The Chuacús Group, of probable Paleozoic age, crops out in the Rio Hondo, San Agustín Acasaguastlán, and El Cimiento quadrangles, east-central Guatemala. Its members, in structurally ascending order, are: the San Agustín Formation (cataclastic gneiss and migmatite), the Jones Formation (dominantly phyllite and mica schist), and the San Lorenzo Formation (marble).
Chemical study of these rocks suggests that the San Agustín Formation is an orthogneiss of quartz monzonitic composition, while the Jones and San Lorenzo Formations comprise a distinct sequence of metasediments. The Jones Formation contains minor greenstones the chemistry of which suggests affinity with calc-alkaline basalts. The sediments probably accumulated in the vicinity of a tectonically active continental margin.
At least two periods of deformation are recorded in the Chuacús Group. The early deformation may have involved formation of large scale recumbent isoclinal folds (?nappes?) in bedding (S0) by transposition along flow planes (S1). The late deformation produced asymmetric slip folds in S1 by differential movement on steeply dipping slip cleavage (S2). These folds are developed in the Jones and San Lorenzo Formations. The same late deformation was responsible for regional cataclasis of the underlying San Agustín Formation.
Although relicts of amphibolite, and even granulite, facies metamorphism are preserved in some parts of the Chuacús Group, the dominant metamorphic grade of these rocks is greenschist to epidote-amphibolite facies. This is believed to be a result of regional retrograde metamorphism associated with the cataclastic deformation.
The character and history of the Chuacús Group, and the nature of the regional geology in adjacent areas, suggests that tectonic evolution of the Motagua Fault Zone involved minimal strike-slip displacement as compared to compression and transport perpendicular to the Motagua trend. A speculative tectonic evolutionary sequence, consistent with available geologic data in the area, could have involved poly-episodic tectonism along a plate boundary of convergent character.
","abstract_html":"<p>The Chuacús Group, of probable Paleozoic age, crops out in the Rio Hondo, San Agustín Acasaguastlán, and El Cimiento quadrangles, east-central Guatemala. Its members, in structurally ascending order, are: the San Agustín Formation (cataclastic gneiss and migmatite), the Jones Formation (dominantly phyllite and mica schist), and the San Lorenzo Formation (marble).</p> <p>Chemical study of these rocks suggests that the San Agustín Formation is an orthogneiss of quartz monzonitic composition, while the Jones and San Lorenzo Formations comprise a distinct sequence of metasediments. The Jones Formation contains minor greenstones the chemistry of which suggests affinity with calc-alkaline basalts. The sediments probably accumulated in the vicinity of a tectonically active continental margin.</p> <p>At least two periods of deformation are recorded in the Chuacús Group. The early deformation may have involved formation of large scale recumbent isoclinal folds (?nappes?) in bedding (S<sub>0</sub>) by transposition along flow planes (S<sub>1</sub>). The late deformation produced asymmetric slip folds in S<sub>1</sub> by differential movement on steeply dipping slip cleavage (S<sub>2</sub>). These folds are developed in the Jones and San Lorenzo Formations. The same late deformation was responsible for regional cataclasis of the underlying San Agustín Formation.</p> <p>Although relicts of amphibolite, and even granulite, facies metamorphism are preserved in some parts of the Chuacús Group, the dominant metamorphic grade of these rocks is greenschist to epidote-amphibolite facies. This is believed to be a result of regional retrograde metamorphism associated with the cataclastic deformation.</p> <p>The character and history of the Chuacús Group, and the nature of the regional geology in adjacent areas, suggests that tectonic evolution of the Motagua Fault Zone involved minimal strike-slip displacement as compared to compression and transport perpendicular to the Motagua trend. A speculative tectonic evolutionary sequence, consistent with available geologic data in the area, could have involved poly-episodic tectonism along a plate boundary of convergent character.</p>","abstract_has_math":false,"creators":["Newcomb, Walter Edwin"],"institution":null,"degree_name":"Doctor of Philosophy (PhD)","degree_level":"Dissertation","degree_discipline":"Geological Sciences","degree_department":null,"school":null,"contributors":["Thomas W. Donnelly","Marc W. Bodine, Jr.","William D. MacDonald"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":1975,"date_issued":"1975-01-01T08:00:00Z","date_published":"1975-01-01T08:00:00Z","updated_at":"2026-07-24T01:10:16Z","subjects":["Geology","Guatemala","Hondo River (Guatemala","Mexico","and Belize)"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://orb.binghamton.edu/dissertation_and_theses/347","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Thomas W. Donnelly","Marc W. Bodine, Jr.","William D. MacDonald"]},{"key":"dc:creator","label":"Author","values":["Newcomb, Walter Edwin"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"thesis:degree_discipline","label":"Discipline","values":["Geological Sciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Geology","Guatemala","Hondo River (Guatemala","Mexico","and Belize)"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://orb.binghamton.edu/dissertation_and_theses/347"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The Chuacús Group, of probable Paleozoic age, crops out in the Rio Hondo, San Agustín Acasaguastlán, and El Cimiento quadrangles, east-central Guatemala. Its members, in structurally ascending order, are: the San Agustín Formation (cataclastic gneiss and migmatite), the Jones Formation (dominantly phyllite and mica schist), and the San Lorenzo Formation (marble).
Chemical study of these rocks suggests that the San Agustín Formation is an orthogneiss of quartz monzonitic composition, while the Jones and San Lorenzo Formations comprise a distinct sequence of metasediments. The Jones Formation contains minor greenstones the chemistry of which suggests affinity with calc-alkaline basalts. The sediments probably accumulated in the vicinity of a tectonically active continental margin.
At least two periods of deformation are recorded in the Chuacús Group. The early deformation may have involved formation of large scale recumbent isoclinal folds (?nappes?) in bedding (S0) by transposition along flow planes (S1). The late deformation produced asymmetric slip folds in S1 by differential movement on steeply dipping slip cleavage (S2). These folds are developed in the Jones and San Lorenzo Formations. The same late deformation was responsible for regional cataclasis of the underlying San Agustín Formation.
Although relicts of amphibolite, and even granulite, facies metamorphism are preserved in some parts of the Chuacús Group, the dominant metamorphic grade of these rocks is greenschist to epidote-amphibolite facies. This is believed to be a result of regional retrograde metamorphism associated with the cataclastic deformation.
The character and history of the Chuacús Group, and the nature of the regional geology in adjacent areas, suggests that tectonic evolution of the Motagua Fault Zone involved minimal strike-slip displacement as compared to compression and transport perpendicular to the Motagua trend. A speculative tectonic evolutionary sequence, consistent with available geologic data in the area, could have involved poly-episodic tectonism along a plate boundary of convergent character.
"]},{"key":"dc:title","label":"Title","values":["Geology, structure and metamorphism of the Chuacús Group, Rio Hondo Quadrangle and vicinity, Guatemala"]}]}],"canonical_facts":{"dc:contributor":["Thomas W. Donnelly","Marc W. Bodine, Jr.","William D. MacDonald"],"dc:creator":["Newcomb, Walter Edwin"],"dc:description.abstract":["The Chuacús Group, of probable Paleozoic age, crops out in the Rio Hondo, San Agustín Acasaguastlán, and El Cimiento quadrangles, east-central Guatemala. Its members, in structurally ascending order, are: the San Agustín Formation (cataclastic gneiss and migmatite), the Jones Formation (dominantly phyllite and mica schist), and the San Lorenzo Formation (marble).
Chemical study of these rocks suggests that the San Agustín Formation is an orthogneiss of quartz monzonitic composition, while the Jones and San Lorenzo Formations comprise a distinct sequence of metasediments. The Jones Formation contains minor greenstones the chemistry of which suggests affinity with calc-alkaline basalts. The sediments probably accumulated in the vicinity of a tectonically active continental margin.
At least two periods of deformation are recorded in the Chuacús Group. The early deformation may have involved formation of large scale recumbent isoclinal folds (?nappes?) in bedding (S0) by transposition along flow planes (S1). The late deformation produced asymmetric slip folds in S1 by differential movement on steeply dipping slip cleavage (S2). These folds are developed in the Jones and San Lorenzo Formations. The same late deformation was responsible for regional cataclasis of the underlying San Agustín Formation.
Although relicts of amphibolite, and even granulite, facies metamorphism are preserved in some parts of the Chuacús Group, the dominant metamorphic grade of these rocks is greenschist to epidote-amphibolite facies. This is believed to be a result of regional retrograde metamorphism associated with the cataclastic deformation.
The character and history of the Chuacús Group, and the nature of the regional geology in adjacent areas, suggests that tectonic evolution of the Motagua Fault Zone involved minimal strike-slip displacement as compared to compression and transport perpendicular to the Motagua trend. A speculative tectonic evolutionary sequence, consistent with available geologic data in the area, could have involved poly-episodic tectonism along a plate boundary of convergent character.
"],"dc:identifier":["https://orb.binghamton.edu/dissertation_and_theses/347"],"dc:subject":["Geology","Guatemala","Hondo River (Guatemala","Mexico","and Belize)"],"dc:title":["Geology, structure and metamorphism of the Chuacús Group, Rio Hondo Quadrangle and vicinity, Guatemala"],"thesis:degree_discipline":["Geological Sciences"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-24T01:10:16Z"}