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Characterization of the Angat Ophiolite: New
insights from bulk major and trace element
geochemistry and petrographic analysis
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et al
2023
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2023 The Sixth International Workshop on Environment and Geoscience (IWEG 2023)
Journal of Physics: Conference Series 2621 (2023) 012006
IOP Publishing
doi:10.1088/1742-6596/2621/1/012006
1
Characterization of the Angat Ophiolite: New insights from
bulk major and trace element geochemistry and petrographic
analysis
Colocar, R.D.A1, De Leon, H.R.R.1, Pagbilao, V.T.M.1,2, Arpa, M.C.B.1 and
Queaño, K.L.1
1 School of Civil, Environmental, and Geological Engineering, Mapua University, 658
Muralla St, Intramuros, Manila, 1002 Metro Manila.
2 Corresponding author’s e-mail: pagbilao.veronicatheresse@gmail.com
Abstract. The Angat Ophiolitic Complex, located north-northeast of Manila, Luzon is perhaps
one of Luzon’s most fundamental suspect terranes. The definite age of the ophiolite is not well-
established, with various authors having different claims. Encarnacion et al. (1993) conducted a
U-Pb age dating for the Angat wherein the Angat Ophiolite was found to have an Early Middle
Eocene age (48 Ma), close to the ZOC age - leading to the assumption that the two ophiolites are
related and underlie most of Central Luzon. Hence, this paper aims to collect samples from the
Eocene and Cretaceous Angat Ophiolite for petrographic and geochemical analyses, identify the
relationship between the separated basalt units from the basalts in the main ophiolite body, and
compare the geochemistry of the Eocene and Cretaceous units of the Angat Ophiolite with the
other well-known ophiolites from the literature. Field investigations were conducted in five
important localities wherein 15 samples were obtained. The results highlighted that the major
mineral phases in the samples collected are plagioclase and augite, with some samples having
hornblende and olivine. All samples appear to have undergone low-grade greenschist facies
metamorphism, which may be attributed to hydrothermal alteration. Chloritization of pyroxene
minerals is also evident, along with the hydrothermal alteration products of plagioclase and
pyroxenes. The relationship between the EAO, MOC, and separated basalt patch in Marilaque
Highway is identified. The Coto Block of the Zambales Ophiolite and the Angat Ophiolite may
be related and formed over a mantle initially enriched by a subduction component.
1. Introduction
The Angat Ophiolite located north-northeast of Manila, Luzon, forms part of the southern Sierra Madre
range. It is a north-south trending, east-dipping ophiolitic complex consisting of dismembered bodies of
pillow basalts, basalt breccias, flows, sediments, diabase dikes, and gabbro [1, 2]. Available major and
trace element geochemistry reveals that the Angat Ophiolite rocks exhibit Mid-Ocean Ridge Basalt –
Island Arc Tholeiite (MORB-IAT) characteristics, which points to a subduction-related origin for the
ophiolite [1, 3]. However, a supra-subduction zone being the environment of formation is not
definitively indicated by the MORB-IAT characteristics of the Angat Ophiolite. A Late Cretaceous age
was given for the Angat Ophiolite based on its proximity to Late Cretaceous strata, along with the
sedimentary rocks associated with its pillow basalts (e.g., [4, 5]). However, mapping the Montalban area
revealed that the ophiolite is cut by several faults that complicate paleontological and sedimentological-
based dating [1]. By 1993, Encarnacion et al. conducted a U-Pb age dating for the Angat; the Angat
2023 The Sixth International Workshop on Environment and Geoscience (IWEG 2023)
Journal of Physics: Conference Series 2621 (2023) 012006
IOP Publishing
doi:10.1088/1742-6596/2621/1/012006
2
Ophiolite was found to have an Early Middle Eocene age (48 Ma), close to the Zambales Ophiolitic
Complex (ZOC) age [6]. This led Encarnacion to assume that the two ophiolites are related and underlie
most of Central Luzon. An issue with this, however, is the lack of geochemical data for the Angat and
the difference in sedimentary cover over the two ophiolites. Accordingly, Angat's age restriction
remained a problem due to the lack of radiometric age information for the pillow basalt portion of the
Angat. Furthermore, there is still no discussion of the connection between the Angat and isolated basaltic
rocks, especially those exposed along the Marilaque Highway.
Hence, this study aims to identify a geochemical relationship between the Eocene and Cretaceous
units of the Angat Ophiolite to understand further its complexity, which will then be compared with
other well-known ophiolites through literature. In particular, the objective of the study are (1) to collect
samples from the Eocene and Cretaceous Angat Ophiolite for petrographic and geochemical analyses;
(2) identify the relationship between the separated basalt units from the basalts in the main ophiolite
body; and (3) compare the geochemistry of the Eocene and Cretaceous units of the Angat Ophiolite with
the other well-known ophiolites from the literature, particularly the Zambales Ophiolite.
2. Methodology
This study aims to characterize the Angat Ophiolite, which forms the southern portion of the Sierra
Madre range, through the geochemical and petrographic analysis of its gabbro, basalt, and diabase units
(Figure 1). Fieldwork observations will provide the data for the lithology, locality, and degree of
weathering. The samples collected will then be analyzed for bulk major and trace element geochemistry,
mineral content and textural relationships. Geochemical analyses were done through submitting the
samples in Intertek Philippines. Data acquired were plotted through GCDkit program [7]. Meanwhile,
petrographic analysis was performed using a petrographic microscope available at Mapua University.
The variations in the rock types from the different sample sites were revealed through transmitted light
microscopy. Focused petrographic examinations were performed on the thin section slides to identify
the primary and secondary components and their textures.
Figure 1. Conceptual Framework.
2023 The Sixth International Workshop on Environment and Geoscience (IWEG 2023)
Journal of Physics: Conference Series 2621 (2023) 012006
IOP Publishing
doi:10.1088/1742-6596/2621/1/012006
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3. Results and Discussions
3.1. Field Investigation
Field investigations were conducted in five important localities across the Angat Ophiolite. All data
used in the study were grouped according to their significant localities. The samples were divided into
groups based on their locality relative to the East Marikina Fault and are shown in Figure 2:
Figure 2. Location of Stations.
2023 The Sixth International Workshop on Environment and Geoscience (IWEG 2023)
Journal of Physics: Conference Series 2621 (2023) 012006
IOP Publishing
doi:10.1088/1742-6596/2621/1/012006
4
(1) The Eocene Angat Ophiolite (EAO) refers to the samples collected west of the fault. These were
collected along the Lacotan and Hanginan Rivers (LR and HR samples, respectively) and represent the
gabbro and sheeted dike section.
(2) The Montalban Ophiolitic Complex (MOC) refers to the samples collected east of the fault.
Samples were acquired from the Mango and Nangka (COGEO) rivers (MR and NR samples,
respectively). These sections represent the supposed pillow basalt section of the Angat.
(3) The Marilaque Highway (MH) sample represents the basalt sample obtained in one of the patches
separated from the main body of the ophiolite, located in Pinugay, Rizal, along the Marilaque Highway.
3.2. Petrographic Interpretation
The major mineral phases in the samples collected from the mafic constituents of the Angat Ophiolitic
Complex are plagioclase and augite. Hornblende and olivine are noted in some samples. All samples
appear to have undergone low-grade greenschist facies metamorphism, which may be attributed to
hydrothermal alteration. Chloritization (partial and complete) of pyroxene minerals (augite) is also
evident, along with the hydrothermal alteration products of plagioclase and pyroxenes (through
saussuritization). It is important to note that the alteration to chlorite may only be due to post-
depositional hydrothermal solutions and weathering. The typical assemblages in the samples include
chlorite and carbonates.
Plagioclase crystals typically show little to no alteration, with some samples exhibiting alteration to
illite fibers, illite ± epidote, or calcite. Chlorite, illite, calcite, and opaques are the common secondary
minerals in all the collected samples. Limonite, chalcedony, epidote, clinozoisite, and zeolite are also
noted under secondary minerals. Textures of the basalt samples vary from aphyric and porphyritic upon
observation. Meanwhile, the gabbro samples exhibit hypidiomorphic, xenomorphic granular, and
hypidiomorphic granular textures.
3.3. Whole-rock Major Element Geochemistry
Generally, the tholeiitic trend of the data from both ophiolites was supported by the fractionation trend
illustrated in Figure 3. The positive correlation between FeOt/MgO and TiO2 is commonly observed in
tholeiitic magma [8]. The Harker-type diagram also supported the crystallization order of the Angat and
ZOC magma (Figure 3). The negative correlation in CaO, Al2O3, and MgO vs. FeOt/MgO may suggest
that olivine was the first mineral to form, followed by plagioclase. The hooked trend in the FeOt vs.
FeOt/MgO may suggest that clinopyroxene formed after plagioclase. This is consistent with the (Ol)-
Pl- Cpx crystallization order observed in the Angat petrography. This trend is also present in the Coto
and is consistent with the (Ol)-Pl-Cpx crystallization order noted by previous studies [3, 9, 10]. One can
observe that the trend of the Acoje in the FeOt vs. FeOt/MgO dipped earlier than the Angat and Coto.
Also, the hooked trend of the Acoje in the Al2O3 vs. FeOt/MgO plot may suggest that the first mineral
to form after the olivine was pyroxene, followed by plagioclase. This is consistent with the (Ol)-Px-Pl
crystallization order observed by [9, 10]. Rock type discrimination diagrams that used immobile trace
elements as proxy for the conventional Na2O+K2O were utilized considering the altered state of the
samples. Figures 4A and 4B revealed that most of the samples from the EAO plot in the sub-alkaline
basalt field, while the MOC samples are scattered, with some plotting in the sub-alkaline basalt field,
while the others plot in the andesite and trachyandesite fields [11]. The scattering of data within certain
plots, such as in SiO2, Al2O3, and Na2O may have been caused by element remobilization during
alteration (Figure 5) [12].
2023 The Sixth International Workshop on Environment and Geoscience (IWEG 2023)
Journal of Physics: Conference Series 2621 (2023) 012006
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doi:10.1088/1742-6596/2621/1/012006
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Figure 3. Harker-type bivariate diagram for Acoje, Coto, EAO, MOC, MH, and Angat Literature
data. Red lines denotes possible fractionation trends for Angat while purple lines denote Acoje trend.
Legends are similar with Figure 4.
Figure 4. Classification diagram after Winchester and Floyd (1977). (A) Zr/TiO2 vs SiO2 plot. (B)
Nb/Y vs. Zr/TiO2 plot.
2023 The Sixth International Workshop on Environment and Geoscience (IWEG 2023)
Journal of Physics: Conference Series 2621 (2023) 012006
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doi:10.1088/1742-6596/2621/1/012006
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3.4. Tectonic Discrimination for the Angat and ZOC
The use of immobile trace elements in tectonic discrimination diagrams has been a common practice
regarding ophiolite geochemistry (e.g., [2, 3, 13, 14]) due to these elements being immobile during
seafloor alteration or low-grade metamorphism [15]. The MORB-IAT characteristic of the Angat could
be seen in the Ti vs. V diagram (Figure 6), where the EAO, MOC, and MH samples plotted in both
MORB and IAT fields (Ti/V = 20 – 50 and Ti/V > 10, respectively) [16]. The Angat data and literature
coincided with the Coto rocks, while the Acoje plot mostly in the Ti/V = 10 field. Aside from this, the
Zr-Th-Nb diagram revealed a distinction between the datasets (Figure 7) [17]. It showed that the EAO
and MOC samples plotted along the MORB field, while the Acoje Boninites plotted mostly in the IAT
field. The Angat literature was plotted in the Enriched Mid-Ocean Ridge Basalt (E-MORB)/Within-
Plate Basalt (WPB) field, while one MH literature sample was plotted near the calc-alkaline basalt (CAB)
field. This may be due to the limited subduction components during the formation of the Angat. The
detail of this shall be discussed in another section.
Figure 5. SiO2 vs. FeOt/MgO
discrimination diagram after Miyashiro
(1974) illustrating the tholeiitic and calc-
alkaline affinity of the Angat and ZOC.
Legends similar with Figure 3.
Figure 6. Ti vs. V plot after Shervais (1982).
Legends similar with Figure 3.
3.5. Relationship between the EAO, MOC, and MH.
It is established that the EAO and MOC are part of one ophiolite suite in the form of the Angat Ophiolite.
This is evident in the consistent plotting of the present study’s samples. Trace element ratio diagrams
(Figures 8 and 9) further delineate this relationship. Accordingly, a fractionation trend between the EAO
and MOC can be observed in the Harker-type diagrams, which may have been produced by fractional
crystallization upon magma rising and reflects the crystallization order observed in the petrography.
Considering that the two units were cut by a strike-slip fault (i.e., the East Marikina Valley Fault),
the two sections could still be correlated based on the presence of sheeted dikes on both sides of the
fault. The relation between the two units would also impart a minimum Early Middle Eocene age for
the Lower Pillow Basalts in the MOC. However, the “Upper” pillow basalts [18] may be older but are
limited to at least the Middle to Late Paleocene.
Determining the relationship of the MOC and MH was challenging due to the sporadic plotting of
the MH samples and literature. MH literature data constantly plotted away from the trend of the Angat,
which plotted more closely to the arc-like range of the Acoje. This difference was further demonstrated
2023 The Sixth International Workshop on Environment and Geoscience (IWEG 2023)
Journal of Physics: Conference Series 2621 (2023) 012006
IOP Publishing
doi:10.1088/1742-6596/2621/1/012006
7
by the contrasting trend of the MH in the La/Sm (N) vs. Ba/La diagram (Figure 8B). Hence, the MH
basalt may be genetically and structurally unrelated to the Angat Ophiolite due to its spatial and
geochemical difference from the MOC.
Figure 7. Ternary tectonic discrimination diagrams based on trace
elements Th-Zr/117 - Nb/16 diagram modified from Woods (1980).
Legends similar with Figure 3.
3.6. Relationship between the Angat and ZOC
The consistent plotting of the present study’s samples in Figure 6, along with the similar crystallization
order of (Ol)-Pl-Cpx [3, 10], trace element ratio diagrams, and fractionating trends between the Angat
and Coto, suggest that the two units may be related and formed from a similar magmatic process. Geary
et al. originally proposed that the Coto experienced two stages of crustal formation: an initial N-MORB
dominant magmatism in possibly a large oceanic or back-arc spreading center followed by the crustal
modification of incipient island arc magmatism, possibly in a proto-forearc setting [19]. IAT dike
intrusions in the mantle section of the Coto and the progressive depletion of the mantle wedge from the
Coto to the Acoje may have been manifestations of this process [3, 20].
Based on Figure 9, the Angat-Coto may have been associated with the magmatism of the Sierra
Madre, given that the trace element signatures of the Angat, Coto, and Caraballo Formation overlap and
share similar trends. It is possible that the subducted slab composition was preserved in the Eocene
volcaniclastics (i.e., Caraballo and its Eocene equivalents). Previous studies found that these units were
the result of the magmatism in Luzon during the Early Cenozoic (e.g., [21, 22]). Also, the sharp contrast
between the data trends suggests that a different subducted slab must have influenced the Acoje. This
relationship could be observed in the Acoje, Angat, Caraballo, and Coto's trend, sharply contrasting the
back-arc Lau Basin trend.
2023 The Sixth International Workshop on Environment and Geoscience (IWEG 2023)
Journal of Physics: Conference Series 2621 (2023) 012006
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doi:10.1088/1742-6596/2621/1/012006
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Figure 8. Trace element ratio
bivariate diagrams. (A) and (B)
were modified from Castillo and
Newhall (2004), while (C) was
from Li et al. (2002). Violet arrow
for Acoje trend; the black arrow
for Coto trend; Yellow arrow for
MH trend; green arrow for Angat
trend. La/Sm (N) are chondrite
normalized after Sun and
McDonough (1989). Legends
same with Figure 9.
Figure 9. Trace element
bivariate plot. Arrows symbol
similar with Figure 9; cyan
arrow for Caraballo trend. The
orange field are samples
compiled from the ODP Leg
135 on the Lau Basin.
2023 The Sixth International Workshop on Environment and Geoscience (IWEG 2023)
Journal of Physics: Conference Series 2621 (2023) 012006
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doi:10.1088/1742-6596/2621/1/012006
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4. Conclusions and Recommendations
4.1. Conclusions
(1) Given the various degrees of alteration in the nature of the rocks, significant chlorite- epidote
alteration in the phenocrysts and groundmass of the samples is evident. This suggests chemical alteration
through iron and magnesium-bearing hydrothermal fluids.
(2) A homogeneous petrographic character is exhibited in the EAO and MOC samples due to the
plagioclase-clinopyroxene phenocryst mineralogy of evolved MORB magmas [23] (Grove and Bryan,
1983). Accordingly, the mineralogic and textural relationships of the samples can be related to cooling
history and provide information on magma chemistry.
(3) The previous conclusion is further supported by the fractionation trend observed in the Harker-
type bivariate plots, showing an apparent decrease in MgO with increasing TiO2, typical of tholeiitic
magmas;
(4) The study confirms that EAO and MOC are part of one ophiolite suite in the form of the Angat
Ophiolite. This is evident in the consistent plotting of the present study’s samples in numerous tectonic
discrimination diagrams and trace element ratio bivariate plots.
(5) The Coto Block of the Zambales Ophiolite and the Angat Ophiolite may be related and formed
over a mantle initially enriched by a subduction component. This conclusion is supported by the similar
crystallization order of (Ol)-Pl-Cpx [3, 10], consistent overlapping of plots and trends, and similar
enrichment pattern range.
4.2. Recommendations
(1) It is advised to increase the number of samples and conduct a test on the complete set of trace
elements, particularly REEs, for the Angat Ophiolite since it still lacks the complete trace element data
to establish its chemical affinity.
(2) Sampling should be accomplished in areas far from the East Marikina Fault since the exposures
where the samples were collected in this study were heavily affected by shearing and/or alteration.
(3) The mapping of exposures of the Angat Ophiolite should be updated, along with further mapping
of the northern part of Montalban.
(4) Updated isotope dating should be conducted to verify the ages given for the Angat Ophiolite.
References
[1] Arcilla, C. A., Ruelo, H. B., & Umbal, J. 1989 The Angat ophiolite, Luzon, Philippines: lithology,
structure, and problems in age interpretation. Tectonophysics 168(1–3) 127–135
https://doi.org/10.1016/0040-1951(89)90372-7
[2] Yumul, G. P. 1993 Angat Ophiolitic Complex, Luzon, Philippines: a cretaceous dismembered
marginal basin ophiolitic complex. Journal of Southeast Asian Earth Sciences 8(1–4) 529–
537 https://doi.org/10.1016/0743-9547(93)90050-y
[3] Yumul, G. P. Jr. 1996 Varying mantle sources of supra-subduction zone ophiolites: REE evidence
from the Zambales Ophiolite Complex, Luzon, Philippines. Tectonophysics 262(1–4) 243–
262
[4] Karig, D. E. 1983 Accreted terranes in the northern part of the Philippine Archipelago. Tectonics
2(2) 211–236
[5] Revilla, G.P. and Malaca, E.R. 1987 Geology of southern Sierra Madre. Philippine Bureau of
Mines & Geosciences, unpublished
[6] Encarnación, J. P., Mukasa, S. B., & Obille, E. C. 1993 Zircon U-Pb geochronology of the
Zambales and Angat Ophiolites, Luzon, Philippines: Evidence for an Eocene arc-back arc pair.
Journal of Geophysical Research: Solid Earth 98(B11) 19991–20004
https://doi.org/10.1029/93jb02167.
[7] Janousek, V., Farrow, C. M., & Erban, V. 2006 Interpretation of Whole-rock Geochemical Data
in Igneous Geochemistry: Introducing Geochemical Data Toolkit (GCDkit). Journal of
2023 The Sixth International Workshop on Environment and Geoscience (IWEG 2023)
Journal of Physics: Conference Series 2621 (2023) 012006
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doi:10.1088/1742-6596/2621/1/012006
10
Petrology 47(6) 1255–1259 https://doi.org/10.1093/petrology/egl013
[8] Miyashiro, A. 1974 Volcanic rock series in island arcs and active continental margins. American
Journal of Science 274(4), 321–355 https://doi.org/10.2475/ajs.274.4.321
[9] Yumul, G. P., & Dimalanta, C. 1997 Geology of the Southern Zambales Ophiolite Complex,
(Philippines): juxtaposed terranes of diverse origin. Journal of Asian Earth Sciences 15(4–5)
413–421 https://doi.org/10.1016/s0743-9547(97)00019-6
[10] Yumul, G. P., Dimalanta, C. B., & Jumawan, F. T. 2000 Geology of the southern Zambales
Ophiolite Complex, Luzon, Philippines. Island Arc 9(4) 542–555
https://doi.org/10.1111/j.1440-1738.2000.00300.x.
[11] Winchester, J., & Floyd, P. 1977 Geochemical discrimination of different magma series and their
differentiation products using immobile elements. Chemical Geology 20 325–343
https://doi.org/10.1016/0009-2541(77)90057-2
[12] Queaño, K. L., Ali, J. R., Aitchison, J. C., Yumul, G. P., Pubellier, M., & Dimalanta, C. B. 2008
Geochemistry of Cretaceous to Eocene Ophiolitic Rocks of the Central Cordillera:
Implications for Mesozoic-Early Cenozoic Evolution of the Northern Philippines.
International Geology Review 50(4) 407–421 https://doi.org/10.2747/0020-6814.50.4.407
[13] Evans, C. A., Casteneda, G., & Franco, H. 1991 Geochemical complexities preserved in the
volcanic rocks of the Zambales Ophiolite, Philippines. Journal of Geophysical Research
96(B10) 16251 https://doi.org/10.1029/91jb01488
[14] Ding, B., Pei, F., Wei, J., Xu, W., Wang, Z., & Sang, T. 2022 Supra-subduction zone ophiolite
generated by the initial subduction of an Early Paleozoic island arc system abutting the
northern North China Craton: Evidence from meta-igneous rocks. Gondwana Research 110
90–106 https://doi.org/10.1016/j.gr.2022.05.021
[15] Pearce, J. A., Lippard, S. J., & Roberts, S. 1984 Characteristics and tectonic significance of supra-
subduction zone ophiolites. Geological Society, London, Special Publications, 16(1) 77–94
https://doi.org/10.1144/gsl.sp.1984.016.01.06
[16] Shervais, J. W. 1982 Ti-V plots and the petrogenesis of modern and ophiolitic lavas. Earth and
Planetary Science Letters 59(1) 101–118 https://doi.org/10.1016/0012-821x(82)90120-0
[17] Wood, D. A. 1980 The application of a Th-Hf-Ta diagram to problems of tectonomagmatic
classification and to establishing the nature of crustal contamination of basaltic lavas of the
British Tertiary Volcanic Province. Earth and Planetary Science Letters 50(1) 11–30
https://doi.org/10.1016/0012-821x(80)90116-8
[18] Arcilla, C. A. 1991 Lithology, age, and structure of the Angat Ophiolite, Luzon, Philippine
Islands. [Unpublished master’s thesis]. University of Illinois
[19] Geary, E., Kay, R., Reynolds, J., & Kay, S. 1989 Geochemistry of mafic rocks from the Coto
Block, Zambales ophiolite, Philippines: trace element evidence for two stages of crustal
growth. Tectonophysics 168(1–3) 43–63 https://doi.org/10.1016/0040-1951(89)90368-5
[20] Yumul Jr., G. P., 1990 Multi-stage melting, evolving mantle sources and ophiolite generation:
Constraints from the Zambales ophiolite complex, Philippines. [PhD Thesis]. University of
Tokyo
[21] Queano, K. L., Ali, J. R., Milsom, J., Aitchison, J. C., & Pubellier, M. 2007 North Luzon and the
Philippine Sea Plate motion model: Insights following paleomagnetic, structural, and age-
dating investigations. Journal of Geophysical Research 112(B5)
https://doi.org/10.1029/2006jb004506
[22] Queaño, K. L., Yumul Jr., G. P., Marquez, E. J., Gabo-Ratio, J. A., Payot, B. D., & Dimalanta,
C. B. 2020 Consumed tectonic plates in Southeast Asia: Markers from the Mesozoic to early
Cenozoic stratigraphic units in the northern and central Philippines. Journal of Asian Earth
Sciences: X, 4, 100033 https://doi.org/10.1016/j.jaesx.2020.100033
[23] Grove, T.L., & Bryan, W.B. (1983) Fractionation of pyroxene-phyric MORB at low pressure: An
experimental study. Contributions to Mineralogy and Petrology 84 293-309
