Savin Hill Fault Mount Hope Fault Newton Quadrangle Boston South Quadrangle 71 o 07’ 30” W 71 o 00’ W 42 o 15’ N 42 o 22’30” N ~609 Ma ~593 Ma (MT08-01) <596 Ma (MT99-4) <595 Ma (MT04-20) ~584 Ma (MT03-09A) ~585 Ma (BOS22A) ~597 Ma LYNN-MATTAPAN VOLCANIC COMPLEX (597-593 Ma) includ- ing N, Neponset Gorge Conglom N Undifferentiated argillite CAMBRIDGE ARGILLITE (<570 Ma) BOSTON BAY GROUP SEDIMENTARY AND VOLCANIC ROCKS ROXBURY CONGLOMERATE Franklin Park member Undifferentiated Brookline- Dorchester-Squantum members including B, Brighton Igneous Suite (585 Ma) WESTWOOD GRANITE (599 Ma) DEDHAM GRANITE (609 Ma) INTRUSIVE IGNEOUS ROCKS B <599Ma (MT10-12) U-Pb zircon date SYMBOLS Inclined, horizontal bedding Anticline, syncline Fault C T, City Tunnel Tunnel alignment C T E, City Tunnel Extension M D T, Main Drainage Tunnel D T, Dorchester Tunnel 25 ~ 585 Ma Entries with sample #’s from Thompson et al., 2014; others are previoulsy published) 5 Field trip stop for 2014 NEIGC Trip B-2 M D T C T E D T C T 1 2 4 3 5 6 7 BEDROCK GEOLOGIC MAP OF THE BOSTON BASIN & ENVIRONS (after Thompson et al., 2014)