.250.240.280.26
Fe3+/FeTot0.210.240.460.500.410.480.390.260.420.390.370.360.200.170.270.180.170.170.160.290.22
T.°C793790792790766767785807801796799818813815812807812811815807810
P.kbar8.808.195.757.035.305.826.218.027.386.466.587.788.398.338.048.558.668.058.318.718.31
log fO2−12.86−13.02−13.29−13.17−14.06−13.96−13.42−12.60−12.84−13.09−13.00−12.35−12.40−12.36−12.47−12.53−12.39−12.50−12.36−12.51−12.49
Note: the program used to calculate the structural formulae of biotite [48,49], the pressure and temperature are calculated by [49] using https://lixiaoyan.shinyapps.io/Biotite_thermobarometer/ (accessed on 1 March 2025), and the oxygen fugacity (log fO2) is calculated using [24]. The equilibrium expression is log fO2 = −30,930/T + 14.98 + 0.142(P−1)/T (P in bars and T in kelvins).
In the classification diagram of the micas [45], all data plots are within the biotite field, near the boundary between magnesian biotite and ferroan biotite (Figure 4b). Due to its high TiO2 content, the first type of biotite (Bt I) plots slightly outside of the conventional biotite range. In the feal-mgli diagram (Figure 4c, [46,50]), all data fall within the magnesian biotite field. According to the IMA classification, biotite is defined as a trioctahedral mica within the Annite [KFe32+AlSi3O10(OH)2]–Phlogopite [KMg3AlSi3O10(OH)2]–Siderophyllite [KFe22+AlAlSi2O10(OH)2]–Eastonite [KMg2AlAlSi2O10(OH)2] (APSE) solid solution series [51]. Biotite with a total octahedral cation sum (∑M) ≥ 0.25 is classified as trioctahedral [51]. The ∑M ranges from 2.81 to 2.95 for Bt I, and from 2.80 to 2.87 for Bt II, indicating that both biotites belong to the trioctahedral biotite group. The Fe/(Fe+Mg) ratios of Bt I range from 0.48 to 0.56 (average = 0.52), and the total Al (∑Al) ranges from 1.26 to 1.53 (average = 1.40). For Bt II, the Fe/(Fe+Mg) ratio ranges from 0.44 to 0.51 (average = 0.50), and ∑Al ranges from 1.31 to 1.49 (average = 1.45). In the APSE classification diagram (Figure 4d), all data fall within the biotite compositional field [47,51].

5. Discussion

5.1. Genesis of Ilmenite

Ilmenite plays an important role in indicating the tectonic setting and magmatic crystallization processes of mafic-ultramafic rocks [52,53,54,55]. Two types of ilmenites were identified from previous studies based on mineral chemistry (Figure 5a–d). One is ilmenite from the Tellnes intrusion, which crystallized from Fe-Ti-rich dioritic magma, characterized by low TiO2 and high Fe2O3 contents (Figure 5a–c). The other is ilmenite with low MgO and Fe2O3 contents and high TiO2, FeO, and MnO contents (Figure 5a–d) found in the Skaergaard and Panzhihua intrusions. The compositional differences of the ilmenite originated from distinct tectonic settings and magmatic processes. The Tellnes intrusion was formed from mantle or lower crustal melting in a post-collision extensional setting, while the Skaergaard and Panzhihua intrusions are believed to have formed in association with continental rifting, probably linked to mantle plume activity [56,57,58,59].
Despite undergoing varying degrees of deformation and alteration (e.g., amphibolization, saussuritization, and chloritization), abundant magmatic ilmenite is preserved in the Luanchuan gabbroic intrusions (Figure 2b,c,e). This ilmenite is characterized by low MgO and Fe2O3 contents and high FeO and MnO contents (Figure 5a–d), showing compositional similarity to the ilmenite in the Skaergaard intrusion and the Panzhihua layered intrusion, suggesting a genetic affinity between the Luanchuan gabbroic intrusions and the Skaergaard and Panzhihua intrusions (Figure 5a–d, [53,54]). Compared with ilmenite in the Panzhihua intrusion, ilmenite in the Luanchuan intrusions more closely resembles that of the Skaergaard intrusion. In the Skaergaard intrusion, ilmenite crystallized relatively late during fractional crystallization [55,60,61,62], whereas in the Panzhihua layered intrusion, it crystallized during the early stage, indicating a high-Ti parental magma [56]. Therefore, the ilmenite in the Luanchuan gabbroic intrusions suggests a similar magmatic origin and evolutionary history with the Skaergaard intrusion. Geochemical data also support the formation of the Luanchuan gabbroic intrusions in a continental rift setting [19].
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Figure 5. Binary diagrams of the major oxide elements versus TiO2 of ilmenite from the Luanchuan gabbroic intrusions. (a) MgO vs. TiO2 diagram; (b) FeO vs. TiO2 diagram; (c) Fe2O3 vs. TiO2 diagram; (d) MnO vs. TiO2 diagram. Data of the ilmenite of the Skaergaard intrusion, Tellnes deposit, and Panzhihua Ti deposit from [52,54,62], respectively.
Figure 5. Binary diagrams of the major oxide elements versus TiO2 of ilmenite from the Luanchuan gabbroic intrusions. (a) MgO vs. TiO2 diagram; (b) FeO vs. TiO2 diagram; (c) Fe2O3 vs. TiO2 diagram; (d) MnO vs. TiO2 diagram. Data of the ilmenite of the Skaergaard intrusion, Tellnes deposit, and Panzhihua Ti deposit from [52,54,62], respectively.
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5.2. Genesis of Biotite

Biotite is a hydrous Fe-Mg phyllosilicate mineral that can be classified as magmatic, re-equilibrated, and hydrothermal types based on petrographic and compositional criteria [62,63,64,65,66,67,68,69]. In igneous rocks, biotite is commonly found in intermediate to acidic compositions, whereas it is rare in mafic-ultramafic rocks. According to previous studies, biotite in mafic rocks typically appears as siderophyllite or ferroan [46,50], and biotite in alkaline rocks varies significantly and may include lepidomelane, ferromagnesian biotite, and phlogopite. Metamorphic biotite is predominantly ferroan-rich (Figure 4c) [34,46].
Biotite in the Luanchuan gabbroic intrusions falls within the alkaline and metamorphic fields in the feal versus mgli diagram (Figure 4c). During the field investigation, varying degrees of regional, dynamic, and hydrothermal metamorphism were observed. This suggests that some of the biotite in the studied intrusions may be related to secondary processes rather than magmatic origins. However, all samples fall within the mafic rock field except for one outlier in the MnO×10-TiO2-Na2O×10 triangular diagram (Figure 6a). In the MgO-FeOT-Al2O3 diagram, both Bt I and Bt II correspond to mafic and alkaline rocks, coexisting with amphibole and ferromagnesian minerals (Figure 6b) [63,64]. Most biotite plots within the re-equilibrated field, with a small portion falling into the primary area in the TiO2-(FeOT+MnO)-MgO ternary diagram (Figure 6c). A total of 1730 data points of magmatic biotite from mafic intrusions were collected from the global GEOROC database and plotted. Most of the data are located near the boundary between primary and re-equilibrated biotite, with numerous data points within the re-equilibrated biotite area (Figure 6c). The consistent distribution indicates a magmatic origin of biotite in the Luanchuan gabbroic intrusions. Additionally, the metamorphic grade of the studied intrusions was reported to have almost reached the greenschist facies [11], which was significantly lower than the metamorphic conditions (amphibolite facies) required for the formation of the studied biotite [24]. Consequently, both types of biotite in the Luanchuan gabbroic intrusions are of magmatic origin, resulting from reactions between early crystallized minerals and residual magma. Bt I with high Ti is associated with ilmenite, while Bt II with low Ti biotite is likely associated with clinopyroxene or amphibole.
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Figure 6. The discrimination diagrams for the biotites. (a) MnO×10-TiO2-Na2O×10 ternary diagram, the biotite data from the mafic rocks from [34]. (b) MgO-FeOT-Al2O3 ternary diagram from [64], I—field of biotites coexisting with amphibole, II—field of biotites unaccompanied by other ferromagnesian minerals, III—field of biotites coexisting with muscovite, IV—field of biotites coexisting with aluminosilicates. (c) TiO2-(FeOT+MnO)-MgO ternary diagram, the fields for magmatic, re-equilibrated, and secondary biotites are from [65], and the 1730 triangle data represent the primary biotite of mafic intrusions from the global GEOROC database (http://georoc.mpch-mainz.gwdg.de/georoc, accessed on 1 March 2025). (d) FeOT/(FeOT+MgO) vs. MgO diagram from [70], with A referring to the Mg-biotite region, B referring to the Mg-biotite region, and C referring to the phlogopite region.
Figure 6. The discrimination diagrams for the biotites. (a) MnO×10-TiO2-Na2O×10 ternary diagram, the biotite data from the mafic rocks from [34]. (b) MgO-FeOT-Al2O3 ternary diagram from [64], I—field of biotites coexisting with amphibole, II—field of biotites unaccompanied by other ferromagnesian minerals, III—field of biotites coexisting with muscovite, IV—field of biotites coexisting with aluminosilicates. (c) TiO2-(FeOT+MnO)-MgO ternary diagram, the fields for magmatic, re-equilibrated, and secondary biotites are from [65], and the 1730 triangle data represent the primary biotite of mafic intrusions from the global GEOROC database (http://georoc.mpch-mainz.gwdg.de/georoc, accessed on 1 March 2025). (d) FeOT/(FeOT+MgO) vs. MgO diagram from [70], with A referring to the Mg-biotite region, B referring to the Mg-biotite region, and C referring to the phlogopite region.
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The MgO and FeO contents of biotite are closely related to the source properties of the host magma. Mantle-derived biotite typically contains high MgO (>15 wt%) and a low FeOT/(FeOT +MgO) ratio [70,71]. Based on variations in the compositions of biotite from crustal and mantle sources, Zhou [70] proposed a source discrimination diagram (Figure 6d). In this diagram (Figure 6d), biotite from the Luanchuan gabbroic intrusions predominantly falls into the mixed crust–mantle source field, indicating a heterogeneous magma source [70].

5.3. Physicochemical Conditions

Biotite records critical information on the T, P, and fO2 conditions of the host rocks [24,25,26,29,71]. Thermobarometers based on Ti and Al in biotite [48,72,73] have been widely applied to estimate the temperature and pressure conditions during biotite formation [48,49,73,74,75]. The genetic origins of biotite can be indicated by its titanium content and the ratio of iron to the sum of iron and magnesium (Fe/(Fe+Mg)), which are highly sensitive to temperature [24,47,76,77,78]. Henry [72] proposed a Ti-in-biotite thermometer calibrated for metapelitic biotites under Ti-saturated, peraluminous, and reduced conditions within the temperature range of 480–800°C. Although this calibration was developed based on metapelites, it has also been applied to granitoid rocks in some cases where the original conditions are not fully met [79,80]. Uchida [81] identified a linear correlation between Al content in coexisting biotites and hornblendes and proposed an Al-in-biotite barometer. Li and Zhang [49] evaluated the reliability of a Ti-in-biotite thermometer [72] and an Al-in-biotite barometer [81] in magmatic systems and developed a user-friendly web-based tool for calculating temperature and pressure over a broad range (625–1325 °C, 1–48 kbar) (https://lixiaoyan.shinyapps.io/Biotite_thermobarometer/, accessed on 1 March 2025).
The TiO2 contents and Fe/(Fe+Mg) ratios of biotite in the Luanchuan grabbroic intrusions indicate the P-T conditions of the amphibolite facies rather than granulite (Figure 7a) [82]. The application of thermobarometers to biotite in the Luanchuan gabbroic intrusions, following the calibration by Li and Zhang [49], yields consistent results for the two types of biotite. Bt I indicates temperatures ranging from 766 °C to 818 °C and pressures from 5.75 kbar to 8.80 kbar, whereas Bt II records slightly higher values, with temperatures from 799 °C to 818 °C and pressures from 6.46 kbar to 8.71 kbar (see Table 2). These temperatures and pressures indicate the tectonic setting of continental orogenic belts (Figure 7b) for the Luanchuan gabbroic intrusions [83,84].
The Fe/(Fe+Mg) ratio of biotite decreases with increasing oxygen fugacity (log fO2) in magmatic and fluid systems [23,84]. Wones and Eugster [24] proposed T-Fe/(Fe+Mg) and log fO2-T diagrams to estimate oxygen fugacity relative to various buffers, including the magnetite–ilmenite buffer (Fe3O4-Fe2O3, HM), the nickel–nickel oxide buffer (Ni-NiO, NNO), and the fayalite–quartz–magnetite buffer (Fe2SiO4-SiO2-Fe3O4, QFM) [85]. In both the T- Fe/(Fe+Mg) (Figure 7c) and log fO2-T diagrams (Figure 7d), the calculated fO2 values fall between the NNO and HM buffers, closely approaching the NNO line. The estimated oxygen fugacity during biotite formation ranges from −14.06 to −12.35.
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Figure 7. Temperature, pressure, and fO2 diagnostic diagrams of biotite. (a) TiO2 vs. Fe/(Mg+Fe) diagram [82]; (b) pressure vs. temperature diagram [83], with Ve and V∞ geotherms from [84]; (c) temperature vs. Fe/(Mg+Fe) ratio diagram [24]. Solid curves indicate Fe/(Fe+Mg) ratios within different oxygen buffers acquired in the experiment, and blue dashed curves indicate buffered QFM, NNO, and HM, respectively; (d) log fO2 vs. T diagram [24]. Numbers 30–80 represent the 100*Fe/(Mg+Fe) values of biotite. HM, NNO, QFM, and WI represent the oxygen fugacity buffers [85].
Figure 7. Temperature, pressure, and fO2 diagnostic diagrams of biotite. (a) TiO2 vs. Fe/(Mg+Fe) diagram [82]; (b) pressure vs. temperature diagram [83], with Ve and V∞ geotherms from [84]; (c) temperature vs. Fe/(Mg+Fe) ratio diagram [24]. Solid curves indicate Fe/(Fe+Mg) ratios within different oxygen buffers acquired in the experiment, and blue dashed curves indicate buffered QFM, NNO, and HM, respectively; (d) log fO2 vs. T diagram [24]. Numbers 30–80 represent the 100*Fe/(Mg+Fe) values of biotite. HM, NNO, QFM, and WI represent the oxygen fugacity buffers [85].
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5.4. Implications for Tectonic Setting

The NCC has been in a long-term extensional environment since its final collisional amalgamation around 1.8 Ga, as evidenced by the ~1.78 Ga Xiong’er Group volcanic rocks and mafic dykes, the 1.72–1.62 Ga AGRS assemblage (Anorthosite-Gabbro-Rapakivi granite-Syenite), the 1.64–1.60 Ga and 1.33–1.30 Ga Yanliao rift belt, the sporadically distributed mafic dykes emplaced between 1.24 to 1.20 Ga, and the mafic beds and dykes developed in the east between 0.94 to 0.89 Ga [5,6,8,86,87]. Alkaline rocks typically originate from three tectonic settings: continental rifts, oceanic/continental environments [88,89,90], and, to a lesser degree, subduction zones [91]. The geochemical data from these intrusions display characteristics of OIB-type mafic cumulate rocks associated with continental rifts [19,21], which are distinct from those of mid-ocean ridge basalts and island arc basalts [92].
The Luanchuan gabbroic intrusions, dated to the Neoproterozoic era (830–870 Ma) [19,20,21], are potash-rich and silica-unsaturated alkaline mafic intrusions [19,21]. The trachyte from the Dahongkou Formation within the Luanchuan Group has yielded ages of 840–846 Ma [40] and 854 ± 8 Ma [22], forming a bimodal magmatic assemblage interpreted to have developed in a continental rift [11,12,40]. This evidence suggests that the southern margin of the NCC underwent multiple cycles of extensional tectonics [9,12,40]. The ilmenite found in the Luanchuan gabbroic intrusions is characterized by low MgO and Fe2O3 and high FeO and MnO, which is consistent with ilmenite from the Skaergaard and Panzhihua intrusions. The biotite in the Luanchuan gabbroic intrusions displays a compositional affinity and oxygen fugacity similar to those of intrusions formed in an extensional tectonic environment, such as the Fanshan complex in China and the Falcon Island intrusion in Canada. The estimated genetic conditions of the Luanchuan gabbroic intrusions indicate a continental rift setting, potentially related to the breakup of the Rodinia supercontinent [12].
Considering the Neoproterozoic magmatic activity in the Qinling orogenic belt, it is inferred that the collision between the North Qinling terrane and the southern margin of the NCC occurred in the early Neoproterozoic (1.0–0.9 Ga) [12,18,93]. The Yangtze Craton may have converged with the North Qinling and NCC during this period [18], possibly contributing to the aggregation process of the Rodinia supercontinent [12,19,93]. The post-collision extensional stage developed at ~890 Ma in the North Qinling orogenic belt [18,93], followed by the transformation of continental non-orogenic extension from post-collision extension at ~844 Ma [13]. According to the previous tectonic evolution model [18], the southern subduction and collision orogeny of the Kuanping paleo-ocean occurred from 1000 to 900 Ma, corresponding to the convergence stage of the Rodinia supercontinent. The Luanchuan alkaline gabbroic intrusions (830 Ma, [19]), along with the Dahongkou trachyte (840–860 Ma, [13]), the Fangcheng alkaline syenite (~844 Ma, [40]), and the Tumen syenite (844–847 Ma, [94]), suggest the Neoproterozoic breakup of the southern margin of the NCC [11,19,40].

6. Conclusions

The Luanchuan Neoproterozoic gabbroic intrusions, characterized by silica-undersaturated, alkaline series, represent a critical portion of the alkaline rock belt along the southern margin of the North China Craton. Limited Ti-Fe mineralization has been discovered within these intrusions, indicating potential for the formation of magmatic Ti-Fe deposits. This study presents the compositional data for ilmenite and biotite in the Luanchuan gabbroic intrusions to assess the physicochemical conditions during its evolution and to evaluate its implications for the tectonic setting. The main conclusions are as follows:
(1)
The ilmenite in the Luanchuan gabbroic intrusions is characterized by low MgO and Fe2O3 content and high FeO and MnO content, showing compositional similarities to ilmenite from the Skaergaard intrusion and the Panzhihua layered intrusion;
(2)
The biotite in the Luanchuan gabbroic intrusions is of magmatic origin, with total Al contents ranging from 1.26 to 1.53 and Fe/(Fe+Mg) ratios varying from 0.44 to 0.56;
(3)
The estimated temperature and pressure for both types of biotite are broadly consistent (766 °C–818 °C and 5.75 kbar–8.80 kbar, respectively), comparable to values reported for the Fanshan complex and the Falcon Island intrusion;
(4)
Integrated regional geology, geochronology, and geochemical evidence indicates that the Luanchuan gabbroic intrusions formed in a continental rift setting, potentially related to the breakup of the Rodinia supercontinent.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/min15060602/s1, Figure S1: MgO, FeO, V2O3, and MnO versus TiO2 diagrams of the ilmenite in the Luanchuan gabbroic intrusions; Figure S2: SiO2, FeOT, Al2O3, and K2O versus TiO2 diagrams of the biotite in the Luanchuan gabbroic intrusions. Supplementary text: Standard deviations of EPMA data; Table S1: The 1730 data of primary biotite of mafic intrusions from the global GEOROC database.

Author Contributions

Methodology, J.H., M.R. and Y.F.; validation, J.H., Z.H. and Y.F.; formal analysis, M.R. and Z.H.; investigation, J.H. and D.C.; data curation, J.H., Y.F. and K.L.; writing—original draft preparation, J.H., Z.H. and M.R.; writing—review and editing, J.H., M.R., Z.H., Y.F., X.H. and K.L.; supervision, K.L. and M.R.; funding acquisition, J.H., M.R. and Y.F. All authors have read and agreed to the published version of the manuscript.

Funding

This study was jointly financially supported by the National Natural Science Foundation of China (Nos. 42003033 and 42102039), the Young Key Teachers Training Program of Henan Province (Grant No. 2024GGJS063), and the Young Key Teachers Training Program of North China University of Water Resources and Electric Power (Grant No. 202413704).

Data Availability Statement

Data are contained within the article.

Acknowledgments

We would like to express our gratitude to Guangzhou Tuoyan Testing Technology Co., Ltd. for their support with the microprobe analysis. We are grateful to the anonymous reviewers who helped to improve this paper and to the editors for handling, editing, and advising.

Conflicts of Interest

Author Danli Chen was employed by the company Henan Third Geological Exploration Institute Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Minerals 15 00602 g002
Figure 2. Field photographs and microphotographs of the Luanchuan gabbro. (a) Field outcrop of the Luanchuan gabbro intruding into the schist of the Meiyaogou Formation; (b) Luanchuan gabbro hand specimen exhibiting dominant plagioclase and amphibole, with a photograph of a thin section revealing minor ilmenite and biotite; (c) microphotograph of biotite I showing a dark reddish-brown fine texture and replacing black residual ilmenite (plane-polarized light); (d) microphotograph of biotite II showing a light gray-grayish brown subhedral texture and associated with amphibole and plagioclase (plane-polarized light); (e,f) BSE images of biotite I and ilmenite showing corona and replaced textures. Mineral abbreviations: Amp—amphibole; Pl—plagioclase; Ttn—titanite; Ilm—ilmenite; Bt—biotite.
Figure 2. Field photographs and microphotographs of the Luanchuan gabbro. (a) Field outcrop of the Luanchuan gabbro intruding into the schist of the Meiyaogou Formation; (b) Luanchuan gabbro hand specimen exhibiting dominant plagioclase and amphibole, with a photograph of a thin section revealing minor ilmenite and biotite; (c) microphotograph of biotite I showing a dark reddish-brown fine texture and replacing black residual ilmenite (plane-polarized light); (d) microphotograph of biotite II showing a light gray-grayish brown subhedral texture and associated with amphibole and plagioclase (plane-polarized light); (e,f) BSE images of biotite I and ilmenite showing corona and replaced textures. Mineral abbreviations: Amp—amphibole; Pl—plagioclase; Ttn—titanite; Ilm—ilmenite; Bt—biotite.
Minerals 15 00602 g002
Table 1. The compositions of ilmenite in the Luanchuan gabbroic intrusions.
Table 1. The compositions of ilmenite in the Luanchuan gabbroic intrusions.
No. 1234567910111418212431373841465556666773748788899598100105106111113
SampleSBG22-4-4SBG22-4-1MYG22-3-5MYG22-3-6
LocationShibaogou (111°34′54″, 33°50′01″)Meiyaogou (111°38′18″, 33°47′54″)
Rockcoarse-grained gabbroilmenite-bearing medium-grained gabbro
TiO250.4649.9250.5449.9450.7150.4250.8850.8151.4450.7452.5652.9551.4653.3453.5352.7852.3651.0752.0552.4251.7952.4952.6052.5852.7952.3552.8552.7852.3553.7552.8153.1753.2052.9252.49
FeOT48.1848.4647.4347.8347.3148.1347.5647.8046.9747.1845.3944.4746.1443.9544.0845.7345.5645.8046.0745.5845.7345.2745.7845.3945.6145.7445.4945.6145.5843.8745.1745.0045.1745.8045.34
Fe2O3calc44.2943.5044.0643.5444.3044.0244.2844.2544.6744.2145.3944.4744.6943.9544.0845.7345.4444.7644.8845.1744.6344.9545.3544.9245.3145.2545.4945.5245.0043.8745.0745.0045.1745.2144.94
FeOcalc4.335.523.744.763.344.563.653.942.553.310.000.001.610.000.000.000.131.161.330.461.220.350.490.530.330.550.000.110.640.000.110.000.000.650.44
MnO1.251.191.211.211.121.171.231.181.371.241.341.471.331.291.231.221.231.231.531.681.461.471.451.801.651.361.401.451.491.841.851.611.761.621.53
MgO0.110.150.120.140.120.120.140.130.130.120.150.110.100.140.120.140.200.090.230.120.190.400.390.180.200.270.280.280.330.310.290.330.390.400.41
Cr2O30.02b.d.l0.010.010.01b.d.l0.030.03b.d.lb.d.l0.030.030.010.010.040.010.040.030.01b.d.l0.04b.d.l0.040.02b.d.lb.d.lb.d.l0.02b.d.l0.060.080.080.040.040.08
NiO0.01b.d.lb.d.lb.d.lb.d.lb.d.lb.d.lb.d.lb.d.l0.01b.d.lb.d.lb.d.l0.01b.d.lb.d.lb.d.l0.01b.d.lb.d.l0.03b.d.l0.020.010.01b.d.l0.010.010.02b.d.lb.d.l0.040.02b.d.lb.d.l
V2O3 0.090.110.080.110.050.090.080.080.070.070.140.110.130.150.130.050.070.050.120.070.06b.d.lb.d.l0.060.01b.d.lb.d.lb.d.lb.d.l0.060.010.050.070.180.21
Total100.49100.2899.7399.6699.61100.30100.25100.40100.2099.6499.5199.0799.2498.9299.0699.9799.4498.38100.0499.9499.4299.68100.54100.14100.3799.79100.05100.1999.8799.91100.24100.33100.64100.8799.92
Site assignment of ilmenite (FeTiO3)
Ti0.960.950.960.950.970.960.960.960.980.971.001.010.981.021.021.001.000.990.991.000.991.000.991.001.000.991.001.000.991.011.001.001.000.990.99
Fe2+0.930.920.930.920.940.930.930.930.940.940.960.940.950.930.930.960.960.960.950.950.950.950.950.950.950.960.960.960.950.920.950.940.940.940.95
Fe3+0.080.100.070.090.060.090.070.070.050.060.000.000.030.000.000.000.000.020.030.010.020.010.010.010.010.010.000.000.010.000.000.000.000.010.01
Mn0.030.030.030.030.020.030.030.030.030.030.030.030.030.030.030.030.030.030.030.040.030.030.030.040.040.030.030.030.030.040.040.030.040.030.03
Mg0.000.010.000.010.000.000.010.000.010.000.010.000.000.010.000.010.010.000.010.000.010.010.010.010.010.010.010.010.010.010.010.010.010.010.02
Cr0.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.00
Ni0.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.00
V0.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.00
Sum2.002.002.002.002.002.002.002.002.002.002.001.992.001.991.982.002.002.002.002.002.002.002.002.002.002.002.002.002.001.992.002.002.002.002.00
Note: b.d.l represents analyses below the detection limit.
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Huang, J.; Huang, Z.; Chen, D.; Li, K.; Huang, X.; Ren, M.; Fan, Y. Tectonic Setting of the Neoproterozoic Gabbroic Intrusions in the Luanchuan Area, Southern Margin of the North China Craton: Constraints from Ilmenite and Biotite Mineralogy. Minerals 2025, 15, 602. https://doi.org/10.3390/min15060602

AMA Style

Huang J, Huang Z, Chen D, Li K, Huang X, Ren M, Fan Y. Tectonic Setting of the Neoproterozoic Gabbroic Intrusions in the Luanchuan Area, Southern Margin of the North China Craton: Constraints from Ilmenite and Biotite Mineralogy. Minerals. 2025; 15(6):602. https://doi.org/10.3390/min15060602

Chicago/Turabian Style

Huang, Jianhan, Zhenzhen Huang, Danli Chen, Kekun Li, Xiaoxiao Huang, Minghao Ren, and Yazhou Fan. 2025. "Tectonic Setting of the Neoproterozoic Gabbroic Intrusions in the Luanchuan Area, Southern Margin of the North China Craton: Constraints from Ilmenite and Biotite Mineralogy" Minerals 15, no. 6: 602. https://doi.org/10.3390/min15060602

APA Style

Huang, J., Huang, Z., Chen, D., Li, K., Huang, X., Ren, M., & Fan, Y. (2025). Tectonic Setting of the Neoproterozoic Gabbroic Intrusions in the Luanchuan Area, Southern Margin of the North China Craton: Constraints from Ilmenite and Biotite Mineralogy. Minerals, 15(6), 602. https://doi.org/10.3390/min15060602

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