Dating zircon grains
The earth’s upper surface is composed of rigid, lithospheric plates of crustal rock (too stiff to flow on geologic time scales, yet stiff enough to break and cause earthquakes) underlain by mantle rock.Surface deformation, volcanic activity, and earthquakes occur more readily at the margins of plates than at their interior.This article reviews currently accepted areas of knowledge, along with topics that are still the subject of ongoing research, where science does not yet have all the answers.This basic subject was discussed more than two decades ago in (Kirkley et al., 1991); since then, there have been major advances in our understanding of diamond geology.Even low elemental concentrations and minute features in diamond can now be analyzed using instruments with higher sensitivity and resolution.
This article reviews current thinking of where, how, when, and why natural diamonds form.
It is hoped that this article will give the gemologist a ready way to convey how nature first created the rough diamonds.
For the reader who is unfamiliar with geologic terms, a glossary is presented at the end of the article.
This graph depicts the rise of temperature with depth (the geothermal gradient) in the lithosphere.
Diamonds are stable under the high pressure and temperature conditions that are only met at great depth in the earth’s mantle.Research into natural diamonds (figure 1) has emerged over the last two decades as one of the keys to understanding the deep earth.Analytical advances, improved geologic knowledge, and the emergence of new diamond-producing regions (such as the Slave craton of Canada) have all contributed to this change.Localities are as follows: (1) Diavik, Ekati, Snap Lake, Jericho, Gahcho Kue, DO-27; (2) Fort a la Corne; (3) Buffalo Hills; (4) State Line; (5) Prairie Creek; (6) Wawa; (7) Victor; (8) Renard; (9) Guaniamo; (10) Juina/Sao Luis; (11) Arenapolis; (12) Coromandel, Abaete, Canasta; (13) Chapada Diamantina; (14) Boa Vista; (15) Koidu; (16) Kan Kan; (17) Akwatia; (18) Tortiya; (19) Aredor; (20) Bangui; (21) Mbuji-Mayi; (22) Camafuca, Cuango, Catoca; (23) Masvingo; (24) Mwadui; (25) Luderitz, Oranjemund, Namaqualand; (26) Orapa/Damtshaa, Letlhakane, Jwaneng, Finsch; (27) Murowa, Venetia, The Oaks, Marsfontein, Premier, Dokolwayo, Roberts Victor, Letseng-la-Terae, Jagersfontein, Koffiefontein, Monastery, Kimberley (Bultfontein, Kimberley, De Beers, Dutoitspan, Kamfersdam, Wesselton); (28) Kollur; (29) Majhgawan/Panna; (30) Momeik; (31) Theindaw; (32) Phuket; (33) West Kalimantan; (34) South Kalimantan; (35) Springfield Basin, Eurelia/Orroroo, Echunga; (36) Argyle, Ellendale, Bow River; (37) Merlin; (38) Copetown/Bingara; (39) Mengyin; (40) Fuxian; (41) Mir, 23rd Party Congress, Dachnaya, Internationalskaya, Nyurbinskaya; (42) Aykhal, Yubileynaya, Udachnaya, Zarnitsa, Sytykanskaya, Komsomolskaya; (43) Ural Mts.; (44) Arkhangelsk; (45) Kaavi-Kuopio; (46) W Alps; (47) Moldanubian; (48) Norway; (49) Rhodope; (50) Urals; (51) Kokchetav; (52) Qinling; (53) Dabie; (54) Sulu; (55) Kontum; (56) Java; (57) New England Fold Belt; (58) Canadian Cordillera; (59) Lappajärvi; (60); Ries; (61) Zapadnaya; (62) Popigai; (63) Sudbury; and (64) Chixculub. (2013), with permission of the Mineralogical Society of America. Plate tectonics is the modern unifying theory that explains the earth’s active geologic processes today, and is thought to have operated perhaps for as long as the latter half of the planet’s history.