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Article

Olivine and Whole-Rock Geochemistry Constrain Petrogenesis and Geodynamics of Early Cretaceous Fangcheng Basalts, Eastern North China Craton

by
Qiao-Chun Qin
1,
Lu-Bing Hong
1,2,*,
Yin-Hui Zhang
1,
Hong-Xia Yu
1,
Dan Wang
1,
Le Zhang
3 and
Peng-Li He
3
1
Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, College of Earth Science, Guilin University of Technology, Guilin 541004, China
2
Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources by the Province and Ministry, Guilin University of Technology, Guilin 541004, China
3
State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(9), 928; https://doi.org/10.3390/min15090928
Submission received: 5 August 2025 / Revised: 22 August 2025 / Accepted: 28 August 2025 / Published: 30 August 2025
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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Abstract

The profound Phanerozoic destruction of the eastern North China Craton (NCC) is well documented, yet its mechanism remains debated due to limited constraints on thermal state and lithospheric thickness during the Early Cretaceous—the peak period of cratonic destruction. We address this gap through integrated geochemical analysis (major/trace elements, Sr-Nd-Pb isotopes, olivine chemistry) of Early Cretaceous (~125 Ma) Fangcheng basalts from Shandong. These basalts possess high MgO (8.14–11.31 wt%), Mg# (67.23–73.69), Ni (126–244 ppm), and Cr (342–526 ppm). Their trace elements show island arc basalt (IAB) affinities: enrichment in large-ion lithophile elements and depletion in high-field-strength elements, with negative Sr and Pb anomalies. Enriched Sr-Nd isotopic compositions [87Sr/86Sr(t) = 0.709426–0.709512; εNd(t) = −12.60 to −13.10], unradiogenic 206Pb/204Pb(t) and 208Pb/204Pb(t) ratios (17.55–17.62 and 37.77–37.83, respectively), and slightly radiogenic 207Pb/204Pb(t) ratios (15.55–15.57) reflect an upper continental crustal signature. Covariations of major elements, Cr, Ni, and trace element ratios (Sr/Nd, Sc/La) with MgO indicate dominant olivine + pyroxene fractionation. High Ce/Pb ratios and lack of correlation between Ce/Pb or εNd(t) and SiO2 preclude significant crustal contamination. The combined isotopic signature and IAB-like trace element patterns support a lithospheric mantle source that was metasomatized by upper crustal material. Olivine phenocrysts exhibit variable Ni (1564–4786 ppm), Mn (903–2406 ppm), Fe/Mn (56.63–85.49), 10,000 × Zn/Fe (9.55–19.55), and Mn/Zn (7.07–14.79), defining fields indicative of melts from both peridotite and pyroxenite sources. High-MgO samples (>10 wt%) in the Grossular/Pyrope/Diopside/Enstatite diagram show a clinopyroxene, garnet, and olivine residue. Reconstructed primary melts yield formation pressures of 3.5–3.9 GPa (110–130 km depth) and temperatures of 1474–1526 °C, corresponding to ~60 mW/m2 surface heat flow. This demonstrates retention of a ≥110–130 km thick lithosphere during peak destruction, arguing against delamination and supporting a thermo-mechanic erosion mechanism dominated by progressive convective thinning of the lithospheric base via asthenospheric flow. Our findings therefore provide crucial thermal and structural constraints essential for resolving the dynamics of cratonic lithosphere modification.

1. Introduction

Cratons, Earth’s oldest continental nuclei, owe their exceptional longevity and stability to thick, refractory lithospheric mantle keels, which confer inherent buoyancy and rigidity [1,2]. These stable roots preserve fundamental records of continental evolution [3]. Despite their inherent resilience, cratonic lithospheres can undergo profound destabilization, as dramatically illustrated by the decratonization of the eastern North China Craton (NCC) [4,5,6]. Stabilized during the Precambrian, the eastern NCC initially possessed a thick (>180 km), cold (~40 mW/m2), refractory Archean mantle keel (>2.5 Ga), evidenced by Paleozoic kimberlite-borne xenoliths [4,7,8,9,10,11]. However, a profound tectonic transition commenced in the Mesozoic marked by intense magmatism and tectonism [6,12,13,14,15,16,17,18]. Cenozoic basalt-borne xenoliths reveal pervasive replacement of this Archean mantle by younger, thinner, hotter, and more fertile Phanerozoic lithospheric mantle [4,7,8,9,10,11,19,20]. This shift from long-term stability to extensive destruction presents a pivotal paradox in global geodynamics.
Decratonization involves lithospheric thinning, asthenospheric upwelling, and elevated geothermal gradients [4,13]. Consequently, reconstructing the thermal evolution during this process is critical for deciphering the underlying mechanisms. Data on xenoliths confirm the NCC’s transformation from a thick, cold Paleozoic regime to a thin, hot Cenozoic state [4,7,9,20,21]. However, robust direct constraints on lithospheric thickness and paleo-thermal conditions during the Early Cretaceous—the peak period of cratonic destruction [6,12,14]—remain scarce. This knowledge gap fuels ongoing debate between two principal models: (1) protracted thermo-mechanic erosion, involving progressive convective erosion of the lithospheric base due to asthenospheric flow [4] and (2) rapid lithospheric delamination driven by gravitational foundering of dense, eclogitized lower crust and attached mantle lithosphere [22,23].
High-MgO volcanics (>10 wt% MgO), derived from mantle sources and dominated by olivine fractionation, offer a valuable probe into mantle conditions. Though relatively scarce, such Early Cretaceous volcanics are preserved within volcanic sequences across the eastern NCC [23,24,25]. Among these, the Fangcheng basalts, with MgO contents up to ~12 wt%, exhibit island arc basalt (IAB)-like trace element signatures and enriched Sr-Nd isotopes, suggesting derivation from metasomatized lithospheric mantle [24,26,27]. This study integrates whole-rock major/trace element geochemistry, Sr-Nd-Pb isotopes, and detailed olivine chemistry from the Early Cretaceous Fangcheng basalts to constrain primary melt compositions and mantle source characteristics. By quantitatively modeling the pressure/temperature (P-T) conditions of melt generation, we aim to quantify lithospheric thickness and thermal state during this critical phase of NCC destruction. Our results provide essential new constraints on the deep geodynamic processes driving cratonic destabilization.

2. Background and Sample Description

The NCC, China’s largest and oldest craton, spans ~1.7 × 106 km2 [28], with continental nuclei dating to 3.6–4.0 Ga [29,30,31,32,33,34,35]. It consists of three major tectonic units, namely, the Eastern Block, the Western Block, and the intervening Trans-North China Orogen, which were amalgamated during the Paleoproterozoic (Figure 1). The craton exhibits an inverted triangular morphology, bounded by Phanerozoic orogenic belts: the Central Asian Orogenic Belt to the north, the Qinling–Dabie Orogenic Belt to the southwest, and the Sulu Orogenic Belt to the southeast (Figure 1). This architecture resulted from multiple convergence events, including Paleozoic southward subduction of the Paleo-Asian oceanic plate and Triassic deep subduction of the Yangtze continental crust, which ultimately led to the amalgamation of the NCC with the Siberian Craton and the South China Block, forming the Central Asian and the Qinling–Dabie–Sulu orogenic belts, respectively.
Shandong Province is situated in the southeastern part of the NCC. This region is divided by the Tan-Lu Fault into the Luxi and Jiaodong areas. Mesozoic igneous rocks here are predominantly plutonic, with subordinate volcanic rocks (Figure 1b). The Fangcheng area lies within the Mengyin Basin of Luxi region, approximately 70 km west of the Tan-Lu Fault. Early Cretaceous volcanic rocks here cover several square kilometers and form a sequence dominated by basalt (~100 m thick), underlain by picrite and overlain by andesite [24]. The Fangcheng basalts, dated by K-Ar at 124.9 ± 1.8 Ma [24], exhibit a porphyritic texture with olivine and pyroxene phenocrysts within a massive groundmass of pyroxene, olivine, plagioclase, and magnetite. These basalts host abundant (1–8 cm across) mantle xenoliths, predominantly olivine-bearing wehrlites and clinopyroxenites with clinopyroxene contents reaching 90 vol% [24].
We examined four representative Fangcheng basalt samples. Hand specimens exhibit a yellowish-brown weathered surface over a fresh gray-black interior. These rocks feature a porphyritic texture and massive structure, containing 2.8–5.3 vol% olivine and 0.1–1.4 vol% pyroxene phenocrysts (Figure 2). Olivine phenocrysts (0.2–1.3 mm) are subhedral to euhedral, displaying irregular fractures; localized alteration occurs along fractures and margins. Some olivines contain primary spinel inclusions (Figure 2e–f). Pyroxene phenocrysts (0.2–0.7 mm) are subhedral to euhedral prisms. The fine-grained groundmass consists of pyroxene, olivine, plagioclase, and magnetite.

3. Analytical Methods

3.1. Whole-Rock Analyses

Major and trace element analyses were conducted at Wuhan Sample Solution Analytical Technology Co., Ltd. (Wuhan, China), following protocols detailed at www.samplesolution.cn. Major elements were determined with wavelength-dispersive X-ray fluorescence spectrometry (WD-XRF) using a ZSX Primus II spectrometer (Rigaku Corporation, Tokyo, Japan). Samples were analyzed on fused glass disks at 50 kV and 60 mA, with analytical precision better than 3% for all reported oxides. Trace elements were quantified with inductively coupled plasma mass spectrometry (ICP-MS) using an Agilent 7700e instrument (Santa Clara, CA, USA). Powdered samples underwent high-pressure digestion in a high-purity HF-HNO3-HClO4 mixture within pre-cleaned Teflon vessels; precision for most trace elements was better than 5%.
Sr-Nd-Pb isotopic compositions were measured using a Neptune Plus multi-collector ICP-MS (MC-ICP-MS) at the Guangxi Key Laboratory of Exploration for Hidden Metallic Ore Deposits, Guilin University of Technology. Sample powders were dissolved in 15 mL Teflon vials using a mixture of ultra-pure HF and HNO3, followed by heating at 120 °C for 5–7 days to ensure complete digestion. The solution was then evaporated to dryness, redissolved in ultra-pure HNO3, and dried again. Subsequently, ultra-pure HCl was added, and the sample was reheated for at least 4 h. After final evaporation, the residue was taken up in ultra-pure HNO3 for subsequent chemical separation. Pb, and Sr were isolated using Sr-specific resin, the REE fraction was separated using AG50W-X12 resin (Bio-Rad, Hercules, CA, USA), and Nd was further purified from the REE fraction via LN resin [39,40]. Mass bias was corrected via internal normalization to 88Sr/86Sr = 8.375209, 146Nd/144Nd = 0.7219, and 205Tl/203Tl = 2.38714. Instrument drift was monitored using NBS987 (Sr), JNdi-1 (Nd), and NBS981 (Pb) standards. Analyses of USGS reference material BHVO-2 yielded 87Sr/86Sr = 0.703473 ± 24 (2SE), 143Nd/144Nd = 0.512977 ± 7, 206Pb/204Pb = 18.638 ± 1, 207Pb/204Pb = 15.522 ± 1, and 208Pb/204Pb = 38.204 ± 3, consistent with recommended values (87Sr/86Sr = 0.703478 ± 34, 143Nd/144Nd = 0.512979 ± 14, 206Pb/204Pb = 18.634 ± 34, 207Pb/204Pb = 15.524 ± 25, and 208Pb/204Pb = 38.146 ± 373) [41].

3.2. Olivine Analyses

Separated olivine grains were mounted in epoxy resin disks at the State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (GIG–CAS), Guangzhou. Chemical analyses were performed at GIG–CAS. Major element compositions were determined using a CAMECA SXFiveFE electron probe microanalyzer (EPMA) operated at 20 kV accelerating voltage and 100 nA beam current with a 5 μm beam diameter. Peak counting times were 10–20 s for Mg, Si, and Fe, and 60 s for Ca. Data reduction utilized the PAP correction procedure [42]. For the trace element analysis, laser ablation–ICP–MS (LA–ICP–MS) was employed following the methodology of Zhang et al. [43], utilizing a 45 μm laser spot at 5 Hz repetition rate. Data processing was performed with the TraceElement MATLAB program [43], applying normalization to Mg without internal standard correction. Calibration was achieved against international reference glasses BHVO-2G, BCR-2G, and GSD-1G. Repeated analyses of BIR-1G yielded relative standard deviations < 10% for most trace elements.

4. Results

4.1. Whole-Rock Geochemistry

Whole-rock compositions of the Fangcheng basalts are presented in Table S1. These basalts exhibit SiO2 (48.80–49.91 wt%) and total alkali (Na2O + K2O; 4.43–5.74 wt%) straddling the alkaline/subalkaline boundary on the TAS diagram (Figure 3a), classifying them as transitional basalts. They display high MgO (8.14–11.31 wt%), Mg# [molar Mg/(Mg+Fe2+)] (67.23–73.69), Ni (126–244 ppm), and Cr (342–526 ppm). Al2O3 (13.32–14.65 wt%), CaO (8.42–8.89 wt%), and Fe2O3Total(8.82–9.00 wt%) show moderate concentrations, while TiO2 (1.09–1.14 wt%) and P2O5 (0.83–0.98 wt%) are relatively low. Systematically decreasing MgO correlates with increasing SiO2, Al2O3, and P2O5; decreasing CaO, Ni, and Cr; and near-constant TiO2 (Figure 3b–h), consistent with previous studies (Figure 3).
Trace element signatures reveal enrichment in large-ion lithophile elements (LILEs; e.g., Ba, Th, U) and pronounced light rare earth element (LREE) enrichment (Figure 4a). These are coupled with relative heavy rare earth element (HREE) depletion and significant negative anomalies in high-field-strength elements (HFSEs; Nb, Ta, Zr, Hf, Ti), alongside weak negative Pb and Sr anomalies (Figure 4a), matching earlier findings. Compared to contemporaneous igneous suites in Shandong, the Fangcheng basalts exhibit a trace element pattern resembling that of carbonatites—characterized by enrichment in LILEs and LREEs, depletion in HREEs and HFSEs, and negative anomalies in Sr and Pb—though with less pronounced LILE/REE enrichment and weaker HFSE depletion. While sharing characteristic LILE enrichment and HFSE depletion with Shandong IAB-type magmas, the Fangcheng basalts lack the prominent positive Sr and Pb anomalies typical of IAB-type rocks. Their signature contrasts markedly with ocean island basalt (OIB)-type magmas, which feature Nb-Ta positive anomalies and Pb negative anomalies (Figure 4b).
The basalts possess enriched Sr-Nd isotopic compositions [87Sr/86Sr(t) = 0.709426–0.709512, 143Nd/144Nd(t) = 0.511805–0.5119, and εNd(t) = −12.60 to −13.10; corrected to t = 125 Ma]. Lead isotopes show unradiogenic 206Pb/204Pb(t) and 208Pb/204Pb(t) isotopic ratios (17.55–17.62 and 37.77–37.83, respectively), and slightly radiogenic 207Pb/204Pb(t) ratios (15.55–15.57). These values align with previous reports [87Sr/86Sr(t) = 0.7094–0.7101, 143Nd/144Nd(t) = 0.511705–0.511831, and εNd(t) = −11 to −15; 206Pb/204Pb(t) = 17.4–17.6, 207Pb/204Pb(t) = 15.4–15.6, and 208Pb/204Pb(t) = 37.4–37.7] (Figure 5). The Sr-Nd isotopes overlap compositionally with their entrained mantle xenoliths and contemporaneous Shandong carbonatites. These values fall within the field defined by contemporaneous Shandong IAB-type magmatic rocks but are distinctly lower than the Nd isotopic compositions recorded by Paleozoic mantle xenoliths and contemporaneous Shandong OIB-type magmas. The Pb isotopic ratios are indistinguishable from entrained xenoliths and show no resolvable difference from contemporaneous Shandong IAB- and OIB-type magmatic rocks.

4.2. Olivine Geochemistry

Olivine compositions in the Fangcheng basalts, determined with EPMA (Table S2) and LA-ICP-MS (Table S3), yield high forsterite contents (Fo = 81.0–91.8) and low CaO concentrations (0.11–0.18 wt%; equivalent to 782–1612 ppm Ca). They exhibit variable Ni (1564–4786 ppm), Mn (903–2406 ppm), Fe/Mn (56.63–85.49), 10,000 × Zn/Fe (9.55–19.55), and Mn/Zn (7.07–14.79) values. At a given Fo content, some olivine compositions align with those crystallized from peridotite-derived melts, while others plot within the field of olivines crystallized from pyroxenite-derived melts (Figure 6).

5. Discussion

5.1. Magmatic Processes During Crustal Transit

Fractional crystallization is a primary mechanism modifying mantle-derived basaltic magmas during crustal ascent or residence. The Fangcheng basalts exhibit unequivocal mantle signatures, including high MgO (8.14–11.31 wt%), Mg# (67.23–73.69), Cr (342–526 ppm), and Ni (126–244 ppm). Petrography reveals phenocryst assemblages dominated by olivine and pyroxene, indicating their role in fractionation. This interpretation is reinforced by systematic geochemical covariations: CaO, Ni, and Cr with MgO increase with MgO, while Al2O3 and P2O5 decrease, and TiO2 remains constant (Figure 3c–h). These trends indicate crystallization dominated by Mg-Ni-rich olivine, and Ca-Cr-rich pyroxene, with negligible contribution from Al-rich plagioclase, Ti-rich oxides, or P-rich apatite. Although negative Sr anomalies occur, constant Sr/Nd ratios (12–15) with decreasing MgO contradict plagioclase fractionation, which would fractionate Sr from Nd (Figure 7a). Concurrently, increasing Sc/La ratios (0.12–0.25) with MgO (Figure 7b) supports pyroxene removal, given its high Sc/La.
Crustal contamination constitutes another significant process potentially modifying mantle-derived melts. Continental crust typically has high SiO2 and Pb contents, low Ce/Pb ratios, and enriched Sr-Nd isotopes [46,47,48,52]. Contamination would therefore depress Ce/Pb ratios and drive Sr-Nd isotopes towards more enriched values as SiO2 increases. The Fangcheng basalts, however, maintain high Ce/Pb ratios (15–24) with no systematic covariation between Ce/Pb, εNd(t) values, and SiO2 (Figure 7c,d), precluding significant crustal contamination.
Therefore, mineralogical and geochemical evidence demonstrates that the Fangcheng basalts evolved dominantly through olivine/pyroxene fractionation without substantive crustal contamination.

5.2. Origin and Nature of the Mantle Source

The lithospheric mantle forms a residue after melt extraction from the convective mantle, stabilizing atop the asthenosphere. Over geological time, this reservoir is commonly modified by hydrous melts/fluids from subducting slabs, enriching fluid-mobile elements (e.g., Rb, Ba, Sr, and Pb) while depleting HFSEs (e.g., Nb, Ta, and Ti) [55,56]. Melting of such metasomatized lithosphere generates IAB-type magmas, whereas melting of convective mantle containing recycled oceanic crust produces OIB-type magmas [57,58]. Early Cretaceous mantle-derived magmatism in Shandong exemplifies this framework. It is dominated by IAB-type rocks exhibiting characteristic Nb-Ta-Ti depletion and enriched Sr-Nd isotopic signatures [4,23,24,26,27,49,59,60,61,62] (Figure 4 and Figure 5), attributed to melting of an ancient enriched lithospheric mantle source [4,16,63,64]. Minor OIB-type rocks—distinguished by Nb-Ta positive anomalies, Pb negative anomalies, and depleted Nd isotopes—occur locally (e.g., Jiaodong area) and are interpreted as products of asthenospheric melting [64,65,66].
The Fangcheng basalts share key geochemical affinities with the contemporaneous IAB-type suite, contrasting with OIB-type rocks: (1) enrichment in LILEs and depletion in HFSEs (Figure 4); (2) enriched Sr-Nd isotopic compositions [87Sr/86Sr(t) = 0.7094 to 0.7101, εNd (t) = −11 to −15] (Figure 5) [24,26,27]. Critically, their Sr-Nd-Pb isotopic signatures are indistinguishable from entrained mantle xenoliths [87Sr/86Sr(t) = 0.7097–0.7102; εNd(t) = −11 to −14; 206Pb/204Pb(t) ≈ 17.4–17.8; 207Pb/204Pb(t) ≈ 15.4–15.6; 208Pb/204Pb(t) ≈ 37.4–38.1] (Figure 5) [26,67,68]. These collective characteristics unequivocally indicate a lithospheric mantle source.
Mantle xenoliths reveal that Paleozoic lithospheric mantle beneath the eastern NCC is characterized by variable 87Sr/86Sr(t) but constant εNd(t) ≈ −5 [10,50,51]. However, Early Cretaceous IAB-type rocks west of the Tan-Lu Fault in Shandong exhibit significantly more enriched Nd isotopes (εNd(t) down to −20), with only minor overlap (Figure 5a). While crustal contamination may explain low εNd(t) locally (e.g., the Jinan complex [59]), most signatures are intrinsic to the mantle source [16,64]. Critically, studies document a distinct spatial isotopic trend: magmas proximal to the Tan-Lu Fault exhibit upper continental crust-like Sr-Nd-Pb isotopes (e.g., 87Sr/86Sr(t)), while distal magmas resemble Paleozoic lithospheric mantle [61,69]. Given that the Triassic Sulu orogen was formed by the subduction and exhumation of the Yangtze Block, this spatial pattern indicates that the lithospheric mantle of the NCC was modified by upper crustal materials derived from the subducted Yangtze slab, and the extent of modification decreases systematically westward with increasing distance from the Tan-Lu Fault zone.
Located ~70 km west of the Tan-Lu Fault, the Fangcheng basalts display pronounced upper continental crust affinity: highly radiogenic 87Sr/86Sr(t) (0.7094–0.7101), slightly radiogenic 207Pb/204Pb(t) (15.4–15.6), low εNd(t) (−11 to −15), and unradiogenic 206Pb/204Pb(t) (17.4–17.7) and 208Pb/204Pb(t) (37.4–37.9) (Figure 5) [24,26,27]. Their proximity to the Tan-Lu Fault and the documented regional isotopic trend strongly indicate that their Sr-Nd-Pb signatures result from modification of the Paleozoic lithospheric mantle by upper crustal material from the subducted Yangtze slab. To quantify this contribution, we performed two-component mixing modeling. The unmodified lithospheric mantle end-member is represented by sample YS14−31 [87Sr/86Sr(t) = 0.705335; εNd(t) = −5.17; 206Pb/204Pb(t) = 16.79; 207Pb/204Pb(t) = 15.32; 208Pb/204Pb(t) = 36.68; Nd/Sr = 0.050; Pb/Sr = 0.008] [49] with Sr = 50 ppm, whose Sr-Nd isotopes closely match the Paleozoic lithospheric mantle, implying minimal Yangtze influence. The upper continental crust end-member utilized trace element concentrations (Sr = 327 ppm, Nd = 27 ppm, Pb = 19.9 ppm) from Rudnick and Gao [52], Sr-Nd isotopes [87Sr/86Sr(t) = 0.743032; εNd(t) = −46.65] [47], and Pb isotopes [206Pb/204Pb(t) = 18.85; 207Pb/204Pb(t) = 15.71; 207Pb/204Pb(t) = 38.88] [48] (see Table S4 for details). The modeling indicates that incorporating 1%–2% upper continental crust into the lithospheric mantle source reproduces the Fangcheng basalt compositions.

5.3. Hybrid Lithology in Mantle Source

Although peridotite dominates lithospheric mantle, subduction-derived melts/fluids can metasomatize it into pyroxenite [70,71,72]. As established, the Fangcheng basalts originate from lithospheric mantle metasomatized by Yangtze Block upper crustal material, a process capable of transforming peridotite into pyroxenite. Olivine, an early-crystallizing phase in basaltic magmas, records critical source lithology information. Mantle olivine primarily hosts Ni but minimally fractionates Fe, Mn, and Zn, exhibiting partition coefficients (D) near unity for Fe/Mn, Zn/Fe, and Mn/Zn. In contrast, garnet (a major Mn reservoir) and clinopyroxene significantly fractionate these elements [(D(Fe/Mn) < 1, D(Zn/Fe) < 1, D(Mn/Zn) > 1] [73]. Consequently, olivine crystallizing from pyroxenite-derived melts exhibits higher Ni, Fe/Mn, and 10,000 × Zn/Fe but lower Mn and Mn/Zn than peridotite-derived equivalents [53,72,74,75].
The Fangcheng olivine phenocrysts, euhedral to subhedral (Figure 2), possess CaO contents (0.11–0.18 wt%) distinct from anhedral mantle xenocrysts (<0.1 wt% CaO; Figure 8a) [23,76], confirming magmatic origin. These olivines exhibit substantial compositional variability in Ni (1564–4786 ppm), Mn (903–2406 ppm), Fe/Mn (56.63–85.49), 10,000 × Zn/Fe (9.55–19.55), and Mn/Zn (7.07–14.79) ranges. At constant Fo, their compositions partially overlap the peridotite-derived melt field but extend distinctly into the pyroxenite-derived melt domain (Figure 6), indicating mixing between peridotite- and pyroxenite-derived melts and implying a hybrid peridotite/pyroxenite source.
The Grossular/Pyrope/Diopside/Enstatite diagram (olivine-projected A-CS-MS system [53]) constrains melt-equilibrated mineral assemblages independent of olivine fractionation. High-MgO Fangcheng samples (Mg# up to 74), minimally affected by clinopyroxene fractionation, plot within the [Liquid + Cpx + Ol + Gt] field at 3–4 GPa and trend subparallel to the [Liquid + Cpx + Ol + Gt] cotectic (Figure 9a). This requires clinopyroxene (Cpx), olivine (Ol), and garnet (Gt), but not orthopyroxene (Opx), as residual phases.
An apparent contradiction exists between the orthopyroxene-absent residue and the typical orthopyroxene enrichment expected from reactions between SiO2-rich slab-derived melts/fluids and mantle peridotite [70,71,79]. This paradox is resolved through metasomatism by CO2-rich agents, which consumes orthopyroxene to form clinopyroxene, thereby transforming peridotite into clinopyroxene-rich lithologies [80,81]. Direct evidence comes from abundant wehrlite and olivine clinopyroxenite xenoliths within the Fangcheng basalts [24,67,68]. Their clinopyroxenes contain CO2-rich fluid inclusions [82] and exhibit diagnostic carbonatitic signatures: low Ti/Eu (517–1867), high (La/Yb)N (13–15), and elevated Ca/Al (7–9) [83]. Apatites in these xenoliths further show carbonatitic crystallization features: high F (~2.8 wt%), elevated Sr (~3800 ppm), low Sr/Y (~15), and extreme (La/Yb)N (~215) [83]. Critically, identical Sr-Nd-Pb isotopes in the host basalts and xenoliths (Figure 5) confirm a shared CO2-rich metasomatic history. The trace element patterns of the basalts—characterized by enrichment in LILEs and LREEs, depletion in HREEs and HFSEs, and negative Sr and Pb anomalies—closely resemble those of contemporaneous Shandong carbonatites (Figure 4b). Their Sr-Nd isotopes [87Sr/86Sr(t) = 0.7094–0.7101; εNd(t) = −11 to −15] overlap carbonatite values [87Sr/86Sr(t) = 0.7098–0.7107; εNd(t) = −14 to −19] (Figure 5) [84]. Collectively, these lines of evidence demonstrate that metasomatism by CO2-rich agents reduced orthopyroxene in the source. The orthopyroxene-free residue thus necessitates metasomatic transformation.

5.4. Reconstruction of Primary Melts and P-T Formation Conditions

Building upon the hybrid pyroxenite/peridotite source for the Fangcheng basalts, we reconstruct primary melt compositions following Herzberg [53]. This method involves two principal steps. First, olivine-controlled basalts are projected along the [Olivine] join in the Grossular/Pyrope/Diopside/Enstatite compositional space (Figure 9a). This projection effectively removes the effects of olivine fractionation, enabling direct determination of equilibration pressures and mineral assemblages for the primary melts. Subsequently, synthetic melts generated by incrementally adding or subtracting equilibrium olivine are projected along the [Diopside] join onto the CATS/Olivine/Quartz diagram (Figure 9b). The composition yielding consistent pressure and phase assemblage estimates between both projections identifies the primary melt.
Key parameters were constrained prior to primary melt reconstruction. Oxygen fugacity estimates (~ΔFMQ + 0.8 [78]) for the Fangcheng basalts yielded Fe2+/ΣFe ≈ 0.84 using Petrolog3 [85]. Water content was determined via the Ca-in-olivine hygrometer [77]. Given that only sample FC-6 exhibits sufficiently high MgO (11.31 wt%) and Mg# (74.91), CaO contents from high-Fo (>87) olivine phenocrysts were utilized. Assuming that the melt CaO and MgO concentrations are equivalent to the whole-rock composition provided a CaO partition coefficient of ~0.015, yielding H2O contents of ~3.88 wt% and H2O/P2O5 = 4.66 (Table S5). Consequently, only high-MgO samples (MgO > 10 wt%) exhibiting minimal clinopyroxene fractionation signatures and dominantly controlled by olivine crystallization were selected for primary melt reconstruction. Within Petrolog3, primary melt compositions were derived by incrementally adding or subtracting equilibrium olivine, applying the parameters Fe2+/ΣFe = 0.84, H2O/P2O5 = 4.66, and the Ford et al. [86] model for olivine/melt Fe-Mg partitioning. This procedure produced primary magmas with compositions of 47.29–48.50 wt% SiO2, 10.45–11.50 wt% Al2O3, 8.79–8.96 wt% FeOTotal, 17.66–19.64 wt% MgO, 7.60–8.63 wt% CaO, and 3.03–3.61 wt% H2O (Table S6).
Considering the residual mineralogy of the Fangcheng basalt source (olivine + clinopyroxene + garnet, lacking orthopyroxene), we calculated P-T conditions of magma generation by applying Sun and Dasgupta’s [87] thermobarometer to the reconstructed primary melts. This approach exploits the pressure-dependent variation in Al2O3 in the melt coexisting with garnet + olivine ± other phases. Calculations record magma formation temperatures of 1474–1526 °C and pressures of 3.5–3.9 GPa (Table S6). As the Fangcheng basalts represent partial melts of lithospheric mantle, their derived P-T conditions imply a thermal state corresponding to a surface heat flow of ~60 mW/m2 (Figure 10). Independently, analysis of pyroxenite mantle xenoliths entrained within these lavas [67] records equilibrated temperatures of 994–1177 °C and pressures of 2.0–3.4 GPa. These xenolith P-T estimates similarly yield an inferred lithospheric thermal state of ~50–60 mW/m2 (Figure 10). The convergence of these two independent methodologies—primary melt thermobarometry and mantle xenolith thermobarometry—on a consistent lithospheric thermal state beneath Fangcheng provides robust validation for our results. This agreement, derived from fundamentally different approaches, strongly reinforces the inferred thermal structure.

5.5. Geodynamic Implications

The mechanism driving lithospheric destruction in the NCC remains debated between two end-member models (Figure 11): (1) protracted thermo-mechanic erosion and (2) rapid lithospheric delamination. Thermo-mechanic erosion involves progressive weakening of the cratonic mantle base primarily through subduction-related processes, with gradual mantle material recycling into the deeper mantle—a protracted bottom-up process potentially active from the Jurassic to Cenozoic periods [4,63,90]. Conversely, delamination requires crustal thickening to form dense eclogitized lower crust, triggering sudden gravitational collapse of the lower lithosphere (eclogitic crust + mantle)—a top-down event typically localized in the Late Mesozoic [22,23].
The Early Cretaceous Fangcheng basalts, derived from a lithospheric mantle provenance at 3.5–3.9 GPa (depths of ~110–130 km) and 1474–1526 °C, have a surface heat flow of ~60 mW/m2. This thermal regime markedly exceeds Paleozoic paleo-geotherms (~40 mW/m2 [4,7,9]) but remains below Cenozoic estimates (60–70 mW/m2) (Figure 10) [9,20,91]. Such conditions unambiguously indicate substantial lithospheric thinning by the Early Cretaceous, consistent with synchronous manifestations of cratonic destabilization: widespread magmatism, extensional basin formation, metamorphic core complex development, and pervasive tectonic deformation [6,12,13,14,15,16,18]. Crucially, the preserved lithospheric thickness (110–130 km) precludes delamination, which predicts a rather thin residual lithosphere (likely <50 km) following removal of mantle lithosphere and eclogitized lower crust. Consequently, thermo-mechanic erosion provides a more consistent explanation for the observed lithospheric architecture, thereby establishing crucial spatiotemporal constraints on NCC evolution.

6. Conclusions

The Fangcheng basalts, characterized by elevated MgO, Mg#, Cr, and Ni contents alongside IAB-like trace element signatures but negative Sr-Pb anomalies, exhibit enriched Sr-Nd isotopic compositions with unradiogenic 206Pb/204Pb and 208Pb/204Pb but slightly radiogenic 207Pb/204Pb. Petrographic evidence, covariations of MgO with major elements, Cr, Ni, and key trace element ratios (Sr/Nd, Sc/La), combined with consistently high Ce/Pb and uniform εNd(t) values despite variable SiO2, collectively demonstrate (olivine+pyroxene)-dominated fractionation without significant crustal assimilation. Trace element systematics and Sr-Nd-Pb isotopes further indicate derivation from lithospheric mantle metasomatized by subducted upper crustal materials. Olivine phenocrysts display high Fo values with significant variations in Ni, Mn, Fe/Mn, 10,000 × Zn/Fe, and Mn/Zn, overlapping compositional fields of melts from both peridotitic and pyroxenitic sources. Their projection within the [Liquid + Cpx + Gt + Ol] field on the Grossular/Pyrope/Diopside/Enstatite diagram confirms a hybrid peridotite/pyroxenite source with residual clinopyroxene, garnet, and olivine but no orthopyroxene. Phase equilibria modeling of high-MgO compositions reconstructs primary melts, which when subjected to melt/garnet/olivine Al2O3-barometry, yield equilibration pressures of 3.5–3.9 GPa (depths of ~110–130 km) and temperatures of 1474–1526 °C, corresponding to an estimated paleo-surface heat flow of ~60 mW/m2. Critically, the 110–130 km source depths constrain the minimum lithospheric thickness at this time, precluding wholesale lithospheric mantle delamination but aligning instead with progressive thinning via thermo-mechanic erosion. We therefore conclude that thermo-mechanic erosion was the predominant mechanism governing the gradual lithospheric thinning and modification of the eastern NCC.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/min15090928/s1. Table S1: Whole-rock compositions of major/trace elements and Sr-Nd-Pb isotopes for Fangcheng basalts, North China Craton; Table S2: Major element compositions (wt%) of olivines in Fangcheng basalts determined with EPMA; Table S3: Olivine chemistry of Fangcheng basalts determined with LA-ICP-MS; Table S4: Parameters of binary mixing for Fangcheng basalts; Table S5: Magmatic water contents of Fangcheng basalts calculated using Ca-in-Olivine Geohygrometer; Table S6: Compositions and P-T formation of primary melts for Fangcheng basalts.

Author Contributions

Conceptualization, L.-B.H. and Y.-H.Z.; methodology, Q.-C.Q., L.-B.H. and Y.-H.Z., formal analysis, Q.-C.Q. and L.-B.H.; data curation, Q.-C.Q., L.-B.H., Y.-H.Z., D.W., H.-X.Y., L.Z. and P.-L.H.; writing—original draft preparation, Q.-C.Q. and L.-B.H.; writing—review and editing, visualization, Q.-C.Q. and L.-B.H.; funding acquisition, L.-B.H. and Y.-H.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was jointly supported by the National Natural Science Foundation of China (42172053), the Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration (GKY20-065-17-07 and GKY20-065-17-08), and Guilin University of Technology (GUTQDJJ 2020015 and GUTQDJJ 2019190).

Data Availability Statement

The original contributions presented in this study are included in the Supplementary Materials. Further inquiries can be directed to the corresponding author (Lu-Bing Hong).

Acknowledgments

We are deeply grateful to the three anonymous reviewers for their insightful comments and constructive suggestions, which have greatly enhanced the quality of this manuscript. We also extend our sincere appreciation to the Editors, Dmitry Konopelko, Keely Luo and Kimura Xia, for his professional oversight and diligent handling of the submission process.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) Geological map of the North China Craton and adjacent regions, showing major tectonic units (after Zhao et al. [36]) and sample localities of Cenozoic and Paleozoic mantle xenoliths. The Fangcheng basalt field is marked by a red cross. (b) Distribution map of Mesozoic plutonic and volcanic rocks in the Luxi and Jiaodong regions, showing the sampling localities of the Fangcheng basalts. These basalts were sampled approximately 70 km west of the Tan-Lu Fault, which divides into two branches in northeastern China [37,38].
Figure 1. (a) Geological map of the North China Craton and adjacent regions, showing major tectonic units (after Zhao et al. [36]) and sample localities of Cenozoic and Paleozoic mantle xenoliths. The Fangcheng basalt field is marked by a red cross. (b) Distribution map of Mesozoic plutonic and volcanic rocks in the Luxi and Jiaodong regions, showing the sampling localities of the Fangcheng basalts. These basalts were sampled approximately 70 km west of the Tan-Lu Fault, which divides into two branches in northeastern China [37,38].
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Figure 2. Photomicrographs of Fangcheng basalt thin sections: (a,b) Porphyritic texture with euhedral to subhedral olivine (Ol) phenocrysts showing alteration along fractures and margins ((a): plane-polarized light; (b): cross-polarized light). (c,d) Euhedral stubby clinopyroxene crystals ((c): plane-polarized light; (d): cross-polarized light). (e,f) Spinel inclusions within euhedral olivine ((e): plane-polarized light; (f): reflected-light microscopy). Mineral abbreviations: Ol—olivine; Py—pyroxene; Sp—spinel.
Figure 2. Photomicrographs of Fangcheng basalt thin sections: (a,b) Porphyritic texture with euhedral to subhedral olivine (Ol) phenocrysts showing alteration along fractures and margins ((a): plane-polarized light; (b): cross-polarized light). (c,d) Euhedral stubby clinopyroxene crystals ((c): plane-polarized light; (d): cross-polarized light). (e,f) Spinel inclusions within euhedral olivine ((e): plane-polarized light; (f): reflected-light microscopy). Mineral abbreviations: Ol—olivine; Py—pyroxene; Sp—spinel.
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Figure 3. Geochemical classification and variation diagrams for Fangcheng basalts: (a) total alkali-silica (TAS) classification diagram [44]; (b–f) MgO variation diagrams for SiO2, TiO2, Al2O3, CaO, and P2O5; (g,h) MgO versus compatible trace elements (Ni, Cr). These transitional basalts exhibit negative SiO2-MgO, Al2O3-MgO, and P2O5-MgO correlations, together with nearly constant TiO2 with variable MgO, indicating absence of plagioclase, Ti-oxides, and apatite fractionation, while positive CaO-MgO, Ni-MgO, and Cr-MgO trends reflect olivine + pyroxene fractionation. Data from the literature on Fangcheng basalts sourced from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ (accessed on 21 July 2025)).
Figure 3. Geochemical classification and variation diagrams for Fangcheng basalts: (a) total alkali-silica (TAS) classification diagram [44]; (b–f) MgO variation diagrams for SiO2, TiO2, Al2O3, CaO, and P2O5; (g,h) MgO versus compatible trace elements (Ni, Cr). These transitional basalts exhibit negative SiO2-MgO, Al2O3-MgO, and P2O5-MgO correlations, together with nearly constant TiO2 with variable MgO, indicating absence of plagioclase, Ti-oxides, and apatite fractionation, while positive CaO-MgO, Ni-MgO, and Cr-MgO trends reflect olivine + pyroxene fractionation. Data from the literature on Fangcheng basalts sourced from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ (accessed on 21 July 2025)).
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Figure 4. Primitive mantle-normalized trace element patterns: (a) Fangcheng basalts; (b) comparison with Early Cretaceous igneous rocks (average values) from Shandong. Fangcheng basalts exhibit strong HFSE depletions (Nb, Ta, Zr, Hf, Ti), moderate Pb-Sr depletions, and significant Ba-Th-U-LREE enrichments—signatures resembling carbonatites and IAB-like igneous suites but contrasting with OIB-like suites. Primitive mantle values are from McDonough and Sun [45]; data from the literature on Fangcheng basalts and comparative data sourced from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ (accessed on 21 July 2025)).
Figure 4. Primitive mantle-normalized trace element patterns: (a) Fangcheng basalts; (b) comparison with Early Cretaceous igneous rocks (average values) from Shandong. Fangcheng basalts exhibit strong HFSE depletions (Nb, Ta, Zr, Hf, Ti), moderate Pb-Sr depletions, and significant Ba-Th-U-LREE enrichments—signatures resembling carbonatites and IAB-like igneous suites but contrasting with OIB-like suites. Primitive mantle values are from McDonough and Sun [45]; data from the literature on Fangcheng basalts and comparative data sourced from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ (accessed on 21 July 2025)).
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Figure 5. Sr-Nd-Pb isotopic compositions of Fangcheng basalts versus contemporaneous Shandong igneous rocks: (a) εNd(t) vs. 87Sr/86Sr(t); (b) 206Pb/204Pb(t) vs. εNd(t); (c) 207Pb/204Pb(t) vs. 206Pb/204Pb(t); (d) 208Pb/204Pb(t) vs. 206Pb/204Pb(t). Fangcheng basalts overlap isotopically with co-occurring xenoliths and carbonatites. While sharing similar Sr-Pb isotopes with OIB-like rocks, they possess significantly lower εNd(t) values, supporting a sub-continental lithospheric mantle (SCLM) origin. Binary mixing models (solid pink lines; 1% and 5% increments marked by small green-bordered and pink-bordered circles, respectively) indicate that partial melting of SCLM incorporating 1–2% upper continental crust (UCC) best explains the basalt compositions. Reference end-members are Lower Continental Crust (LCC; Sr-Nd-Pb: Ying et al. [46]), Upper Continental Crust (UCC; Sr-Nd: McCulloch and Wasserburg [47]; Pb: Desem et al. [48]), and SCLM represented by sample YS14-31 (Sr-Nd-Pb: Kong et al. [49]). YS14-31 was selected based on its isotopic consistency with Paleozoic kimberlites and mantle xenoliths (light blue shading) [10,50,51] defining representative SCLM of the NCC. End-member trace element compositions derive from LCC (Ying et al. [46]), UCC (Rudnick and Gao [52]), and SCLM (50 ppm Sr, Nd/Sr, and Pb/Sr ratios equivalent to YS14-31). All isotopic data are age-corrected to ~125 Ma. Data sources from the literature compiled from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ (accessed on 21 July 2025)).
Figure 5. Sr-Nd-Pb isotopic compositions of Fangcheng basalts versus contemporaneous Shandong igneous rocks: (a) εNd(t) vs. 87Sr/86Sr(t); (b) 206Pb/204Pb(t) vs. εNd(t); (c) 207Pb/204Pb(t) vs. 206Pb/204Pb(t); (d) 208Pb/204Pb(t) vs. 206Pb/204Pb(t). Fangcheng basalts overlap isotopically with co-occurring xenoliths and carbonatites. While sharing similar Sr-Pb isotopes with OIB-like rocks, they possess significantly lower εNd(t) values, supporting a sub-continental lithospheric mantle (SCLM) origin. Binary mixing models (solid pink lines; 1% and 5% increments marked by small green-bordered and pink-bordered circles, respectively) indicate that partial melting of SCLM incorporating 1–2% upper continental crust (UCC) best explains the basalt compositions. Reference end-members are Lower Continental Crust (LCC; Sr-Nd-Pb: Ying et al. [46]), Upper Continental Crust (UCC; Sr-Nd: McCulloch and Wasserburg [47]; Pb: Desem et al. [48]), and SCLM represented by sample YS14-31 (Sr-Nd-Pb: Kong et al. [49]). YS14-31 was selected based on its isotopic consistency with Paleozoic kimberlites and mantle xenoliths (light blue shading) [10,50,51] defining representative SCLM of the NCC. End-member trace element compositions derive from LCC (Ying et al. [46]), UCC (Rudnick and Gao [52]), and SCLM (50 ppm Sr, Nd/Sr, and Pb/Sr ratios equivalent to YS14-31). All isotopic data are age-corrected to ~125 Ma. Data sources from the literature compiled from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ (accessed on 21 July 2025)).
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Figure 6. Olivine compositional variation in Fangcheng basalts: (a) Ni, (b) Ca, (c) Mn, (d) Fe/Mn, (e) 10,000 × Zn/Fe, and (f) Mn/Zn versus Fo. Variability in Ni, Mn, Fe/Mn, 10,000 × Zn/Fe, and Mn/Zn at constant Fo overlaps fields for both peridotite- and pyroxenite-derived melts, supporting a hybrid source. Olivine compositions for partial melts of peridotite KR-4003 in (a–c) are from Herzberg [53], while comparative data for typical peridotitic and pyroxenitic melts are compiled after Hong et al. [54].
Figure 6. Olivine compositional variation in Fangcheng basalts: (a) Ni, (b) Ca, (c) Mn, (d) Fe/Mn, (e) 10,000 × Zn/Fe, and (f) Mn/Zn versus Fo. Variability in Ni, Mn, Fe/Mn, 10,000 × Zn/Fe, and Mn/Zn at constant Fo overlaps fields for both peridotite- and pyroxenite-derived melts, supporting a hybrid source. Olivine compositions for partial melts of peridotite KR-4003 in (a–c) are from Herzberg [53], while comparative data for typical peridotitic and pyroxenitic melts are compiled after Hong et al. [54].
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Figure 7. Geochemical variations in Fangcheng basalts: (a) Sr/Nd vs. MgO; (b) Sc/La vs. MgO; (c) Ce/Pb vs. SiO2; (d) εNd(t) vs. SiO2. Constant Sr/Nd but decreasing Sc/La with decreasing MgO, and invariant Ce/Pb and εNd(t) across variable SiO2 contents indicate olivine+pyroxene fractionation without crustal assimilation. Data source from the literature for the Fangcheng basalts from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ (accessed on 21 July 2025)).
Figure 7. Geochemical variations in Fangcheng basalts: (a) Sr/Nd vs. MgO; (b) Sc/La vs. MgO; (c) Ce/Pb vs. SiO2; (d) εNd(t) vs. SiO2. Constant Sr/Nd but decreasing Sc/La with decreasing MgO, and invariant Ce/Pb and εNd(t) across variable SiO2 contents indicate olivine+pyroxene fractionation without crustal assimilation. Data source from the literature for the Fangcheng basalts from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ (accessed on 21 July 2025)).
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Figure 8. (a) Olivine CaO (CaO_Olivine) vs. Fo (Fo_Olivine) and (b) olivine/melt CaO partition coefficient (DCaOolivine/melt) vs. whole-rock MgO (MgO_Whole rock) for Fangcheng basalts. Olivines exhibit CaO > 0.1 wt%, implying magmatic origin. Low DCaOolivine/melt values at given MgO contents, suggesting high magmatic water contents. Magmatic water contents and comparative data for lavas from different tectonic environments (MORB, OIB, and arc lavas) in (b) are from Gavrilenko et al. [77] and Hong et al. [78].
Figure 8. (a) Olivine CaO (CaO_Olivine) vs. Fo (Fo_Olivine) and (b) olivine/melt CaO partition coefficient (DCaOolivine/melt) vs. whole-rock MgO (MgO_Whole rock) for Fangcheng basalts. Olivines exhibit CaO > 0.1 wt%, implying magmatic origin. Low DCaOolivine/melt values at given MgO contents, suggesting high magmatic water contents. Magmatic water contents and comparative data for lavas from different tectonic environments (MORB, OIB, and arc lavas) in (b) are from Gavrilenko et al. [77] and Hong et al. [78].
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Figure 9. Projection (mol%) of primary melts for Fangcheng basalts: (a) from [Olivine] onto the Grossular/Pyrope/Diopside/Enstatite plane; (b) from [Diopside] onto the Olivine/Quartz/Calcium Tschermak (CATS) plane (projection scheme: Herzberg [53]). Olivine-controlled samples (MgO > 10 wt%) plot within the [L + Ol + Cpx + Gt] cotectic field at 3–4 GPa in (a), indicating residual olivine, clinopyroxene, and garnet in the mantle source. Primary melts were calculated through iterative olivine addition/subtraction until melt compositions in (b) intersect the [L + Ol + Cpx + Gt] cotectic at pressures constrained by (a). Data source from the literature for the Fangcheng basalts is from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ (accessed on 21 July 2025)).
Figure 9. Projection (mol%) of primary melts for Fangcheng basalts: (a) from [Olivine] onto the Grossular/Pyrope/Diopside/Enstatite plane; (b) from [Diopside] onto the Olivine/Quartz/Calcium Tschermak (CATS) plane (projection scheme: Herzberg [53]). Olivine-controlled samples (MgO > 10 wt%) plot within the [L + Ol + Cpx + Gt] cotectic field at 3–4 GPa in (a), indicating residual olivine, clinopyroxene, and garnet in the mantle source. Primary melts were calculated through iterative olivine addition/subtraction until melt compositions in (b) intersect the [L + Ol + Cpx + Gt] cotectic at pressures constrained by (a). Data source from the literature for the Fangcheng basalts is from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ (accessed on 21 July 2025)).
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Figure 10. Pressure/temperature conditions for Fangcheng primary melts calculated using the model of Sun and Dasgupta [87] indicate mantle formation at 1474–1526 °C and 3.5–3.9 GPa (~60 mW/m2 surface heat flux). Comparative data: Early Cretaceous Fangcheng mantle xenoliths [67], Cenozoic NCC mantle xenoliths (Huang and Xu [20]), and global cratonic xenoliths (Lee et al. [2]). Thermodynamic constraints show steady-state conductive geotherms (black lines; 40–80 mW/m2; Lee et al. [2]); dry lherzolite solidus (Dry Lher. Solid.; green line) [88]; and mantle potential temperature (Tp) adiabats [Tp = 1280–1400 °C [89], light blue field; normal mantle; Tp = 1500 °C, pink line]. Fangcheng basalt data sourced from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ accessed on 21 July 2025)).
Figure 10. Pressure/temperature conditions for Fangcheng primary melts calculated using the model of Sun and Dasgupta [87] indicate mantle formation at 1474–1526 °C and 3.5–3.9 GPa (~60 mW/m2 surface heat flux). Comparative data: Early Cretaceous Fangcheng mantle xenoliths [67], Cenozoic NCC mantle xenoliths (Huang and Xu [20]), and global cratonic xenoliths (Lee et al. [2]). Thermodynamic constraints show steady-state conductive geotherms (black lines; 40–80 mW/m2; Lee et al. [2]); dry lherzolite solidus (Dry Lher. Solid.; green line) [88]; and mantle potential temperature (Tp) adiabats [Tp = 1280–1400 °C [89], light blue field; normal mantle; Tp = 1500 °C, pink line]. Fangcheng basalt data sourced from GEOROC Database (https://georoc.mpch-mainz.gwdg.de/georoc/ accessed on 21 July 2025)).
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Figure 11. Two distinct mechanisms are proposed for the destruction of the North China Craton: (a) lithospheric delamination and (b) thermo-mechanical erosion. Delamination involves crustal thickening followed by the formation of a dense eclogitic root, which induces rapid gravitational removal of the lower lithosphere. In contrast, thermo-mechanical erosion entails progressive weakening and thinning of the cratonic mantle lithosphere from below, facilitating mantle recycling and reflecting a gradual, bottom-up thinning process.
Figure 11. Two distinct mechanisms are proposed for the destruction of the North China Craton: (a) lithospheric delamination and (b) thermo-mechanical erosion. Delamination involves crustal thickening followed by the formation of a dense eclogitic root, which induces rapid gravitational removal of the lower lithosphere. In contrast, thermo-mechanical erosion entails progressive weakening and thinning of the cratonic mantle lithosphere from below, facilitating mantle recycling and reflecting a gradual, bottom-up thinning process.
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Qin, Q.-C.; Hong, L.-B.; Zhang, Y.-H.; Yu, H.-X.; Wang, D.; Zhang, L.; He, P.-L. Olivine and Whole-Rock Geochemistry Constrain Petrogenesis and Geodynamics of Early Cretaceous Fangcheng Basalts, Eastern North China Craton. Minerals 2025, 15, 928. https://doi.org/10.3390/min15090928

AMA Style

Qin Q-C, Hong L-B, Zhang Y-H, Yu H-X, Wang D, Zhang L, He P-L. Olivine and Whole-Rock Geochemistry Constrain Petrogenesis and Geodynamics of Early Cretaceous Fangcheng Basalts, Eastern North China Craton. Minerals. 2025; 15(9):928. https://doi.org/10.3390/min15090928

Chicago/Turabian Style

Qin, Qiao-Chun, Lu-Bing Hong, Yin-Hui Zhang, Hong-Xia Yu, Dan Wang, Le Zhang, and Peng-Li He. 2025. "Olivine and Whole-Rock Geochemistry Constrain Petrogenesis and Geodynamics of Early Cretaceous Fangcheng Basalts, Eastern North China Craton" Minerals 15, no. 9: 928. https://doi.org/10.3390/min15090928

APA Style

Qin, Q.-C., Hong, L.-B., Zhang, Y.-H., Yu, H.-X., Wang, D., Zhang, L., & He, P.-L. (2025). Olivine and Whole-Rock Geochemistry Constrain Petrogenesis and Geodynamics of Early Cretaceous Fangcheng Basalts, Eastern North China Craton. Minerals, 15(9), 928. https://doi.org/10.3390/min15090928

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