Meteorite composition : Meteorite composition Major groupings:
Stony meteorites
Chondrites
Achondrites
Iron meteorites
Octahedrites, hexahedrites, ataxites
Stony-iron meteorites
Pallasites
Mesosiderites
Slide3 : Chondrites
Carbonaceous chondrite class
CI chondrite (Ivuna-like) group
CM-CO chondrite (mini-chondrule) clan
CM chondrite (Mighei-like) group
CO chondrite (Ornans-like) group
CV-CK chondrite clan
CV chondrite (Vigarano-like) group
CV-oxA chondrite (oxidized, Allende-like) subgroup
CV-oxB chondrite (oxidized, Bali-like) subgroup
CV-red chondrite (reduced) subgroup
CK chondrite (Karoonda-like) group
CR chondrite clan
CR chondrite (Renazzo-like) group
CH chondrite (Allan Hills 85085-like) group
CB chondrite (Bencubbin-like) group
CBa chondrite subgroup
CBb chondrite subgroup
Ordinary chondrite class
H chondrite group
L chondrite group
LL chondrite group
Enstatite chondrite class
EH chondrite group
EL chondrite group
Other chondrite groups, not in one of the major classes
R chondrite (Rumuruti-like) group
K chondrite (Kakangari-like) grouplet (a grouplet is a provisional group with <5 members)
Chondrites : Chondrites Stony meteorites – most common meteorites and represent the oldest solids that are the building blocks of the solar system
Parent bodies were small-medium asteroids, not planetoids!
Contain up to 80% chondrules, which were freely floating molten drops in space Few mm to 1 cm spheres
Mostly olivine and pyroxene, also feldspathic glass or crystals with minor troilite (FeS), chromite, phosphates
15 groups of chondrites
Chondrite groups : Chondrite groups Ordinary – make up 80% of the meteorites and 90% of chondritic meteorites, abundant chondrules, variable Fe-Ni lead to H, L, and LL chondrites
Carbonaceous chondrites –less the 5% of chondritic meteorites, few chondrules, more lithophile elements (Ca, Mg, K, Cr, Al, Cl,…), high levels of water and organic compounds - many types based on characteristic specimen
Enstatite Chondrites – 2% of chondritic meteorites, very chemically reduced – enstatite-rich chondrules and abundant metal and sulfide minerals
Peekskill Meteorite : Peekskill Meteorite Peekskill Meteor: October 9, 1992. This famous fireball was seen and filmed across several eastern states. It broke up into many fragments, one of which hit the trunk of Michelle Knapp's 1980 Chevy Malibu. When Ms. Knapp investigated a crash sound outside her Peekskill, NY home, she discovered the damaged trunk and found a warm 12-kg meteorite lying beside the car. 12-kg Ordinary Chondritic meteorite
Car – $10K
Meteorite – $75K
Achondrites : Achondrites Stony meteorite similar to terrestrial basalts or plutonic rocks, represent 8% of meteorites grouped on the basis of Fe/Mn and 17O/18O ratios characteristic of the parent body
2/3 of these meteorites are HED type, originating from one asteroid, Vesta 4 - there is a large impact crater observed on this asteroid
Also includes Martian and lunar meteorites Lunar Meteorite Allan Hills 81005 The Johnstown Diogenite.
Martian Meteorites : Martian Meteorites All are igneous, lherzolitic to basaltic composition, and some contain hydrated carbonates and sulfates, evidence of liquid water
ALH84001 is 4.5 ga, contains carbonate veins 3.6 – 4 ga, Organic matter (PAH), aligned magnetite crystals, proposed nanofossils (careful!!) – very controversial… ALH84001 Nahkla Meteorite ALH84001 – round carbonate grains
Iron Meteorites : Iron Meteorites 5% of meteorites, but 90% of the mass of recovered meteorites and all of the largest meteorites (66 tons is the record) - primarily composed of iron-nickel alloy intergrowths:
Kamacite – Fe-Ni alloy at 90:10 to 95:5 Fe:Ni
Taenite – Fe-Ni alloy at 80:20 to 45:65 Fe:Ni
Widmanstätten pattern – finely interweaved Kamacite and Taenite (Octahedrites)
Classified on Ni content: Ataxites>Octahedrites>Hexahedrites
Stony-iron Meteorites : Stony-iron Meteorites Mix of iron-nickel alloy and silicate minerals (mostly olivine), 1% of meteorites
Pallasites are thought to form a the core-mantle boundary of differentiated asteroids
Mesosiderite – equal parts metal alloy and silicate with a breccia texture
Identifying a meteorite : Identifying a meteorite Fusion crust – dull black to dark brown, often soft, can be weathered to red (but can flake off)
Density – generally dense
Chondrules are specifically meteoritic
Never porous, but can be ‘dimpled’ with surface depressions
99% of meteorites are magnetic
Unusually high Ni content
Slide12 : Fusion crust forms on entry through the atmosphere
Meteorite/ Comet Impacts : Meteorite/ Comet Impacts P/T space??
Chicxulub, Yucatan Peninsula, Mexico : Chicxulub, Yucatan Peninsula, Mexico K/T event at 64.98 ma, formed from a 6-12 mile diameter asteroid impact (50 megaton blast)
Slide15 : Barringer Meteor Crater, Arizona, formed from Canyon Diable Meteorite
Impact Craters : Impact Craters Clearwater lakes, Quebec – 36+26km diameter, 290 ma Many famous impact craters, hundreds known on earth (why might there have been plenty more??)
Sudbury, Ontario (250km diameter, 1.85 ga)
Chesapeake Bay (90km diameter, 35 ma)
Manson, Iowa (35km, 74ma)
Barringer, Arizona (1.2km, 49 ka)
Serpent Mound, Ohio (8km, 320 ma)
Megatsunamis : Megatsunamis Meteorite impact in the ocean displaces huge quantities of water instantly
The Chixculub crater impact generated a megatsunami 150-300 feet high
Energy of an impact : Energy of an impact Kinetic energy – going from very fast to stopping is a BIG change in energy
What happens to that energy??
Impactite – any mineral formed as a result of this impact Shatter cone
Materials indicating Meteorite Impacts : Materials indicating Meteorite Impacts Tektites
Glass formed from impact
Diaplectic Glass : Diaplectic Glass Glass formed through fusion of different minerals – not melted, but fused…
What Happens to minerals that are there but not melted? : What Happens to minerals that are there but not melted? Shock Quartz
Lamellae retaining evidence of impact
Diamonds : Diamonds Very small diamonds can form from impacts and are found in meteorite impact craters around the world
Diamonds can also form in meteorites- these can be gray to black
Lonsdalite - Hexagonal allotrope of diamond, specific to meteorite impacts, thought to form from graphite in meteorites
Quartz Polymorphs : Quartz Polymorphs Coesite and Stishovite found associated with impact craters