We identified two sizable regions of good tomographic coverage without identified lithosphere in our 52 Ma reconstruction (Figures 23 and S4), which are therefore potential sites of origin of the Mesozoic nucleus of the Philippine Sea plate. Gap 1 spans the equatorial junction between the East Asian Sea and the Pacific, extending east and west of the present position of the proposed long‐lived (minimum 52 Ma) Manus plume [cf. Macpherson and Hall, 2001]. We will herein also adopt a stable, long‐lived Manus plume in our plate models based on: (1) a prominent lower mantle slow‐velocity anomaly in our MITP08 tomographic analysis at 0°/150°E (Figures 16c to 16f and 17b), (2) a plume‐like low‐velocity conduit in the lower mantle (i.e., the “Indonesia” anomaly) detected by a recent global shear wave velocity model SEMUCB‐WMI [French and Romanowicz, 2015], and (3) plume‐like helium isotope signatures within Manus back‐arc basin rocks [e.g., Macpherson et al., 1998]. The part of the equatorial gap within the East Asian Sea west of the Manus plume is a region of poorer imaging and therefore potentially may not be a region of missing lithosphere. Gap 2 is east of the NS eastern edge of the Sunda slab and north of Australia at ~10–20°S latitudes (Figure 23a). We argued above in section 4.1 that the Molucca Sea likely reconstructs within Gap 2, just east of the Sunda slab, and is part of the 52 Ma NE Indian Ocean, north of Australia. However, Gap 2 is sufficiently large that it potentially could also contain the Mesozoic nucleus of the northern West Philippine basin and the Philippine Trench slab (cf. Figure 21c).

Presently available paleolatitude constraints for the Philippine Sea plate near 52 Ma are extremely limited. However, a 50 ± 5 Ma paleolatitude of 13.2°S ± 5.6° from ODP Site 294 at the southern edge of the Daito Ridge (Figure 1) [Louden, 1977] is consistent within errors with either Gap 1 or Gap 2. A few other sites 40 Ma and older yielded −5° to 0° paleolatitudes, with equatorial ambiguity, including ODP 292 and 1201 (see Figures 26a and 26c). Therefore, either Gap 1 or 2 appears to be viable for a site of origin of the Philippine Sea plate from the point of view of available paleolatitude data (see also section 5.1).

We input our slab constraints and reconstructed Philippine Sea plate forward to its present‐day location from its two possible origins, which we call “Model 1: Manus plume‐derived” (Figure 24) and “Model 2: northern Australia‐derived” (Figure S5). A comparison between the two models is shown in Figure 25. These plate‐reconstruction figures show the major active tectonic features at progressive 10 Ma periods. Subduction zones were inferred from relative plate motions and tectonic relationships. Fully animated plate reconstruction movies and GPlates files are available in the supporting information. White gaps (grey gaps in Movies S1–S3) at each stage are unfilled spaces that could be due to slab unfolding or mapping errors, thermal erosion of slab tomographic anomalies, spreading ridges, or mantle reference errors. It is emphasized that each of these two reconstructions represents a separate class of solutions that can accommodate a number of second‐order modifications in the light of existing or new constraints. The Manus plume‐derived model (i.e., Model 1) is our preferred solution, based on comparison to Philippine Sea plate paleomagnetism and regional geology (sections 5.1 and 5.2); Model 2 is presented as an alternative. Comparisons between the two models in terms of Philippine Sea positions, predicted latitudes and declinations are shown in Figures 26 – 28-26 – 28, respectively. A summary of the comparisons between Models 1 and 2 is given in section 5.3.

Comparison between (a) Model 1 and (b) Model 2 predicted Philippine Sea plate motions from this study. Philippine Sea plate outlines are shown at 10 Ma increments. Present‐day coasts are shown in grey fill. The present‐day Philippine Sea plate position is shown by the black dashed line. The trend of the Pacific slab wall anomalies from Figures 15 and 19 are shown in purple. Model 1 predicts that the eastern Philippine Sea plate boundary was a zone of dextral transpression against a Pacific plate boundary, which would be favorable to produce clockwise local block rotations. Model 1 also predicts that the western Philippine Sea plate boundary was a sinistral transpressional zone. In contrast, Model 2 predicts that the western Philippine Sea plate was largely a strike‐slip tectonic boundary.

Comparison between modeled Philippine Sea paleolatitudes from this study (red and blue dots) against published Philippine Sea paleolatitudes for six widely scattered sites (see Figures 1 and 3 for locations and references). Alternate paleolatitudes (hollow brown dots) are shown for relevant data. The superscript 1 = Includes ODP DSDP site 782, 784, 786, 787, 792, and 793. Referenced to Izu 32°N, 140°E. The superscript 2 = Referenced to Baguio City 16.4°N, 120.6°E. The superscript 3 = Includes ODP DSDP site 453, 454, 456, 458, and 459. Referenced to Saipan 15.1°N, 145.7°E.

Whole‐plate clockwise rotation of the West Philippine basin from differential changes in paleolatitude between ODP sites 292 and 1201 (Figure 1 ). (a) The current difference in latitude is 3.5° whereas their difference in paleolatitude is 9°–10° at 40 Ma, suggesting that the line connecting the two sites, which has an angular separation of 10.6°, was oriented more nearly N‐S, in contrast with its current 71° azimuth. The contrasting rates of change of paleolatitude between the sites suggests whole‐plate rotation during the period ~25–40 Ma. (b) Estimated whole‐plate rotations compared to our preferred plate Model 1. Rotations were computed based on observed differences in paleolatitude (Figure 27 b) corrected for our West Philippine basin seafloor‐spreading model. In spite of large uncertainties, the estimated clockwise rotations are in broad agreement with our plate Model 1 and with paleomagnetic declination observations (e.g., Figure 28 ). (c) Present‐day difference in latitude between ODP 292 and 1201. (d) 40 Ma difference in paleolatitude predicted by Model 1.

Comparison between published and the modeled Philippine Sea plate declinations for three locations along the eastern plate margin (see Figures 1 and 3 for site locations and references). (a) The whole‐plate rotation Models 1 and 1b produced up to 80° clockwise Philippine Sea plate rotation. The migrating Japan triple junction Model 1b showed slightly higher (up to 20°) rotations in the Miocene. (b) The minimal rotation Model 2 showed small rotations (±25°) due to the opening of adjacent back‐arc basins. All models from this study predict declinations that are generally less than the observed declinations. We consider our models to be viable from the limited perspective of paleomagnetic declination constraints because any gaps between the modeled and observed rotations could be ascribed to local block rotation along the Philippine Sea plate eastern margin. Modeled locations: superscript 1 = Izu (32°N/140°E); superscript 2 = Saipan (15.1°N/145.7°E).

4.2.1 Philippine Sea Plate Model 1: Manus Plume Origin

Model 1 represents a class of models that positions the small initial Mesozoic core of Philippine Sea plate at 52 Ma within the elongate equatorial Gap 1 that extends east and west of the present location of the Manus plume and places a minimum‐sized Molucca Sea slab into Gap 2 north of Australia (Figure 23c). The present version of Model 1 has the main Philippine Sea core overlapping the present‐day position of the Manus plume at 0°/150°E near a western Pacific transform plate boundary (Figure 24a). This choice is consistent with the Philippine Sea nucleating at a hot spot that formed the proposed Benham Rise‐Oki‐Daito hot spot track (Figures 1 and 14; see section 1.3). This starting Philippine Sea plate configuration allowed multiple plate orientations, and we chose to longitudinally align the Izu‐Bonin‐Marianas arcs along our inferred Pacific plate boundary (Figure 24a). This initial Philippine Sea plate configuration implied maximum ~80° whole‐plate clockwise rotation, which would fit within published paleomagnetic declinations if a small amount (20° to 30°) of local block rotation were included (Figure 27). We positioned Luzon and the Huatung Basin to the west of the main nucleating Philippine Sea (Figure 23c), implying that these are fragments of the East Asian Sea that were amalgamated to the Philippine Sea during its subsequent westward and northward journey. Under this interpretation the Cretaceous Huatung Basin [Deschamps et al., 2000] is apparently the only remaining fragment of intact East Asian Sea oceanic crust, as opposed to arc crust.

At 52 Ma the Pacific plate was moving NW whereas the Eurasian and Australian plates were slow moving. These three major plates were separated by the East Asian Sea, a swath of now‐vanished oceans that stretched from the Eurasian margin at ~30°N near proto‐Taiwan and the Ryukyus to the northern Australian margin at 30°S (Figure 24a). The proto‐South China Sea was located west of the East Asian Sea, between south China and Borneo (Figure 24a). The western Pacific plate boundary stretched NW‐SE from south of Japan to offshore eastern Australia (Figures 19, 20c, and 24a). The orientation of the Pacific plate boundary relative to pre‐50 Ma Pacific motions suggests transform or highly oblique subduction (Figures 19 and 24a). We reconstructed the Molucca Sea in Gap 2 to be part of the NE Indian Ocean north of the proto‐Banda Sea. Slow northward drift of Australia from Antarctica drove slow Indian Ocean subduction along Java and east Sumatra (Figure 24a), and some subduction may have begun prior to 52 Ma (see section 4.1). East of New Guinea northward drift of Australia was accommodated by slow subduction of the southern East Asian Sea under NE Australia that may have began as early as 84 Ma within the global model.

After ~50 Ma there was a major regional plate reorganization. The Pacific plate changed direction to move rapidly WNW toward Eurasia, resulting in fast westward Pacific subduction under the East Asian Sea at the proto‐Marianas (Figures 19 and 24b). North of the proto‐Marianas, we infer the initiation of a STEP fault transform that accommodated westward motion of the Izu‐Bonin Pacific flat slabs, which overrode and subducted the northernmost East Asian Sea slabs (Figure 24b). With continued Pacific motion the leading edge of the proto‐Izu Bonin slabs eventually subducted under Eurasia to emplace the regional Pacific flat stagnant slabs (i.e., Japan slabs) seen in Figures 7d and 17c. During the same period the Tonga Pacific slabs began to subduct rapidly westward under eastern Australia and the southern East Asian Sea (Figure 24b). The Philippine Sea nucleated and spread rapidly above the Manus plume, staying stationary with minor rotation behind the Pacific subduction zone (Figure 24b). During this stationary phase of the Philippine Sea plate, age‐progressive oceanic plateaus formed across the Central Basin rift to produce the Benham‐Oki‐Daito Rise hot spot track, similar to the model envisioned by Ishizuka et al. [2013]. Philippine Sea plate spreading and growth were accommodated by East Asian Sea and Pacific subduction along circum‐Philippine Sea plate subduction zones (Figure 24b). Luzon and the Huatung Basin were amalgamated to the growing Philippine Sea plate along a transpressional boundary between 52 and 34 Ma.

We reconstructed the Philippine Trench slab lithosphere to have formed prior to 45 Ma based on our interpretation of a subducted plateau within the Philippine Trench slab (Figure 14) and following a predicted ~45 Ma minimum plateau age from Ishizuka et al. [2013]. Reconstruction of the Ryukyu slab was more problematic because most of the slab is north of the Luzon‐Okinawa fracture zone (Figure 14), which is a possible transform or major tectonic boundary. Magnetic age modeling of the small preserved part of the Philippine Sea plate north of the Luzon‐Okinawa fracture zone indicates a nonsymmetric magnetic age sequence similar in age to the West Philippine Basin but progressively younger toward the Ryukyu Trench [Doo et al., 2014]. The lack of conjugate magnetic anomalies implies that a subducted ridge may exist within the Ryukyu slab. Therefore, we reconstructed the Ryukyu slab to form within a separate subbasin offset from the West Philippine basin by the Luzon‐Okinawa fracture zone (Figure 24b). The spreading of this subbasin was not modeled due to insufficient constraints but instead was approximated by artificially displaying the Ryukyu slab in its entirety at 40 Ma.

Around 40 Ma the Indian‐Australian spreading ceased and the new combined Indo‐Australian plate began to rapidly converge NNE toward Eurasia (Figure 24b). This resulted in faster northward subduction along the Sunda trench (Figure 24b). East of Java, the East Asian Sea subducted southward beneath the northern Molucca Sea (Figure 24b). We followed the global model to initiate ~43 Ma north‐south Melanesian arc spreading at NE Australia and this further consumed southern East Asian Sea by fast southward subduction (Figure 24b). The Celebes Sea opened as a back‐arc basin behind a rotating NW Borneo subduction zone, subducting the western East Asian Sea (Figure 24b).

Around ~36 Ma the Caroline Sea nucleated and began spreading N‐S above the Caroline mantle plume near 5°N, 166°E (Figure 24c). Recent full‐waveform global tomography indicates that the Caroline hot spot is deeply rooted to a plume‐like slow anomaly that can be traced to the core‐mantle boundary [French and Romanowicz, 2015]. Opening of the Caroline Sea was accommodated by southward trench migration over the Pacific plate (Figure 24c). The lost Pacific plate during Caroline Sea opening (i.e., proto‐Caroline Sea Pacific slabs) is today in the lower mantle under the Ontong Java plateau (i.e., Ontong Java deep slabs; Table 1 and Figures 24b and 24c). We tentatively interpret the southern Caroline Sea arc to be the Torricelli Terrane that collided with the leading arc of the Australian plate in the Miocene and is now incorporated into New Guinea (Figures 24d and 24e), as previously suggested by Hill and Hall [2003].

The N‐S opening Caroline Sea impinged on the SE Philippine Sea around 34 to 30 Ma and apparently torqued the Philippine Sea plate (Figure 24c). This coincided with up to 60° clockwise rotation of the entire Philippine Sea plate between 40 and 20 Ma (Figure 27). With continued Caroline Sea westward motion, the Philippine Sea plate experienced an escape or extrusion to the north and west (Figures 24c – 24e). In Model 1 the Philippine Sea rotational escape was accommodated by its overriding both the west and the north East Asian seas, with what became the northern Philippine Sea arc at the leading edge of the now subducted Ryukyu slab (Figures 24b–24d). The northern Philippine Sea arc eventually collided with the Eurasian margin along the Ryukyus and Japan around 20 Ma (Figures 24d and 28). Differential rotations between the Philippine Sea and Caroline Sea plates between 20 and 40 Ma were accommodated by spreading of a new ocean that was later subducted (i.e., deep Ayu Trough detached slabs in Figures 24d and 24e). During this phase our model indicates that the Palau basin at the southern Philippine Sea tracked across the Manus plume (Figure 24c). This suggests the enigmatic shallower bathymetry within the Palau Basin possibly could be a result of hot spot‐related plateau eruptions or underplating. We interpret that West Philippine Basin spreading terminated around 34 to 30 Ma as it moved away from the Manus plume due to the Caroline Sea‐SW Philippine Sea collision. Anomalous along‐axis dextral shear recorded during the final West Philippine basin spreading phase [Deschamps et al., 1999] could be an expression of this collision.

Shikoku‐Parece Vela basin back‐arc spreading began shortly after ~30 Ma (Figures 24c and 24d). Our Model 1 suggests that the Shikoku‐Parece Vela basins did not open fully by classic slab rollback, given the largely stationary Marianas subduction zone, but by westward motion of the Philippine Sea plate during the rotational tectonic escape driven by impinging Caroline Sea/Pacific plate (see Model 1 in Movie S1 between 30 and 15 Ma, discussed more fully in section 5.4). Furthermore, the two subbasins have different kinematics and plate tectonics. The Parece Vela basin widens southward associated with clockwise rotation of the West Philippine basin relative to the anchored Marianas. In contrast, the northward widening Shikoku basin began moving over the Pacific plate at the beginning of back‐arc spreading ~27 Ma (Model 1 in Movie S1) and shows some evidence of Pacific slab rollback (Figures 18 and S8).

The Philippine Sea plate continued to be driven westward and rotated by the Caroline‐Pacific leading plate edge until around 25 Ma, when the northern Indo‐Australian margin converged and collided with the southern Philippine Sea plate and potentially contributed to the northward Philippine Sea motion (Figures 24c and 24d). The collision at ~25 Ma caused the Molucca Sea to be torn from the Indian Ocean along the Sorong strike‐slip zone (Figure 24d). The Molucca Sea was then rapidly subducted westward under Sundaland at the Sangihe trench after ~ 25 Ma (Figure 24d).

As early as 25–20 Ma, a regional plate reorganization initiated as the northern Philippine Sea plate arc approached the Eurasian margin between Ishigaki in the western Ryukyus (Figure 22c) and southwest Japan (Figure 24d). Concurrently, the Bonin‐Marianas arcs at the northeastern Philippine Sea margin approached the proto‐Marianas arc at the eastern margin of the East Asian Sea (Figure 24d). The proto‐Marianas arc was lost and subducted along with the East Asian sea slab during this arc‐arc amalgamation or collision, which is further discussed in section 5.4. Our model suggests that the present‐day preserved Izu arc segment was not involved in this amalgamation because it had moved across a transform at the northern margin of the East Asian Sea (Figures 24c and 24d). Continued convergence of the Indo‐Australian, Philippine Sea, and Pacific‐Caroline plates toward Eurasia caused the final remnants of the East Asian Sea to be subducted by 15–20 Ma (Figure 24d).

Between 15 and 20 Ma the northern Philippine Sea arc fully collided with the formerly subducting Eurasian margin, creating a collisional mountain belt that was formed between Ishigaki and southwest Japan (Figure 29b). Sediment from the collisional mountain belt was carried southward by extensive (~1000 km long) turbidite fans, one of which was drilled in the Shikoku Basin at ODP 1177, as well as within the Nankai accretionary prism (Figures 29b and 29c) [Clift et al., 2013; Pickering et al., 2013]. The Japan Sea opened and escaped eastward in response to the Philippine Sea‐Eurasian collision between 16 and 14 Ma (Figures 29b and 29c). In this model we invoked the Izu‐Bonin arc to arrive near Tokyo at 15 Ma, and therefore, Philippine Sea plate rotations are minimal after 15 Ma (Figure 27). However, our slab constraints also allow a migrating trench‐trench‐trench triple junction near Japan and Izu‐Bonin arc arrival near Kyushu at 15 Ma. This alternative reconstruction is provided in the supporting information (see Model 1b in Movie 2) and will be later discussed. Around 16–17 Ma the Philippine Sea began to subduct northward under Japan and the Ryukyus east of Ishigaki, with associated fore‐arc magmatism (Figures 24e and 29b). These effects of Miocene Philippine Sea plate collision are discussed more fully in section 5.4.

Figure 29 Open in figure viewer PowerPoint Ishizuka et al. [ 2013 Philippine Sea plate initiation and growth based on our preferred Philippine Sea plate tectonic reconstruction Model 1. (a) The pre‐Philippine Sea plate tectonic configuration was a NW‐SE Pacific‐East Asian Sea transform boundary near the equator. The Cretaceous‐aged Daito ridges and Luzon‐Huatung basin were located nearby. (b) The Philippine Sea plate initiated above the Manus plume at 150°E/0° and began to spread, centered above the hot spot. (c) The Philippine Sea plate remained stationed above the plume and grew outward by seafloor spreading, consuming parts of the East Asian Sea and Pacific plates by opposing subduction zones. The Ryukyu slab was formed during this period, potentially within a spreading center across the Luzon‐Okinawa fracture zone (LOFZ). Excess plume magmatism formed an age‐progressive chain of plateaus on either side of the spreading ridge (after. []). The Huatung basin and Luzon were amalgamated to the Philippine Sea along a transpressive boundary shortly after 40 Ma. After 40 Ma the Philippine Sea plate was driven westward from the Manus plume by the newly formed, westward moving Caroline Sea plate in Figure 29 c.

The Philippine Sea continued to be driven northward with a westward component by the Pacific‐Caroline plates. By 15 to 20 Ma, South China Sea spreading was nearly completed and the Eurasian and newly formed South China Sea lithosphere between Ishigaki and Palawan‐Mindoro began to subduct beneath the western Philippine Sea (Figures 22c, 24d, and 29b). A constraint on post ~15 Ma motions of the Philippine Sea plate is provided by the East Taiwan ophiolite, which is incorporated within the Pliocene‐aged Lichi Melange of the Coastal Range, eastern Taiwan [Suppe et al., 1981]. This ophiolite formed at ~15 Ma and is generally interpreted as a preserved fragment of South China Sea spreading ridge or near‐ridge seamount fragment [Chung and Sun, 1992; Huang et al., 1979; Jahn, 1986; Suppe et al., 1981]. This conclusion requires that the trajectory of the Taiwan Coastal Range arc and fore‐arc accretionary complex pass over the South China Sea spreading axis after or synchronously with the formation of the ophiolite at 15 Ma. The dominantly northward motion of the Philippine Sea plate with small westward component in all of our models ensures that the Taiwan Coastal Range passes over the ridge at 10–15 Ma (e.g., Figures 30b and 30c).

Figure 30 Open in figure viewer PowerPoint Early to mid‐Miocene collision between the Philippine Sea plate and Eurasia predicted by the preferred Model 1 plate reconstruction. PSP, Philippine Sea plate; Mar, Marianas arc; Luz, Luzon arc; KPR, Kyushu‐Palau arc.

After 15 Ma the southeast Philippine Sea plate‐Caroline plate boundary became a NE‐SW transpressive zone with limited, highly oblique subduction under the southern Marianas, Yap, and Palau trenches (Figure 24e). From 22 to 15 Ma the southern Caroline arc (i.e., the Torricelli Terrane) collided with predicted northern Australian arcs whereas a final New Guinea arc‐continent collision was much later (1 to 2 Ma). From 15 to 2 Ma the Philippine Sea plate moved NNW and the South China Sea and its margins were subducted at the Manila trench (Figures 24e, 24f, and 29c). At ~2 Ma the Philippine Sea began to move with its present‐day, Pacific‐like WNW direction, apparently due to greater coupling between the Philippine Sea and Pacific‐Caroline plates (e.g., Figure 1b).