MINERAL CHEMISTRY IN DIORITIC HORNBLENDITES FROM WADI ARABA, SOUTHWEST JORDAN

The mineral chemistry of dioritic rocks from Wadi Araba, southwest Jor dan, has been determined by electron microprobe, with special emphasis on the amphiboles. These are calcic amphiboles, according to Leake (1 978), since all analyses have (Ca+Na)>1.34 and Na-B<0.67. The observed chemical variations in the amphiboles are attributed to a combination of edenite, pargasite, hornblende and hastingsite end-member substitu tions. Calculated average pressures of emplacement using four Al-in-ho rnblende barometers are 2.41 +/- 1.33, 3.47 +/- 1.60 and 4.52 +/- 1.42 kbar for the pegmatitic diorite (PD), biotite-hornblende diorite (BHD ) and diopside-hornblende diorite (DHD), respectively. The correspondi ng temperatures of crystallisation according to the Holland and Blundy (1994) thermometer are 730 +/- 40, 763 +/- 37 and 783 +/- 103 degrees C. The variation of temperature of equilibration is almost within the uncertainty range of the applied thermometer. However, if this variat ion is real, the studied hornblende shows both temperature and pressur e dependent substitutions. The calculated pressures fall within the es timated range (2.4 to 5.5 kbar), as deduced from the metamorphic grade of the metasedimentary rocks exposed at the same crustal level. (C) 1 998 Elsevier Science Limited.