Oceanic core complexes and back-arc basin spreading

As usual, it has been a little while since I have posted. Today I thought I was switch it up a bit and provide a more scientifically written article. As you may know, I am involved in several ongoing research projects with Japanese colleagues. One of which is the continued exploration of the world's largest oceanic core complex, which happens to lie along an extinct back-arc spreading ridge, the Godzilla Megamullion.

When I first began my work on Godzilla as a lowly undergraduate, I felt the need to write up a nice summary of why working on Godzilla was important to me and the scientific community. Looking back on that paper now, I find that its relevance has not degraded and in fact may have grown with time. That being said, I felt that a few minor things needed to be updated. So I have taken the liberty in adding to that paper and presenting here on Fiery Low-Down Rock Talk as an informative post. Many may not know so much about back-arc basins and/or oceanic core complexes, and I am certain that many do not know much about the Godzilla Megamullion.

So for your enjoyment and enlightenment I present:

Oceanic core complexes and back-arc basin spreading

Considered as analogs to Mid-Ocean Ridges (MORs), back-arc spreading systems generate a large portion of the magmatic basement that forms the Earth’s oceanic crust that of which is doomed to be subducted. The study of back-arc spreading systems has a strong bearing on two very important aspects of the Earth’s evolution, as it relates intimately with both subduction zone and mid-oceanic ridge dynamics. However, this important tectonic setting is much less well understood than are arcs or mid-oceanic ridges (Ohara et al, 2003). In both MORs and back-arc spreading systems, new oceanic crust is created by the upwelling of asthenospheric mantle. The melting of the mantle, accumulation of melt in lithospheric magma chambers and extrusion in volcanic centers, forms the same or similar structures as true mid-ocean ridges. It is believed that an over-representation of these systems may be present in the geologic record, due to their proximity to arcs, which makes them more likely to be obducted alongside arc and forearc lithosphere during ocean-continent convergence and continent-continent collision. None of the many active or extinct back-arcs worldwide have actively produced oceanic lithosphere for more than a few million years. Continuous crustal accretion over millions of years is normal for MORs, but back arc rifts once born from rifting of the rear of an island arc volcanic system will spread for a few million years and die.  

Formation of Back-arcs

Since the inception of plate tectonics, geologists have been searching for the reasons behind why and how extensional basins open near the boundaries between convergent plates, and suddenly stop opening. There have been two basic concepts proposed for the formation of back-arc basins. In one case, the rate at which the subducting plate descends into the mantle can be greater than the rate of convergence with the overriding plate. In this case, the subducting slab will roll back from the overriding plate and a smaller portion of the “arc” or “forearc” plate might break off that will remain in contact with the trench, while the portion left behind of the overriding plate trails behind (Elsasser, 1971; Moberly, 1972). In the second proposed case, the overriding plate may pull away from the trench; this anchors the slab in the mantle, causing the trench to resist migration with the retreating overriding plate (Scholz and Campos, 1995). As in the first case, a small piece breaks off from the overriding plate and remains in contact with the subducting plate along the subduction hinge. The truth is, both of the cases tend to act simultaneously. ( See figure 1)

Figure 1. Modes of back-arc basin opening. The panels from top to bottom show a schematic time sequence of back-arc basin opening. Left-hand panels show the case of slab roll back (Elsasser, 1971; Moberly, 1972) in which the trailing plate is considered fixed (indicated by black dot) and the trench hinge moves relatively seaward (indicated by small right-pointing arrow), breaking off a section of the overriding plate that moves with the trench from a trailing plate that remains fixed. In the right-hand panels, the trench hinge is considered to resist motion (black dot) because of a slab “sea anchor” force (Scholz and Campos, 1995). (Martinez et al, 2007)

When arc systems rift, the breakup generally occurs in the vicinity of the arc volcanic front (Molnar and Atwater, 1978), defined usually as the maximum locus of volcanism in the arc (Tatsumi, 1986; Tatsumi and Eggins, 1995). The arc volcanic front is a region of thickened crust, melt emplacement, high heat flow, and large gravitational stresses, all of which tend to towards breaking apart if extensional stresses are enacting upon the area. Breakup is not always exactly centered on the volcanic front and may occur as far as ±50 km (Taylor and Karner, 1983) so that some leeway is seen as some systems may rift behind the arc while others will rift in the forearc. Local weaknesses in the overriding plate are not the only factors controlling breakup. Other effects, such as the motion and geometry of the subducting slab and traction with the mantle wedge during breakup, may also be important. After breakup, some basins, appear to have began rifting at a central area and then grown by typical MOR processes as well as widening of the rift, that is, the progressive extension of the rift along strike into the arc volcanic front (Stern et al., 1984). Other basins, such as the Havre Trough, appear to be opening more uniformly along their entire lengths (Delteil et al., 2002). These basins would seem to be better analogs to MORs.

Conditions for Formation

Recent published findings by Sdrollias and Muller have placed a limit to backarc spreading usually occuring when oceanic crust that is older than 55 million years is subducted. The older, colder slab sinks into the mantle at a high intermediate dip angle of always 30° or greater to backarc spreading, causing slab rollback which exerts a large amount of tension on the overriding plate. Back-arc basin formation is usually precluded by a pull of the overriding plate away from the subduction hinge. This creates accommodation space between the overriding and subducting plates, which allows for both spreading and subducting to continue to occur. Once back-arc extension is established, it continues regardless of the motion of the overriding plate. This indicates that back-arc spreading is not a simple consequence of overriding plate behavior (Sdrollias and Muller 2005). Tectonic extension in the arc and forearc is usually shown by volcanism in the areas, but in the backarc, active mantle upwelling is induced in the mantle wedge by the traction of the subducting plate on the mantle wedge in the overlying arc. The upwelling causes mantle melting which feeds the production of oceanic crust in the backarc. The zone of upwelling will push any back arc spreading that initiates directly above it landward due to accretion of crust to both sides of the rift. Once back-arc extension is established, subduction hinge rollback appears to be the main force responsible for continued creation of accommodation space. As the system migrates away from the arc with time, the backarc spreading system will take on the appearance of being more like a MOR. The accretion of material derived from a fertile mantle source over the course of the spreading systems era of productivity will gradually change into a thickened crust fed by less-mixed depleted melt. Overall, the driving mechanisms for back-arc extension have been shown to be a combination of surface kinematics, properties of the subducting slab, the effect of mantle flow on the slab, and mantle wedge dynamics. (Sdrollias and Muller 2005).   

Oceanic Core Complexes in Back-arc Spreading Systems

Oceanic core complexes (OCCs) are morphological features that were first noted and characterized along the Mid-Atlantic Ridge (e.g., Karson, 1990; Tucholke and Lin, 1994; Cann et al., 1997; Blackman et al., 1998; Tucholke et al., 1998). OCCs usually occur near the intersection of transform faults and the axis of a spreading ridge (i.e., a ridge-transform intersection), and are characterized by a domal/curviplanar surface, corrugations oriented parallel to the spreading direction (referred to as megamullion surfaces), and exposed lower crust and mantle material (Figure 2) (e.g., Cann et al., 1997; Blackman et al., 1998; Tucholke et al., 1998; Karson et al., 2006). These features are general found along regions of a spreading ridge where tectonic extension dominates over magmatic processes. Such a tectonic environment leads to asymmetric plate spreading and the formation of OCCs (Blackman et al., 1998; Tucholke et al., 1998; Smith et al., 2006, 2008).Compared with continental metamorphic core complexes, OCCs along a spreading axis are likened to represent the exhumed footwalls of oceanic detachment faults (e.g., Karson, 1990; Dick et al., 1991; Cann et al., 1997; Blackman et al., 1998; Tucholke et al., 1998; Karson, 1999; Dick et al., 2000; MacLeod et al., 2002; Escartin et al., 2003; Ildefonse et al., 2007). Oceanic detachment faults are long-lived, low-angle, large offset extensional faults that efficiently accommodate a significant portion of plate separation (up to 60-100% extension) on-axis during asymmetric spreading (Buck, 1988; Tucholke and Lin, 1994; Tucholke et al., 1998; Buck et al., 2005; deMartin et al., 2007; Grimes et al., 2008; Smith et al., 2008; Morris et al., 2009). It is generally agreed that these detachment faults do not initiate at low angles, but instead initiate as steep normal faults at depth and shallow into a low angle normal fault through footwall rotation (Morris et al., 2009). Many questions still remain regarding where and how the detachment fault roots and ultimately why they form and cease in the first place (Tucholke et al., 2008; MacLeod et al., 2009; Olive et al., 2010; Escartin and Canales, 2011).

Figure 2: From Schoolmeesters et al. (2012) which modified after Grimes et al. (2008) and Escartin and Canales (2011). “Cartoon of a slow-spreading ridge showing asymmetric plate spreading and associated formation of an oceanic core complex. Image highlights main attributes, including the breakaway – location where the oceanic detachment fault originally surfaced on the seafloor; spreading-parallel corrugations on the surface of the core complex; gabbro plutons within upper mantle peridotite denuded by the fault (red indicates recently intruded melt rich plutons, orange indicates partially crystallized plutons, and blue indicates fully solidified plutons); and the termination where the oceanic detachment fault dips below the axial valley. The detachment fault forms via a rolling hinge model, initially with a moderate-to steep dip beneath the rift valley and flattens as it emerges to the seafloor at the rift valley wall.” (Schoolmeesters et al., 2012)

 The largest OCC currently being studied in the world, as reported by Ohara et al (2001) and Ohara et al (2003a), is the Godzilla Megamullion (Figure 3), which is 10 times larger than OCCs commonly found along the Mid-Atlantic Ridge. The significance of Godzilla Megamullion is that it is an OCC that formed on a back-arc spreading ridge (i.e. the Parece Vela Basin). Compared to typical OCC-forming spreading rates [ultraslow- (Southwest Indian ridge full rate: ~1.2–2 cm/y; Dick et al., 2003) or slow-spreading ridges (Mid-Atlantic Ridge full rate: 1–4 cm/y)] the Godzilla Megamullion developed at a spreading ridge that records seemingly intermediate spreading rates (full rate: 7.0 cm/y; Ohara et al., 2001). Recent U-Pb dating of zircons from gabbroic and leucocratic rocks from Godzilla Megamullion (Tani et al., 2011) constrain the duration of fault-induced spreading contemporaneous with magmatic accretion at the ridge axis to ~4 Ma and determined that the spreading rate gradually decreased until cessation of the PVR at ~7-9 Ma or later. It is estimated that the average half-spreading rate for the Godzilla Megamullion is 2.54 cm/yr. Although magnetic lineations in the Parece Vela Basin (PVB) are weak due to spreading occurring when the basin was near the equator (Okino et al., 1998, 1999), estimations based on poorly constrained data set the full-rate of spreading in the central basin at ~7.0 cm/yr (Ohara et al., 2001). The presence of well-ordered abyssal hills southwest of the breakaway for the Godzilla Megamullion suggests that prior to the formation of the detachment fault the western PVB experienced robust magmatism and little variation in its spreading rate. The Godzilla Megamullion is unusual in that it extends along the full length of the spreading segment (Ohara et al., 2001). (See Figure3)

Figure 3: Left: Major bathymetric features of the Western Pacific Ocean (after Ohara et al., 2001). The rectangle shows the location of the study area at the site of the Godzilla Megamullion, Parece Vela Basin. Right: Bathymetric map of the Godzilla Megamullion (outlined by dashed line), showing the location of dredge site D (Harigane et al 2008)

The presence of a huge megamullion structure in the PVB is a distinct morpho-tectonic characteristic that indicates a spreading dominated by tectonic extension and small melt volumes, and gives us an insight into the formation and life of back-arc spreading ridges. Peridotites have been recovered in abundance over the megamullion surface, as well as at a segment termination. Very notable is the small scale (i.e. single dredge haul) emplacement of fertile peridotite and depleted peridotite (dunite and plagioclase- peridotite). The Fertile (F-type) peridotite has been interpreted as being the residue of a small degree of melting (~4% near-fractional melting of a MORB-type mantle), whereas Dunite (D-type) and plagioclase-bearing peridotite (P-type) are products of melt-mantle interaction (Ohara et al 2003; Snow et al., 2009; Loocke et al., 2009). Godzilla Megamullion has provided a window not only into the inner-workings of our planet, but provides evidence which supports the hypotheses regarding the lifecycles of back-arc spreading ridges (Snow et al., submitted). 

In short, oceanic core complexes represent a significant feature that is synonymous between mid ocean ridges and back-arc spreading ridges. The continued study of the two allows for in depth examination of the inner workings of our earth and provides a better understanding of magmatic processes and mantle dynamics at mid ocean spreading ridges and subduction zones.  The magmatic histories of these structures, though short-lived, are relatively complex. It is with a better understanding of these histories, that we can interpret the formation of these structures, their significance in the creation of new oceanic crust, and their overall lifespan more precisely.

References

Blackman, D.K., Cann, J.R., Janssen, B., Smith, D.K., 1998. Origin of extensional core complexes: evidence fromtheMid-Atlantic Ridge at Atlantis fracture zone. J. Geophys. Res. 103, 21315–21333

Buck,W. R. (1988), Flexural rotation of normal faults, Tectonics, 7, 959–973, doi:10.1029/TC007i005p00959.

Buck, W. R., L. L. Lavier, and A. N. B. Poliakov (2005), Modes of faulting at mid-ocean ridges, Nature, 434, 719–723, doi:10.1038/nature03358.

Cann, J.R., Blackman, D.K., Smith, D.K., McAllister, E., Janssen, B., Mello, S., Avgerinos, E., Pascoe, A.R., Escartin, J., 1997. Corrugated slip surfaces formed at ridge-transform intersections on the Mid-Atlantic Ridge. Nature 385, 329–332.

deMartin, B. J., R. A. Sohn, J. P. Canales, and S. E. Humphris (2007), Kinematics and geometry of active detachment faulting beneath the Trans-Atlantic Geotraverse (TAG) hydrothermal field on the Mid-Atlantic Ridge, Geology, 35, 711– 714, doi:10.1130/G23718A.1.

Delteil, J., E. Ruellan, I. Wright, and T. Matsumoto. 2002. Structure and structural development of the Havre Trough (SW Pacific). Journal of Geophysical Research 107, doi:10.1029/ 2001JB000494.

Dick, H.J.B., Schouten, H., Meyer, P.S., Gallo, D.G., Bergh, H., Tyce, R., Patriat, P., Johnson, K.T.M., Snow, J., Fischer, A., 1991. Tectonic evolution of the Atlantis II fracture zone. Proc. Ocean Drill. Program Sci. Results 118, 359–398.

Dick, H.J.B., Natlamd, J.H., Alt, J.C., Bach,W., Bideau, D., Gee, J.S., Haggas, S., Hertogen, J.G.H., Hirth, G., Holm, P.M., Ildefonse, B., Iturrino, G.J., John, B.E., Kelley, D.S., Kikawa, E., Kingdon, A., LeRoux, P.J., Maeda, J., Meyer, P.S., Miller, D.J., Naslund, H.R., Niu, Y., Robinson, P.T., Snow, J., Stephan, R.A., Trimby, P.W., Worm, H., Yoshinobu, A., 2000. A long in situ section of the lower ocean crust: results of ODP Leg 176 drilling at the Southwest Indian Ridge. Earth Planet. Sci. Lett. 179, 31–51.

Dick, H.J.B., Lin, J., Schouten, H., 2003. An ultraslow-spreading class of ocean ridge. Nature 426, 405–412.

Elsasser, W.M. 1971. Sea-floor spreading as thermal convection. Journal of Geophysical Research 76:1,101–1,112.

Escartin, J., Mevel, C., MacLeod, C.J., McCaig, A.M., 2003. Constraints on deformation conditions and the origin of oceanic detachments: the Mid-Atlantic Ridge core complex at 15°45′N. Geochem. Geophys. Geosyst. 4 (8), 1067. doi:10.1029/2001GC000278.

Escartín, J., and J. P. Canales (2011), Detachments in oceanic lithosphere: Deformation, magmatism, fluid flow, and ecosystems, Eos Trans. AGU, 92(4), 31, doi:10.1029/2011EO040003.

Grimes, C. B., B. E. John, M. J. Cheadle, and J. L. Wooden (2008), Protracted construction of gabbroic crust at a slow spreading ridge: Constraints from 206Pb/238U zircon ages from Atlantis Massif and IODP Hole U1309D (30N, MAR), Geochem. Geophys. Geosyst., 9, Q08012, doi:10.1029/2008GC002063.

Ildefonse, J., Blackman, D.K., John, B.E., Ohara, Y., Miller, D.J., MacLeod, C.J., Integrated Ocean Drilling Program Expeditions 304/305 Science Party, 2007. Oceanic core complexes and crustal accretion at slow-spreading ridges. Geology 35 (7), 623–626. doi:10.1130/G23531A.

Karson, J.A., 1990. Seafloor spreading on the Mid-Atlantic Ridge: implications for the structure of ophiolites and oceanic lithosphere produced in slow-spreading environments. In: Malpas, J., et al. (Ed.), Ophiolites and Oceanic Crustal Analogues: Proceedings of the Symposium “Troodos 1987”. Geol. Surv. Dept., Nicosia, Cyprus, pp. 125–130.

Karson, J.A., 1999. Geological investigation of a lineated massif at the Kane transform: implications for oceanic core complexes. Philos. Trans. R. Soc. Lond., Ser. A 357, 713–740

Karson, J. A., G. L. Fruh-Green, D. S. Kelley, E. A. Williams, D. R. Yoerger, and M. Jakuba (2006), Detachment shear zone of the Atlantis Massif core complex, Mid-Atlantic Ridge, 30N, Geochem. Geophys. Geosyst., 7, Q06016, doi:10.1029/2005GC001109.

Loocke, M., Snow, J. E., Ohara, Y., 2009. Systematics of plagioclase impregnation in peridotites from Godzilla Mullion. Eos Trans. AGU, Fall Meet. Abstract T21A-1776.

MacLeod, C.J., Escartin, J., Banerji, D., Banks, G.J., Gleeson, M., Irving, D.H.B., Lilly, R.M., McClaig, A.M., Niu, Y., Allerton, S., Smith, D.K., 2002. Direct geological evidence for oceanic detachment faulting: the Mid-Atlantic Ridge, 15°45′N. Geology 30, 879–882

MacLeod, C. J., R. C. Searle, B. J. Murton, J. F. Casey, C. Mallows, S. C. Unsworth, K. L. Achenbach, and M. Harris (2009), Life cycle of oceanic core complexes, Earth Planet. Sci. Lett., 287, 333–344, doi:10.1016/j.epsl.2009.08.016.

Moberly, R. 1972. Origin of lithosphere behind island arcs, with reference to the western Pacific. Pp. 35–55 in Studies in Earth and Space Sciences: A Memoir in Honor of Harry Hammond Hess, Memoir 132. R. Shagam, R.B. Hargrave, W.J. Morgan, F.B. Van Houten, C.A. Burk, H.D. Holland, and L.C. Hollister, eds, Geological Society of America, Boulder, Colorado.

Molnar, P., and T. Atwater. 1978. Interarc spreading and Cordilleran tectonics as alternates related to the age of subducted oceanic lithosphere. Earth and Planetary Science Letters 41:330–340.

Morris, A., J. S. Gee, N. Pressling, B. E. John, C. J. MacLeod, C. B. Grimes, and R. C. Searle (2009), Footwall rotation in an oceanic core complex quantified using reoriented Integrated Ocean Drilling Program core samples, Earth Planet. Sci. Lett., 287, 217–228, doi:10.1016/j.epsl.2009.08.007.

Ohara, Y., K. Fujioka, T. Ishii, and H. Yurimoto, Peridotites and gabbros from the Parece Vela backarc basin: Unique tectonic window in an extinct backarc spreading ridge, Geochem. Geophys. Geosyst., 4(7), 8611, doi:10.1029/2002GC000469, 2003.

Okino, K., Kasuga, S., and Ohara, Y., 1998. A new scenario of the Parece Vela Basin genesis. Marine Geophysical Researches 20, 21–40.

Okino, K., Ohara, Y., Kasuga, S., Kato, Y., 1999. The Philippine Sea: new survey results reveal the structure and the history of the marginal basins. Geophysical Research Letters 26, 2287–2290.

Olive, J. A., M. D. Behn, and B. E. Tucholke (2010), The structure of oceanic core complexes controlled by the depth distribution of magma emplacement, Nat. Geosci., 3, 491–495, doi:10.1038/ngeo888.

Scholz, C.H., and J. Campos. 1995. On the mechanism of seismic decoupling and back arc spreading at subduction zones. Journal of Geophysical Research 100:22,103–22,115.

Sdrolias, M., and R. D. Muller (2006), Controls on back-arc basin formation, Geochem. Geophys. Geosyst., 7, Q04016, doi:10.1029/2005GC001090.

Smith, D. K., J. R. Cann, and J. Escartín (2006), Widespread active detachment faulting and core complex formation near 13N on the Mid-Atlantic Ridge, Nature, 442, 440–443, doi:10.1038/nature04950.

Smith, D. K., J. Escartín, H. Schouten, and J. R. Cann (2008), Fault rotation and core complex formation: Significant processes in seafloor formation at slow-spreading mid-ocean ridges (Mid-Atlantic Ridge, 13–15N), Geochem. Geophys. Geosyst., 9, Q03003, doi:10.1029/2007GC001699.

Snow, J. E., Ohara, Y., Nelson, W., Loocke, M., Harigane, Y., Hellebrand, E., Ishii, T., Loocke, M., Michibayashi, K., Ishizuka, O., Ishii, T., Dick, H.J.B., Submitted. Death of a backarc: Mantle rocks from Godzilla Megamullion in the Parece Vela Rift, Philippine Sea. To be submitted to Geochemistry Geophysics Geosystems.

Stern, R.J., N.C. Smoot, and M. Rubin. 1984. Unzipping of the Volcano Arc, Japan. Tectonophysics 102:153–174.

Tani, K., Dunkley, D. J., and Ohara, Y., 2011. Termination of backarc spreading: Zircon dating of a giant oceanic core complex. Geology 39, 47 – 50.

Tatsumi, Y. 1986. Formation of the volcanic front in subduction zones. Geophysical Research Letters 13:717–720.

Tatsumi, Y., and S. Eggins. 1995. Subduction Zone Magmatism. Blackwell Science, Cambridge, Mass., USA, 221 pp.

Taylor, B., and G.D. Karner. 1983. On the evolution of marginal basins. Reviews of Geophysics and Space Physics 21:1,727–1,741.

Tucholke, B.E., Lin, J., 1994. A geological model for the structure of ridge segments in slow spreading ocean crust. J. Geophys. Res. 99, 11937–11958.

Tucholke, B.E., Lin, J., Kleinrock, M.C., 1998. Megamullions and mullion structure defining oceanicmetamorphic core complexes on the Mid-Atlantic Ridge. J. Geophys. Res. 103, 9857–9866

Tucholke, B. E., M. D. Behn, W. R. Buck, and J. Lin (2008), Role of melt supply in oceanic detachment faulting and formation of megamullions, Geology, 36, 455–458, doi:10.1130/G24639A.1.

Illustrations

Harigane, Y., Michibayashi, K., Ohara, Y. 2008. Shearing within lower crust during progressive retrogression: Structural analysis of gabbroic rocks from the Godzilla Mullion, an oceanic core complex in the Parece Vela backarc basin. Tectonophysics. 457, 183–196

Martinez, F. , Okino, K., Ohara, Y.,  Reysenbach, A., Goffredi, S. Back-Arc Basins. Oceanography. 20, 116- 127.

Schoolmeesters, N., Cheadle, M.J., John, B.E., Reiners, P.W., Gee, J., Grimes, C.B., 2012. The cooling history and the depth of detachment faulting at the Atlantis Massif oceanic core complex. Geochemistry Geophysics Geosystems, 13, Q0AG12, doi:10.1029/2012GC004314

Incidental Geotourism

So, lots of new stuff going on.
Although I have been feverishly finishing up my thesis writing and sending off several manuscripts as of late, I have had this blog burning at the back of my mind for quite some time. Good news is on the horizon though. I will be moving to Wales in the Fall to pursue new avenues in geosciences. So, that's all fine and dandy. And that means that I have an entire summer of research time, vacation, and of course blog time!

I'm going to start this blog with a little bit of what I like to call 'inciddental geotourism'. Back in 2009, I went out on my first research cruise. The purpose of the cruise was to use the Japan Agency for Marine Science and Technology's (aka JAMSTEC) deep sea submersible, the Shinkai 6500 (or 6K for short) to study the world's largest oceanic core complex (i.e. a footwall of a long-lived, large offset, low-angle detachment fault known to occur along mid-ocean ridges) known as the Godzilla Megamullion located in the southern Parece Vela Basin in the Western Pacific (see map below).

Map of the Philippine Sea Plate in the Western Pacific. Japan is to the North and the Philippines are visible on the Western portion of the map.

I will most likely talk in further detail on Godzilla in a later post, but what concerns this post is less of the actual cruise and more of what happened after it. So when it comes to planning cruises, you have to know where you will be getting on the boat and where you will be getting off. It turned out that the research cruise which was scheduled to use the 6K sub after our cruise was intending to work on the inner trench slope of the Bonin Ridge, just East of the island of Chichi-jima. So it was worked out that our cruise would disembark in the tiny (1 major dock) port of Futami Harbor where the next cruise's scientific party would be waiting.

Futami Harbor

Well, as it turns out, Chichi-jima is the type locality of the ultra-depleted volcanic rock boninite. Chichi-jima is the main island in the Bonin Islands. See the connection there. Needless to say, our chief scientist knew what he was doing when he chose our port of harbor. The crazy thing is, the only way to get to the island aside from research vessels is by a ~27 hour high-speed ferry out of Tokyo bay that visits every 3 or 4 days and stays for about 2. Its safe to say that my stay on the island was definitely a rare opportunity for geologists.

The island is pretty small, ~24 km^2 with a permanent population of about 2000. But don't let its size fool you, there is plenty of first class geology and UNESCO branded history on the island. From dozens of rusted shipwrecks and decaying bunkers dating all the way back to its use as a Japanese radio relay station during world war II, to loads of fantastic outcrops exhibiting type localities for intraoceanic arc volcanics, there is enough on the island to keep you busy for weeks.

I personally recommend a visit to Chichi-jima for anyone, geologist or common man alike, to go and spend a week or two. I have a geologic map of the island, albeit in japanese. And I have all of the information needed to plan a trip there, if you are willing to spend a long time on trains, planes, and boats. I will leave you with several pictures of the island and outcrops. If you would like any information, email me and I can send it to you.

A new beginning...

I know it has been a while, but I have a good reason for being silent for so long on this blog.
I have been very busy since August 2010.

• I finished my undergraduate degree
• Had another succesful field season working on the Santa Elena peninsula in Costa Rica. My focus was on melt-rock reaction textures, pegmatoidal gabbros and plagioclase peridotites
• Attended field camp at the Yellowstone-Bighorn Research Association
• Wrote a thesis on my work with plagioclase-bearing peridotites from the Godzilla Megamullion Oceanic Core Complex
• Began working on lunar meteorite DHO910- element mapping and geochemical analysis of clasts and glass in the impact breccia
• Went on a second submersible diving cruise to the Godzilla Megamullion (R/V Yokosuka YK11-08) where we found some amazing new stuff while examining the abyssal hills southwest of the breakaway and the termination/paleo-ridge axis.
• Began working on petrography and geochemical analysis of lower-crustal and upper mantle peridotites, troctolites, and gabbros from the inner trench wall of the Bonin Ridge.
• Finished a manuscript for my work on the Godzilla Megamullion
• Attended the IODP workshop on Ultra-deep drilling into arc crust (https://www.jamstec.go.jp/ud2012/form/)
• And began work on a manuscript for my first round of data from my Bonin Ridge samples.
• I have established a domain to use as a personal website for my work and published papers

Needless to say, I've been very busy.

My plan for this blog in the near future is simple: I am going to begin weekly or bi-weekly posts which pertain to interesting topics in my and my colleague's research. This blog will be associated with and displayed on my personal website. Although it is not up and completely running yet, my website is www.matthewloocke.com

Be on the lookout for the launch of my site in the next week or two. I will have links to all of my various profiles and pdfs or links to my publications.

That's it for now. Until next time, keep your mind lucid and your rocks intrusive!
Matt Loocke

Behind... Obviously

So I started this blog about a year and a half ago with the intentions of posting my experiences with traveling for research and conferences with my geology research and such. So far, I have written down what to put in these blogs, but never gotten around to posting them. Over the next few days I will be workling on getting these many experiences posted.

Since beginning this blog I have spent 30 days on a Japanese led expedition in the Philippine Sea and subsequently a week in port on the island of Chichi Jima, numerous trips with undergraduate courses to Big Bend National Park and Central Texas for mapping projects and geo-tourism, 2 weeks in Costa Rica for both preliminary field work for a petrological and field mapping project of an ignored oceanic mantle section on the Northwest coast ( which was followed of course by some more geo-tourism), a week-and-a-half in Cyprus for the AGU Chapman conference on detachment faulting in oceanic lithosphere, a week in Chiba, Japan for the Japanese Geophysical Union annual meeting, and a week and a half at the Woods Hole Oceanographic Institute this summer investing some time with my advisor, Dr. Jon Snow's, PhD advisor Dr. Henry Dick into examining my current research interest of plagioclase in abyssal peridotites.

Its been a very busy and worthwhile year. And the greatest thing is that its not slowing down anytime soon!

So I hope whoever reads these next posts finds something in them that makes the time you spent reading them worthwhile.

Cheers,

Matt

Welcome

Well, This is my first post, and if you are reading this I woul like to thank you for taking the time to check in and see what I have been up to. The main purpose of this blog is to create a way for me to keep track of travels abroad and here at home in geology. I am currently studying geology at the University of Houston, and have so far gotten some great opportunities that are quickly giving me a wealth of knowledge and experience in a subject that I have a true passion for.

I will post up some experiences of the pastyear or so that have left an imprint on my mind, and that have given me vital experience, as well as begin covering in real time my experiences in the near and distant future. Currently I am set to depart Houston for Tokyo Japan on May 1st to work on a submersible research dive on the Godzilla Mullion north of The ogasawara islands of japan. i will hopefully be able to keep a daily blog of that trip, so as to keep all of you who are interested up to date.

Thanks for reading, and happy travels!
Matt