1. Intraplate magmatism

2. Intraplate magmatism Hotspots
Rift zones (often associated with hotspots)
Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB = Oceanic Islands Basalts), some differenciated alkaline terms
Intra-continental plate:
either large tholeitic basaltic provinces (CFB = Continental Flood Basalts), occasionally bimodal (ass. with rhyolites)
or smaller, alkaline to hyper-alkaline, differenciated intrusions/volcanoes (syenites/phonolites; carbonatites; kimberlites; and more…)

3. Ocean islands and seamounts Commonly associated with hot spots
More enigmatic processes and less voluminous than activity at plate margins
No obvious mechanisms that we can tie to the plate tectonic paradigm
As with MORB, the dominant magma type for oceanic intraplate volcanism is basalt, which is commonly called ocean island basalt or OIB
41 well-established hot spots Estimates range from 16 to 122
Figure After Crough (1983) Ann. Rev. Earth Planet. Sci., 11,

4. Oceanic islands

5. Hotspots

6. Mantle convection and mantle plumes

7. Two principal magma series
Types of OIB Magmas
Two principal magma series
Tholeiitic series (dominant type)
Parental ocean island tholeiitic basalt, or OIT
Similar to MORB, but some distinct chemical and mineralogical differences
Alkaline series (subordinate)
Parental ocean island alkaline basalt, or OIA
Two principal alkaline sub-series
silica undersaturated
slightly silica oversaturated (less common series)
Modern volcanic activity of some islands is dominantly tholeiitic (for example Hawaii and Réunion), while other islands are more alkaline in character (for example Tahiti in the Pacific and a concentration of islands in the Atlantic, including the Canary Islands, the Azores, Ascension, Tristan da Cunha, and Gough)

8. Cyclic, pattern to the eruptive history
Hawaiian Scenario
Cyclic, pattern to the eruptive history
1. Pre-shield-building stage somewhat alkaline and variable
2. Shield-building stage begins with tremendous outpourings of tholeiitic basalts
Early, pre-shield-building stage that is more alkaline and variable, but quickly covered by the massive tholeiitic shields
Recent studies of the Loihi Seamount encountered a surprising assortment of lava types from tholeiite to highly alkaline basanites.
Shield-building: Kilauea and Mauna Loa (the two nearest the hot spot in the southern and southeastern part of the island) are presently in this stage of development
This stage produces 98-99% of the total lava in Hawaii

9. Hawaiian Scenario
3. Waning activity more alkaline, episodic, and violent (Mauna Kea, Hualalai, and Kohala). Lavas are also more diverse, with a larger proportion of differentiated liquids
4. A long period of dormancy, followed by a late, post-erosional stage. Characterized by highly alkaline and silica-undersaturated magmas, including alkali basalts, nephelinites, melilite basalts, and basanites
The two late alkaline stages represent 1-2% of the total lava output
Note all three OIB series are represented in Hawaii
Is this representative of all islands? Probably not

10. Evolution in the Series
Tholeiitic, alkaline, and highly alkaline
Figure After Wilson (1989) Igneous Petrogenesis. Kluwer.

11. Thus all appear to have distinctive sources
Trace Elements
The LIL trace elements (K, Rb, Cs, Ba, Pb2+ and Sr) are incompatible and are all enriched in OIB magmas with respect to MORBs
The ratios of incompatible elements have been employed to distinguish between source reservoirs
N-MORB: the K/Ba ratio is high (usually > 100)
E-MORB: the K/Ba ratio is in the mid 30’s
OITs range from 25-40, and OIAs in the upper 20’s
Thus all appear to have distinctive sources

12. Trace Elements
HFS elements (Th, U, Ce, Zr, Hf, Nb, Ta, and Ti) are also incompatible, and are enriched in OIBs > MORBs
Ratios of these elements are also used to distinguish mantle sources
The Zr/Nb ratio
N-MORB generally quite high (>30)
OIBs are low (<10)

13. Trace Elements: REEs
Note that ocean island tholeiites (represented by the Kilauea and Mauna Loa samples) overlap with MORB and are not unlike E-MORB
The alkaline basalts have steeper slopes and greater LREE enrichment, although some fall within the upper MORB field
Note also that the heavy REEs are also fractionated in the OIB samples (as compared to the flat HREE patterns in N- and E-MORB). This indicates that garnet was a residual phase
These melts must have segregated from the mantle at depths > 60 km
Figure After Wilson (1989) Igneous Petrogenesis. Kluwer.

14. MORB-normalized Spider Diagrams
OIBs are enriched in incompatible elements over MORB (values > one)
Broad central hump in which both the LIL (Sr-Ba) and HFS (Yb-Th) element enrichments increase with increasing incompatibility (inward toward Ba and Th)
The pattern we would expect in a sample that was enriched by some single-stage process (such as partial melting of a four-phase lherzolite) that preferentially concentrated incompatible elements.
The pattern is regarded as typical of melts generated from non-depleted mantle in intraplate settings
Figure Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Sun and McDonough (1989).

15. Generation of tholeiitic and alkaline basalts from a chemically uniform mantle
Variables (other than X)
Temperature
= % partial melting
Pressure
Fig indicates that, although the chemistry may be the same, the mineralogy varies
Pressure effects on eutectic shift
Figure 10-2 After Wyllie, P. J. (1981). Geol. Rundsch. 70,

16. Pressure effects: Ne Fo En Ab
SiO2
Oversaturated
(quartz-bearing)
tholeiitic basalts
Highly undesaturated
(nepheline - bearing)
alkali basalts
Undersaturated E
3GPa
2Gpa
1GPa
1atm
Volatile-free
Figure 10-8 After Kushiro (1968), J. Geophys. Res., 73,
Increased pressure moves the ternary eutectic minimum from the oversaturated tholeiite field to the under-saturated alkaline basalt field
Alkaline basalts are thus favored by greater depth of melting

17. Tholeiites favored by shallower melting
25% melting at <30 km ® tholeiite
25% melting at 60 km ® olivine basalt
Tholeiites favored by greater % partial melting
20 % melting at 60 km ® alkaline basalt
incompatibles (alkalis) ® initial melts
30 % melting at 60 km ® tholeiite

18. Isotope Geochemistry
Isotopes do not fractionate during partial melting of fractional melting processes, so will reflect the characteristics of the source
OIBs, which sample a great expanse of oceanic mantle in places where crustal contamination is minimal, provide incomparable evidence as to the nature of the mantle

19. Simple Mixing Models Ternary Binary
All analyses fall between two reservoirs as magmas mix
Ternary
All analyses fall within triangle determined by three reservoirs
Figure Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

20. Figure 14-6. After Zindler and Hart (1986), Staudigel et al
Figure After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).

21. Mantle Reservoirs 1. DM (Depleted Mantle) = N-MORB source
Figure After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).
Shows low values of 87Sr/86Sr and high values of 144Nd/143Nd as well as depleted trace element characteristics

22. 2. BSE (Bulk Silicate Earth) or the Primary Uniform Reservoir
Figure After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).
Reflects the isotopic signature of the primitive mantle as it would evolve to the present without any subsequent fractionation i.e. neither depleted nor enriched…just plain old mantle
Several oceanic basalts have this isotopic signature, but there are no compelling data that require this reservoir (it is not a mixing end-member), but falls within the space defined by other reservoirs

23. 3. EMI = enriched mantle type I has lower 87Sr/86Sr (near primordial)
4. EMII = enriched mantle type II has higher 87Sr/86Sr (> , well above any reasonable mantle sources
Figure After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).
Since the Nd-Sr data for OIBs extends beyond the primitive values to truly enriched ratios, there must exist an enriched mantle reservoir
Both EM reservoirs have similar enriched (low) Nd ratios (< )

24. 5. PREMA (PREvalent MAntle)
Figure After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).
Also not a mixing end-member
PREMA represents another restricted isotopic range that is very common in ocean volcanic rocks
Although it lies on the mantle array, and could result from mixing of melts from DM and BSE sources, the promiscuity of melts with the PRIMA signature suggests that it may be a distinct mantle source

25. Note that all of the Nd-Sr data can be reconciled with mixing of three reservoirs: DM EMI and EMII since the data are confined to a triangle with apices corresponding to these three components. So, what is the nature of EMI and EMII, and why is there yet a 6th reservoir (HIMU) that seems little different than the mantle array?
Figure After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).

26. Pb Isotopes Pb produced by radioactive decay of U & Th
238U  234U  206Pb
235U  207Pb
232Th  208Pb
Pb isotopes also characterize the different reservoirs (see paper presentation Hart 1984)
All three elements are LIL
Fractionate into the melt (or a fluid) phase (if available) in the mantle, and migrate upward where they will become incorporated in the oceanic or continental crust

27. Figure 14-8. After Wilson (1989) Igneous Petrogenesis. Kluwer
Figure After Wilson (1989) Igneous Petrogenesis. Kluwer. Data from Hamelin and Allègre (1985), Hart (1984), Vidal et al. (1984).
Note that HIMU is also 208Pb enriched, which tells us that this reservoir is enriched in Th as well as U
This highly enriched EM component has been called the DUPAL component, named for Dupré and Allègre (1983), who first described it

28. Kellogg et al. (1999)

29. A Model for Oceanic Magmatism
Continental
Reservoirs DM
OIB
EM and HIMU from crustal sources (subducted OC + CC seds)
Figure Nomenclature from Zindler and Hart (1986). After Wilson (1989) and Rollinson (1993).

30. “Marble cake” model for mantle convection & mixing

31. Continental Flood Basalts
Large Igneous Provinces (LIPs)
Oceanic plateaus
Some rifts
Continental flood basalts (CFBs)
Figure Columbia River Basalts at Hat Point, Snake River area. Cover of Geol. Soc. Amer Special Paper 239. Photo courtesy Steve Reidel.

32. Trapp volcanism

33. LIPs (Large Igneous Provinces)

35. CFB’s Associated to major continental break-up
… or/and to plume head impact

37. Figure Flood basalt provinces of Gondwanaland prior to break-up and separation. After Cox (1978) Nature, 274,

38. Figure Relationship of the Etendeka and Paraná plateau provinces to the Tristan hot spot. After Wilson (1989), Igneous Petrogenesis. Kluwer.

39. Geochemistry
Deccan traps basalts

40. Bimodal magmas Basalts and rhyolites Secondary melting?
Effect of the two eutectics?

41. Figure Condrite-normalized rare earth element patterns of some typical CRBG samples. Winter (2001). An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Hooper and Hawkesworth (1993) J. Petrol., 34,

42. Figure Present setting of the Columbia River Basalt Group in the Northwestern United States. Winter (2001). An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Also shown is the Snake River Plain (SRP) basalt-rhyolite province and proposed trace of the Snake River-Yellowstone hot spot by Geist and Richards (1993) Geology, 21,

43. Melting within a heterogeneous plume head (initial stages of the Yellowstone hot spot).
The plume head contains recycled stringers of recycled oceanic crust that melts before the peridotite, yielding a silica-rich basaltic magma equivalent to the main Grande Ronde basalts and leaves a garnet-clinopyroxene residue.
The large plume head stalls and spreads out at the base of the resistant lithosphere and the basaltic magma ponds (underplates) at the base of the crust, where it melts some crust to create rhyolite.
Basalt escapes along a northward trending rift system to feed the CRBG.
Figure A model for the origin of the Columbia River Basalt Group From Takahahshi et al. (1998) Earth Planet. Sci. Lett., 162,

44. Figure Diagrammatic cross section illustrating possible models for the development of continental flood basalts. DM is the depleted mantle (MORB source reservoir), and the area below 660 km depth is the less depleted, or enriched OIB source reservoir. Winter (20010 An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

45. LIPs and mass extinctions

46. Continental alkaline series
Alkali volcanoes – basaltic strombolian cone in front,
trachytic pelean dome behind– in the West European rift

47. Continental alkaline series
Rift (or hotspot) related
Large diversity (possibly > 80% of the rock names, for <1% volume !)
Strange rocks (carbonatites…)

48. Common features of continental alkali series
Alkaline (!)
Undersaturated to just oversaturated
Peralkaline

49. Alkaline series
Mildly alkaline
Strongly alkaline

50. Figure Alumina saturation classes based on the molar proportions of Al2O3/(CaO+Na2O+K2O) (“A/CNK”) after Shand (1927). Common non-quartzo-feldspathic minerals for each type are included. After Clarke (1992). Granitoid Rocks. Chapman Hall.

51. Trace elements enriched
Figure Chondrite-normalized REE variation diagram for examples of the four magmatic series of the East African Rift (after Kampunzu and Mohr, 1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

52. Enriched mantle source
Figure Nd/144Nd vs. 87Sr/86Sr for East African Rift lavas (solid outline) and xenoliths (dashed). The “cross-hair” intersects at Bulk Earth (after Kampunzu and Mohr, 1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

53. Generated from low to very low melt fractions
Figure Grid showing the melting products as a function of pressure and % partial melting of model pyrolite mantle with 0.1% H2O. Dashed curves are the stability limits of the minerals indicated. After Green (1970), Phys. Earth Planet. Inter., 3, Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

54. The alkali eutectic
Figure Phase diagram for the system SiO2-NaAlSiO4-KAlSiO4-H2O at 1 atm. pressure. Insert shows a T-X section from the silica-undersaturated thermal minimum (Mu) to the silica-oversaturated thermal minimum (Ms). that crosses the lowest point (M) on the binary Ab-Or thermal barrier that separates the undersaturated and oversaturated zones. After Schairer and Bowen (1935) Trans. Amer. Geophys. Union, 16th Ann. Meeting, and Schairer (1950), J. Geol., 58, Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

55. Diversity of alkaline continental magmas – some examples
Saturated alkaline series
Undersaturated alkaline series
Carbonatites
Lamprophyres, kimberlites & co.
Series with a true geological importance
Oddities and curiosities – but economic importance!

56. Figure 19-1. Variations in alkali ratios (wt
Figure Variations in alkali ratios (wt. %) for oceanic (a) and continental (b) alkaline series. The heavy dashed lines distinguish the alkaline magma subdivisions from Figure 8-14 and the shaded area represents the range for the more common oceanic intraplate series. After McBirney (1993). Igneous Petrology (2nd ed.), Jones and Bartlett. Boston. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

57. The West-european rift sytem

58. Continental Alkaline Magmatism. The East African Rift
Figure Map of the East African Rift system (after Kampunzu and Mohr, 1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

59. East African rift (Afar) – mildly alkaline

60. Central African Rift – Strongly alkaline

61. Two main series
Basalts-Trachydandesites-Trachydacites-Rhyolites (stronly bimodal): (just) saturated alkali series
A-type granites can be formed there
Role of the preexisting crust?
Basanite-Foidite (nephelinite)-Phonolite: strongly undersaturated alkali series

62. Figure Hypothetical cross sections (same vertical and horizontal scales) showing a proposed model for the progressive development of the East African Rift System. a. Pre-rift stage, in which an asthenospheric mantle diapir rises (forcefully or passively) into the lithosphere. Decompression melting (cross-hatch-green indicate areas undergoing partial melting) produces variably alkaline melts. Some partial melting of the metasomatized sub-continental lithospheric mantle (SCLM) may also occur. Reversed decollements (D1) provide room for the diapir. b. Rift stage: development of continental rifting, eruption of alkaline magmas (red) mostly from a deep asthenospheric source. Rise of hot asthenosphere induces some crustal anatexis. Rift valleys accumulate volcanics and volcaniclastic material. c. Afar stage, in which asthenospheric ascent reaches crustal levels. This is transitional to the development of oceanic crust. Successively higher reversed decollements (D2 and D3) accommodate space for the rising diapir. After Kampunzu and Mohr (1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp and P. Mohr (personal communication). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

63. Bimodal associations again (the « Daly gap »)
Mantle vs. Crustal sources?
Remelting of underplated basalts?
Simply an effect of the different eutectics?

64. The oddities…
Carbonatites
Lamproites, kimberlites, etc.

65. Chapter 19: Continental Alkaline Magmatism. Carbonatites

66. Carbonatites
Figure Idealized cross section of a carbonatite-alkaline silicate complex with early ijolite cut by more evolved urtite. Carbonatite (most commonly calcitic) intrudes the silicate plutons, and is itself cut by later dikes or cone sheets of carbonatite and ferrocarbonatite. The last events in many complexes are late pods of Fe and REE-rich carbonatites. A fenite aureole surrounds the carbonatite phases and perhaps also the alkaline silicate magmas. After Le Bas (1987) Carbonatite magmas. Mineral. Mag., 44, Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

67. Chapter 19: Continental Alkaline Magmatism. Carbonatites
Figure Silicate-carbonate liquid immiscibility in the system Na2O-CaO-SiO2-Al2O3-CO2 (modified by Freestone and Hamilton, 1980, to incorporate K2O, MgO, FeO, and TiO2). The system is projected from CO2 for CO2-saturated conditions. The dark shaded liquids enclose the miscibility gap of Kjarsgaard and Hamilton (1988, 1989) at 0.5 GPa, that extends to the alkali-free side (A-A). The lighter shaded liquids enclose the smaller gap (B) of Lee and Wyllie (1994) at 2.5 GPa. C-C is the revised gap of Kjarsgaard and Hamilton. Dashed tie-lines connect some of the conjugate silicate-carbonate liquid pairs found to coexist in the system. After Lee and Wyllie (1996) International Geology Review, 36, Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

68. Chapter 19: Continental Alkaline Magmatism. Carbonatites
Figure Schematic cross section of an asthenospheric mantle plume beneath a continental rift environment, and the genesis of nephelinite-carbonatites and kimberlite-carbonatites. Numbers correspond to Figure After Wyllie (1989, Origin of carbonatites: Evidence from phase equilibrium studies. In K. Bell (ed.), Carbonatites: Genesis and Evolution. Unwin Hyman, London. pp ) and Wyllie et al., (1990, Lithos, 26, 3-19). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

69. Lamproites and kimberlites
… many, many, many rock types
… many, many different names – mostly purely local and after the one known occurrence of that rock type (Vosgesite, Wyomingite, …)

70. Chapter 19: Continental Alkaline Magmatism. Kimberlites

71. Chapter 19: Continental Alkaline Magmatism. Lamproites
Figure 19-18a. Initial 87Sr/86Sr vs. 143Nd/144Nd for lamproites (red-brown) and kimberlites (red). MORB and the Mantle Array are included for reference. After Mitchell and Bergman (1991) Petrology of Lamproites. Plenum. New York. Typical MORB and OIB from Figure for comparison. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

72. Chapter 19: Continental Alkaline Magmatism. Lamproites
Figure Chondrite-normalized rare earth element diagram showing the range of patterns for olivine-, phlogopite-, and madupitic-lamproites from Mitchell and Bergman (1991) Petrology of Lamproites. Plenum. New York. Typical MORB and OIB from Figure for comparison. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

73. Chapter 19: Continental Alkaline Magmatism. Kimberlites
Figure Model of an idealized kimberlite system, illustrating the hypabyssal dike-sill complex leading to a diatreme and tuff ring explosive crater. This model is not to scale, as the diatreme portion is expanded to illustrate it better. From Mitchell (1986) Kimberlites: Mineralogy, Geochemistry, and Petrology. Plenum. New York. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

74. Chapter 19: Continental Alkaline Magmatism. Kimberlites
Figure 19-20a. Chondrite-normalized REE diagram for kimberlites, unevolved orangeites, and phlogopite lamproites (with typical OIB and MORB). After Mitchell (1995) Kimberlites, Orangeites, and Related Rocks. Plenum. New York. and Mitchell and Bergman (1991) Petrology of Lamproites. Plenum. New York. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

75. Chapter 19: Continental Alkaline Magmatism. Kimberlites
Figure 19-20b. Hypothetical cross section of an Archean craton with an extinct ancient mobile belt (once associated with subduction) and a young rift. The low cratonal geotherm causes the graphite-diamond transition to rise in the central portion. Lithospheric diamonds therefore occur only in the peridotites and eclogites of the deep cratonal root, where they are then incorporated by rising magmas (mostly kimberlitic- “K”). Lithospheric orangeites (“O”) and some lamproites (“L”) may also scavenge diamonds. Melilitites (“M”) are generated by more extensive partial melting of the asthenosphere. Depending on the depth of segregation they may contain diamonds. Nephelinites (“N”) and associated carbonatites develop from extensive partial melting at shallow depths in rift areas. After Mitchell (1995) Kimberlites, Orangeites, and Related Rocks. Plenum. New York. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.