Epoch/Period/Era
|
Age (Ma)
|
Unit
|
Petrology
|
Tectonic event
|
Dating technique
|
Reference
|
|---|---|---|---|---|---|---|
Early Jurassic
|
200
|
Dikes
|
Diabase
|
Late-stage continental rifting
|
Ar/Ar hornblende
|
Kunk and others, 1992.
|
Mississippian
|
340
|
Greenschist-facies cleavage Alleghanian orogeny
|
Ar/Ar muscovite
|
Burton and others, 1992b. Kunk and others, 1993.
|
||
Early Cambrian
|
Tomstown Formation
|
Dolomite
|
Passive margin
|
|||
Antietam Formation
|
Sandstone
|
|||||
Harpers Formation
|
Siltstone
|
Rift to passive margin transition
|
||||
Weverton Formation
|
Quartzite
|
|||||
Loudoun Formation
|
Conglomerate,
phyllite |
|||||
Late
Proterozoic |
570-565
|
Catoctin Formation
|
Metabasalt,
metarhyolite |
Continental rifting
|
Rb/Sr pyroxene
|
Badger and Sinha, 1988.
|
Dikes
|
Metadiabase,
metarhyolite |
Continental rifting
|
U/Pb
|
Aleinikoff and others, 1995.
|
||
Swift Run Formation
|
Metasedimentary rocks
|
Alluviation during continental rifting
|
||||
730-700
|
Robertson River
Igneous Suite |
Granitoids
|
Anorogenic pluton of incipient rift
|
U/Pb
|
Tollo and Aleinikoff, 1992.
|
|
Middle
Proterozoic |
1000-920
|
Diorite
|
Cooling age of granulite-grade Grenville metamorphism
|
Ar/Ar hornblende
|
Kunk and others, 1993.
|
|
1058
|
Leucocratic
metagranite |
U/Pb
|
Aleinikoff and others, 1993.
|
|||
1060
|
Charnockite
|
Diorite, monzonite
|
Pb/Pb
|
Herz and Force, 1984.
|
||
1070
|
Garnet monzogranite
|
Plutonism of Grenville orogeny
|
U/Pb
|
Aleinikoff and others, 1993.
|
||
1110
|
Hornblende gneiss
|
Quartz monzonite
|
U/Pb
|
Aleinikoff and others, 1993.
|
||
1127+-7
|
Biotite granite
|
U/Pb
|
Aleinikoff and others, 1993.
|
|||
1092-1139
|
Granite gneiss
|
U/Pb
|
Aleinikoff and others, 1993.
|
|||
1144
|
Porphyroblastic
granite gneiss |
U/Pb
|
Aleinikoff and others, 1993.
|
|||
1800
|
Paragneiss
|
Gneiss, schist, quartzite, and phyllonite
|
Pb/Pb
|
Herz and Force, 1984.
|